Here is an interesting web-site that argues that for dv < 3km/s water is the ideal propellant.http://neofuel.com/staiff1999/index.htmlI wonder though what the maximum isp of monopropellant HTP is in a vacuum and whether it would be better to keep the reactor on the moon and use it to supply a fleet of ships with HTP. Or perhaps use a two stage system with the first stage using nuclear produced HTP, and a water NTR second stage.
The cost of rocket fuel and other mass in space can drop by orders of magnitude because Earth can launch "pumps." A pump delivers orders of magnitude more mass than its own mass. Like a pump, each ton of hardware sent to space to operate a steam rocket architecture can return between 10,000 and 100,000 times its mass in rocket fuel at Low Earth Orbit. This is completely equivalent to orders of magnitude drop in costs. A chemical architecture would only return 100's of times its mass.
I would really love a political climate in which launching uncritical reactors made from low enriched uranium was not an intractably expensive thing to do, and did not have political risks to missions, I don't see any realistic prospect of this any time in the near future.
Quote from: speedevil on 10/21/2018 12:37 amI would really love a political climate in which launching uncritical reactors made from low enriched uranium was not an intractably expensive thing to do, and did not have political risks to missions, I don't see any realistic prospect of this any time in the near future.FWIW I think any Earth launched reactor is going to be highly enriched. The design considerations are similar to naval reactors except even more so. And I don't think it's politics except inasmuch as they have to keep cutting things to fund shuttle derived launchers.