Messrs Bezos and Branson blasted off to experience the zero-gravity in space last year. Soon they were followed by four more tourists in a capsule made by Elon Musk’s SpaceX. The race to space is heating up. The winner will be decided by the efficient use of rocket fuel. So, rocket scientists are looking for a better fuel option and they have stumbled upon nuclear fission to power the rockets.
Defense Advanced Research Project Agency (DARPA), a US government agency is working on spacecraft powered by nuclear thermal propulsion. Such spacecraft carry a small nuclear reactor producing heat through fission. The heat then will be used to expand the liquid hydrogen on the spacecraft to produce thrust. This thrust will be enough for the spacecraft to climb geostationary orbit, nearly 36000 km up within hours. The satellite that burns normal rocket fuel take days to achieve this fleet. Another method is to use the energy to generate electricity is to ionize a propellant gas like xenon which with the help of propellant gas can produce thrust.
Another proposal is to use radioisotope thermal generators (RTGs), a type of nuclear battery. RTGs have been used for deep space probes where solar power is especially feeble. Rather than using nuclear fission, RTG uses radioactive decay heat to generate electricity. It uses a device called a thermocouple to produce a modest amount of electricity from heat released by the decay of radioactive isotopes. Plutonium-238 has been used by NASA for all its voyager probe and curiosity rover still rolling on Mars.
What happens if it explodes on the launchpad? Such an event would present as much danger as the explosion of a conventional spacecraft. The reactor would not be switched on at that point in time to pose any radiological hazard.
A bigger problem would be the reactor crashing into the sea. Water encourages the start of a chain reaction in which uranium atoms split and release neutrons that can go on to split further uranium atoms. The fuel is configured in such a way that “poison wires” made from boron will remain in place. Boron is used to controlling the chain reaction or to even stop it. To avoid an accidental atmospheric re-entry DARPA’s nuclear reactor will not be flown in low orbits.
NASA keen to put astronauts on Mars is studying nuclear powered electric propulsion. NASA also wants a nuclear plant to power a base on the moon. All this means space is entering its nuclear age.