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FCC Approves 5 Year Satellite Deorbiting Rule

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Re: FCC Approves 5 Year Satellite Deorbiting Rule

#61

Post by mikeyouse »

Retric wrote: post #59
mikeyouse wrote: post #26

Earlier quoted context omitted.

The timeframe varies widely based on the shape of the object and the altitude. There are something like 5 orders of magnitude pressure difference between an object at 100km and one at 500km which is the difference between deorbiting in days vs years.

Huge constellations with stable orbits under active control are irrelevant. It’s really the a pair of uncontrolled satellites colliding that’s a meaningful risk, and that risk grows exponentially with age. To the point where the difference between 1 day and 1 year is effectively meaningless while the difference between 5 years and 50 years is huge.

If we're launching 15k satellites per year as some people expect, the difference between 1 day deorbit and 5 years deorbit is something like 75,000 satellites.

Re: FCC Approves 5 Year Satellite Deorbiting Rule

#62

Post by mikeyouse »

bisby wrote: post #54
mikeyouse wrote: post #39

Earlier quoted context omitted.

What? Starlink eventually wants 40,000 satellites - with 5 year lifetimes that'll be 8,000 per year... there are numerous other planned constellations, so figure something like 15,000 LEO per year within a few decades. 15k satellites per year with a 5 year lifespan and a 1-year decay means you'll be stable at 75k satellites. 5 year lifespan with a 3-year decay means you'll eventually be stable at over 100k satellites…

The rule is 5 years. You've given 2 examples under 5 years. If everything is going to re-enter within 5 years without boosting then your point is moot, because even in your "massively more collision risky" example, it still abides by the rules. If something was going to deorbit within 1 minute, or was going to deorbit within 4 years, 6 months... It doesn't matter to the creator, because they don't have to change thei…

Just responding to a comment that said "If deorbiting in years is sufficient, the difference in time is not relevant" where it's obviously relevant.. this doesn't seem remotely controversial.

Re: FCC Approves 5 Year Satellite Deorbiting Rule

#63

Post by hinkley »

elliekelly wrote: post #16
rzimmerman wrote: post #12

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…

> 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…

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?

Re: FCC Approves 5 Year Satellite Deorbiting Rule

#64

Post by wpietri »

MichaelCollins wrote: post #30
elliekelly wrote: post #16

Earlier quoted context omitted.

> 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…

https://www.youtube.com/watch?v=mQT5aMa_7iI "Gabbard Diagram for Low Earth Orbit 1959-2021" See how the stuff in the lower left corner speeds up towards the lower left corner? That's low flying debris falling out of space.

I am generally allergic to video, but that was fascinating to watch. Thanks for sharing it.

Re: FCC Approves 5 Year Satellite Deorbiting Rule

#65

Post by hinkley »

rzimmerman wrote: post #12

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…

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?

Re: FCC Approves 5 Year Satellite Deorbiting Rule

#66

Post by Fatnino »

hinkley wrote: post #63
elliekelly wrote: post #16

Earlier quoted context omitted.

> 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…

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 th…

I assume it means deorbit within 5 years after the satellite is decommissioned.

Re: FCC Approves 5 Year Satellite Deorbiting Rule

#67

Post by ntrz »

hinkley wrote: post #63
elliekelly wrote: post #16

Earlier quoted context omitted.

> 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…

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 th…

The article says "5 years after completing their mission", not 5 years after launch.

Re: FCC Approves 5 Year Satellite Deorbiting Rule

#69

Post by FairlyInvolved »

hinkley wrote: post #65
rzimmerman wrote: post #12

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…

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…

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.

Re: FCC Approves 5 Year Satellite Deorbiting Rule

#70

Post by bisby »

mikeyouse wrote: post #62
bisby wrote: post #54

Earlier quoted context omitted.

The rule is 5 years. You've given 2 examples under 5 years. If everything is going to re-enter within 5 years without boosting then your point is moot, because even in your "massively more collision risky" example, it still abides by the rules. If something was going to deorbit within 1 minute, or was going to deorbit within 4 years, 6 months... It doesn't matter to the creator, because they don't have to change thei…

Just responding to a comment that said "If deorbiting in years is sufficient, the difference in time is not relevant" where it's obviously relevant.. this doesn't seem remotely controversial.

You're arguing a different thing. The topic was satellite design for satellites under 450km.

If deorbiting in years is sufficient, the difference in 1 minute vs 4 years is NOT relevant -> to a satellite builder worried about the law.

If everything deorbits within 5 years, the only way for more things to accumulate is to launch things faster. But that's a separate discussion. If everything launched today is deorbited within 5 years, then in 5 years, all satellites will be new satellites launched after today. If everything launched today is deorbited within 5 months, then in 5 years, all satellites will be new satellites launched after today. Deorbit speed under a threshold has no bearing on accumulation beyond that threshold.

If SpaceX launches a trillion Starlink satellites, and they all deorbit within a year, then yes. it's going to be a very crowded year, and we'll have to drastically rethink how much stuff we have in LEO, but at the same time SpaceX would not be in violation of the 5 year deorbit window, so the issue is about how much stuff we're sending up, and not how fast it de-orbits.

"Amount of junk below 450km, total" and "Amount of junk below 450km, that hasn't deorbited after 5 years" are very different things. You're making points about total, while the original point was about deorbit speed.

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