How do we ensure a new orbit/route of a LEO satellite or even a swarm of LEO satellites doesn’t collide with currently existing ones when planning a mission?

I’ve thought about running a simulation calculating positions of every near object in the same time interval, but it would just be time/energy inefficient. Any plausible or does anyone knows how organizations like NASA or SpaceX does this?


2 Answers 2


And thus you detected the field of "space situational awareness"...

How do we assure an orbit doesn't interfere with other orbits? -> We don't.

Dedicated organizations (civilian and/or military - e.g. "18SDS" (US), EUSST (EU), GSSAC (GER), French, Spanish, Chinese, Egyptian and plenty others) do basically in short exact what you suggested: propagate orbit of every known object in the near future and crosscheck every orbit against another. If a close conjunction is detected, the operator of the satellite is informed and in critical cases risk mitigation operations are performed.

Unfortunately due to orbit perturbations, only looking few days into future makes sense, so these checks are done around the clock.

US Space Force (18SDS) is sharing most of the results in public: see "www.space-track.org"

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    $\begingroup$ As long we don't talk about GEO (Geostationary) Missions, yes. As said: due to orbit perturbations, we cannot even plan potential encounters more than few days in the future. Checking an orbit for a mission which will be launched in some weeks/months would be complete nonsense thus. $\endgroup$
    – CallMeTom
    Aug 24, 2022 at 11:05
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    $\begingroup$ @CallMeTom surely some sort of planning is done for future missions? I find it hard to believe that millions of dollars would be spent preparing to launch, and only then checking to see if the proposed orbit is OK. 5-4-3-2-Woops, there is another sat in the orbit we wanted to use, guess we'll just forget about it. Send that booster back to SpaceX. $\endgroup$ Aug 24, 2022 at 14:55
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    $\begingroup$ @OrganicMarble Space is big, space vehicles are rather small. Collisions are pretty much rare exactly because of this. And if a particular mission is endangered by a particular orbiting object, one needs only a few seconds of launch delay in order to completely avoid it. Launch windows of less than an hour are pretty much unknown. $\endgroup$
    – fraxinus
    Aug 24, 2022 at 18:28
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    $\begingroup$ @OrganicMarble If they are indeed in the "same orbit", they move at identical speed and will never collide. If they are not in the same orbit, the orbits either never cross, or cross at at most two point in space. It's unlikely that a planned orbit would intersect an already-existing one, and even less likely that it would result in a collision. And in a few days, the already-existing orbit will likely have been perturbed to result in a non-intersection of orbits anyway. There are only ~5k satellites occupying the billions of cubic km of space around the earth, it's not too crowded up there. $\endgroup$ Aug 24, 2022 at 18:29
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    $\begingroup$ @SteveMelnikoff But those are usually launches that want to hit another object up there, say the ISS. $\endgroup$
    – linac
    Aug 25, 2022 at 15:06

One thing that helps is that satellites are deployed to specific elevations (or "shells"). Thus, objects in space are not in a situation where they would hit ANY other orbiting body - just the ones in their shell. For example, a starlink satellite (550 km shell) is not going to collide with the International space station (400 km elevation), because they are at different elevations. With the exception of when the satellites are being raised to their shell, this limits the number of candidates for collision. This applies to satellites that are doing active station-keeping, which most are.

So, this does not ensure that there are no collisions, but helps to mitigate the risk of one. (Note: I had this as a comment, but felt like it addressed, at least partially, the question.)


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