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Possibilities of Electrical Space Ship Propulsion

  • E. Stuhlinger

Abstract

A study on feasibility and performance of an electrical propulsion system for interplanetary space ships is presented. A propulsion system is proposed in which a suitable propellant (cesium or rubidium) is vaporized and ionized at incandescent platinum surfaces. Ions and electrons are accelerated and expelled at equal rates; they recombine immediately after leaving the thrust chambers. The power for the accelerating fields is obtained from turbo-electric generators. Heat source is the sun. A thermo-electric pile would be about ten times less efficient than a turbo-electric plant with the same total mass. The acceleration of a space ship equipped with an electrical propulsion system is of the order of 4 × 10-5 G. A space ship with a pay load of 50 tons, a total initial mass of 270 tons, and a total flight time of one year would cover a distance of about 183 • 106 km if it started with the velocity zero and traveled through space without gravity fields. Application of the results to a ship travelling from an earth satellite orbit to a mars satellite orbit and back will be presented in a later paper.

List of Symbols

Note:

CGS — units are to be used in all formulae of this paper with the following exceptions:

Voltages (U, E, e)

volts

Currents (I, j)

amperes

Resistances (R)

ohms

Resistivities (ϱ)

ohm cm

Temperatures (T)

: degrees Kelvin

Amir

= area of mirror, cm2

Acon

= area of condenser, cm2

ai

= initial acceleration of ship, cm sec-2

a

= specific power of powerplant, erg sec-1 g-1

Dτ

= distance covered by ship after the time τ, cm

δa

= density of thermocouple component a, g cm-3

δb

= density of thermocouple component b, g cm-3

E

= total emf of thermocouple, volts

e12

= differential thermo-electric force of thermocouple, volts degr-1

ε

= electric charge of ion, amp sec

η

= efficiency of ideal steam engine

ηc

= efficiency of thermocouple

Fa

= cross-section of thermocouple component a, cm2

Fb

= cross-section of thermocouple component b, cm2

F1

= input area of thermocouple, cm2

F2

= output area of thermocouple, cm2

G

= earth’s acceleration, cm sec-2

γ

= efficiency reduction factor for steam engine

γc

= efficiency reduction factor for thermocouple

i

= current density, amp cm-2

I

= total ion current, amp

j

= current through thermocouple, amp

xa

= heat conduction coefficient for thermocouple component a, erg sec-1 cm-1 degr-1

xb

= heat conduction coefficient for thermocouple component b, erg sec-1 cm-1 degr-1

L

= total power for acceleration of ions, erg sec-1

1

= length of thermocouple, cm

MF

propellant mass, g

Mi

= total mass of ions, g

Me

= total mass of electrons, g

MD

= dry mass of ship, g

MO

= total initial mass of ship, g

mp

= mass of power plant without condenser and working fluid, g

mc

= mass of condenser and working fluid, g

mmir

= mass of mirror, g

ms

= mass of ion source, g

m0

= mass of payload, g

mth

= mass of thermocouple pile, g

MF

= rate of propellant consumption, g sec-1

μ

= mass of one ion, g

v

= efficiency of ideal thermodynamic cycle

pr

= specific radiation loss, erg sec-1 amp-1

Prad

= radiation loss, erg sec-1

P12

= Peltier coefficient at hot junction, erg sec-1 amp-1

P21

= Peltier coefficient at cold junction, erg sec-1 amp-1

Q1

= input power, erg sec-1

Q2

= heat power leaving cold junction of thermocouple, erg sec-1

Qc

= heat power conducted through thermocouple, erg sec-1

Qp1

= Peltier heat at hot junction, erg sec-1

Qp2

= Peltier heat at cold junction, erg sec-1

qc

= specific mass of condenser and working fluid, g cm-2

qm

= specific mass of mirror, g sec erg-1

qp

= specific mass of power plant, g sec erg-1

qs

= specific mass of ion source, g amp-1

Ra

= Resistance of component a of thermocouple, ohm

Rb

= Resistance of component b of thermocouple, ohm

RL

= Resistance of load, ohm

r

= reflectivity of mirror

Qa

= resistivity of component a of thermocouple, ohm cm

Qb

= resistivity of component b of thermocouple, ohm cm

S

= solar constant, erg sec-1 cm-2

σ

= STEFAN-BOLTZMANN constant, erg sec-1 cm-2 degr-4

T1

= boiler temperature or hot junction temperature, degr K

T2

= condenser temperature or cold junction temperature, degr K

Th

= total thrust developed by thrust chamber, g cm sec-2

Thi

= thrust developed by ions, g cm sec-2

The

= thrust developed b electrons, g cm sec-2

τ

= total time of propulsion, sec

U = Ui=

voltage to accelerate ions, volts

Ue

= voltage to accelerate electrons, volts

v0

= end velocity of ship, cm sec-1

Vex = vi

= exhaust velocity of ions, cm sec-1

x

= distance, cm

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References

  1. 1.
    See e. g. H. Oberth, Wege zur Raumschiffahrt. München and Berlin: R. Oldenbourg, 1929.Google Scholar
  2. L. Spitzer, Jr., J.Brit.Interplan. Soc. 10, 249 (1951).Google Scholar
  3. H. Preston-Thomas, Bristol (England), Private communication; also: J. Brit. Interplan. Soc. 11, 173 (1952).Google Scholar
  4. 2.
    Maria Telkes, J. Appl. Physics 18, 1116 (1947).ADSCrossRefGoogle Scholar

Copyright information

© Springer-Verlag Wien 1955

Authors and Affiliations

  • E. Stuhlinger
    • 1
  1. 1.Guided Missile Development DivisionRedstone ArsenalHuntsvilleUSA

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