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Comment by gh02t | Hacker News Reader

It's not really a concern. U235 is basically radiologically inert, it doesn't become significantly radioactive until after the reactor has been running for a while. The concern with fission reactors in space is for stuff that might return to Earth after it's been in operation long enough to build up other isotopes that are radioactive and subsequently burning up in the atmosphere. For a vehicle that is on a one-way trip to Mars, and where the reactor will be brought online after it's out of Earth's orbit, this isn't a problem.

Edit: even on a round trip it wouldn't be a big deal, the reactor can just be jettisoned before re-entering Earth's gravity well. You just can't have a fission reactor with spent fuel anywhere near Earth orbit. Space reactors in general are pretty interesting, because the design criteria are so different from terrestrial power reactors.

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> the reactor can just be jettisoned before re-entering Earth‘s gravity well

I think if there’s one thing to be learned from previous missions, it’s that nothing will „just work“. If the ejection mechanism is damaged, or the spacecraft is hit by some object and rendered useless shortly before ejection, then the radioactive payload will make it to Earth. I think a roundtrip would be dangerous, and the core should be left at Mars.

in that case you could still divert the vehicle itself, assuming it's unmanned. My point is: yes, leaving it on mars is a pretty safe solution, but it's not the only one.

The political fallout will probably be more dangerous than adding another kilowatt-class nuclear reactor to decaying megawatt-class ones on sunken submarines.

This actually happened in the past. A Russian radar satellite failed to eject its nuclear reactor to a safe parking orbit and fell in Canada instead.

https://en.wikipedia.org/wiki/Kosmos_954

Never heard about this before, thanks for above link. Good link on Kosmos 954 recovery operation here: http://nationalinterest.org/feature/operation-morning-light-...

things are more and more likely to work now we can simulate things with computers first.

Triple redundancy usually works really well. Fail safes are great too.

"Hal, perform the earth orbit insertion burn" "I'm sorry Dave, I can't let you do that" "Hal, come on, not this shit again?" "Dave, the reactor core cannot be ejected, and cannot be allowed to enter orbit" "Hal, WTF?" "Crew ejection will occur in 3, 2, 1...Goodbye Dave"

Ah, ok. Thanks for the explanation.

> For a vehicle that is on a one-way trip to Mars, and where the reactor will be brought online after it's out of Earth's orbit, this isn't a problem.

Polluting the new homeland from the start, eh?

Just bury it out back, we'll clean it up later just like we did in Hanford. No problemo https://en.wikipedia.org/wiki/Hanford_Site.

More seriously, we can afford to have a small amount of nuclear waste there, but we need to plan for it better than we have previously. First, document where it is and what it contains. Second, I don't know.

Fun fact: right across from the Hanford Site is a massive Conagra plantation. Source: visited Hanford Site, looked up the company associated with the plantation across the road.

Or Runit Island: https://en.wikipedia.org/wiki/Runit_Island

Yep, Hanford Site was/is an epic disaster.

The correct response is reprocessing. Most of the "waste" generated by power reactors is actually still usable as fuel. It also eliminates the really long-lived stuff, so that the small amount of leftover waste only has to be kept stored for a much more manageable 500-1000 years.

That's so when the Martian Congressional Republic eventually decides to declare war on Earth, they'll be weakened from the get-go. It's called playing the long game...

How does pollution work exactly in an environment that's already hostile to life as we know it?

It adds one more element to overcome when we decide we would like to live there.

It's not like radiation is a non-existent problem to begin with on a planet that does not have enough atmosphere.

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