this post was submitted on 29 Jul 2026
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Sounds like you're remembering the Bussard Ramjet, which sucks up hydrogen from the interstellar medium to fuel a fusion reactor. It's technically possible on paper, but not even close to practical for a variety of reasons, among those being that the density of the interstellar medium is too low to provide enough fuel and fusion reactors aren't efficient enough.
So that's where star trek got the idea of Bussard collectors from.
I love the kind of problems for which fusion reactors are not efficient enough!
Why not scoop up junk and expel it behind you at a greater velocity, using whatever energy source you have.
That is essentially the concept of the ramjet, yes.
I thought ramjet was combustion. In space, you just need inertia?
Both. The concept is that hydrogen gets fused to produce power, which creates a self sustaining loop for the spacecraft. The exhaust is then ejected at greater speeds than the intake velocity. In theory that allows us to sidestep one of the biggest issues of spacecraft, the need to carry your own propellant / energy supply.