Nuclear Salt-water Rocket - Limitations

Limitations

The vessel's exhaust would contain radioactive isotopes, but these would be rapidly dispersed after travelling only a short distance; the exhaust would also be travelling at high speed (in Zubrin's scenario, faster than Solar escape velocity, allowing it to eventually leave the Solar System). This is however, little use on the surface of a planet, where a NSWR would eject massive quantities of superheated steam, still containing fissioning nuclear salts. Terrestrial testing might be subject to reasonable objections; as one physicist wrote, "Writing the environmental impact statement for such tests might present an interesting problem ..." It is also not certain that fission in a NSWR could be controlled: "Whether fast criticality can be controlled in a rocket engine remains an open question.".