India Mulls Using Nuclear Power For Its Chandrayaan-2 Mission To the Moon

MarkWhittington writes: India is preparing its second mission to the moon, the Chandrayaan-2, as Space Insider noted. The mission will consist or an orbiter, a lander, and a rover. It will be launched on an Indian-built Geosynchronous Satellite Launch Vehicle (GSLV) in late 2017 or early 2018. Defense Daily reported that officials at the Indian Space Research Organization are mulling making the lunar mission nuclear powered, presumably with plutonium-fueled radioisotope thermoelectric generators (RTGs). RTGs use the heat of the decaying fuel to create electricity. Both the American and the Soviet space programs have used RTGs in their various spacecraft, the most recent one being the New Horizons space probe that recently flew past Pluto.

Comments

238Pu?

[Rei]

Does India actually have a stockpile of 238Pu? If not then where are they supposed to get it in two years? It's not like the world is awash in the stuff, and it takes time to set up a program and make it.

Honestly, Chandrayaan-2 is only a near-Earth mission, and not a super-long one - they don't need a long half-life element like 238Pu. Dirt-cheap 90Sr probably makes more sense, it's a widely available waste product. Or if India really wanted to impress the world, they'd make an actual nuclear reactor for space missions, not just an RTG, and offer to make them for sale to other countries. Russia made a few of them near the end of the Cold War (TOPAZ), but it's anything but off-the-shelf technology today. Another option to do something actually noteworthy would be to make a stirling RTG and leave on the moon, racking up operational hours in a space environment to demonstrate its reliability. A flight-tested stirling RTG would also be something that the west doesn't have.

Re:238Pu?

[Rei]

That is, of course, not how 238Pu is made. Neutron bombardment of uranium yields far too much 240Pu mixed in with the 238Pu**, and it's too much cost and difficulty to separate them. Instead, it's made by first taking nuclear waste and isolating the 237Np from it, which makes up only a very small fraction, so you have to process a lot. You then expose the relatively pure 237Np to a heavy neutron flux (which is expensive, as neutron flux is valuable), very slowly converting it to 238Pu via 238Np. You then regularly have to extract out either the 238Np, 238Pu, or both. It's an expensive process. 238Pu is a manufactured product, not a waste product.

** Uranium is mainly 233U, 235U, and 238U. We'll ignore 233U because it's so far away from 238Pu for now, and we'll ignore fissions, which are very unlikely to lead to Pu. 238U captures to 239U, which quickly decays to 239Np. This captures up to 240Np, which decays to 240Pu. 235U captures to 236U, which has too long of a half-live to be relevant. It captures to 237U. This can then either capture up to 238U (leading most likely to more 240Pu), or decay to 237Np. This then gives us the above route to 238Pu. But the longer series of bombardment chains needed, the comparative rarity of 235U to 238U in most reactors, and the cross sections involved, usually mean that under 2% of plutonium in nuclear waste is 238Pu.