Power Systems for Small Satellites

Abstract

The satellite power system is a vital component of all satellites and involves a number of parts. All of these parts play an important role in the success or failure of a small satellite mission. Since electrical power systems have been around since the beginning of the space age, and their function has been well established, this part of a satellite design for this reason might be taken for granted. It also may be outside the expertise of cubesat builders with limited experience. This is a serious problem, as many telecommunications systems, on the ground or in space, often fail due to a power failure. This can be not only because the power generation or storage system fails but for other seemingly mundane factor such as a simple short in a wiring system that causes a satellite to fail due to a lack of critical power supply or even an electrical fire that destroys the entire satellite. Other sources of failure can come from as simple a problem as the leads from solar cells or photovoltaic cells failing due to contamination or oxidation that creates an overall power failure for a satellite. Experience over the years have confirmed the need to carefully design, manufacture, and test all aspects of a satellite’s electrical power system in terms of safety, resilience, and lifetime performance. This important work is often overlooked or minimized in cubesat projects.

This chapter discusses all aspects of electrical power generation, an electrical power distribution system, power storage, and effective design of an electrical power system for all types of satellites that range from a femtosat (10 to 100 grams), a picosat (100 grams to 1 kg), a nanosat (from 1 kg to 10 kg) that includes cubesats, a microsat (from 10 kg to 100 kg), and a minisat (from 100 kg up to 500 kg in some definitions and from 100 to 1000 kg in others). The point is that power systems can command a good deal of the mass and volume of a satellite regardless of its size, and thus the power-to-mass ratio is important in satellites designs and especially so in the case of small satellites. Different approaches to power can thus be taken for different types of small satellites depending on their mission, lifetime requirements, and overall mass and volume. Finally, this chapter seeks to provide information developed by NASA and other objective sources about the suppliers of critical elements of an electrical power system for small satellites and especially with regard to solar power cells and power storage units.

Annex 1

Photovoltaic Cell and Solar Array Suppliers

There are a growing number of global suppliers of solar cells and complete solar arrays that include the solar cells with the integrated struts for ready deployment in space. Some manufactures such as Spectrolab can provide either individual solar cells or the fully integrated solar array. Research projects around the world are seeking to drive efficiency up about the current highest levels of around 45%. These research activities are exploring new high valence substrate and absorber materials, spectrum matching techniques, as well as lower-cost fabrication and new production techniques such as the IMM cell that uses metamorphic multi-junction manufacturing techniques. The following listing of multi-junction solar cell and solar array manufacturers is indicative of some of the well-known and tested suppliers.

Representative Photovoltaic Cell Manufacturers

Azur Space

This is a supplier of multi-junction solar cells that are typically triple-junction in design. These cells use a combination of gallium arsenide, germallium, and GaInP materials, and they achieve an efficiency of solar radiation to electrical energy output in the range of 28% to 30%.

Bharat Electronics Ltd. of India

Bharat Photovoltaics has developed its manufacturing capabilities in cooperation with the Indian Space Research Organization (ISRO). ISRO has licensed solar cell and solar panel technology from other suppliers in the USA and other countries and then partnered with Bharat Electronics Ltd. to create a lower-cost supply to the Indian market. Bharat can supply both solar cells and solar panels. These products include monocrystalline, polycrystalline, and thin-film solar cells. It also provides inverters, mounting systems, solar cables, as well as complete photovoltaic systems, terrestrial power systems, as well as satellite applications.

CESI/ENE

The CESI single-junction gallium arsenide solar cells that are deposited on a germanium wafer by ENE are thicker than some three-junction solar cells, but this lower-cost photovoltaic cell can provide a 20% efficiency under the AMO spectrum rating system. This type of cell has been used by the Surrey Space Technology Ltd for small satellite manufacture. Triple-junction solar cells with efficiencies around 27% are also available from these Italian and Belgium teams.

Emcore Corporation

Emcore also manufactures triple-junction solar cells in two different versions. The efficiency of solar energy conversion for these solar cells is typically in the range of 28.5% to 29.5%. Emcore cells are provided in standard sizes but can be provided to custom order in different sizes as well. NASA has used these cells on their own missions.

SolAero Technologies

SolAero Technologies is unique in that it is a collaborative effort with the US Air Force. SolAero Technologies and the USAF are currently developing a new type of cell known as the “metamorphic multi-junction (IMM)” solar cell. This special manufacturing technique has resulted in a lightweight and higher-efficiency cell that is in developmental testing. Current SolAero cell have an efficiency level in the 28% to 30% range. They offer at least four optional solar cell products with ZTJ cell having had extensive in-flight experience. The ATJ, ATJM, and BJT cells are particularly offered to support small spacecraft missions.

Spectrolab

This company has been one of the oldest and most comprehensive providers of solar cells as well as integrated solar arrays. There solar cells range in efficiency from 26% to 30%. The most common products by Spectrolab are the XJT Prime, XTJ, and UTJ solar cells. They are offered in standard and customized sizes. All of the Spectrolab’s solar cells are also of the triple-junction design. The UTJ devices are rated at TRL 9 spacecraft applications.

Umicore

Umicore is another provider of triple-junction solar cells. It has been providing high-quality solar cells since the 1990s. Its solar cells with triple N-P junctions or bandgaps for its solar cells consist of indium gallium phosphide (InGaP), indium gallium arsenide (InGaAs), and germanium (GE) layer. These cells are made using a metal-organic chemical vapor deposition (MOCVD) process whereby the InGaP and InGaAs are deposited on germanium wafers. These solar cells have been demonstrated above 30% efficiencies under the AMO spectrum rating system.

Solar Panels and Array Manufacturers

Many of the companies that produce solar or photovoltaic cells also produce solar panels and arrays. In some instances, these panels also include magnetorquers, sun sensors, temperature sensors, and other features. Here are some of the typical providers of high-quality solar arrays from around the world. This is not an exhaustive list, but it includes many of the leading suppliers.

AAC Microtec and Clyde Space

The AAC Clyde Space photon solar arrays and solar panels are optimized to provide power to cubesat and multiple units of cubesats. These systems are designed to provide a high level of power generating efficiency by providing panels that can be position on the long sides of cubesats. If additional power is required, it is possible to have deployed, extendable solar arrays. These panels and arrays are designed to provide convenience in achieving reliable platform integration. Spectrolab XTJ Prime solar cells are typically included on AAC Clyde solar panels and arrays (AAC Clyde Space 2019).

Bharat Electronics Ltd.

See as noted in above information.

DHV Technology

DHV is one of the leading providers of solar panels and arrays. Its website maintains that it has participated in over 50 projects, that 35 satellites are currently utilizing its arrays and panels, and that this adds to some 1700 days of successful operation in space.

Endurosat

Endurosat makes several versions of solar panels. These are of a triple-junction indium gallium phosphide/gallium arsenide/germanium design and the solar cells used in these panels rated to 29.8% efficiency. The panels are of the 1-unit and 3-unit design, and their respective masses are 0.04 kg and 0.155 kg, and this includes a magnetorquer in the configuration. Maximum cell voltages are 2.33 V per cell (Endurosat, Solar Panels 2019).

EXA

The EXA DSA/1A (Titanium Deployable Solar Array for 1 U) is the entry-level product of a family of deployable solar arrays based on artificial muscles for cubesats in the range of 1 U to 6 U. The arrays are composed of five panels, 3 on top and 2 on the bottom, that are attached to the cubesat structure. Available on request are deploy and release contact sensors and also custom options such as sun and temperature sensors. Seven panel configurations are available for very high power missions.

GomSpace

GomSpace, which can undertake complete small satellites, is able to provide two different power systems for cubesats. These both use 30% efficient cells. These units are designed to include a magnetorquer, sun sensors, and gyroscopes. The customizable panels have a maximum output of 6.2 W and 7.1 W, respectively. Cubesat panels can be ordered with an integrated magnetorquer with only a slight mass addition. The 1-unit cubesat panel produces 2.3–2.4 W.

Innovative Solutions in Space (ISIS)

MMA Design, LLC

MMA’s latest solar panel design is known as the rHaWK. It seeks to provide for high kW/m³ solar electrical power production plus longer life, a high level reliability, through new manufacturing techniques significantly lower mass and volume. At the beginning of life, the MMA rectangular rHaWK solar panel can normally produce up to 90 kW/m³ and at 28 °C over 150 W/kg. The efficiency rating for the solar cells used in the array is currently based on a configuration of the array at 29.5%. The lower-cost ZTJ cells produce 80 kW/m³ and 130 W/kg at the beginning of life. MMA arrays have been used by both the US Air Force and NASA (MMA Design LLC 2019).

NanoAvionics

The solar panels provided by NanoAvionics are designed for 1-unit to 3-unit cube satellites. This array uses an epitaxial structure. These cells use a combination of gallium indium phosphide, gallium indium arsenide, and germanium for its structural makeup. Its solar panel efficiency is rated to be very close to 29%.

SolAero Technologies Corp

See as noted in above information.

Spectrolab

See as noted in above information.