3 ms·

It depends on how long, and how often, you burn those engines. If you’ve got a big torch that can sustain a large fraction of one gee for weeks or months, and y

It depends on how long, and how often, you burn those engines. If you’ve got a big torch that can sustain a large fraction of one gee for weeks or months, and your fuel is cheap enough, why turn it off at all? On the other hand, if it’s only good for a big push at the beginning and end of your trip, and you’ll spend the whole time coasting, spin is absolutely the way to go. The Expanse, as mentioned in other comments, showcases both these designs. Most ships fly a brachistochrone trajectory with a mid-point “flip and burn,” but the Mormons’ giant colony ship has a drum.

yellowapple 6y ago
> why turn it off at all? Because once I get into an orbit I'd generally prefer to stay there :) I mean, I guess you could just keep spinning around to constantly counteract nudging yourself out of orbit, but that just seems like a centrifugal habitat with extra steps. On another note, though, today I learned the word "brachistochrone", so thanks!
- rbanffy 6y ago
  > Because once I get into an orbit I'd generally prefer to stay there :) Or you can just be geostationary at 100 km with the engine on.
therealcamino 6y ago
I loved The Expanse. But you just made me wonder how the colony ship could possibly be practical, because it has to function in both those modes and I don't know how you'd design the interior spaces for that. Unless you had spaces that could only be used in one mode or another, which seems like a big waste.
- m4rtink 6y ago
  It was built as an interstellar colony ship - even with the ridiculously powerful and efficient drive technology they have in the Expanse it would take many years, possibly decades after reaching cruise speed before it would break at the destination. So I assume the colonists would just wait in a part of the ship perpendicular to the thrust axis during the acceleration burn and then move from that section (which would be now in micro gravity) to the rotating section. Then in reverse for the deceleration.

yellowapple 6y ago

> why turn it off at all? Because once I get into an orbit I'd generally prefer to stay there :) I mean, I guess you could just keep spinning around to constantly counteract nudging yourself out of orbit, but that just seems like a centrifugal habitat with extra steps. On another note, though, today I learned the word "brachistochrone", so thanks!

rbanffy 6y ago
> Because once I get into an orbit I'd generally prefer to stay there :) Or you can just be geostationary at 100 km with the engine on.

therealcamino 6y ago

I loved The Expanse. But you just made me wonder how the colony ship could possibly be practical, because it has to function in both those modes and I don't know how you'd design the interior spaces for that. Unless you had spaces that could only be used in one mode or another, which seems like a big waste.

m4rtink 6y ago
It was built as an interstellar colony ship - even with the ridiculously powerful and efficient drive technology they have in the Expanse it would take many years, possibly decades after reaching cruise speed before it would break at the destination. So I assume the colonists would just wait in a part of the ship perpendicular to the thrust axis during the acceleration burn and then move from that section (which would be now in micro gravity) to the rotating section. Then in reverse for the deceleration.