This question flows from the recent question Would rocket engine exhaust create pockets of gas in space which could hinder further space exploration? it talks about daily Earth — Moon trips

If we establish shipping lanes in space for these daily deliveries,

Answers there indicate that gas just disperses, so no worries.

There are also 150+ posts about debris that talk about stuff in orbit around Earth and the risk that those items cause. Which is a separate perspective, they are not occupying the same space, the are following the Earth on its journey through space.

On Earth, shipping lanes reach between two locations on land, via sea (or air) and relative to Earth things are fairly static. If a ship passes, a few hours later another ship is likely to travel through the same water and any debris the first ship left behind.

On the Earth — Moon "shipping lane", there is nothing static. The Moon moves around the Earth, the Earth moves around the Sun, the Sun moves around the Milky Way's center, the Milky Way moves around the universe.

Once a ship leaves Earth's atmosphere, is there any possibility of it occupying the same space (relative to the Sun?) as another ship had previously?

A year later, the Earth is kind of the same place, but is it really in the same place?

  • $\begingroup$ This is one of those questions, that might not have flowed clearly from my mind to the page. $\endgroup$ Commented Nov 1, 2019 at 17:57
  • $\begingroup$ I think you're right in terms of there being nothing static, but the movements of planets are certainly periodic, and predictably so. I think any docking maneuver from the shuttle or otherwise to the ISS proves we can make multiple craft occupy the same space... Relative to the sun is interesting, but the sun moves too. We don't ask if any earth shipping lane occupied the same space relative to the sun. $\endgroup$
    – mothman
    Commented Nov 1, 2019 at 18:16
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    $\begingroup$ You're asking about the spatial coordinate. "The same space" sounds more like a ill-defined philosophical question like "can you jump into the same river two times?" $\endgroup$ Commented Nov 1, 2019 at 22:50
  • $\begingroup$ Which of your questions are you asking: whether orbital debris tends to stay "static" relative to the sun, or what it means to be in "the same place" relative to something else in space? Try to ask one question per post. $\endgroup$
    – Erin Anne
    Commented Nov 3, 2019 at 21:10

1 Answer 1


"Yes", and in fact there are spacecraft that do this all the time in Earth orbit - the geostationary communications satellites. There is only one such orbit, realistically, and therefore, at least to a first order approximation, these spacecraft are in the same space relative to the sun as others. Really you're just asking if it's possible to send two or more spacecraft out on the same orbit, and sure we can, it would just take a crazy amount of planning and timing.

The more general question is "is it possible for a spacecraft to encounter the debris left by another", which is far easier to answer yes to since we see this happen (or nearly happen) a lot - spacecraft need to maneuver around debris or, at the very least, to maneuver to reduce the slim possibility of hitting that debris.

Now, the answer to what appears to be the original question - can one spacecraft travel in exactly the same orbit as another and encounter its debris - is not really. The debris will be travelling with the spacecraft that released it, plus any extra velocity that it obtained during its jettison. Let's assume that this jettison imparts absolutely no further energy. This could happen if, say, a spacecraft gently split apart (it released its Earth Escape Stage, say, very gently) and then maneuvered away for whatever reason. This debris is now on that spacecraft's previous orbit. In order for another spacecraft to encounter it and for that spacecraft to be on the same orbit then the chase craft has to initiate a rendezvous maneuver.

This is because it is possible to send two spacecraft out on the same orbit with appropriate timing, but if you do so then, neglecting orbital perturbations, the two will forever chase each other around the sun. Being on the same orbit means that they one will never catch up, since if it did then it would be on a different orbit. This is more or less what happened with the early Gemini flights, when the astronauts tried to catch the target but kept missing because as they sped up to try to catch the target their orbit changed.

So, in order for this encountering to happen, you'd have to plan for it or be extremely unlucky, where your orbital insertion happened at exactly the wrong time and you insert exactly where and when the debris is passing.

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    $\begingroup$ The question was about the same space referenced to the Sun, but not referenced to Earth. $\endgroup$
    – Uwe
    Commented Nov 2, 2019 at 18:02
  • $\begingroup$ @Uwe: Yes, I was using the example of geostationary orbit to illustrate that it is possible and done, not as a definitive answer to what is already done in solar orbits $\endgroup$ Commented Nov 3, 2019 at 15:58
  • $\begingroup$ I think the third paragraph and on, while correct in a point-mass sort of sense, should consider that debris leaving a spacecraft in Orbit A ends up in a crossing orbit. If Orbit A is LEO, like ISS' orbit, then hopefully atmospheric drag will separate those orbits before it becomes a concern. If not, then the odds are that eventually other craft in Orbit A will need to maneuver around that debris. For that not to happen as the number of orbits tends to infinity, the debris' orbit would have to be in resonance with the other spacecraft. I have upvoted though. $\endgroup$
    – Erin Anne
    Commented Nov 3, 2019 at 21:20
  • $\begingroup$ @ErinAnne: thanks. I did specify that I was neglecting perturbations. $\endgroup$ Commented Nov 3, 2019 at 21:35

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