E-Newsletter


Power Generation

Power Generation for spacecraft can be divided into the following types:

  • Solar Arrays
  • Fuel Cells
  • Batteries
  • Nuclear
  • Microwave

Solar Arrays provide electrical power to spacecraft by the photovoltaic conversion of solar power and are the best choice for providing electrical power to satellites in an orbit around the earth.  Two main types of solar cells are currently on the market; silicon, and Gallium Arsenide.  Gallium Arsenide cells are 40% more efficient than Silicon (Silicon cells are 18.5% efficient), and are much less susceptible to radiation damage than silicon.  They are however, significantly more expensive than Silicon, although they do offer a weight saving which may be a factor in launch costs.   The efficiency of silicon cells degrades by 0.5% per degree celcius increase in temperature whereas Gallium Arsenide cell efficiency degradation with °C increase in temperature is around 0.25%.  Solar panels have limitations in certain environments, for example on Mars, where panels do not function well after a few months due to the build up of dust on the panel surfaces.   

Fuel cells produce electricity by the direct reaction of a fuel (on the anode side) and an oxidant (cathode side).  A fuel cell functions in the same way as a battery, except that for fuel cell operation, both fuel and oxidant must be supplied, (and products removed) continuously.  A battery is a closed system in which the reactants will eventually 'run out' and the battery will either be 'dead' or will require recharging.    Aerospace applications generally use hydrogen-oxygen fuel cells since hydrogen has a very high energy density when stored as a cryogenic liquid.  In this reaction energy is produced when  hydrogen and oxygen combine exothermically, generating water as a by-product.   

Battery systems are described more fully in the Power Storage section of this site.   Batteries are a very important source of spacecraft power, and are often used as a secondary supply of power, for example where solar panels are used, batteries provide power during eclipse periods, and are recharged via the solar panels when the spacecraft is in sunlight. 

Nuclear power is generated by converting the heat energy produced by the decay of radioisotopes.  These systems are called Radioisotope Thermoelectric Generators or RTG.  RTGs generally use Plutonium-238 or Uranium-235.   Radioisotope power is compact, and removes dependence on the sun.  These systems were used on the Apollo Missions.  

Spacecraft power generation generally occurs on the spacecraft; another method used  is to generate the power on another spacecraft, and transmit it, via microwaves, to the spacecraft.   This eliminates the mass of the power generating equipment on the user spacecraft.