Nuclear Propulsion Possibilities Discussion

[ecarfan]

This news from NASA is relevant to this thread; Eric Berger reports The US government is taking a serious step toward space-based nuclear propulsion

The nuclear-powered vehicle will launch within the payload fairing of a Falcon 9 or Vulcan rocket, Dodson said, and look much the same as the upper stage of a conventional rocket. It will consist of a large hydrogen fuel tank, a nuclear reactor, a supporting spacecraft structure, and a nozzle. Once it reaches a safe orbit, the reactor will be turned on. The liquid hydrogen will then be heated from 20 Kelvin—just 20° Celsius above absolute zero—to 2,700 Kelvin in less than a second.

And then? Well, we'll see. There are some unknowns about the performance of a reactor and its uranium fuel in zero gravity.

The reactor will be launched “cold” and won’t be turned on until it reaches a high-ish LEO of 700 to 2,000km.

The point is to radically reduce the amount of fuel needed to get to Mars and back.

The basic idea is straightforward: A nuclear reactor rapidly heats up a propellant, probably liquid hydrogen, and then this gas expands and is passed out a nozzle, creating thrust. But engineering all of this for in-space propulsion is challenging, and then there is the regulatory difficulty of building a nuclear reactor and safely launching it into space.

The engineering challenges are enormous. Safely storing liquid hydrogen in space for not just months but years; after all, you have to get back home! Building a very small nuclear reactor that operates reliably and safely in space and on Mars for years.

To my very non-expert mind that seems nearly impossible. The SpaceX approach of in-orbit refueling and insitu propellant production on Mars, while obviously very difficult, seems more feasible.