You may have heard a lot of buzz in the news recently about the Traveling Wave Reactor, a concept being developed by TerraPower Inc, which uses depleted uranium (aka U238), instead of the usual rarified U235. http://en.wikipedia.org/wiki/Traveling_wave_reactor Apparently, the supercomputer-modeling done by TerraPower has been extensive enough to win over a lot of skeptics, so that they are now garnering the funding they seek to develop the concept to fruition. I'd like to then ask if the Traveling Wave Reactor could be useful for propulsion purposes? From a safety standpoint, while U238 is chemically toxic, it is not considered to be a radiation hazard like U235 is. Furthermore, the Traveling Wave reaction is supposed to burn up radioactive decay-chain products, to keep their levels under control. One might intuitively say that if a Traveling Wave Reactor of reasonable size could be designed for stationary powerplants, then it could probably be adapted for nuclear-powered ocean-going vessels such as aircraft carriers, submarines and ocean-liners. Okay fine, but I wanted to take it further. Would it be possible in principle to harness the Traveling Wave Reactor for aerospace propulsion? Could the Traveling Wave Reaction be adapted as a particle-bed reactor design, to allow it to serve the higher power demands and variable power demands of aerospace propulsion applications? For example, could it be used to power a launch vehicle for the ~20minutes it might take to get to orbit? So far, there have been estimates of Traveling Wave Reactors being built to run for 60 years uninterruptedly. Could a reactor be constructed with suitable fuel elements to run at a very high power level for ~20 minutes, instead of 60 years at moderate power levels? So perhaps instead of a moderatable/throttleable fission reactor which is analogous to a throttleable liquid rocket engine, this would instead be the nuclear analog to the Solid Rocket Booster (SRB) which is not throttleable.