ISRO has developed a credible Cryogenic and Semi-Cryogenic engines for its launch vehicles

India’s space agency, ISRO, is jointly developing a nuclear-powered engine along with Bhabha Atomic Research Centre (BARC), it is reliably learnt.

Chemical engines, such as those that power the thrusters in satellites, are fine up to a point, but if you want to send a spacecraft deep into space, such as into interplanetary missions, they will not do — neither can they carry that much fuel nor can they be solar powered because sunlight will not reach a solar panel at such long distances.

Hence, nuclear-powered engines. According to sources, ISRO-BARC are developing what are called Radio thermoelectric generators (RTGs). “The work has already begun and has been identified as a major task that has to be completed soon,” said the source.

The nuclear engines are not to be thought of as nuclear fission reactors that generate electricity. The RTGs use radioactive materials, such as Plutonium-238 or Strontium-90, which release heat as they decay.

Essentially, the engine contains two parts — the radioisotope heater unit (RHU) which generates heat — and the RTG, which converts the heat into electricity.

Thermocouple

This heat is transferred to a ‘thermocouple’ — a material that develops a voltage if there is a heat gradient across it. To put it in simple terms, think of it as a rod — if one end is hot and the other end is not, there will be a voltage across the rod (Seebeck Effect). The voltage can be harnessed to charge batteries that can provide motive force to a satellite. ISRO is targeting a 5W RTG, it is learnt.

“RTGs are independent of solar proximity and planetary alignment. This characteristic would help in minimising constraints like the ‘launch windows’ that the scientists have to operate within,” says Nitansha Bansal, a cyber security specialist with Columbia University, in an article for the Observer Research Foundation (ORF).

RTGs, however, are not entirely new. US spacecrafts such as the Voyager, Cassini and Curiosity have been powered by RTGs.