Agreed, but to be pedantic, it applies to all momentum machines which carry its own "propellant", not "fuel". For instance, in a NERVA rocket, the "fuel" is th

Agreed, but to be pedantic, it applies to all momentum machines which carry its own "propellant", not "fuel". For instance, in a NERVA rocket, the "fuel" is the uranium rods in the reactor, the "propellant" is the liquid hydrogen that is heated and shot out the exhaust bell.