ULA (United Launch Alliance) mentioned a new upper stage they are working on that will use IVF. Sounds like an internal combustion engine, running a generator, fueled on propellant and oxidizer that would otherwise be vented.
Ok, clever way to generate power on an upper stage, since a IC engine can be small and efficient. Burning hydrogen is simple and known technology.
But they keep talking about how this makes it reusable? But really it sounds like it just provides power, removing the need for solar panels, batteries, hydrazine driven generators, etc. A nice feature, but how is this a game changer?
Sure this means the second stage can stay alive much longer, but right now, that does not quite seem to be the major bottleneck?
The main reuse suggested seems to be refueling in orbit. But again, that is not entirely what is usually meant by reuse in this context.