Assuming this was meant to be a serious question: Well, it is simply too dangerous. What if that thing blows up on start or while in the atmosphere/orbit? More generally, this project is a combination of:

1) spacecraft / rocket science, a technology where we still make a lot of mistakes and need a lot of room for experimentation

2) nuclear power, a technology where we have no room for errors, as small mistakes quickly sum up to a major catastrophe

Those two simply don't line up, until we achieve major advances in both areas.

Which major catastrophe? Doomsayers love to say "catastrophe" and then not say what they mean.

Are you talking about Chernobyl, the catastrophe where they literally had to disable every single safety in the system? Yes, if you disable every safety and intentionally ignore your engineers, the next two thousand years are going to have a bad time in that area.

But if you're saying that in the general case people are unable to build safe systems that harness nuclear power, that seems empirically mistaken.

(It would be better to assume every question on HN is a serious one. The point of HN is to be smart, and smart people rarely resort to offhandedness to make their points.)

The point of HN is to discuss 'Anything that good hackers would find interesting.' This isn't the same as being smart. I don't think it's a good idea to use that language as the basis for trying to influence someone, as it's easily interpreted as an underhanded suggestion that others are not as smart as you, and it implies that smartness is the major relevant scale with only one notable axis; omitting knowledge and experience, for example.

Nor does it seem useful to equate "smart" to "serious" or a lack of "offhandedness". Shows like QI, the puns in scientific journals (eg, in Angewandte Chemie at http://pipeline.corante.com/archives/2009/10/13/those_zanies...), the IgNobel awards, and the humor of David E. H. Jones in his Daedalus columns, etc. strongly suggest that your observation of a strong anti-correlation between those traits is more a personal belief.

https://www.google.com/search?q=deaths+per+kilowatt

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

The risks of nuclear power are:

Nuclear contamination at mining locations. Around 80% of the Uranium stays in the mining waste and gets washed out with time. Germany so far paid over 5 billion euro to clean up the uranium mining of the GDR. (from 1952 until 1990 5275 workers got bronchial cancer through inhaled radionuclides, but this isn't that huge an effect)

Contaminations through reactor explosions. This is quite rare, but when it happens large areas of land become uninhabitable for a pretty long time. Fukushima and Chernobyl both happened in relatively low population density areas. Economic damages occur even in very far regions. A big percentage of boars in Germany today aren't considered safe for consumption because of too high radiation.

Contamination through unsafe storage of nuclear waste. Places that have been considered safe are now known to be inappropriate for storing nuclear waste. Salt stocks for instance will have water leaking inside.

Part of the reason for detonating the first atomic bomb 500m above Hiroshima was to minimize residual radiation in the hopes that US troops could soon occupy the city.