Imagine a starship with a tonnage of 600,000 metric tons that must maintain an average speed of 10km/s to remain in Near Earth Orbit, that's probably going to consume much more energy than simply cruising in interstellar space.

Suppose the large vessel requires to upgrade its antimatter containment units and main artillery batteries and the parts used for the assembly are transported bit by bit between Earth and the starship in orbit, how to remain in lower power mode during the servicing period of 32 months?

No FTL and I'm thinking of using solar power however there will be frequent eclipses going inside Earth's shadow.

  • $\begingroup$ Escape velocity from Earth is actually 11.2 km/s. I thought I understood your question until I got to "how to set to lower power mode during the servicing period of 32 months? No FTL and I'm of using solar power however there will be frequent eclipses and that's not good!" At that point I said WTF, I have no idea what he's asking. $\endgroup$ – ohwilleke Oct 27 '16 at 1:06
  • $\begingroup$ @ohwilleke: actually the starship is already in space and not launching from Earth. $\endgroup$ – user6760 Oct 27 '16 at 1:08
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    $\begingroup$ @user6760: No, maintaining orbit around a planet does not* use up energy. Basic physics, plus the real-life example of hundreds of natural & artificial satellites. (*OK, neglecting a bit of atmospheric drag & tidal effects, which are negligible over 32 months.) $\endgroup$ – jamesqf Oct 27 '16 at 5:16
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    $\begingroup$ The Moon seems to stay in orbit without expending power. Heck, it's gradually getting further and further away... $\endgroup$ – Eric Towers Oct 27 '16 at 5:37
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    $\begingroup$ @Tezra: Where did you get the idea that the moon masses only 10 metric tons? It's quite a bit more than that: nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html In fact, the Apollo LM landers massed rather more than 10 metric tons - 15-16 metric tons at launch, per Wikipedia. $\endgroup$ – jamesqf Oct 28 '16 at 4:08

It doesn't need to anything. Orbital velocity is approximately 8 km/s, so this vessel has a higher orbital velocity. It can lose a considerable amount of velocity and still remain in orbit.

Without checking, an orbital velocity of 10 km/s won't be in near-Earth orbit. Most likely it will be in a higher orbit. It seems as if this question is based on a fallacy that spacecraft need to be powered to maintain a given velocity. Momentum and Newton's laws of motion will kept it in orbit.

The only systems on the vessel that need to be on power mode will be life support, heating and cooling (for crew), lighting and instrumentation. Propulsion systems don't need to do anything. Possibly, as smithkm suggests, the occasional nudge from a space tug might be needed.

The basic physics of space travel is simple enough. Perhaps a little reading to expand your knowledge wouldn't go astray.

  • $\begingroup$ "Without checking, an orbital velocity of 10 km/s won't be in near-Earth orbit. Most likely it will be in a higher orbit." Higher orbits have lower orbital speeds. Having a higher orbital speed than necessary for a given altitude produces an elliptical orbit with a lower average speed- I don't think a spacecraft could physically maintain an average orbital speed of 10km/s while in Earth orbit since that's higher than the orbital speed at the edge of the atmosphere. $\endgroup$ – Catgut Oct 27 '16 at 11:44
  • $\begingroup$ @Catgut Of course! I was thinking about spacecraft spiraling away into higher orbits as they accelerate away from the planet. Back to basic orbital mechanics for me. $\endgroup$ – a4android Oct 27 '16 at 11:51
  • $\begingroup$ Questions like this come from people watching too much Bad Trek Science (which is a kissing-cousin to Coyote Physics). A ship loses power and instantly begins to fall from orbit. As the old lady says in the TV ad, "That's not how it works." $\endgroup$ – EvilSnack Nov 1 '16 at 3:15
  • $\begingroup$ Coyote Physics!?? Of course, you mean Cartoon Physics. Or a spaceship shuts down its drive and stops moving. Bad sci-fi physics especially bad media sci-fi science has a lot to answer for. $\endgroup$ – a4android Nov 1 '16 at 6:09
  • $\begingroup$ You too would fall out of "orbit" if you did what they did in star trek -- the manual says they operate at a low orbit altitude while using the warp drive to allow them to hover over one spot as though it were geosync. $\endgroup$ – Joshua Dec 6 '16 at 19:53

You are only "in orbit" if you have sufficiently low drag that you don't have to worry about it in the short term. The ISS is in a low orbit subject to fairly significant (by orbital standards) drag and generally only gets boosted once a month, although it can go much longer.

I would expect a spacecraft like you describe to have auxiliary power able to operate its reaction control/station keeping drives/thrusters even while its main power system and manoeuvring drive are off line. Failing that a small space tug could give it a nudge every month or two. Or you could just use a higher orbit. The higher you are the less drag and the more room you have to descend.


I am not sure what you're asking but my understanding of La Grange points suggests that this may be of some help in answering your question. These are points in a 3 body system such as Earth/Moon/Sun that have a relatively stable equilibrium and can be used to park an object like a spaceship in orbit with a relatively low expenditure of energy to maintain position.


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