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Medical Evacuation Risk and Crew Transport

  • Smith L. JohnstonIII
  • Kieran T. Smart
  • James M. PattariniEmail author
Chapter
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Abstract

Space is a uniquely remote and hazardous environment. For humans to live and work effectively in low Earth orbit (LEO) and beyond, significant technological support must be provided to overcome the physical and psychological challenges of space flight. This operational environment places great demands on a crew, particularly during emergency situations, where the life of a crewmember may rest in the hands of a crew medical officer (CMO) who is also a colleague. In over five decades of human space flight and exploration, our knowledge, activities, and capabilities have grown tremendously, resulting in the International Space Station (ISS) and a permanent human presence in LEO. The need for an evacuation capability from a LEO space station derives from basic principles underlying escape and egress systems of the earliest manned spacecraft.

This chapter will examine key aspects of present-day spaceflight medical transport and evacuation and its terrestrial parallels, enumerate current challenges, and suggest possible solutions for future spaceflight activities. This will include a discussion on present and future standards of medical care on the ISS and the current transport vehicle used for travel to and from the station, the Russian Soyuz. Programs now under active development such as the NASA/Lockheed Orion Multi-Purpose Crew Vehicle, Space Exploration Technologies’ (SpaceX) Crew Dragon Capsule, and the Boeing CST-100 Capsule may also be developed with limited medical transport capability.

Keywords

Space crew recovery Spaceflight medical transport Crew return vehicles, spaceflight medical events LEO evacuation capability 

Space is a uniquely remote and hazardous environment. For humans to live and work effectively in low Earth orbit (LEO) and beyond, significant technological support must be provided to overcome the physical and psychological challenges of space flight. This operational environment places great demands on a crew, particularly during emergency situations, where the life of a crewmember may rest in the hands of a crew medical officer (CMO) who is also a colleague. In over five decades of human space flight and exploration, our knowledge, activities, and capabilities have grown tremendously, resulting in the International Space Station (ISS) and a permanent human presence in LEO. The need for an evacuation capability from a LEO space station derives from basic principles underlying escape and egress systems of the earliest manned spacecraft [1]. Indeed in 1957 even before humans were launched into orbit, designs for crew recovery from disabled manned space vehicles, including the concept of a space “lifeboat,” were proposed [2, 3, 4]. In over 130 person-years of human space flight, the medical treatment of ill or injured crewmembers has been required with a low yet appreciable frequency. Between 1971 and 2015, one evacuation, two early returns to Earth, and several emergent medical events have occurred. From this experience and that of analogous remote environments, it is possible to estimate the likelihood of a serious medical event, defined as one that would require skilled, high-level care in a terrestrial setting, for a crew aboard a LEO platform such as the ISS. For a full crew of six individuals in the current complement of the ISS, such a medical contingency may be anticipated to occur, on average, approximately every 3–6 years, most of these managed using onboard medical capabilities. The likelihood of a critically ill or injured crewmember requiring transport to a terrestrial definitive medical care facility (DMCF) is estimated to be lower—once or twice over the planned lifespan of the ISS.

Whether in a terrestrial, aviation, marine, or space environment, the priorities of triage and the principles of medical evacuation remain constant. These priorities are predicated on several factors [5]:
  • Severity of the illness or injury

  • Environmental conditions at the scene and during medical transport

  • Capabilities and proficiency of the first responders

  • Available medical equipment and capabilities

  • Telecommunications capabilities

  • Safety and performance of the transport vehicle

  • Flight duration of medical transport vehicle

  • Safety of the transport flight profile

  • Onboard medical capabilities during transport

  • Medical capabilities of the receiving facility

These factors affect the care of ill or injured patients in any environment, from large urban areas to small community hospitals and clinics, as well as remote isolated environments such as cruise ships, submarines, oil platforms, military deployments, wilderness base camps, and LEO platforms like the ISS. Shen and others have described clinical care in a remote, hazardous environment as “fourth world medicine,” with some advanced technology diagnostic (ultrasound and ECG), therapeutic (defibrillator, ventilator, advanced life support [ALS] medications), and evacuation capabilities to augment limited medical officer training and support [6].

This chapter will examine key aspects of present-day spaceflight medical transport and evacuation and its terrestrial parallels, enumerate current challenges, and suggest possible solutions for future spaceflight activities [7, 8, 9]. This will include a discussion on present and future standards of medical care on the ISS and the current transport vehicle used for travel to and from the station, the Russian Soyuz. Programs now under active development such as the NASA/Lockheed Orion Multi-Purpose Crew Vehicle, Space Exploration Technologies’ (SpaceX) Crew Dragon Capsule, and the Boeing CST-100 Capsule may also be developed with limited medical transport capability. The issues that medical evacuations in space flight raise include:
  • Likelihood and types of spaceflight medical events requiring evacuation

  • Standards of spaceflight medical care and projected capabilities for LEO space stations, lunar exploration, and interplanetary missions

  • Physiological deconditioning of astronauts returning from long duration weightless exposure and the consequences for medical evacuation

  • Psychological aspects of crew performance in medical emergencies during and after long duration space flight

  • Inherent risks associated with medical evacuation due to the weightless environment and the dynamics of reentry and landing

  • Medical requirements and capabilities of an LEO transport and return vehicle

  • Human factors aspects of a medical crew work station in return vehicles

  • Ethical issues and medical standards for evacuation from LEO and other space environments where return to definitive medical care is delayed or impossible (such as a Mars surface station)

Emergency Crew Return Vehicle History

The vehicle concepts that have been developed to take people to and from LEO fall into two broad classes: lifting bodies and ballistic entry vehicles. Several specific vehicle concepts and test articles have been proposed and developed over the years that never made it into production but are useful for review as new vehicles are being considered.

The earliest planned US space station, the USAF Manned Orbital Laboratory (MOL), intended to use a Gemini capsule for primary transportation and emergency return to Earth [10, 11]. Although this program did not materialize, the subsequent Skylab program utilized the three-crewmember Apollo capsule in a similar fashion, analogous to the use of the Soyuz in servicing a line of Russian stations as well as ISS. A modification of the Apollo capsule was evaluated to accommodate six crewmembers in the event that an Earth-originated rescue was needed. This capsule was later considered as part of the early post-Challenger Assured Crew Return Vehicle (ACRV) studies [12]. In the late 1980s, the European Space Agency (ESA) developed the concept of an Apollo-type capsule for use as a potential Crew Rescue Vehicle during studies for the proposed free flying Columbus European Space Station (ESS), which was not subsequently built. The main mission of the permanently docked Escape Vehicle was to allow the evacuation of and separation from ESS, followed by safe return to Earth and recovery of the entire crew by ground teams [13, 14]. Subsequent to the Challenger accident, the Crew Emergency Return Vehicle office was established at NASA Johnson Space Center to examine alternatives to using the Shuttle as a main rescue vehicle [15]. One such development by the Johnson Space Center engineering team was the Simplified Crew Rescue Alternative Module (SCRAM), conceived as a low-cost water lander configured to seat up to eight crewmembers and to sustain them for 24 h [16]. The vehicle consisted of a pressurized crew module to be attached to Space Station Freedom, the ISS progenitor, with an on-orbit life of up to 10 years once delivered. The aim was to use compatible tried and tested technology and existing search and rescue capabilities to minimize operational costs.

In the 1980s and early 1990s, NASA expended considerable effort to determine the need for escape and rescue provisions of manned space stations [17], particularly for the planned Space Station Freedom, with the Assured Crew Return Vehicle (ACRV) program. As attention turned to building and servicing the ISS, crew return concepts were focused once again on lifting bodies in the form of the X-38 CRV. Considerable development work, including drop testing of a prototype flight vehicle, was performed until the cancelation of the program in 2002. This has added significantly to the knowledge base of next generation orbital lifting bodies and their role in evacuation and medical transport [18]. Another lifting body design partially developed by NASA in the early 1990s was the HL-20. Although it did not progress to the flight test phase, the Sierra Nevada Corporation’s Dream Chaser, which has undergone preliminary flight testing, is derived from the HL-20 program and recently gained approval for payload delivery and return operations to and from the ISS between 2019 and 2024. Because of their relatively gentle entry acceleration loads and cross-range capabilities, lifting body designs will likely remain an attractive option for science payloads (and potentially astronauts requiring medical evacuation) for whom the relatively high impact acceleration forces of capsule landings are contraindicated. Figure 10.1 shows two lifting bodies, one used for a pioneering flight test program and the other the Sierra Nevada Dream Chaser.
Fig. 10.1

The X-24a Lifting Body (a) developed and tested during the 1960s, and the Sierra Nevada Corporation’s Dream Chaser (b) currently in development for ISS payload delivery and return operations. (Courtesy of NASA).

Capsule-based crew transport has been the most reliable means to orbit, consistently employed by the Russian Space Agency for decades. With the end of the Space Shuttle program, the US manned space program has similarly shifted its focus back to capsule utilization for future space flight. The Soyuz capsule in its basic design has provided on-orbit assured escape and crew return capability for the Salyut, Mir, and ISS stations along with its primary role of transporting crewmembers for nominal missions. The vehicle has limitations in both habitable volume and anthropometry, in addition to the requirement for the crew to wear a Sokol launch and entry suit to mitigate the risk from inadvertent depressurization. The Soyuz has undergone several improvements over many decades and was upgraded in 2010 to increase the size range of the crew it could accommodate due to a reconfigured and modernized crew cabin (Soyuz TMA-M) before being supplanted in 2016 by the Soyuz TMA-MS, which incorporated further avionics and technical improvements and is currently in service. The Soyuz has successfully provided a crew return capability since the beginning of the ISS program and will continue in this role for the foreseeable future (Figs. 10.2 and 10.3). New US crew vehicles will augment crew transport and allow further expansion of ISS crew size and mission options.
Fig. 10.2

The Russian Soyuz TM vehicles with the basic Soyuz design have successfully ferried crews to and from orbital space stations for three decades. (a) View from the International Space Station during proximity operations. (b) Crewmembers in Sokol pressure suit in form fitting ascent and entry couches. (Courtesy of NASA).

Fig. 10.3

Details of the Soyuz interior.

Evidence-Based Evacuation Risk: The Need for Transport

Long duration missions aboard the ISS require planning for a variety of potential adverse medical events. These events include possible medical evacuations, both urgent and anticipated. Spaceflight crews are very carefully selected, screened, and medically supported; despite these careful provisions, illness, accidents, life support system malfunctions, and logistic support problems may still occur. Though every effort is made to limit these risks, a medical event that exceeds onboard medical support capabilities should be anticipated with contingency plans developed to the greatest degree possible. Risk analysis is the first step in any medical contingency planning and is essential to justify allocation of time and resources. Successful planning could determine the difference between serious inflight morbidity or mortality and a favorable outcome with expedient and appropriate evacuation to a DMCF on Earth.

Since human space exploration began with the launch of Yuri Gagarin on Vostok 1 on April 12, 1961, over 550 astronauts and cosmonauts have flown, including 24 lunar surface or lunar orbit crew. Eighteen fatalities have occurred during space flight, including one during the Soyuz 1 mission, three in Soyuz 11, seven in the Space Shuttle Challenger, and seven in the Space Shuttle Columbia. In addition, three crewmembers were lost during the Apollo 1 fire in preparation for lunar missions. Further, a number of mishaps associated with high-altitude flight in preparation for space flight have occurred; notable incidents include the X-15 mishap that caused the death of astronaut Michael Adams and the recent Scaled Composites Spaceship Two mishap that killed pilot Michael Alsbury [19, 20, 21]. Launch aborts, aborts to lower than planned orbits, and mishaps during reentry have each presented life-threatening circumstances, and in several cases resulted in fatalities. A chronology of these spaceflight events, including flight contingencies, fatalities, near fatalities, and significant medical events, is detailed in Table 10.1 [17, 22, 23, 24, 25]. While not comprehensive, these events illustrate the complex human hazards associated with the spaceflight environment and the variety and nature of risks.
Table 10.1

Spaceflight medically related contingencies, Morbidity and Mortality, 1961–2003.

Date

Mission

Description

3/23/1961

Soyuz ground test

Cosmonaut Bondarenko died on March 23, 1961, in a spacecraft simulator fire with 100% oxygen environment

5/16/1963

Mercury 9

Elevated CO2 levels and loss of power to control system, required manual reentry

3/18–19/1965

Voskhod 2

Manual deorbit and service module failed to separate during reentry, landed 1200 miles off target. Crew rescued next day

3/16/1966

Gemini 8

Docked vehicles rotated out of control near structural limits. Crew landed early—waited overnight before ocean recovery

6/5/1966

Gemini 9

Astronaut’s helmet faceplate continually fogged over during EVA, impairing vision

1/27/1967

Apollo 1

Fire in crew module during ground test, with 100% oxygen environment. Three crewmembers, Chaffee, Grissom, and White, perished

4/24/1967

Soyuz 1

Parachute system did not deploy after reentry; capsule destroyed on impact, resulting in death of cosmonaut Komarov

1/18/1969

Soyuz 5

Spacecraft tumbled during entry, landing 2000 km off target, with hard impact. Cosmonaut had minor injuries

4/11–17/1970

Apollo 13

Mission to Moon aborted after oxygen tank ruptured. Crew returned safely. One crewmember developed urosepsis

4/23–25/1971

Soyuz 10

Failed docking with Salyut 1. During landing Soyuz air supply became contaminated and cosmonaut lost consciousness

6/29/1971

Soyuz 11

Cabin pressure failure during reentry. Three crewmembers, Dobrovolsky, Volkov, and Patsayev, perished

12 /1972

Apollo 17

Back strain from drilling core sample during walk on lunar surface

4/5/1975

Soyuz

18-A

Launch vehicle malfunction, second stage abort subjecting crew to nearly 20 +Gx. Crew landed in Eastern Russia and rescued the next day. Crewmember suffered minor internal injuries

7/24/1975

Apollo-Soyuz

Apollo crewmembers developed airway reactivity/pneumonitis from toxic contaminants during reentry, requiring hospitalization

8/24/1976

Soyuz 21/Salyut 5

Mission curtailed due to crewmember illness—related to environmental control systems problem

10/16/1976

Soyuz 23

After failure to dock with Salyut 6, capsule landed in blizzard conditions at night onto ice-covered Lake Tengiz; rescue team unable to recover capsule until next morning

11/11/1982

Salyut 7

Acute abdominal pain, probable kidney stone, resolved on orbit

9/26/1983

Soyuz T-10A

Launch abort due to pad fire, crew landed safely via capsule escape system

6/85–9/1985

Soyuz T-13

Hypothermia and CO2 toxicity during reactivation of Salyut 7

11/21/1985

Salyut 7

Crewmember became ill with prostatitis and urosepsis. Return to Earth required 56 days into a 216-day mission

1/28/1986

STS-51L

Solid rocket booster seal failure resulted in Space Shuttle destruction 73 s into flight. Seven crewmembers perished (Jarvis, McAuliffe, McNair, Onizuka, Resnik, Scobee, Smith)

1987

Mir 2

Crewmember developed persistent tachydysrhythmia during EVA, returned early on next mission of opportunity

6/1991

STS-40

Freezer motor malfunction causing formaldehyde toxicity and headaches, exacerbated by cabin noise

1995

Mir 18

Crewmember experienced episode of asymptomatic, sustained ventricular tachycardia. No mission impact

1995

Mir 18

Traumatic eye injury resolved with onboard treatment

2/23/1997

Mir 23

Fire due to oxygen generator failure; smoke and potentially toxic fumes in station. Mild second degree burns and reactive airway changes. Onboard treatment given

1997

Mir 23

Three crewmembers experienced upper airway irritation and dermal reaction following exposure to ethylene glycol

6/25/1997

Mir 23

Progress resupply vehicle collided with Spektr module during manual docking, resulting in station depressurization

8/14/1997

Soyuz TM-25

Soft-landing engine misfire at high altitude; hard landing

2/1998

Mir 24

Three crewmembers exposed to elevated carbon monoxide levels, with headache symptoms

10/1998

STS-95

Five crewmembers were exposed to a contaminated water supply leading to ingestions of potentially toxic trialkylamines

2/1/2003

STS-107

Space Shuttle Columbia was destroyed on entry; all crew were lost (Anderson, Brown, Chawla, Clark, Husband, McCool, Ramon)

5/4/2003

Soyuz-TMA-1

Ballistic reentry. Vehicle rolled due to high winds, crewmember suffered radial nerve palsy requiring treatment

4/19/2008

Soyuz-TMA-11

Ballistic reentry, nominal landing. Back injury requiring hospitalization

9/16/2011

Soyuz-TMA-21

Kazbek restraint strap failure resulting in knee injury after impacting control panel during nominal landing

3/16/2013

Soyuz-TMA-06M

Seat stroke mechanism fail, no injuries recorded

7/2013

ISS Expedition 36

During EVA, one crewmember experienced water filling the helmet causing difficulty seeing and breathing, requiring early termination of the EVA

Given the range of events described in the table, NASA developed three scenarios, or Design Reference Missions (DRMs), used as operational and developmental guidelines for an emergency transport vehicle [12]:
  • Loss of crew return or resupply capability, e.g., loss of a nominal transportation vehicle such as the Soyuz on the ISS

  • Escape from a time-critical ISS emergency, e.g., fire, decompression, and environmental control system failure

  • Full or partial crew return due to a medical emergency

The last category of DRM of the medical evacuation mission will be the primary focus of this chapter. The second scenario also carries the possibility of one or more crewmembers becoming ill or injured while evacuating from a time-critical event such as a fire, a contaminated station atmosphere, or a rapid decompression. This requires a transport/evacuation vehicle to have some stand-alone emergency medical equipment, along with cabin purge and atmospheric scrubbing capabilities, and a medical kit augmented for respiratory problems. Such an event happened to three American astronauts returning from the Apollo-Soyuz mission in 1975. The Apollo crew was exposed to nitrogen tetroxide (N2O4) gas when inadvertent reaction control system (RCS) firings allowed the gas to enter the command module through the cabin relief valve, which was open during descent. All three crewmembers required 100% oxygen, anti-inflammatory medication, and bronchodilator therapy after landing and were hospitalized for chemical pneumonitis for 3–7 days [26, 27].

Medical Event Risk Analysis Using Analog Space Crew Populations

In addition to reviewing medical data from astronauts and cosmonauts in long duration space flight, epidemiological risk data obtained from ground analog populations provide a source of representative medical events that might occur aboard a space station. The extrapolation of ground-based data to the space environment must be qualified for several reasons. Space flight involves specific physiologic adaptations and unique operational and occupational risks that are not duplicated on the ground and which are compounded by isolation from medical attention and preventive measures that might be used on Earth. In addition, the astronaut population is highly select, healthy, and receives extensive preventive medical care prior to launch; this population is poorly emulated by most ground analog populations. As a result, only approximate estimates can be made in attempting to predict frequency and type of medical events and their potential mission consequences in future LEO space activities or during a voyage to the Moon or Mars.

Despite these limitations, ground analogs remain the most appropriate means of supplementing inflight data to predict background medical events that have never occurred in space flight. To facilitate contingency planning, medical event incidence rates, expressed as events per person-year, are calculated to anticipate the likelihood of a possible evacuation occurrence for a crew of up to seven onboard the ISS. Here we will consider three examples derived from unique populations. The first is a ground-based analog population representing medical evacuations from the US National Science Foundation’s (NSF) Polar Medicine Program at US Antarctic stations. The second involves hospitalizations among US astronauts from 1959 to 2018. The third looks at actual Russian cosmonaut inflight events and evacuation data from 1971 to 2018.

Antarctic stations provide useful study analogs for space exploration programs. The Antarctic environment is one of the most extreme on Earth, with temperature, humidity, and microclimate providing conditions similar to those on the Martian surface [28, 29, 30]. Like spaceflight missions, the remoteness of Antarctic stations requires that the isolated facilities have stand-alone medical care capabilities. Evacuation capabilities are limited and may be nonexistent for up to 8 months due to weather, seasonal runway lighting, and sea-ice conditions. Additionally, their populations are medically screened; while their health characteristics differ significantly from those of the astronaut population, screening data provide a useful baseline to inform risk predictions, similar to risk analysis employed for space flight [31, 32, 33, 34].

The largest Antarctic station is McMurdo, typically with approximately 1200 occupants during the 4 austral summer months (November–February) and 200 occupants during the 8 winter-over months (March–October). A closer analog to ISS is perhaps Amundsen-Scott South Pole Station. With its smaller summer population peaking around 150 and its winter nadir at a mere 50 individuals, combined with its high field elevation of over 9,200 ft (2800 m) and correspondingly more severe temperatures, South Pole Station’s remoteness is an order of magnitude greater than that of McMurdo. All US Antarctic stations have extremely limited evacuation capabilities during the winter season. In 1998, the team physician, Dr. Jerri Nielsen, at McMurdo was self-diagnosed with breast cancer and began chemotherapy treatment prior to evacuation, necessitating a dangerous winter airdrop of chemotherapy agents and ultrasound equipment. Another dramatic Antarctic event occurred decades earlier at the Russian Novolazarevskaya Station. General practitioner Dr. Leonid Rogozov worked as the sole doctor in a team of 13 researchers. In April 1961, Rogozov developed appendicitis and after conservative treatment measures failed, performed his own appendectomy, and ultimately survived to become the head of surgery at the St. Petersburg Research Institute for Tubercular Pulmonology. More recently, a critically ill individual was evacuated from Amundsen-Scott South Pole Station in 2016 in a daring rescue during the Antarctic winter. These experiences underscore the remoteness and inaccessibility of such a location and suggest a need for more than a single expeditionary medical officer to be trained, in the event this individual becomes ill, injured, or otherwise incapacitated.

Medical evacuation (MEDEVAC) rates at US Antarctic stations have been studied retrospectively over different time windows; however, no fully comprehensive study exists to date. One large study reported MEDEVACs from McMurdo Station during the 5-year period from 1992 to 1996 [35]; more recent analysis has examined MEDEVACs from all major US stations from 2002 to 2014 [31, 32]. Detailed characteristics of evacuations originating from McMurdo Station from 1992 to 1996 are provided in Table 10.2. Over the 2002–2014 periods across 3 US Antarctic stations, 235 medical evacuations were reported, with a mean of 19.6 evacuations annually. Of these, 156 (66.4%) originated from McMurdo, unsurprising given its larger population year-round. Forty-eight (20.4%) MEDEVACs were performed from Amundsen-Scott South Pole Station over the same period, with the remainder originating from Palmer Station, the only US station residing above the Antarctic Circle. Statistics for all US Antarctic station medical evacuations during this period are summarized by disease or pathology category in Table 10.3.
Table 10.2

Incidence of medical evacuation events from McMurdo Station, Antarctica, 1992–1996 (total = 71).

Category

Number (%)

Trauma (by system)

34 (48%)

Orthopedic

23

Surgical

5

Dental

3

Ophthalmology

2

Neurology

1

Cardiopulmonary

8 (11%)

Arrhythmia

Angina

Pneumonia

Pulmonary embolism

Lung carcinoma

2

3

1

1

1

Dental conditions

7 (10%)

Internal medicine

6 (8%)

Insulin-dependent diabetes mellitus

Deep vein thrombosis

Other

2

1

3

Obstetric—Gynecological

5 (7%)

Breast disorders

Gynecology

4

1

Genito-urological

4 (6%)

Kidney stone

Testicular carcinoma

Prostatitis

Urinary tract infection

1

1

1

1

Psychiatric

3 (4%)

Surgical

2 (3%)

Neurology

2 (3%)

Table 10.3

Incidence of medical evacuation events from all US Antarctic Stations, 2002–2014 (total = 235).

Category

Number (%)

All medical

131 (55.7%)

Trauma

71 (30.2%)

Dental conditions

1 (0.4%)

Psychiatric

10 (4.3%)

Altitude-related

15 (6.4%)

Other/unknown etiology

7 (3.0%)

There are significant differences between both the population and the medical capabilities of US Antarctic stations and the ISS; even so, comparative rates of evacuation are useful analogs. The incidence of medical evacuation from Amundsen-Scott South Pole Station is calculated as 0.33 evacuations per operational month, equivalent to a 12-year average annual incidence of approximately 0.044 evacuations per person-year overall. Assuming roughly comparable medical capabilities of US Antarctic stations and ISS, the evacuation rates for the space station can be approximated. In reality, the capacity at the US stations extends beyond that of ISS in year-round number of trained medical providers, medical equipment, and pharmacological interventions available. The availability of even a limited supply of IV antibiotics places these stations closer to terrestrial standards than ISS; however, this makes their use as a predictive tool for MEDEVAC a “best case” approximation. Extrapolating from the South Pole Station analog population to a full ISS crew of six yields an estimate of approximately 0.26 evacuations from ISS per year. Based on this data, a possible evacuation event might be anticipated to occur onboard ISS about once every 4 years for the full crew complement, assuming comparable medical screening for these populations. With the knowledge that the astronaut population has more stringent health requirements and preventive medicine measures, it could be expected that actual ISS evacuation would be far less common than even our “best-case” analog above despite fewer medical resources. This has been borne out by our operational experience and affirms the ISS medical screening standards as effective in limiting medical events.

Where a flight-ready aircraft maintained at the US Antarctic stations at all times, the ISS analogy would be more accurate, though the risk of even winter transport in a C-5 Galaxy is fundamentally different than an emergency deorbit maneuver in a Soyuz or similar capsule. Minimal round-trip aeromedical transport time from McMurdo during a winter scenario without an on-site airframe, from time of request for transfer to time of arrival at the referral DMCF in Christchurch, New Zealand, is approximately 20 h. Flight time by C-130 Hercules aircraft is around 8 h one way. C-5 Galaxy operations, supported only at certain times of the year due to runway conditions, can cut Christchurch-McMurdo transit time down to 5 h. However, due to weather, the need for ground preparation prior to transportation, and margin for equipment failure, actual transport time is often greater than 48 h. The need for staged transport for patients not immediately located at McMurdo station (e.g., Amundsen-Scott South Pole Station, field camp locations) can extend total transport time to definitive care even further. By comparison, one Russian Soyuz per three crewmembers is always docked to the ISS, each having an on-orbit life of 210 days. The approximate time required for a Soyuz to be prepared on demand for a LEO emergency evacuation attempt can be measured in hours to days. During the early design evaluations of Space Station Freedom and until the Challenger tragedy of 1986, Space Shuttle evacuation from the space station was considered an optimal method of emergency crew return. However, later program reevaluation assessed this option as no longer viable for emergency rescue due to the long preparation time for a rescue Space Shuttle [36, 37]. On-orbit return capability, as with the current Soyuz spacecraft on ISS, offers clear logistical advantages, and with the ending of the Space Shuttle Program, the Soyuz remains the only option until additional vehicles are operational.

In many respects, the medical events that would necessitate evacuation from an Antarctic station are similar to several of the serious medical events associated with space flight (Tables 10.2 and 10.3) [31, 32, 33]. We can anticipate that treatment capabilities required for rescue from the ISS will be roughly analogous to those of Amundsen-Scott South Pole Station, though there will be unique differences due to microgravity. Both are isolated outposts, where rescue is difficult at best and impossible at times and where medical treatment will be required onsite. It should be noted, however, that in the event of a medical evacuation, the Soyuz is not comparable to a C-130 or C-5 with dedicated medical equipment and personnel onboard, due to severely limited medical support capability and volume. (Table 10.4)
Table 10.4

Representative nonfatal significant medical events during space flight, 1961–2013 (total = 27) (US and Russian events summarized from Table 10.1).

Category

Number of events

Trauma

Orthopedic

Skin exposure to glycol

Second-degree burns

Other

1

1

1

1

Cardiopulmonary

Dysrhythmias

Toxic inhalation/pneumonitis

Reactive airway disorders

Water in helmet during EVA

3a

3

3

1

Internal medicine

Chronic headache

Cellulitis upper extremity

Toxic ingestion

Other unspecified

1a

1

5

1

Genitourinary

Renal stone

Prostatitis

Urosepsis

Urinary retention

1

1a

2

1

aEarly crew return due to event in this category

Significant medical events occurring during space flight have generally not been related to orthopedic or surgical trauma [38]. More common, for example, are respiratory problems due to atmospheric contamination in the closed cabin environment. Morbidity from gravity-based events on Earth (e.g., falls) and other accidental injuries (e.g., motor vehicle accidents) is not represented in weightlessness. Additionally, common metabolic conditions such as insulin-dependent diabetes mellitus are effectively screened out by selection and preflight medical evaluations and would be very unlikely to develop during space flight of moderate duration. Medical screening standards are therefore an important factor in medical risk analysis and are discussed in Chap.  11, Medical Evaluation and Standards.

A study of astronauts conducted in 1999 to estimate the occurrence, type, and severity of injury and illness onboard the ISS used retrospective data review of records from the NASA Johnson Space Center Lifetime Surveillance of Astronaut Health (LSAH) to characterize astronaut hospitalizations [39]. The LSAH archives comprise clinical and hospitalization data collected from 1959 to the present (Table 10.5). Each medical event was characterized according to whether, if it had occurred inflight, satisfactory treatment could have been accomplished utilizing the Health Maintenance System (HMS), a component of the Crew Healthcare System (known as CHeCS), currently deployed on ISS.
Table 10.5

ISS medical event classification.

Class

Description

Class I medical event

No mission impact, e.g., minor muscle strain

Class II medical event

Significant medical event requiring use of the ISS HMS

Class II a

Manageable with the HMS and not likely to require evacuation or affect mission duration, e.g., prostatitis

Class II b

Manageable with the HMS but may require the astronaut to return at next available opportunity for further evaluation and treatment, e.g., breast mass

Class II c

Manageable with the HMS but may necessitate emergent evacuation if condition does not improve or worsens, e.g., cardiac dysrhythmia

Class II x

An event unlikely to occur in a microgravity environment or one that would be detected in a pre-mission evaluation, e.g., herniated nucleus pulposus

Class III medical event

An event requiring emergent evacuation from the ISS, e.g. acute appendicitis, cerebral hemorrhage

More recently, medical events requiring hospitalization were identified from the LSAH in 2018 and categorized according to the same criteria. The results, shown in Tables 10.6, 10.7, and 10.8, describe the individual medical events. There were a total of 119 hospitalizations distributed among active US astronauts between 1959 and 2018, not including hospitalizations of retired or former astronauts. This nearly 60-year time period represents a total of over 4430 person-years. An estimate of potential evacuation events applicable to the ISS setting can be made by subtracting from the total hospitalizations the Class II x events (n = 29) that are either unlikely to occur in a microgravity environment or that would be detected and effectively screened out in a pre-mission evaluation. Using all non-preventable events, the anticipated evacuation incidence would be about 0.02 events per person-year. If it is assumed that an onboard HMS can be used to manage some events that would otherwise require evacuation (Class II c, n = 19), the anticipated evacuation incidence is reduced further and may approach about 0.004 per person-year. In effect, availability of an onboard HMS can significantly decrease the likelihood of a medically necessary evacuation. The importance of a well-equipped and staffed onboard medical system for risk mitigation is evident.
Table 10.6

Class II LSAH Astronaut Hospitalizations, 1959–2018 (total = 101).

Class II a medical events (n = 23)

Class II b medical events (n = 30)

Ventricular tachycardia, exercise-induced

Infectious colitis

Atrial septal defect

Abdominal pain, right lower quadrant

Internal hemorrhoids

Urinary tract infection

Severe epistaxis

Traumatic subluxation of left shoulder

Neck pain

Cellulitis

Venous varicosity

Postherpetic neuralgia

Fracture of the 4th metacarpal

Fracture of the 5th metacarpal

Fracture of the tip of terminal phalanx

Freiberg’s disease (incomplete fracture without displacement of the fragments)

Cartilaginous loose bodies in joint

Minor superficial surgical wound infection

Irritated compound nevus

Paroxysmal idiopathic atrial fibrillation

Diarrhea, Clostridium difficile

Meniere’s disease

Transient exercise-induced visual loss

Thyroid papillary carcinoma with lymph node metastases

Thyroid nodule

Asymmetric goiter

Cervical dysplasia

Paralysis of right vocal cord

Inguinal hernia (left, right, bilateral)

Testicular trauma with fluid collection

Impingement syndrome of shoulder

Severe lumbosacral spasm

Left infrascapular pain with paresthesia of left fingers

Fracture of lateral malleolus

Fracture of 5th metatarsal

Anterior cruciate ligament tear

Meniscus tear (medial, lateral)

Anterior talofibular ligament tear

Class II c medical events (n = 19)

Class II x medical events (n = 29)

Traumatic pneumothorax

Hemopneumothorax

Pneumonia

Viral pneumonitis and pleuritis

Recurrent cardiac arrhythmia

Ulcerative colitis

Active duodenal ulcer

Cholelithiasis/chronic cholecystitis

Acute diverticulitis

Left flank pain

Hemorrhagic corpus luteum

Dysmenorrhea

Corneal ulcer

Shoulder dislocation

Septic arthritis of knee

Infectious mononucleosis

Urosepsis

Near syncope

Incidental finding of anomaly of the coronary artery

Joint replacement surgery

Fracture of the left 4th through 10th ribs

Cervical radiculopathy/cervical spondylosis

Back pain/Lumbar radiculopathy

Lumbar radiculopathy secondary to HNP

C5-6 HNP and osteophyte

C7 radiculopathy secondary to HNP

Comminuted fracture of left radius and ulna

Compound fracture of left ankle and right hand

Excision of exostosis

Styloidectomy

Lumbar vertebral fusion

Vasectomy

Colectomy

Fracture of first four metatarsals of left foot

Symptomatic buried hardware in left foot

Childbirth, both cesarean and vaginal delivery

Class II—Ground-based significant medical events requiring ISS HMS intervention if occurring on-orbit. (HNP = herniated nucleus pulposis)

Table 10.7

Class III LSAH astronaut hospitalizations, 1959–2018 (total = 18).

Class III—medical events (n = 18)

50% total body surface area burn/30% third-degree burn

Diffuse chemical pneumonitis from toxic inhalation (of nitrogen tetroxide) (three individuals)

Anaphylactoid reaction to intravenous tracer

Acute appendicitis

Ruptured retroperitoneal appendix

Pancreatitis/choledocholithiasis

Pulmonary embolism

Nephrolithiasis

Cholecystitis

Cholelithiasis

Tendon rupture

Retinal detachment

Cervical spinal stenosis with central cord syndrome

Cervical spondylosis with Brown-Sequard syndrome

Metastatic melanoma

Cerebrovascular accident

Class III—Ground based significant medical events requiring evacuation if occurring on-orbit

Table 10.8

Categories of LSAH astronaut hospitalizations, 1959–2018.

Total hospitalizations

119

Trauma

14

Neurological

17

Gastrointestinal

10

All surgical (musculoskeletal)

32 (19)

Pulmonary

9

Obstetrical

18

Cardiac

6

Other

13

The most useful and directly applicable data for estimating spaceflight medical evacuation risk stems from careful analysis of actual spaceflight medical events. The Russian space program has returned three cosmonauts prematurely for medical reasons; there have been no other evacuations for medical contingencies in manned spaceflight history. Only one of these was from the Mir station, which operated from February 1986 to May 2000, resulting in a Mir evacuation rate of 1 per 31 person-years. Including space flight during Apollo, Skylab, Mir, Space Shuttle, and ISS programs, there have been a total of 141 person-years of space flight as of ISS Expedition 55. This yields an overall evacuation rate of 0.022 evacuations per person-year of space flight. Risk data from the populations discussed above, including Antarctic station evacuations, LSAH astronaut hospitalizations, spaceflight medical events, and the NASA Medical Operations provide a basis for estimating ISS evacuation event incidence rates for a six-person crew during a hypothetical 1-year mission (Table 10.9).
Table 10.9

Evacuation estimates for ISS from ground analog and inflight populations for 1-year mission.

Population

Evacuation events

Estimated incidence

Estimated yearly

evacuation rate

Estimated time between evacuations

 

Events/person-years

Events per person-year

Evacuations/year

Years/evacuation

Analog

    

(1) 2002–2014 Amundsen-Scott South Pole Station

Total 48

48/1100

0.044

0.131 (3 crew)

0.264 (6 crew)

7.6 years (3 crew)

3.7 years (6 crew)

(2) LSAH astronaut hospitalizations

Class II c (19) and III (18), i.e., events

requiring evacuation

37/4430

0.008

0.024 (3 crew)

0.048 (6 crew)

41.6 years (3 crew)

20.8 years (6 crew)

Inflight

    

(3) Cosmonaut evacuations (Primarily long duration flight)

All Events—1959–2018

3/74

0.041

0.122 (3 crew)

0.243 (6 crew)

8.2 years (3 crew)

4.1 years (6 crew)

Medical Events Only

2/74

0.027

0.081 (3 crew)

0.162 (6 crew)

12.3 years (3 crew)

6.2 years (6 crew)

Mir Station—1987–5/2000

1/31

0.032

0.096 (3 crew)

0.194 (6 crew)

10.4 years (3 crew)

5.2 years (6 crew)

(4) Astronaut evacuations (Primarily short duration flight)

1961–2018

0/54

0.000

(5) NASA Medical Risk Study

Likely mission impact/possible evacuation, Class II

0.059

0.177 (3 crew)

0.354 (6 crew)

5.5 years (3 crew)

2.8 years (6 crew)

Critical medical events

Requiring Evacuation

Class III

0.010

0.030 (3 crew)

0.060 (6 crew)

33.3 years (3 crew)

16.6 years (6 crew)

More recently, the NASA Human Research Program Exploration Medical Capabilities Element at Johnson Space Center has analyzed significant medical events across the Space Shuttle program, Mir, and ISS through Expedition 13 [40, 41]. Reported medical events are detailed in Table 10.10.
Table 10.10

Number of occurrences of reported medical conditions that have affected US astronauts during prior space missions, through ISS Expedition 13.

Medical condition

Events

Medical condition

Events

Allergic reaction (mild to moderate)

11

Oral ulcer

9

Ankle sprain/strain

11

Nasal congestion (space adaptation)

389

Back injury

31

Neck injury

9

Back pain (space adaptation)

382

Nose bleed

6

Barotrauma (ear/sinus block)

31

Otitis externa

3

Choking/obstructed airway

3

Otitis media

3

Constipation

113

Paresthesias

26

Diarrhea

33

Pharyngitis

11

Elbow sprain/strain

12

Respiratory infection

33

Eye abrasion (foreign body)

70

Shoulder sprain/strain

22

Eye chemical burn

6

Sinusitis

6

Eye infection

5

Skin abrasion

94

Finger dislocation

1

Skin infection

13

Fingernail delamination (EVA)

16

Skin laceration

1

Gastroenteritis

4

Skin rash

94

Headache (CO2 associated)

20

Smoke inhalation

3

Headache (late)

49

Space motion sickness (space adaptation)

325

Headache (space adaptation)

233

Urinary incontinence (space adaptation)

5

Hemorrhoids

2

Urinary retention (space adaptation)—Female

5

Herpes zoster reactivation (shingles)

1

Urinary retention (space adaptation)—Male

4

Indigestion

6

Urinary tract infection—Female

5

Influenza

1

Urinary tract infection—Male

4

Insomnia (space adaptation)

299

Neuro-ophthalmic syndrome (space adaptation)

15

Insomnia (late)

133

Wrist sprain/strain

5

Knee sprain/strain

7

  

From [40, 41]

Using the most conservative rates from the NASA Medical Risk study, a Class II event (significant medical event requiring the HMS, with potential for mission impact and or evacuation) can be expected to occur approximately once every 5.6 years for a crew of three and every 3.2 years for a crew of six occupying ISS, while a Class III medical evacuation event might be expected to occur one to three times during a 15-year period of ISS operations for a crew of six based on flight surgeon assessment of risk [42]. This low but significant probability prompted the initial development of a medical evacuation capability. The potential need for evacuation drove an allowable contingency where an ill crewmember might be returned unsuited, allowing airway access, physiological monitoring, and other interventions where appropriate. While technically possible on the Soyuz, this is well outside of operational norms and would confer considerable additional risk in the event of a landing mishap. This has additionally driven NASA medical experts to consider the requirements for more advanced treatment of ill and injured crewmembers prior to return from the ISS on the Soyuz. It is noteworthy that these estimates are based solely upon primary medical events and do not consider possible failures of onboard life support systems or nonmedical emergencies such as vehicle system failures.

The Exploration Medical Capabilities Element (ExMC) at NASA is specifically tasked with establishing evidence-based methods of monitoring and maintaining astronaut health as future mission profiles extend beyond the relative proximity of LEO. The utilization of probabilistic risk assessment modeling (PRA) offers a powerful tool toward this end, and PRA has been employed by the ISS program as a method for quantifying medical risk as a component of human systems integration with vehicle safety concerns since the late 1990s. While PRA had been extensively utilized by the engineering community, its use for the purpose of predicting medical risk associated with human spaceflight activities was initially hampered by a paucity of inflight event data, with initial PRA models based primarily upon medical expert opinion. By contrast, the current Integrated Medical Model (IMM) now incorporates all NASA inflight medical event reports, the evidence base of the terrestrial analogs discussed here, and the available medical diagnostic and treatment resources maintained on ISS [43, 44]. The benefits such an approach to risk quantification can offer are myriad. The ability to compare predicted risk for a given medical scenario across different DRMs in an objective way will help inform the medical capability trade-offs that will need to be made for longer, exploration-class missions. More immediately, the communication of health and safety risks from the NASA medical community to the engineering community has been a perennial challenge, as experts in each field draw on different backgrounds with different conceptions of risk. These communities can find a common vocabulary in the use of PRA to communicate scenario-specific medical risk in quantifiable terms.

Standards of Medical Care in Space Flight

Physicians and medical support personnel have been involved with flight since the earliest days. The French physician Jean-Francois Pilâtre de Rozier was one of two crewmembers of the first manned balloon flight in 1783. Aeromedical transport as well has evolved throughout the history of flight. In the United States, air evacuation began soon after the Wright brothers flew in 1903. By World War II, the use of aircraft to carry injured soldiers had become widespread, and flight crews were being specifically trained for medical transport [45]. Helicopter evacuation to Mobile Army Surgical Hospital (MASH) units began during the Korean War and continued in the Vietnam War era, with decreasing transport time contributing to improved battlefield survival. By the 1970s, civilian aeromedical emergency care began in earnest in the United States. Since then, standards of care for the medical treatment, stabilization, and transportation of patients by air have steadily evolved along with ground-based standards. Advancements in the fields of emergency medicine, triage, and evacuation have contributed significantly to the safety, efficiency, and acceptance of aeromedical transport. Technical developments in medical sensors, equipment miniaturization, telecommunications, and emerging life support and therapeutic modalities, along with advanced ambulance capabilities, helicopter, and fixed-wing aircraft designs, have contributed to the utilization and success of aeromedical transport.

Terrestrial ground and air ambulance standards of care are an appropriate starting point to develop standards for advanced life support (ALS) stabilization and transport/evacuation capabilities for space flight. Human space flight has always provided a means of return for crewmembers in the event of an emergency. This may be the transport vehicle itself, such as the Apollo capsule or the Space Shuttle. In the case of space stations, this may be a dedicated return vehicle such as the Soyuz that is attached, periodically rotated, and remains ready for use. The ALS standards of care for the ISS HMS and the CRV evolved from standards of care set forth by the American Heart Association’s cardiopulmonary resuscitation (CPR) and Advanced Cardiac Life Support (ACLS) programs, the American College of Surgeons’ Advanced Trauma Life Support (ATLS) program, the US Naval and NASA Hyperbaric Medicine Teams, and the NASA Medical Operation’s Exploration Medical Capability Team.

Efforts to develop the equipment, techniques, and training protocols for the delivery of emergent healthcare to an astronaut population in the unique environment of space have been significant and ongoing at NASA Johnson Space Center. Ground models, reduced gravity parabolic flights, and space-based simulations have all been utilized in the development of ALS capabilities [46]. An ALS animal model for performing parabolic-flight microgravity ACLS and ATLS research and training has also been developed and has been used to train flight surgeons and provide supplemental training for crewmembers of the ISS [47]. These efforts have led to the inclusion of limited ALS capabilities, including cardiac defibrillators, airway management items, and cardiac drugs on the Mir station and now the ISS (see Chap.  6, Spaceflight Medical Systems).

Other key elements contribute to support a given standard of care. First is the training of the designated CMO in assessing an injured companion and the ability to send a diagnostic evaluation to the flight surgeon. Currently ISS crewmembers receive dedicated medical training, enhanced where feasible with “hands-on” clinical activities, as the CMO is not a physician in most cases. CMO training is a mix of basic and advanced medical topics. Though crewmembers are trained in ACLS protocols, they do not have the experience of a full-time practicing emergency medical technician (EMT) or paramedic. Furthermore, the typically intensive training schedules that crewmembers follow in the pre-mission phase limits the time available for dedicated medical training. Onboard proficiency reviews and periodic emergency medical drills help to mitigate the remote training effect.

A second element readily available with secure telecommunications is consultation with ground medical specialists [48, 49]. The high bandwidth capabilities of the ISS allow for video, audio, and data channels to support medical events in essentially real time. In addition, processes, procedures and training are developed to enable crewmembers to medically intervene without ground support should this be necessary. While such real-time consultation is invaluable for near-Earth operations, future mission profiles beyond cislunar space will introduce communication delays necessitating increased crew autonomy, with adjunctive just-in-time training likely necessary to supplement delayed ground-based medical consultation.

The minimum standards for spaceflight ALS (Table 10.11) are based upon US standards for ground transport via ambulance. These represent the desired capabilities of a first responder in an ISS emergency care scenario. Projected medical capabilities (Table 10.12) reflect the anticipated diagnostic and therapeutic standards of care necessary for LEO, lunar, and planetary mission scenarios, derived from various working groups within NASA Medical Operations and incorporating advanced biotechnologies, medical informatics, and enhanced CMO training and skills.
Table 10.11

Required medical capabilities for minimum care standards on ISS.

Level of care

Minimum capabilities required

Basic

Basic CPR and first aid, including splinting and bandaging

Intermediate

Limited or modified ACLS and ATLS capabilities:

 • Crew medical restraint system (CMRS)

 • Intravenous and intramuscular therapeutics

 • Electrocardiography monitoring

 • Defibrillation

 • Airway management including medical suction

 • Mechanical ventilation

Augmented

Limited or modified hyperbaric treatment

(using the combined pressure of cabin and EVA suit)

Advanced

24 h medical evacuation time to definitive medical care

facility with hyperbaric chamber capability

CPR cardiopulmonary resuscitation, ACLS advanced cardiac life support, ATLS advanced trauma life support, EVA extravehicular activity

Table 10.12

Projected medical capabilities for low Earth orbit and beyond (Moon, Earth/Sun and Earth/Moon libration points, and mars).

Advanced life support capabilities

CMO training

Time to DMCF—24 h

 

Low Earth Orbit (ISS)

Skill level

Specialized restraint systems

Intravenous/intramuscular medications

Oral and endotracheal airway/cricothyrotomy

Automated pneumatic ventilator

Blood pressure monitoring and pulse oximetry

BLS protocols

Emergency medical technician

Informatics/telemedicine remote medical direction

Defibrillator with external cardiac pacing

ECG monitoring

IV fluids

Modified ACLS and ATLS protocols

Paramedic

Hyperbaric treatment

Ultrasonography (abdominal, cardiac, thoracic)

Physician

Lunar missions/stable Lagrangian platforms

 

Time to DMCF—days to weeks

 

Low Earth orbit/ISS capabilities with augmented supplies

Radiation shelter

Physician and paramedic

or

paramedic and paramedic with advanced training

Mars and other expeditionary missions

 

Time to DMCF 9–30 months

 

Lunar capabilities with augmented supplies

Stand-alone capabilities:

 • Limited surgical intervention

 • Banked or synthetic blood

 • Banked bone marrow

 • Informatics/expert systems/clinical decision-support tools

 • Radiographic/MRI diagnostic imaging

 • Recuperation and convalescence capabilities

Physician (with surgical training) and paramedic

or

physician and paramedic with advanced training

CMO crew medical officer, DMCF definitive medical care facility

Biodynamic Aspects of Returning Vehicles

Any spacecraft in stable low Earth orbit will by definition be traveling over the ground at speeds in excess of 17,000 mph; to return a spacecraft and crew safely to Earth, several hurdles must be cleared. For landings such as those on the lunar surface or similar rocky body without an appreciable atmosphere, rocket-powered deceleration slows a spacecraft for a soft landing. For returning crew vehicles to the Earth, the atmosphere provides a natural source of drag that can be harnessed to slow a returning vehicle without the need for large amounts of fuel. However, the spacecraft must dissipate enough kinetic energy to allow a pre-landing velocity that is slow enough for a safe recovery by parachute or other final landing systems and must dissipate that energy in a manner that does not cause either excessive spacecraft heating or acceleration forces that are incompatible with human life.

Whether discussing capsule or lifting body operations, once the initial deorbit burn is complete, the spacecraft will be on a trajectory that ensures intersection with the atmosphere and eventual return to the ground. Once atmospheric entry interface occurs, atmospheric drag will dissipate energy at a rate defined:

dE/dt = D · v

where dE/dt is the change in interaction energy between the vehicle and the atmosphere in unit time, D is the atmospheric drag force experienced by the vehicle, and v is vehicle velocity.

As is evident, the longer the entry time, the less energy per unit time will need to be dissipated. This will reduce the peak acceleration delivered to vehicle (and crew).

For comparison, the Space Shuttle’s lifting body design resulted in an atmospheric entry period that lasted approximately 1800 s with a nominal peak acceleration < 2.0G, whereas nominal Soyuz entry lasts approximately 400 s with peak acceleration > 4.25G [50]. Crew body orientation differences between vehicles resulted in Space Shuttle forces being delivered primarily in the head-to-toe (+Gz) vector for non-recumbent seats, while Soyuz accelerations are primarily in the chest-to-back (+Gx) direction.

Sustained Acceleration

The past half-century of capsule and lifting body spacecraft design has drawn from human tolerance data gathered from high performance aircraft and human centrifuge trials to ensure acceleration forces delivered to crew allow for continued functional capacity throughout launch, entry, descent, and landing operations. NASA details time-variable safety limits for translational accelerations experienced by returning crew, with sustained limits established for each axis and direction (±Gy indicating lateral acceleration forces; Gx and Gz vectors as described above) [51]. These limits are further broken out into limits for nominal operations and contingency events including abort or emergency entry. Exposure to acceleration above these limits risks significantly affecting human performance of critical tasks that may require interaction with the spacecraft.

The deconditioning and adaptive effects of prolonged exposure to microgravity are taken into account in the lower tolerance limits established for return to Earth compared to launch operations. As shown in Fig. 10.4, NASA observes a 0.5 s nominal duration limit of 8.3 +Gz on launch, but only 2.0 +Gz for the same duration on return and landing. Conversely, in the extreme condition of a launch abort or emergency entry, acceleration limits are significantly higher for good reason: it may be necessary to expose crew to accelerations outside of the range where normal human performance is possible in order to preserve their lives. In these scenarios, the need for the performance of critical crew tasks is engineered out to the greatest degree possible, so that once an abort is initiated the crew may ideally remain passive until excessive acceleration loading has dissipated. The accelerations required to reach a safe radius may be extreme, e.g., for a launch pad explosion, however, the emergency/abort limits established ensure that the loads will remain compatible with human life. Exposure to translational acceleration rates greater than these higher limits significantly increases the risk of crew incapacitation, ultimately threatening survival [51].
Fig. 10.4

NASA +Gz (head to foot, “eyeballs down”) Sustained Translational Acceleration Limits vs time. Compared with launch loads, limits are set lower for return considering the effects of spaceflight deconditioning and susceptibility to orthostatic intolerance. Abort limits are more severe but should preserve life in emergency scenarios.

Due to accelerations in Gx being relatively well tolerated in both positive and negative vectors [52, 53, 54, 55, 56], crew return vehicle designs have uniformly sought to orient crew body positioning to direct the majority of launch and entry acceleration loading into +Gx for both healthy and deconditioned crew. Minimizing +Gz loading becomes more important for returning crew, as the risk of orthostatic intolerance following long duration space flight is not insignificant [57, 58].

An assessment of both capsule and lifting body spaceflight experience shows crew have historically been exposed to only a narrow range of acceleration forces along the Gz vector irrespective of vehicle design [59]. While limiting the magnitude and duration of +Gz exposure for crew at risk of orthostasis makes empirical sense, the rationale for limiting sustained –Gz exposure is more subtle. The first is that –Gz is poorly tolerated as an impact vector, and crew orientations that impart –Gz loads immediately prior to landing risk directing landing impulse accelerations toward the head and shoulder restraints instead of the seat or couch designed to protect them. The second is due to the unique pathophysiology of deconditioning associated with space flight, discussed in detail below. The third is historical precedent: to date, the lowest magnitude sustained Gz exposure for a crew returning to Earth from a microgravity environment, independent of mission duration or vehicle, has been approximately +0.2Gz [59].

There is a risk of sustained acceleration loads exacerbating or otherwise contributing to underlying pathophysiology in the case of a medical evacuation. Even for nominal returns, the advent of commercial space flight poses the opportunity for less than ideally healthy individuals who can pay for access to space to be exposed to all of the physiological stressors of space flight. They can be expected to do this without the benefit of the rigorous selection screening, longitudinal physical conditioning, and close medical care historically enjoyed by US and international partner astronauts. To better quantify these new risks, research conducted by the University of Texas Medical Branch with the FAA Center of Excellence for Commercial Space Transportation in 2014 examined how the presence of several known medical diseases affected acceleration tolerance for simulated launch and reentry profiles. Results suggest that disease processes including hypertension, cardiovascular disease, diabetes, obstructive pulmonary disease, and back or neck orthopedic injury or disease may withstand the acceleration forces of launch and reentry without serious exacerbation or deterioration [60, 61]. That evidence suggests persons with a range of disease processes may do well through the stresses of entry with adequate control, and close monitoring informs our risk assessment for medical evacuations or expedited returns.

Angular Acceleration

Translational sustained loads are largely unavoidable for any returning vehicle—mitigation is thus limited to directing these forces in the most tolerable vectors for the human occupants. Angular accelerations, however, can be limited to a much greater extent and should be eliminated if possible given their potentially severe impact on crew performance. While sustained rotational accelerations can indeed also post a danger to crew, the threshold for impact on performance is markedly lower than that at which such accelerations become a threat to crew health. NASA requirements for crew vehicles recognize that crewmembers are not expected to tolerate sustained (>0.5 s) rotational accelerations in excess of 115 deg/s2 without significant discomfort and disorientation and further established a limit for cross-coupled effect of no greater than 2 rad/s2 in pitch, roll, or yaw [51, 62]. For cross-coupling beyond this magnitude, significant impacts on neurovestibular and sensorimotor performance affecting physical reach and cognition are expected. Such detrimental impacts of angular and rotational acceleration are an important concern for any loss of control scenario such as uncontrolled jet firing, incomplete module separation during launch or entry operations, or uncontrolled venting from another pressurized gas source. Such incidents have precedent within the US space program’s history: in 1966, the Gemini VIII astronauts Neil Armstrong and David Scott were exposed to rotational velocities up to 50 rpm with exposure to ±0.92 Gy and −0.89 Gz for 46 s due to a malfunctioning orbital flight attitude thruster [63, 64]. While control of the vehicle was eventually achieved, the crewmembers reported impaired vision, vertigo, and near incapacitation.

Impact Criteria of Returning Vehicles

Protection of crewmembers during landing presents a significant design challenge. Tolerance to linear acceleration depends on a variety of factors including acceleration magnitude and direction, onset rate and duration of acceleration, effectiveness of vehicle and crewmember protection, and physiological condition and deconditioning. Research has shown that with properly designed seats outfitted with side supports and restraints, even relatively high accelerations can be tolerated. NASA protection standards for landing impact loads are based on the Brinkley Dynamic Response Criterion (BDRC) [65]. The BDRC, which is incorporated into NASA–STD-3001, uses a mathematical model of impact mechanics to evaluate the risk of injury to a crewmember based on the dynamic response of the body to a given impact acceleration event. Using linear acceleration and angular velocities, along with assumptions of padding and restraint characteristics and conformality of seats, the seat and occupant motion can be calculated. The dynamic response of a crewmember can be assessed by use of a model incorporating 6 degrees of freedom. For each body axis (x, y, and z), an injury risk level can be determined. In the BDRC model, the probability of injury is categorized as low (0.5%), medium (5.0%), or high (50%).

To match the conditions of restraints for which the dynamic response model is valid, crewmembers must be restrained in such a manner to restrict pelvic, torso, and negative Gz movement. This would entail a five-point harness that meets or exceeds civil aircraft restraint standards as determined by the Society of Automotive Engineers [66]. During dynamic flight, particularly with an injured crewmember with impaired limb control, flail injuries are possible. Therefore a suit and or restraint system should address this concern with lateral restraints such as shoulder and leg bolsters or garters. It is noteworthy that the majority of testing in the development of the BDR model was conducted on subjects less than 30 years old, where spaceflight crewmembers range in age from the mid-30s to the mid-50s. Using the model as a predictor of risk in older crewmembers, along with the added factor of spaceflight deconditioning, may require a more conservative approach.

New Earth orbiting transport vehicles under development closely emulate prior capsules, with largely ballistic atmospheric entry profiles and parachute systems. It is highly instructive to look at injury risk classifications for prior programs to best inform design and risk assessment of these new spacecraft. The Mercury capsule, nominally water landing, demonstrated a low probability of injury for land and water touchdowns, with a BDRC of 0.32–0.99%. Apollo capsules, also nominally water landing, showed a low probability of injury for all scenarios with a BDRC of 0.25–0.34%. The BDRC has also been used to evaluate tests of the Russian Soyuz prior to its adoption as a regular mode of transit to ISS for US crewmembers. These analyses included BDRC limits for both Mir and modern era Soyuz capsules (TM/TMA) and for long duration, deconditioned crewmembers [62]. While Soyuz BDRC values are not approved for public release, nominal Soyuz landings post-2010 are publicly reported to approximate a 5G load at impact, delivered predominantly in the +Gx and +Gz vectors [67].

In capsules lacking roll control (i.e., the capsule rotates freely under canopy during descent, making any direction along the 360° rotation a potential impact orientation), a nominal return orientation providing crew couch/seat inclines greater than +0.5Gz prior to impact was chosen by the former USSR, Russia, and the United States, minimizing both sustained –Gz and impact –Gz impulses to the crew [59]. Newer capsule vehicles that lack role control are expected to deliver a greater fraction of the total vertical impact load into the +Gx vector, which as noted above is relatively well tolerated. The trade-off in design this presents is the potential for impact loads from any capsule lateral motion to be delivered along the ±Gz or ±Gy vectors, which are far less tolerable. The Orion Multi-Purpose Crew Vehicle (MPCV) design includes the use of reaction control thrusters to provide roll control during nominal descent under canopy, ensuring landing loads can predominantly be directed into the more tolerable ±Gx and +Gz.

Pathophysiology of Deconditioned Returning Crewmembers

Another step in the delineation of spaceflight medical transport and evacuation capabilities requires discussion of the deleterious effects of microgravity exposure on the physiologic state of a crewmember returning to a 1Gz environment. This section will summarize the pathophysiologic state encountered during the transition from microgravity to normal gravity and how this transition may influence medical transport of an ill or injured crewmember to an Earth-based DMCF.

During readaptation to Earth’s gravity, three physiological systems are significantly compromised: musculoskeletal, neurovestibular, and cardiovascular. These physiologic decrements can produce serious functional and performance limitations for returning deconditioned crewmembers. Returning from missions of up to 14 days, such as were typical for prior Space Shuttle and Soyuz taxi flights to the ISS, most crewmembers are sufficiently readapted to be able to walk satisfactorily, though with a slightly abnormal gait, within 30–60 min following landing. During the NASA Skylab, Space Shuttle-Mir, and ISS programs involving long duration flights of 1–6 months, returning crewmembers were occasionally unable to ambulate normally for several hours, due to neurovestibular and cardiovascular compromise, made worse by the musculoskeletal deconditioning accompanying weightlessness. Bone mineral density losses associated with Mir missions, for example, ranged from 1 to 1.5% per month in the lumbar spine and pelvis. With the current suite of countermeasures equipment on ISS, these losses have been significantly reduced [68, 69].

The immediate readaptive state of deconditioned long duration crewmembers (>30 day flight duration) upon reentry and exposure to a 1G environment is marked by functional deficits, described in detail in Chap.  20 (Physical Performance, Countermeasures, and Postflight Reconditioning).

A more recently recognized phenomenon that may relate to sustained acceleration in the Gz axis involves mildly elevated intracranial pressure and neuro-ophthalmic structural changes as a result of prolonged exposure to microgravity. A constellation of findings including optic disc edema and optic nerve sheath distension, globe flattening, choroidal folds and other retinal findings, and moderately elevated intracranial pressure (ICP) as assessed by postflight lumbar puncture has been recognized in the last decade [70, 71, 72]. Findings have been collectively known as vision impairment/intracranial pressure (VIIP) disorder, microgravity ocular syndrome, spaceflight-associated neuro-ocular syndrome (SANS), and other monikers by various investigators. This text will use the most recent designation of SANS. These effects are being newly considered for their possible effects on tolerance to sustained and impact acceleration forces following long duration space flight.

To date, long duration crewmembers returning to Earth, either recumbent on the Space Shuttle middeck or in the Soyuz, have been exposed to minimal sustained +Gz due to the long-recognized increase in susceptibility to orthostasis imparted by adaptation to microgravity. In the Soyuz this is a magnitude of +0.54Gz during entry, descent, and landing with no cases of inflight orthostatic intolerance or underperfusion recorded. In the Space Shuttle, loads during this same phase remained between +0.2–0.5Gz [59]. In addition to orienting crew body position to limit +Gz exposure, further measures of salt and fluid loading combined with lower body counter-pressure garments are currently employed to further bolster tolerance to +Gz loading. With the discovery of SANS and evidence suggesting that returning crewmembers may have elevated ICP, such measures enter into a risk-balance consideration, as the same interventions historically employed to safeguard against orthostasis may further elevate ICP values in the period immediately prior to landing [73, 74]. Crew body positioning with respect to entry loads in particular bears new consideration: while historical focus has been on limiting +Gz, the potential for –Gz exposure has not been considered a unique risk. As noted above, vehicle architectures have thus far spared returning crewmembers from –Gz exposures even prior to the discovery of SANS. This newly discovered constellation of neuro-ocular pathology provides new rationale for not only eliminating the potential for headward acceleration loads during entry and landing for long duration crewmembers but providing a small but potentially protective magnitude of +Gz in the return profile. A small +Gz load (+0.2G) has serendipitously been provided for all returning crewmembers to date regardless of vehicle architecture; preserving this design feature for any future vehicle tasked with returning long duration crewmembers to the Earth is recommended, as terrestrial evidence and medical standard of care supports head elevation (e.g., +Gz exposure) to allow for a decrease in ICP in patients with end-organ pathology [59, 75, 76, 77, 78, 79].

Given the typical profile of physical deconditioning associated with space flight, the prospect of medical return of an ill or injured crewmember in a further compromised physiologic state becomes daunting. While some returning long duration crewmembers have functioned fairly well immediately on return, others have struggled to make even minimal physical efforts on their own behalf. It is reasonable to surmise that some otherwise healthy, returning, deconditioned crewmembers, on exposure to reentry and landing acceleration forces, may be unable to aid another injured or ill crewmember, may be unable to egress their seat for 30 min to several hours, and possibly could be completely incapacitated.

The decision to utilize an unscheduled or emergency return may be problematic both medically and logistically. A crewmember with compromised cardiac function could be placed at increased risk by returning to Earth prematurely following a cardiac event. This must be taken into consideration when deciding whether to recuperate in LEO before transport to a DMCF. For example, the deconditioned crewmember suffering an uncomplicated myocardial infarction several months into a LEO mission would be further compromised if returned while in the acute injury phase. LEO evaluation and rehabilitation with low levels of exercise and possibly artificial gravity from a future human centrifuge might be the therapy of choice, rather than immediately subjecting the crewmember to the insults and risk of reentry and landing. However, the capability and the personnel must be onboard to provide supportive treatment and facilitate such a course of action.

Psychological Considerations for Returning Crewmembers

In an emergency situation, crewmembers are called upon to act with decisive, clear, and appropriate actions to prevent a crisis from deepening and to preserve their own lives and the lives of their colleagues. This is not always an easy task, particularly with non-physician CMOs following a prewritten protocol during a medical event. Such factors relating to the human-machine interface and the crew’s living and working environment can affect their interventional capacity. As a result, these factors present some of the most significant challenges for medical response performed by a spaceflight crew, particularly given the additional physiological stresses that such situations may incur.

The adverse effects of confinement, isolation, noise, environmental challenges, and the group dynamics associated with these situations have been well documented in analog situations such as the Antarctic and on submarines [80, 81, 82]. Additional psychological stressors may arise from limited communications, on-orbit equipment failures, difficult living conditions, and high workloads, particularly in emergencies. These may be compounded by crew interpersonal tensions, multicultural issues, lack of privacy, and deprivation of the usual sensory and motor stimulation [83, 84, 85]. In space, isolation can lead to sleep disturbances, headaches, irritability, anxiety, depression, boredom, restlessness, anger, homesickness, and loneliness. These behavioral findings are particularly relevant to the actions and performance of crews in emergency medical situations, where time is of the essence and effective leadership and decision-making are paramount. These issues are further discussed in Chap.  25 Behavioral Health and Performance Support.

Design Challenges of a Crew Return Vehicle

For any crewed spacecraft, there are substantial challenges in designing the environmental systems, seat and cockpit configurations, medical systems, restraint systems, and extraction capabilities for the transport of crewmembers within a required anthropometry range. In addition to providing for the proper functioning of these systems within the mass, volume, thermal, pressure, and anthropometric constraints of nominal launch and reentry operations, human factors design considerations must account for the ability of crewmembers to function during off-nominal or contingency scenarios where risk trades between safety/redundancy and function become paramount.

The first consideration in design is mission profile. Factors ranging from habitable volume, consumable stores, and distance/expected duration of free-flight operations will either be influenced by, or themselves drive, decisions on radiation shielding and whether pressure suits are required, among many others. For example, an Orion or Apollo mission profile in which the vehicle operates as sole source of life support for the crew differs from the Soyuz and upcoming Commercial Crew Vehicle profiles that anticipate docking with ISS for extended durations.

The critical decision to require all crewmembers to wear pressure suits during launch, entry, and other dynamic operations was arrived at independently by both NASA and the Russian Space Agency and in both cases was prompted by tragedy. Russian Soyuz crewmembers began donning Sokol launch and entry suits based on the recommendation of the investigating government commission after the deaths of the Soyuz 11 crew during a depressurization on entry in 1971. It would take the loss of Challenger in 1986 to prompt a similar NASA requirement, with all Space Shuttle operations after STS-51-L employing the use of the Launch Entry Suit until STS-65 in 1994, superseded by the advanced crew escape suit (ACES) thereafter. This requirement is being carried forward in both Orion and commercial crew vehicle design to protect against decompression injury or toxic atmosphere. When considering the impact on dexterity and access to a fellow crewmember who requires medical care in the event of a MEDEVAC, additional design considerations must be made:

Will Respiratory Support Be Necessary?

Current NASA crew vehicle requirements dictate that the use of 100% medical oxygen (O2) at 6 L/min flow be provided; however, no requirement for ventilator interface exists. An intubated patient would require manual ventilatory support throughout the acceleration loads of entry interface. The simple use of 100% O2 by nasal cannula or mask raises the question of risk balance between respiratory support to a single injured crewmember and flammability risk limits as the cabin atmosphere becomes oxygen rich. Total cabin pressure maintenance and dilution with inert gas to offset introduced oxygen are yet further necessary considerations.

Will Use of a Pressure Suit Be Required for the Patient? For the CMO?

As noted above, the risk of decompression is well recognized and currently addressed by an added layer of protection in the use of pressure suits for all critical operations. In a MEDEVAC scenario, the use of a pressure suit is likely to make direct palpation and assessment of an injured crewmember difficult or impossible, and the ability to seal such a suit if respiratory support is needed is unlikely. The use of a suit by the treating party presents its own drawbacks: sensation of temperature is eliminated and dexterity is diminished to a degree that would make removal of suit gloves a necessity in order to provide any meaningful medical intervention. This is discussed in detail below (see “Patient Accessibility and Treatment Capabilities”).

Will Acceleration Tolerance Be Affected by Injury or Disease Pattern?

Will Use of Counter-Pressure Garments or Fluid Loading Protocols Be Affected?

A patient having difficulty oxygenating will face a risk of hypoxia as acceleration loads increase work of breathing and atelectasis. Those same entry, descent, and landing loads pose a risk of worsening orthopedic injuries, while fluid loading protocols and counter-pressure garments may be contraindicated in patients with ocular trauma or closed head injuries. Conversely, the decision to hold antihypertensive medications may be made to reduce the risk of orthostasis prior to entry loading.

As for any terrestrial analog scenario, the crew return capability for medical emergencies during space flight requires dedicated procedures and checklists to ensure that further deterioration of an ill or injured crewmember is minimized and the likelihood of a successful recovery is maximized [23]. Per design and placement parameters, medical equipment controls and supplies are positioned within the vehicle to allow access to the patient and monitoring equipment during different phases of flight. A returning crewmember requiring respiratory support can serve as an example. If a patient is being manually ventilated via bag mask, the CMO may encounter difficulty sustaining this support once perceptible acceleration forces are encountered. However, if the patient is mechanically ventilated, the CMO could adjust the settings with the aid of remote access to ventilator controls and readout. Human factors considerations play an important role in the design of the patient restraint system, guiding the provision of an interface for advanced life support equipment, such as a ventilator, defibrillator, oxygen supply, and intravenous (IV) infusion supplies [86].

An ill crewmember’s degraded condition will also drive search and rescue (SAR) team requirements such as response time and medical capabilities. In particular the crew may be unable to extract themselves from the vehicle after landing; therefore, any SAR team must be familiar with aspects of spaceflight deconditioning and utilize appropriate crew extraction techniques.

While there is arguably an ideal or minimum vehicle internal working volume required to execute a rescue mission, medical mission planners are usually necessary to work with the fixed habitable volume and internal anthropometric constraints of a specific vehicle [87, 88]. Habitable volumes of various historical and present-day vehicles are shown in Table 10.13.
Table 10.13

Habitable volumes for various spacecraft.

Vehicle

Habitable volume (m3)

Crew

Volume per crewmember (m3)

Space Shuttle orbiter

65.8

7

9.4

Apollo command module

6.2

3

2.1

Mercury spacecraft

1.7

1

1.7

SpaceX Dragon

Boeing CST-100

Lockheed Orion

Sierra Nevada Dream Chaser

10

19

10

8.95

>4–7

4–7

>4–7

2–6

1.4+

2.8+

1.4+

1.2+

Soyuz descent module

4.0

3

1.3

Gemini spacecraft

2.6

2

1.3

Ground ambulance—box type (for comparison)

11.0

2 + patient

3.6

Available habitable volumes are further limited by additional vehicle components, onboard supplies, and the crews themselves. Ultimately, most vehicles can provide only minimal space within which medical interventions must take place (Fig. 10.5).
Fig. 10.5

Cabin views of SpaceX Crew Dragon (a) and Boeing Starliner CST-100 (b), demonstrate that while both vehicles have been developed in recent years, they will still offer constrained space for patient transport and stabilization activities.

Risks in Aeromedical Transport and Evacuation

An inflight CMO or a ground-based flight surgeon must address a number of considerations in making a triage decision:
  1. 1.

    What diagnostic tools the CMO has available to ascertain the unique pathophysiologic conditions of a returning crewmember

     
  2. 2.

    How the disease process or injury is affected by the spaceflight environment (including weightlessness, elevated carbon dioxide, etc.)

     
  3. 3.

    How the disease process or injury is impacted by the crewmember’s level of spaceflight adaptation and/or deconditioning

     
  4. 4.

    What level of physiological monitoring or intervention may be required for initial stabilization and triage (pulse oximetry, IV fluid resuscitation, medical oxygen, etc.)

     
  5. 5.

    What level of physiological monitoring and resources may be required during entry, descent, and landing operations should a medical evacuation be indicated

     
  6. 6.

    The capabilities and risks to both the injured party and the crewmembers providing medical monitoring and support, inherent in the transport/evacuation vehicle to be utilized

     
  7. 7.

    The availability of ground resources capable of responding to the injury or disease process identified, either remotely, via telemedicine guidance, or directly in the event a medical evacuation is initiated

     

Factored into any decision to use aeromedical transport must be the added risk inherent in evacuation and transport itself, such as weather, the conditions at the recovery site, and transport vehicle factors. Occasionally the risk associated with these factors may outweigh any benefit of immediate transport. EMS MEDEVAC, rescue operations, and hospital transfers are not risk-free, and injuries occur each year. However, the aeromedical transport fatality rate due to air mishaps is quite low, estimated in a 2001 assessment to be approximately 6 per 100,000 transports [89]. There will be occasions, given the hazards of the evacuation process and availability of onboard medical care, when definitive treatment may be deferred despite evacuation capability. For example, aboard commercial ocean freighters or cruise ships, patients with acute abdominal processes, such as acute appendicitis, are seldom evacuated by air even when within helicopter range but are often managed non-operatively and may be transported ship-to-ship before definitive land-based care is reached [90].

Emergency medical transport and evacuation from an orbiting space platform clearly carries risk. While it is difficult to assess these risks given the limited current experience base, different risks may be viewed as occurring along an evacuation timeline, with each phase presenting unique environmental hazards and corresponding concerns. The major risks and suggested mitigation actions are outlined in Table 10.14.
Table 10.14

Risks associated with spaceflight medical evacuation and transport.

Timeline event

Risks

Risk mitigation design factors

Decision to transport/evacuate

Delayed or premature decision

Incorrect decision (e.g., medical condition likely to worsen with evacuation)

Major mission impact

Anticipate possible scenarios

Establish standing flight rules to guide decisions

Allow real-time crew decisions independent of ground support if communication fails

Cabin environment

Space-limited medical access for monitoring, procedures, and resuscitation

Nonsuited configuration is zero-fault-tolerant cabin environment to entire CRV crew for depressurization or toxic atmosphere event

Cockpit configuration

Evacuation timeline

Life support system consumables adequate to evacuation timeline

Crew time constraint of ~3 h from departing station to landing

Medical capabilities of vehicle

Suited configuration limits medical access, especially for airway management and resuscitation

Design allows unsuited transport; seat design allows CMO access to patient

Autonomous reentry

Limited landing opportunities

Thermal, noise, and vibration issues

Acceleration profile on reentry—nominal vs. ballistic

Chute deceleration effects

Large cross-range capability, along with deorbit opportunity every 2 or 3 orbits

Low entry G profile

Autonomous, unpowered return

Controlled reentry G limits:

4 +Gx, 1 ±Gy, 0.5 +Gz

Landing

Limited sight and obstruction avoidance

Land impact vs. water impact

Potential impact injuries

Maybe autonomous

Inertial navigation system, Global Positioning System guidance

Steerable parafoil to limit landing speeds

Landing site selection and navigational aids

Recumbent crew seating

Landing impact attenuation system

Egress and rescue

Impaired performance in one G due to deconditioning

Unaided egress may not be possible

Land vs. water egress

Remote environment exposure

Risk to search and rescue (SAR) personnel

unplanned deployment, toxic propellants, unspent pyrotechnics

SAR/ground force availability and response time

Prelanding countermeasures:

 • Fluid loading

 • Pharmacologic, sympathomimetic agents

 • Anti-G suits

Crew survival training

SAR readiness and exercises

Evacuation to DMCF

Additional transport event

Medical facility capabilities at landing site may be diminished

Medical Operations Contingency Support and Implementation Plan to define requirements for US and international emergency landing sites

Patient Accessibility and Treatment Capabilities

Analysis of the relative capabilities of suited and unsuited crew configurations for different types of medical events allows an estimate of the overall relative capability of one scenario compared to the other. A panel of NASA flight surgeons estimated the relative projected medical care capabilities for specific events, by quartiles, comparing the suited versus unsuited configurations (Tables 10.15 and 10.16) [91, 92]. For each medical event category and assuming equal event frequencies within each category, an overall fractional capability of the suited configuration relative to the unsuited configuration can be made. Wearing a pressure suit does inevitably limit the physical capabilities of the CMO and limit access to a crewmember receiving medical care; however, the mission profile extends to the wearing of pressure suits in medical transport scenarios. This is shown in Table 10.14 as estimated percent relative capability for each category. When this relative capability is weighted by the incidence of each medical event category, an overall relative capability of the suited configuration is estimated to be approximately 54%. In other words, the suited configuration during return to Earth does not provide appropriate capability for handling about half of the potential events that would prompt medical return. For critical respiratory and circulatory events, the medical mission capabilities of the suited configuration are only around 17% and 10%, respectively, of the unsuited configuration. This degraded capability for respiratory and circulatory care is primarily due to loss of patient exposure and airway access in the suited configuration.
Table 10.15

Projected relative medical capabilities of suited (unmodified Soyuz-TM) vs. unsuited (CRV) configurations.

Medical event

Requiring transport/evacuation

Incidence

(per 100 person-yrs)

Estimated % relative capability for category

Incidence-weighted suited % capability

Trauma and toxicity

 Anaphylactic reaction

 Respiratory depression

 Major fracture

1.72

66%

19%

Gastrointestinal

 Severe gastroenteritis

 Ileus

 Appendicitis

 Pancreatitis

 Cholecystitis

0.87

50%

7%

Neurologic/psychiatric

 Vertigo

 Psychosis

 Seizure activity

 Intracranial bleed

 Cerebral aneurysm

 Cerebrovascular accident

0.8

46%

6%

Respiratory

 Pneumothorax

 Pneumonia

 Toxic pneumonitis

 DCS chokes

 Reactive airway

 Airway obstruction

 Respiratory arrest

 Acute respiratory distress syndrome

Pulmonary embolus

0.60

17%

2 %

Circulatory

 Dysrhythmia

 Coronary disease/angina

 Myocardial infarction

 Shock—hypovolemic

 Shock—anaphylactic

0.43

10%

1%

Genitourinary

 Renal calculi

 Urosepsis

 Pyelonephritis

0.34

42%

2%

Infectious disease

 Sepsis

 Meningitis

0.30

38%

2%

Dermatology

 Cellulitis/abscess

 Urticaria

 Exfoliative dermatitis

0.28

100%

5%

General internal medicine

 Cancer

 Endocrine/nutritional/others

0.6

100%

10%

Total ~6 events/100 person-years

5.94

 

54%

Table 10.16

Medical capabilities in transport and evacuation from the ISS: suited vs. unsuited scenarios.

Medical capability

Unsuited

(crew return vehicle)

Suited

(Soyuz-TM)

Patient assessment

Limited

Minimal

Exposure/airway access

Present

Minimal

Patient restraint device/cervical spine restraint

Present with patient restraints

Possible

Second provider assist

Possible

Minimal

Advanced life support pack

Sub-packs

Some supplies

Diagnostic equipment

Present

Minimal

Pharmaceuticals

Present

Limited

Intravenous fluids

Present

Possible

Oxygen supply—100%

Ventilator and mask

Suit

Cardiac monitor

Present

Possible

Defibrillator, blood pressure monitor, pulse oximeter

Present

Minimal

Survival kit (post landing)

Present

Present

Current ISS operations for a six person crew utilize only the suited configuration in the Soyuz as the escape vehicle to accommodate any evacuation scenario. As discussed the estimated combined crew risk of a medical event potentially requiring evacuation in the ISS is 0.36 per person-year or about once in 36 months.

Medical Considerations for a Crew Return Vehicle

There are numerous factors to consider when designing an appropriate vehicle for crew return. Documented requirements parameters for crew return vehicles include vehicle and system performance, environmental control specifications, human factors guidelines, medical limitations, and mission support requirements. The aim of medical requirements is to ensure that a vehicle utilized to transport ill or injured crewmembers will meet the minimum standards for patient care during a return mission from the ISS or beyond. The medical requirements are subdivided into those addressing patient care, crew compartment configuration, and crew compartment environmental control and life support systems (ECLSS).

There are dedicated requirements for medical life support adequate for a minimum of one ill or injured crewmember for scenarios including ventilation, physiological monitoring with defibrillation, intravenous fluid therapy, and pharmacotherapy. In addition, emergency medical and survival kits are essential to cover injuries and illnesses during any mission phase, including after landing until the arrival of SAR forces.

To ensure that the patient transport time is minimized, the medical mission timeline must ensure that the maximum time from ISS separation to landing is minimized, with mission planning, spacecraft ingress, undocking, landing site selection, SAR notification, and subsequent landing from any point in the ISS-mated portion of the mission within 24 h [93]. DoD response pre-posturing on launch and landing days allow 24-h response for most of the globe; for emergency return during normal mated ISS operations, the DoD will render assistance on a “best effort” basis following notification, with the goal of providing on-site paramedic-level care within 24 h. Finally, the entire crew returning from ISS may be incapacitated for several hours due to neurovestibular, cardiovascular, and musculoskeletal deconditioning. SAR teams must be capable of performing appropriate extraction techniques specific to the return vehicle. As described below, the wide variation in vehicle return profiles demands the capability for timely extraction exist for both remote land, sea, and airfield landing scenarios.

Design for the Orion MPCV displays and controls places an increased emphasis on human-computer interaction and usability. Orion’s development incorporates a greater degree of automation than in previous vehicles, and benefits from early design work to mitigate or limit adverse physiological effects on crewmembers. This is being accomplished by close integration of human factors into the technology and engineering solutions, to maintain a safe functioning crew compartment, at all stages of development [94].

Crew seat design parameters for a medical mission ideally incorporate and address the following considerations:
  • Head-torso-lower extremity centerline axis alignment

  • Five-point restraint system adjustable to accommodate 5–95% of the anthropometric envelope and prevent occupant flail movements, including for an unconscious patient

  • Head restraint with lightweight communication and protection systems that allow a fixed visual reference point

  • Crew medical officer displays and controls that minimize crewmember head and arm movement and effort during entry

  • Vehicle spin and rotation limits not exceeding 5 rpm sustained due to crew intolerance (neurovestibular provocation)

  • Adequate attenuation properties to minimize acceleration loading in all axes of the human body as described above

  • Parachute deploy and impact load limits (acceleration-time profiles) for deconditioned crew [51, 57, 91, 95, 96]

Dedicated real-time medical communications capabilities are required between the MPCV and Mission Control Center-Houston (MCC-H). These would include the means to support the transfer of medical data, including but not limited to continuous cardiac monitoring and real-time video, whenever possible. In addition, voice communication between the MPCV and SAR forces should be available.

Crew Compartment Environmental Control and Life Support Systems (ECLSS)

The atmosphere and environment of a medical mission vehicle should maintain a comfortable level of temperature, humidity, and ventilation for the duration of the mission to enable shirtsleeve operation. However as stated above, entry and landing would most likely be made wearing pressure suits due to safety concerns. One potential scenario may be for the ill or injured crewmember to remain unsuited in order to provide better access for ongoing care and monitoring, while remaining crewmembers are suited for reentry; this scenario maximizes the potential for medical intervention while minimizing the risk of additional contingencies (such as decompression injury in a depressurization event) for the uninjured crew. Current NASA medical requirements anticipate the potential use of respiratory support, either via nasal cannula, mask, or definitive airway, during a medical evacuation scenario. No requirement for respiratory support that preserves the launch/entry suit pressure seal currently exists, with the potential for a novel suit/airway support interface that could extend protection from decompression injury to the injured crewmember an outstanding area for future medical capability development.

Vehicle ECLSS capabilities should extend beyond the moment of landing to include adequate time for the removal of the deconditioned or ill or injured crewmembers or any delay in SAR team arrival. Environmental controls must also be capable of maintaining crew within physiological norms during the acceleration loading and heat buildup of entry and landing, which may contribute to orthostatic intolerance and neurovestibular dysfunction, resulting in nausea and impaired coordination among returning crewmembers. The vehicle should also be capable of purging the interior environment of toxic products, which would additionally allow the vehicle to act as a safe haven where astronauts could take refuge while the ISS environmental control system scrubs a toxin, controls a fire, or repressurizes the station. In the event of a contingency return to a secondary or tertiary landing site, the ability of ECLSS systems to purge return vehicle toxic atmosphere and maintain crew entry suit oxygen flow, carbon dioxide removal, and temperature management in the immediate post-landing period is critical.

Loss of pressure is a potential ISS failure. The lowest pressure at which a crewmember can survive on 100% oxygen for a significant period of time is around 3.0 psi (155 mmHg) or the equivalent atmospheric pressure of 38,000 ft (11,600 m) in altitude. Historically, the earliest extravehicular activity suit concepts and some high-altitude pressure suits, such as utilized for aircraft like the SR-71 Blackbird, were as low as 2.8 psi. The nominal repressurization rate limit (from 3.0 psi to the nominal 14.7 psi within 30 min, at a rate not to exceed 13.4 psi/min) was established to avoid problems with middle ear blockage and barotrauma. Although survivable, decompression from the station cabin atmosphere pressure to minimal pressures would likely involve some degree of decompression sickness (DCS); ideally, crew should remain on 100% O2 for several hours to mitigate DCS risk after such an event. It is important to note that the threshold for crew action and evacuation from the ISS is currently set well above 3.0 psi, at 8.0 psi. This higher threshold is observed to allow adequate time for return vehicle power-on and leak check completion, maintain pressure- and temperature-sensitive ISS hardware within operational limits while crew remain on station, and ensure emergency egress procedures can be completed before DCS and hypoxia risk constrain crew safety and performance.

Emergency and supplemental O2 is required for use in event of toxic atmospheric contamination or a cabin depressurization. This is required for a period long enough to restore an adequate breathing environment and treat embarrassed respiration of exposed crewmembers. In addition the vehicle must provide independent O2 for the ill or injured crewmember at a maximum rate of 6 standard liters per minute. This in turn necessitates a means for dumping or recycling the exhaled O2 so that cabin concentration limits are not exceeded with consequent flammability risks (Table 10.17). This can be mitigated with an O2 concentrator, which, while it may not provide 100%, will ensure adequate oxygenation for the patient from ISS separation to evacuation by SAR teams after landing without undue enrichment of the cabin atmosphere.
Table 10.17

Crew return vehicle environmental control and life support system design parameters.

Parameter

Range

Total pressure

14.0–14.9 psia

Partial pressure (pp) carbon dioxide

0–0.077 psia

pp Oxygen

2.82–3.30 psia

pp Nitrogen

<11.6 psia

Relative humidity

25–75%

Atmospheric temperature

18.3–26.7 °C

Dew point

4.4–15.6 °C

Intramodule circulation

0.051–0.2 m/s

Intermodule ventilation

66 ± 2.4 L/s

Fire suppression oxygen concentration level

10.50%

Particulate concentration (0.5–100 mm diameter)

Average <0.05 mg/m3

Temperature of surfaces

4 °C < touch temperature < 45 °C

Atmospheric leakage per module

Max 0.23 kg/day at 14.7 psi

From ISS Crew Transportation and Services Requirements Document. Commercial Crew Program, NASA John F. Kennedy Space Center. CCT-REQ-1130, Rev E 2016. Available online at https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20170001943.pdf

Postlanding Recovery

Crew recovery after evacuation from a vehicle such as the ISS does not end until the crew has reached definitive medical care. Requirements and procedures have been and continue to be developed to ensure that an injured or ill crewmember will reach a DMCF within a predetermined period from station evacuation. This has consequences for the requirements placed on the recovery vehicle and the SAR forces, as a result of the time required to land a vehicle and where it will land. For example, a vehicle that can depart the ISS or other LEO platform and land within 3 h at a number of different locations would require the SAR team to respond more quickly and to more locations than for a typical Soyuz landing. For a Soyuz landing, local SAR teams (augmented by NASA personnel when US astronauts are on board) are utilized in locating the capsule and extracting the crewmembers. The Soyuz descent module is equipped with radio and light beacons to assist in determining its location, and a handheld GPS and satellite phone are available to crewmembers to communicate position to SAR personnel.

Recovery of a crew in an emergency return is different from the well-choreographed and planned nominal landings of the Soyuz. Emergency recovery is not without danger to SAR forces, in large part due to the many toxic substances carried by spacecraft for propulsion and cooling. This is compounded if the vehicle lands in a remote and inaccessible area of the world.

Specific planning must be in place for crew recovery at different locations where a crew may land, which is theoretically anywhere between 51.6 degrees north/south latitude for the ISS. Other considerations include the specific vehicle being recovered and whether the crew is returning from a short or long duration mission. The required capabilities of recovery forces are specified in NASA documentation and include rescue personnel, crewmember extraction capabilities, and medical evacuation capability via ground or aircraft. SAR forces at all potential landing sites are required to be familiar with the space vehicles used for evacuation. These plans also take into account whether there is a planned or emergency evacuation of the space station. For the new US crew vehicles, this is expected to include both ocean and land landings and will necessitate comprehensive vehicle-specific training planned for SAR forces and recovery theater-specific hardware. Crew extraction and vehicle recovery from a dynamic marine environment as anticipated for both SpaceX Crew Dragon and Orion vehicles is expected to share little in common with the ground resources necessary for a remote desert recovery for the Boeing CST-100. In addition secure communications between MCC-Houston, the SAR team, and the returning vehicle are necessary for the success of a medical mission.

Ethical Issues of Medical Evacuations from LEO

While the practice of space medicine shares many commonalties with terrestrial preventive medicine, this field also requires the exercise of unique medical experience and judgment. Like other fields of preventive and occupational medicine, aerospace medicine emphasizes optimizing workplace performance of essentially healthy individuals. Medical decision-making concerning civil and military aviators and astronauts regularly involves weighing priorities between the safety, well-being, and career livelihood of an individual and the attainment of mission success. Achieving and maintaining this balance permeates every phase of space medicine practice, including mission design, development and prescription of countermeasures, astronaut and crew selection, training, mission preparation and execution, inflight medical monitoring, and long-term astronaut follow-up.

Unlike terrestrial medical practice, the potential hazards of the space environment pose unique challenges involving the safety, survival, and successful return to Earth of individual astronauts and even entire crews. Long-term space flight itself poses additional inherent risks. Prudence dictates careful deliberation of possible medical events well in advance of their occurrence, including consideration of preflight preparation, inflight management, return capabilities, potential positive or adverse outcomes, and mission impact. NASA has, over several decades, adopted risk management guidelines aimed at minimizing individual risk while maintaining overall mission effectiveness. Longer duration LEO and expeditionary flights to other planets present the possibility that other limitations on certain types of missions may be required, such as a career limit of one or two ISS type missions for a few crewmembers based on cumulative radiation exposure.

While every sort of inflight medical contingency cannot be predicted, generalized onboard protocols for anticipated medical scenarios can provide a framework for crew and ground personnel decisions. Despite such forethought, any medical event requiring evacuation from LEO will inevitably involve real-time judgment. Where possible, effective communication between an ill or injured crewmember, an onboard medical provider, ground-based medical support (flight surgeon), and overall mission support (flight director and mission managers) will be important to facilitate integrated decision-making. However, the crew in LEO must be prepared and equipped to make independent decisions; with expeditionary missions, this is likely to be the norm in the initial phases of a medical emergency.

In many ways, a vehicle capable of assuring crew return from LEO in a medical evacuation poses more questions than it does answers. While some scenarios may be unambiguous, e.g., irreparable station depressurization, others are less clear. How long, for instance, should a well-trained CMO with relatively limited onboard resources care for an acutely ill crewmember on orbit before calling for evacuation to a DMCF? In the event that a crewmember is evacuated, then that vehicle’s full complement crew will descend. The principle here is that there would never be crewmembers left on orbit without a seat in a docked vehicle. For the Soyuz, if one person has to be evacuated, then three crewmembers will descend. How do the risks of evacuation and landing compare to those of administering further care on orbit? Does the occurrence of a predictably fatal illness or injury alters medical evacuation decisions? In view of other mission objectives and potential additional risks, what responsibility does a crew have to recover and return a deceased crewmember? Though difficult questions, these raise ethical issues worthy of advance consideration. While flight rules and decision algorithms governing medical evacuation are designed to minimize real-time deliberation, it will ultimately be a weighty responsibility for a flight surgeon and flight director to determine, with the onboard crew, the need for medical evacuation.

The frontier medical-legal issues raised by such questions are numerous. The broad groundwork underlying these issues and questions lies in the US Space Act and the United Nations Space Treaty. Therefore, as space agencies have accepted the moral obligation to address medical emergencies from the earliest days of human space flight, the agencies have a legal duty, in the form of these international treaties, to provide for crew rescue. The first of several treaties related to crew rescue was the Treaty on Principles Governing the Activities of States in the Exploration and Uses of Outer Space, including the Moon and other celestial bodies. In a tragic irony, this treaty was signed on January 27, 1967, the day astronauts Gus Grissom, Ed White, and Roger Chaffee died in the capsule of Apollo 1. The treaty identifies principles related to the rendering of all possible assistance on Earth and in space, the prompt and safe return of crew, and the dissemination of information about possible hazards.

The second treaty, the Agreement on the Rescue of Astronauts, the Return of Astronauts, and the Return of Objects Launched into Space, was signed in December 1968, soon after cosmonaut Vladimir Komarov perished in the capsule of Soyuz 1 on its return to Earth. The rescue treaty specifically requires immediate notification of accidents, provision of rescue and assistance to spacecraft personnel, and their prompt and safe return to the launching authority.

More recently, these matters have been addressed specifically with regard to crew return from the ISS by the partnering international space medical community and their respective agency management. Memoranda of Understanding, which define partner roles in the ISS, have been elevated to international treaty status. Though partner nations have reached consensus on a few specific concerns, such as standardizing medical care inflight and for ground support, discussion of other topics is ongoing and questions remain. What constitutes a medical disability resulting from illness or accidental injury during space flight? How is investigation of the causes of an accident resulting in medical disability conducted? What nation or nations maintain jurisdiction onboard an international space station? Does a hosting nation have liability for medical consequences of a guest crewmember’s injury or illness? How do we train, qualify, and certify space medicine physicians and ensure their competence and currency? What differences, if any, should exist between standards for ground-based versus inflight care providers? Addressing these questions as well as the technical challenges is a fundamental step toward readying ourselves for further space exploration.

Beyond Earth Orbit: The Moon and Mars

Potential medical transport and evacuation scenarios turn even more complex in considering a mission beyond LEO. Compared to a transport time of several hours from LEO, evacuation from a lunar base or a space station at one of five Earth-Moon fixed Lagrangian points would require several days at best. For a Mars mission, the one-way communication time may be up to 20 min duration, and there may be no evacuation capability. Clearly, injuries and illnesses that would be potentially treatable in LEO will carry more threatening implications if they occur in remote space.

For many reasons including medical concerns, missions beyond LEO will require levels of spacecraft and crew autonomy and self-sufficiency beyond what is currently realized. The NASA/Lockheed Orion Multi-Purpose Vehicle is being developed for such a scenario. Just as fault-tolerant design of vehicle components and systems will be enhanced, crewmembers will be more highly cross-trained. The crew of a Mars or other deep space mission will likely have to anticipate how to carry their objectives through to completion despite possible incapacitation or loss of a crewmember. Additional onboard capability to manage a disabling medical condition over the relatively long time frame of several months may be required, as well as means to deal with a deceased crewmember. In a much greater context, the expansion into the solar system will be in a staged fashion, with decreasing capabilities expected at increasingly remote sites. Medical evacuation from a deep space mission could one day be to a fallback position on Mars where a greater level of care is available, rather than by default back to a very distant Earth. Such staged medical evacuations have a long lineage of terrestrial precedent to draw upon, from military MEDEVACs to patient movements out of remote Antarctic field camps.

Exploratory missions truly mark a change in potential risks to both the mission and individuals. Issues such as crew selection criteria, age at mission start, optimization of physical and mental condition, informed consent of mission risks, notification of family of medical events, and mission-consequence long-term health effects are just some of the concerns attending medical operations planning for the future.

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  • Smith L. JohnstonIII
    • 1
  • Kieran T. Smart
    • 2
  • James M. Pattarini
    • 3
    Email author
  1. 1.NASA Johnson Space CenterHoustonUSA
  2. 2.Department of Primary CareBay Pines VA Healthcare SystemBay PinesUSA
  3. 3.Space Medicine Operations DivisionNASA Johnson Space CenterHoustonUSA

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