Comment by pbhjpbhj
8 years ago
> A hypothetical example with zero velocity would allow you to gather fuel without any drag. //
What do you mean by this, zero velocity within an atmosphere won't gather anything?
8 years ago
> A hypothetical example with zero velocity would allow you to gather fuel without any drag. //
What do you mean by this, zero velocity within an atmosphere won't gather anything?
Space is not an absolute vacuum which is why this works in the first place. If your ship sits in the interstellar medium so it's not being pushed around on net then by definition it's drag is zero. However, it's possible to collect some non zero amount of hydrogen and thus energy by putting a high vacuum pump to empty space. Efficiency left as an exercise to the reader. But, it would operate the same way as a vacuum pump inside an atmosphere, just vastly slower with random particle motion providing a continuous stream of new particles.
Rest of the idea:
The Ramjet works by collecting hydrogen and Helium from a large area because you have a high relative velocity to the medium which also imposes drag. Think filter feeding whales. So you are collecting linearly more matter and thus energy per unit time with increased speed. However, drag is a function of matter collected AND relative speed so something like velocity ^3.
This suggests there is some point where you get less energy from collecting that you lose in drag. But, this also means below some speed you get more.