Spacecraft power systems generate, store, condition and distribute electricity for space missions of all types – ranging from launchers to interplanetary probes or the International Space Station. They must operate reliably throughout their missions.
Recharging spacecraft millions of miles from Earth is impossible, so they must produce or store enough energy to last through decades in orbit. To accomplish this feat, spacecraft require multiple long-lived power sources.
Battery
As with any machine, spacecraft require power sources for optimal functioning. Depending on their mission, solar, chemical or nuclear sources could provide power production.
Near-Earth satellites rely on solar energy as an energy source; however, as missions further from Earth extend their orbital journeys it becomes increasingly challenging to generate and store enough power over long durations of time.
Aerojet Rocketdyne was chosen by Sierra Nevada Corporation’s Dream Chaser spacecraft to design, fabricate, test and commission an Electric Power System (EPS). This EPS will regulate solar panel-generated power for distribution among various sensor and payload modules on board; an easy integration will be made possible using standardized modules featuring solar panel interface, battery interfaces, charge/discharge regulators and distribution electronics all integrated together for flight-proven operation.
Solar Panels
Solar panels convert solar radiation into electrical power, serving as the main source of power for spacecraft in orbit and deep-space missions.
Solid-state relays control solar array power distribution to various equipment on board a satellite, ensuring it remains within its battery voltage range while relaying current telemetering to ground control for operators to keep an eye on overall satellite health. If any abnormal events arise, these relays can also disconnect units to prevent their receiving excessive current or voltage charging which could otherwise damage its subsystems and disrupt satellite performance.
Solar power is widely utilized by satellites orbiting inner planets such as Mercury (0.4 AU), Venus (0.7 AU), and Earth (1 AU). Solar provides more energy density than alternative power sources like nuclear fuel cells or non-rechargeable batteries, plus solar panels are lightweight enough to be folded for launch or unfurled upon need – NASA is also researching semiconductor materials like gallium arsenide that make production of solar panels more cost effective and more efficient.
Radioisotope Thermoelectric Generators (RTGs)
RTGs use heat generated from radioactive decay of isotopes to generate electricity, making this technology exceptionally long-lived – such as powering spacecraft missions to the Moon, outer planets (Pioneer and Voyager) and recently Mars Rover Curiosity.
Early versions of the power system contained small amounts of radioisotope material designed to disintegrate during an accidental reentry, while later designs encased plutonium within high-strength graphite blocks with an outer iridium layer and was tested successfully during both the 1968 launch of a weather satellite as well as Apollo 13’s failed reentry attempt that left its lander floating aimlessly over South Pacific waters.
The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), is currently powering Curiosity on Mars. This power system combines the GMHS RTG with PbTe/TAGS thermoelectric generators which produce approximately 100W electric from 10 kg of Pu-238 fuel pellets.
Nuclear Power
Nuclear power uses fission reactors to generate electricity, typically using Plutonium-238 as the fuel of choice, which undergoes intense alpha decay processes that produce heat which can then be converted to electricity by thermocouples. Furthermore, there is minimal radioactive gamma radiation produced which requires shielding.
Nuclear powered spacecraft have proven invaluable for deep space exploration. They have been utilized as planetary rovers, stationary science stations on planet surfaces and electric propulsion systems that help spacecraft traverse around our Solar System.
Nuclear reactors have recently drawn increasing interest as power sources for spacecraft missions that demand an abundant amount of power, such as trips to outer planets or human Mars missions that would need an electric propulsion system. Energy produced from nuclear reactors could use positive charging technology on propellants pushed out through thrusters to propel forward motion in an energy efficient manner compared to chemical rockets; in fact, The 1992 Principles Relevant to the Use of Nuclear Power Sources in Outer Space regulate their manufacture, operation, and inspection for spacecraft use by spacecraft manufacturers, operatorss and inspectors.