Nuclear Reactors for Space
Radioisotope power sources have been used as essential sources of energy since 1961. Nuclear power reactors use nuclear fission by the method of chain reaction. Special absorbers control this chain reaction, so the produced power depends on the demand for energy.
What are radioisotope thermoelectric generators?
Radioisotope thermoelectric generators (RTG) are a source of power in which a chain reaction does not happen. So it this case, the power does not depend on the demand for energy but on the initial radioscope that is used as fuel.
The power is produced when the radioscope decays and generates heat. This heat is converted into energy. Most radioscopes use plutonium – 238. There is some inconvenience of using RTG – it cannot be shut down, so there should be provided batteries just in case.
RTGs can be used if the spacecraft needs not more than 100kW. If the spaceship requires more than that, then fission systems would be much more efficient.
The Office for Outer Space Affairs of the United Nations (UNOOSA) regards nuclear power sources as very essential because of being compact and endurable.
Radioisotope systems have been the primary power source for the USA space missions since 1961. Plutonium- 238 has high decay heat, which makes it a great source of electricity in the RTGs of spacecraft and satellites.
The European Space Agency also tend to favor the American – 241. However, it has high levels of low-energy gamma radiation. RTGs are safe and free to maintain, and they can be reliable to provide heat or electricity for long years in severe conditions.
In 2014 the European Space Agency’s Rosetta mission landed the Philae probe. However, it could provide only 64-hour data. Why did this happen? Simply because it ran out of battery, and it could not use solar power because of the position on which it landed. This case proved once again that RTGs are essential.
The space vehicles using RTGs
So far, there were 25 US spaceships that used RTGs. The RTGs that were used for this purpose were around 45. Some of the space vehicles that got powered by them are Apolo, Pioneer, Viking, Voyager, Galileo, and New Horizons. There were also a lot of military and civil satellites that used RTGs.
The Cassini spacecraft, which got launched in 1997 to explore Saturn, used three RTGs, which provided 870 watts of power. It functioned very well from 1997 to 2017. Voyager 1 and 2 also use RTGs to send back signals from distant planets. They have been in space since 1977 and are expected to operate there until 2025.
Galileo was launched in 1989 and had a 570-watt RTG. The Viking and Rover also depended on RTGs’ power. The Mars Science Laboratory rover launched in 2011, also operates with an RTG. There were three RTGs that were used as heat sources on the Pathfinder Mars lander robot, which was launched in 1996.
The newest plutonium-powered RTG is the GPHS RTG, which is a 290-watt system.