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Comment by th8700 | Hacker News Reader

Nobody would accept the fallout if it's a ground launch. And if it's a space launch, why not go directly to Project Orion?

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Nobody would accept the fallout if it was a space launch either, given that crud might either hang about in LEO poisoning it for everyone else, fall out onto the planet below, or drift around in space forming a radiation hazard for future travel. You'd have to get its speed up to solar escape velocity to ensure it wouldn't be captured somewhere.

Use it for the later stages in a many stage interstellar rocket. First stages are chemical, then NERVA style contained nuclear rockets, then open cycle nuclear when you are already well past solar system escape velocity.

I’m thinking of something like an interstellar flyby probe for the Centauri system. It wouldn’t be able to stop or do much course correction but you could send basically an autonomous space telescope that transmitted back observations. It would be able to see planets in the system much better than we can from here.

> drift around in space forming a radiation hazard for future travel.

Do you realize how big space is?

Do you realise that it isn't a wide open flat space, and things put into orbits stay in them?

Radiation hazard of single digit nuclear rocket launches will completely pale in comparison to total amount of radiation coming from Sun, and space.

Do you understand how much radiation it is in space? All human nuclear experiments in 20th century together wouldn't be even a rounding error there.

This does not follow. Photons from the sun are not radioactive isotopes that can rain down on us as they decay from orbit. And the magnetosphere protects us from the bulk of the solar wind's traces of heavier isotopes. How much plutonium or whatever, is in near-Earth space, other than what we've sent up there? The old Soviet reactor-powered RORSAT series have their cores in orbit still. They'll come down eventually. See https://en.wikipedia.org/wiki/Kosmos_954 which crashed in the Canadian arctic. A cleanup operation was attempted over a wide area, as it survived reentry with pieces intact.

> They were ultimately able to recover twelve large pieces of the satellite, ten of which were radioactive.[1] These pieces displayed radioactivity of up to 1.1 sieverts per hour, yet they only comprised an estimated 1% of the fuel. One fragment had a radiation level of 500 R/h, which "is sufficient to kill a person ... remaining in contact with the piece for a few hours."

A more pragmatic argument is that, after the fission of literal tonnes of plutonium in the atmosphere in the previous century, the small risk of losing a few kg more here or there pales in comparison. Even all those RORSATs barely register in comparison to that.

Not with an isp measured in the thousands of seconds. This is greater than earth escape velocity. Past the earth, it'll diffuse enough to not be a significant issue.

It could make an excellent fourth stage, however.

Given economic considerations, both the open cycle gas core, and NSWR may beat practical Orion drives.

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