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In Cibola Burn the ships Edward Israel, Barbapiccola and Rocinante started drifting toward Ilus/New Terra once their reactors stopped working.

But if they had enough velocity, shouldn't they be able to stay in the same orbit without drifting?

Alex also mentions that he has enough battery that can put Roci so far from the planet that they will be drifting their whole life before crashing. If the velocity was an issue, why not use the battery to get the velocity to stop drifting?

As far as I understand that's how Earth satellites work, they don't need to use fuel to continuously increase velocity, so why is this an issue for the spaceships?

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The Barbapiccola was in a low orbit to make it easier to shuttle the Lithium ore up from the settlement. It exposed them to more atmospheric drag than ideal, so the velocity gradually dropped without thrust.

Yeah, the Barb's orbit is decaying ... we've all been keeping pretty low (Alex Kamal)

They talk about hitting atmosphere, which is fairly meaningless- it gradually gets thicker, there isn't a hard transition from vacuum to air. There will be a point where it becomes thick enough to cause rapidly increasing drag and start the ships burning up.

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    Yes, orbit decay is why Skylab crashed in 1979. Increased solar activity made the Earth's atmosphere expand, which exposed Skylab to more atmospheric drag than was planned. en.wikipedia.org/wiki/Skylab#Solar_activity – Winchell Chung May 19 '20 at 13:46
  • Thank you, thanks also for the link... So the orbits decay also on all earth satellites? Or that is only true if the satellites are too close? How come for example moons work then, why their orbits don't decay? – Robert May 19 '20 at 17:07
  • There are multiple factors at play. For low earth orbit satellites, atmospheric drag is the main driver and leads to decay. There can be some interesting tidal effects that can increase the orbit - for the moon, these outweigh atmospheric drag and so it's moving out into a wider orbit (by about 4cm a year). Wikipedia has it's flaws, but some information en.wikipedia.org/wiki/Orbital_decay and en.wikipedia.org/wiki/Orbit_of_the_Moon#Tidal_evolution – Michael May 19 '20 at 17:17

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