With the decline of massive GEO satellites and a big increase in smallsat and cubesat, especially those in constellations, I wonder what their impact is on space debris.

Those smaller satellites do have considerable less mass than the "big old" satellites that were the most common to be launched, so each satellite of their own contributes less to potential space debris (and the now so often discussed Kessler syndrom).

Nevertheless the overall amount of satellites (planned to be) launched into LEO is incredible if compared to the last decades.

So my question is how much of a danger/increase in danger are those constellations to an inflation to space debris and launch windows?

My toughts:

  • Will launch windows be carefully adjusted because of the density of the constellations?
  • All the constellations are for telecommunication (and future ones for OE) so they are supposed to be active as long as possible -> therefore no fast decaying orbit how you can do it with scientific satellites.
  • Is the impact way smaller, than I think, because of the sheer (quite hard to imagine) "size" of LEO/MEO.
  • Is modern tracking/planning preventive enough to avoid any collisions?

Planned constellations for reference:

  • OneWeb : 650 (+1900) satellites @ 1200km
  • StarLink : 4400 (+7500) satellites @ 550km (340km)
  • Boeing : 1400-3000 satellites @ 1200km
  • LeoSat : 100 satellites @ 1400km
  • Telesat : 110-510 satellites @ 1200km

For clarification: I would like to have a quantitative estimation how much all those planned constellations impact the chance of collisions and launch windows. This can be done for an example (like the ISS) or done generally with (justified) self-made assumption.


1 Answer 1


I was an orbit analyst, in the LEO regime for 11 years. My co-worker had been in GEO for nearly 30. Here is a summary of what I have learned on the subject.

Note: Keep in mind the 3 basic sizes of space debris.
1) Objects that are big enough to damage a satellite, and can be theracked.
2) Objects that are too small to damage a satellite, and are too small to be tracked.
3) Objects that are big enough to damage a satellite, but are too small to be tracked.

I theory, a close approach analysis is done on the Space Vehicle (SV) and the Launch Vehicle (LV) before launch. If the analysis shows a "bad conjunction" to launch time will be adjusted. Maybe seconds, maybe to the next window, depends on how much of a change is required to reduce the collision probability to an acceptable number.
In practice, this isn't always done. Maybe the SV owner doesn't have the resources to do it. Maybe an initial analysis shows it wouldn't be an issue. Maybe they don't care. Maybe they don't know. etc.

Small Sat vs. Big Sat
Small Sats are cheaper, can be built & launched faster and replaced/replenished quicker. That is a big advantage. The failure rate is also less important. OF course, the problem of "Space Junk" grows exponentially with Small Sats.

In theory, once a SV has reached End Of Life (EOL) it should be "disposed of properly." What this means varies widely. Some things to consider:
How long will it take for the orbit to decay?
Can I place the SV in a "disposal orbit?" An orbit that will move it out of the way of the next useable satellite (usually a higher orbit) or one that will accelerate its orbital decay?
Should I just "walk away" and leave it there for someone else to deal with? Can I minimize the risk of it breaking apart or exploding?

Many "small-sat" builders don't consider these implications.

Your question has no easy answer. Sadly, there are no global standards in place to answer these questions.

  • $\begingroup$ Thank you for your answer. But apart of the third paragraph your answer does not help a lot with the asked question. A quantitative example for a close approach analysis today(how high the conjunction risk are/how often one needs to be done) and one projected close approach analysis if those constellations would be operational would be a good answer. And there are international guidelines on how to mitigate/deal with space debris by the UNOOSA. $\endgroup$
    – GittingGud
    May 22, 2019 at 8:41
  • $\begingroup$ In my experience, the "acceptable probability" varies greatly, based upon the owners/operators of the satellite. There are "text book" answers, and there are "this is how we do it answers." For example, the ISSs in runs COLA analysis 7 days in advance. Any COLA with a Pc of 1:10000 REQUIRES a maneuver plan. AN owner on one of my SVs demanded that we actually move EVERY TIME. It made no sense. Are you looking for how to do a COLA? $\endgroup$
    – Scottie H
    May 22, 2019 at 8:51
  • $\begingroup$ I would like to have a quantitative estimation how much all those planned constellations impact the chance of collisions and launch windows. This can be done for on example (like the ISS) or done generally with (justified) self-made assumption. $\endgroup$
    – GittingGud
    May 22, 2019 at 8:57
  • $\begingroup$ That is a non-trivial task. I no longer have to tools to answer those types of questions. Papers presented at the conferences of AIAA, AAS or other such organizations may have current answers. You ought to be able to browse titles and maybe abstracts. In the mean time, I'll also look and see if I can find those links. $\endgroup$
    – Scottie H
    May 25, 2019 at 23:58

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