Nuclear thermal rockets may have great benefits for Solar system exploration. But one consideration is that the launch of a nuclear engine from Earth's surface, as the payload on a chemical rocket, might fail.

  • How should the danger of such a scenario be assessed? Would the heavy metal radiactive engine piece fall almost intact on one place? Or would it create a radiactive cloud which dangerously contaminates a wide area? Could a failure for example be compared with one of many hundreds nuclear bomb tests in the atmosphere?

  • What saftey measures could lower this risk? Maybe an abort system like that used on the crewed Apollo missions, which could separate the payload and land it in a controlled way.

  • Should they maybe be launched from Western Sahara where their trajectories cover a uninhabited area (4 million people live in Sahara, most of which in the far eastern parts along the Nile river and the rest mostly in a few concentrated oasis) and where the polluted sites could relatively easily be cleaned by scooping up contaminated sand.

For example, assume a 20 ton nuclear thermal rocket engine component was the payload of one of these two recently failed Proton launches, what would the environmental impact be?

9 minutes after launch: http://www.spaceflight101.com/ekspress-am4r---proton-launch-updates.html

A few seconds after launch: http://www.spaceflight101.com/proton-m-block-dm-03-glonass-launch-2013.html

  • $\begingroup$ How about deafness? From the roar of outrage from the protesters! Reactors have been launched before, no big deal. $\endgroup$ Commented Feb 9, 2017 at 23:35
  • $\begingroup$ I have a hard time believing anyones going to go to the sahara to scoop up sand. What are they gonna do with that sand? They scooped up the fukushima topsoil, put it in bags, and are letting it rot in giant piles because they've no better idea. The sahara is just desert and a few poor people, no need for cleanups. $\endgroup$
    – Innovine
    Commented Feb 12, 2017 at 11:18

2 Answers 2


It's not dangerous.

The core would never be operated on Earth, and so would not become radioactive like you're thinking. A nuclear reactor on Earth that has been in operation is extremely radioactive due to the fission products, but the original fuel was not. The unburned U-235 fuel has a half-life of 700 million years, which means that its radioactivity is extremely low. If the launch vehicle blew up and somehow dispersed the material, the effect would be minimal. Even that is unlikely, since the reactor would be designed to contain the material in the event of a launch failure. The force of a catastrophic launch failure explosion on the payload is not that great. As an example, the entire shuttle cabin survived the Challenger explosion, and some of the astronauts remained conscious immediately after the explosion (three emergency air packs were manually activated, though one that was found was not).

The main issue would probably be one of proliferation. You'd want to make sure that you picked up the bigger pieces or the intact reactor so that no one could make a bomb out of it. Though making a bomb from the material would be hard, since reactor fuel is not enriched nearly as much as bomb fuel needs to be.

  • 2
    $\begingroup$ Uranium is still toxic (it's a heavy metal, after all). "Not dangerous" is a bit misleading there. Then again, chemical rocket fuels have included far more toxic compounds. $\endgroup$
    – MSalters
    Commented May 20, 2014 at 10:59
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    $\begingroup$ I concur. It's not more dangerous. $\endgroup$
    – Mark Adler
    Commented May 20, 2014 at 16:19
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    $\begingroup$ The problem isn't whether it is dangerous so much as the widespread perception that "nucular" power is incredibly dangerous by the non-scientific public, the media, and politicians. The Fukushima disaster did not help in this regard. $\endgroup$ Commented May 20, 2014 at 20:13
  • $\begingroup$ One should also note that there would be post-incident forensic investigation & cleanup anyway. $\endgroup$ Commented May 22, 2014 at 2:50
  • $\begingroup$ just like they cleaned up all those other accidents $\endgroup$
    – Innovine
    Commented Feb 12, 2017 at 11:20

I believe that any spacecraft that will be beyond the use of solar power, will, for now, use nuclear technology. They use a form of plutonium (238), that can actually be hand held. This isotope has a span of 80+ years, before it decays. Also, it decays to Uranium-234, not 235, and then to Lead-206. According to the wiki articles,there is only enough Pu238 to last for missions planned to 2022. We'll either have to find more, or, we won't be sending spacecraft beyond Mars,for a while.

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    $\begingroup$ You are writing about radioisotope thermoelectric generators. The question is asking about nuclear thermal rockets. They are very different beasts. $\endgroup$ Commented May 20, 2014 at 20:18
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    $\begingroup$ I sure wouldn't hold Pu238 in my hand. The stuff glows red hot. $\endgroup$
    – Mark Adler
    Commented May 20, 2014 at 22:38
  • $\begingroup$ OK, you are right... But I wonder, are the elements used for propulsion different than those used for nuclear powered rockets? just curious. $\endgroup$
    – ICL1901
    Commented May 20, 2014 at 22:40
  • $\begingroup$ @Mark Adler: I would not pick this stuff up, at least intentionally, however this site has an interesting image: chemistry.about.com/od/plutonium/a/10-Plutonium-Facts.htm $\endgroup$
    – ICL1901
    Commented May 20, 2014 at 22:49
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    $\begingroup$ Plutonium 238 is not found, it is produced in special nuclear reactors. $\endgroup$
    – Uwe
    Commented Feb 9, 2017 at 11:35

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