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I think this is generally a good thing to do, with some caveats that I hope the FCC considers. For most satellites below ~450km, this is really a non-issue. At

I think this is generally a good thing to do, with some caveats that I hope the FCC considers. For most satellites below ~450km, this is really a non-issue. Atmospheric drag will generally be sufficient to deorbit the satellite in a few years. For big Earth-observing constellations, Starlink and friends, and many small missions, this doesn't change anything. Debris don't really accumulate dangerously in this zone and collision avoidance is a well-studied problem with a lot of people doing great work. The 18th SDS with the US Space Force, LeoLabs, Starlink/SpaceX, and a lot of other constellation operators take this very seriously and do a good job. For satellites in the 800km+ range, this is also not a meaningful change. The 25-year rule meant that these satellites needed a deorbit plan anyway. 800km is a rough estimate, in real life it depends on the satellite mass + geometry and the solar cycle. For satellites in the 450-800km range (again - hand waving here) this is actually a big deal. Satellites that would decay naturally between 5 and 25 years now need an active deorbit plan or need to launch lower and keep themselves up with propellant. Small satellite propulsion is becoming cheaper and more available, so this isn't that onerous for commercial operators. But I do worry a little about educational and non-profit launchers of satellites. They'd be excluded from using launches to this orbital range unless the FCC allows waivers (which I'm hopeful they will). Overall I don't think this has a particularly big impact. It's a sensible revision of an old rule that was a little too lax. But there aren't that many satellites launching at the high end of the 450-800km range without propulsion. The 1000km-2000km area is a more important area for debris mitigation and that was really already covered. As for the FCC having this jurisdiction vs. the FAA or the USSF, as Spock would say - "it is not logical, but it is true."

hinkley 4y ago
How high can the debris loft after a particularly nasty collision? Two satellites hitting at an acute angle should produce a cone of debris in front of them, of which about a third deorbits and a third goes up into a higher orbit that's an average of the two. Two satellites that hit at an obtuse angle, well, they pancake and produce a donut of debris. The stuff headed straight up is on a parabolic orbit that will hit the atmosphere on the way back down, but in the meantime any other satellite that crosses paths with it is effectively hitting a wall of stationary debris, creating a new cone that ladders up higher. Is there enough space that the ladder stops, or does it just keep building?
- FairlyInvolved 4y ago
  I don't think debris 'going higher' isn't much of a problem. Whenever this happens the orbit is going to be more eccentric - meaning a lower periapsis, and consequentially lots of drag that will cause a rapid deorbit. On the second point about parabolic orbits I also find that probably relatively low risk because we are only talking about a fraction of an orbit for a collision to occur so unless the debris field was massive the chance of another collision is probably still low. Remember when we are modelling orbit collisions normally we are often talking over 25+ years - 100,000 + orbits. I think the main problem is busy orbits (e.g. sun-synchronous polar orbits at popular altitudes) where most of the debris remains roughly in the same orbit following an acute collision but has a lot of other potential collision targets. Also as satellites are disabled by a collision they lose the ability to avoid other objects already in the same crowded orbit - i.e. the fraction of objects able to take avoidance decreases increasing the chance that future collisions are from 2 incapacitated satellites, removing the possibility of avoidance.
- jessaustin 4y ago
  Angular momentum is subject to a conservation law.
  - hinkley 4y ago
    What does angular momentum have to do with Kessler syndrome?
- nwallin 4y ago
  After a collision, the periapsis is at most as high as the point of collision, and the apoapsis is at least as high as the point of collision. In plain English, if two satellites collide with each other at an altitude of 450km, it doesn't matter what the original orbits were; 100% of the debris will have a low point in their orbit at or below 450km, and 100% of the debris will have a high point in their orbit at or above 450km. One of the quirks of debris deorbiting is that drag is exponentially higher the lower you are in orbit, and any drag that the debris experiences at any point along its orbit will manifest in a reduction of altitude 180 degrees along is orbit on the other side. So if you have a piece of debris with an eccentric orbit, let's say 300km at periapsis and 1,000km at apoapsis, after a fairly brief amount of time you'd expect the debris to have a periapsis of 299.9km and an apoapsis of 500km. Then perhaps 299km periapsis and a 350km apoapsis. etc. I'm making these numbers up but you get the idea: the high point in an orbit is the part that drops the quickest. Even if you were to launch 100,000,000 full sized satellites into orbit at 400km altitude and deliberately orchestrated Kessler syndrome, space would be unusable for a few years, but would be 100% back to normal after 5 years. The dangerous orbits are those in the 500-2,000km range. Satellites whose orbits never bring them low enough to experience significant atmospheric drag. Those are the satellites this new rule is targeting.
elliekelly 4y ago
> Debris don't really accumulate dangerously in this zone and collision avoidance is a well-studied problem with a lot of people doing great work. I think this line of thinking is dangerously incorrect. Sure it’s not a problem right now but we’re poised to have a lot more stuff in orbit than we’ve ever had before. Plastic waste didn’t initially “accumulate dangerously” either but once it became more widely used (and did accumulate dangerously) it was much more difficult to try to reign it back.
- hinkley 4y ago
  In this case it's policy reflecting Little's Law: population = arrival rate X duration of visit If suddenly someone wants to launch twice as many satellites, you either have to reduce tenancy or accept a higher population in the system. If you have a policy that's at most 25 years and a lot of satellites de-orbit in say 15 years on average, you can still triple your launches by pulling that down to 5. I am worried though, do we really build satellites that are expected to only work for 5 years? Are we disincentivizing people from building 20 year satellites this way?
  - Fatnino 4y ago
    I assume it means deorbit within 5 years after the satellite is decommissioned.
  - ntrz 4y ago
    The article says "5 years after completing their mission", not 5 years after launch.
    - hahajk 4y ago
      time to assign 25 year missions to satellites built to last 10 years!
      - simonh 4y ago
        Every mission has to pass FCC approval, and we're just discussing a super high level gloss of the rules. Thee's no way that would pass, so that's really not an issue.
ortusdux 4y ago
Several companies have been developing deorbit add-on modules, and I hope this requirement spurs on this growing industry. I would love it if it became the norm that satellites have a passive failsafe deorbit system that activates at after a set amount of time or if ground communications fail for a set duration. https://www.nasa.gov/smallsat-institute/sst-soa/deorbit-systems https://www.nasa.gov/smallsat-institute/sst-soa/deorbit-syst...

hinkley 4y ago

How high can the debris loft after a particularly nasty collision? Two satellites hitting at an acute angle should produce a cone of debris in front of them, of which about a third deorbits and a third goes up into a higher orbit that's an average of the two. Two satellites that hit at an obtuse angle, well, they pancake and produce a donut of debris. The stuff headed straight up is on a parabolic orbit that will hit the atmosphere on the way back down, but in the meantime any other satellite that crosses paths with it is effectively hitting a wall of stationary debris, creating a new cone that ladders up higher. Is there enough space that the ladder stops, or does it just keep building?

FairlyInvolved 4y ago
I don't think debris 'going higher' isn't much of a problem. Whenever this happens the orbit is going to be more eccentric - meaning a lower periapsis, and consequentially lots of drag that will cause a rapid deorbit. On the second point about parabolic orbits I also find that probably relatively low risk because we are only talking about a fraction of an orbit for a collision to occur so unless the debris field was massive the chance of another collision is probably still low. Remember when we are modelling orbit collisions normally we are often talking over 25+ years - 100,000 + orbits. I think the main problem is busy orbits (e.g. sun-synchronous polar orbits at popular altitudes) where most of the debris remains roughly in the same orbit following an acute collision but has a lot of other potential collision targets. Also as satellites are disabled by a collision they lose the ability to avoid other objects already in the same crowded orbit - i.e. the fraction of objects able to take avoidance decreases increasing the chance that future collisions are from 2 incapacitated satellites, removing the possibility of avoidance.
jessaustin 4y ago
Angular momentum is subject to a conservation law.
- hinkley 4y ago
  What does angular momentum have to do with Kessler syndrome?
nwallin 4y ago
After a collision, the periapsis is at most as high as the point of collision, and the apoapsis is at least as high as the point of collision. In plain English, if two satellites collide with each other at an altitude of 450km, it doesn't matter what the original orbits were; 100% of the debris will have a low point in their orbit at or below 450km, and 100% of the debris will have a high point in their orbit at or above 450km. One of the quirks of debris deorbiting is that drag is exponentially higher the lower you are in orbit, and any drag that the debris experiences at any point along its orbit will manifest in a reduction of altitude 180 degrees along is orbit on the other side. So if you have a piece of debris with an eccentric orbit, let's say 300km at periapsis and 1,000km at apoapsis, after a fairly brief amount of time you'd expect the debris to have a periapsis of 299.9km and an apoapsis of 500km. Then perhaps 299km periapsis and a 350km apoapsis. etc. I'm making these numbers up but you get the idea: the high point in an orbit is the part that drops the quickest. Even if you were to launch 100,000,000 full sized satellites into orbit at 400km altitude and deliberately orchestrated Kessler syndrome, space would be unusable for a few years, but would be 100% back to normal after 5 years. The dangerous orbits are those in the 500-2,000km range. Satellites whose orbits never bring them low enough to experience significant atmospheric drag. Those are the satellites this new rule is targeting.

elliekelly 4y ago

> Debris don't really accumulate dangerously in this zone and collision avoidance is a well-studied problem with a lot of people doing great work. I think this line of thinking is dangerously incorrect. Sure it’s not a problem right now but we’re poised to have a lot more stuff in orbit than we’ve ever had before. Plastic waste didn’t initially “accumulate dangerously” either but once it became more widely used (and did accumulate dangerously) it was much more difficult to try to reign it back.

hinkley 4y ago
In this case it's policy reflecting Little's Law: population = arrival rate X duration of visit If suddenly someone wants to launch twice as many satellites, you either have to reduce tenancy or accept a higher population in the system. If you have a policy that's at most 25 years and a lot of satellites de-orbit in say 15 years on average, you can still triple your launches by pulling that down to 5. I am worried though, do we really build satellites that are expected to only work for 5 years? Are we disincentivizing people from building 20 year satellites this way?
- Fatnino 4y ago
  I assume it means deorbit within 5 years after the satellite is decommissioned.
- ntrz 4y ago
  The article says "5 years after completing their mission", not 5 years after launch.
  - hahajk 4y ago
    time to assign 25 year missions to satellites built to last 10 years!
    - simonh 4y ago
      Every mission has to pass FCC approval, and we're just discussing a super high level gloss of the rules. Thee's no way that would pass, so that's really not an issue.

ortusdux 4y ago

Several companies have been developing deorbit add-on modules, and I hope this requirement spurs on this growing industry. I would love it if it became the norm that satellites have a passive failsafe deorbit system that activates at after a set amount of time or if ground communications fail for a set duration. https://www.nasa.gov/smallsat-institute/sst-soa/deorbit-systems https://www.nasa.gov/smallsat-institute/sst-soa/deorbit-syst...