FAA debris risk report from large constellation disposal

[FutureSpaceTourist]

https://www.faa.gov/about/plansreports/congress/risk-associated-reentry-disposal-satellites-proposed-large

Risk Associated with Reentry Disposal of Satellites from Proposed Large Constellations

Thursday, October 5, 2023
2023
P.L. 116-260

[FutureSpaceTourist]

SpaceX attack report saying based on outdated data, flawed analysis etc:

https://spacenews.com/spacex-slams-faa-report-on-falling-space-debris-danger/

SpaceX slams FAA report on falling space debris danger
Jason Rainbow
October 9, 2023

A stack of Starlink V2 Minis, which SpaceX says are designed to fully demise during atmospheric reentry like the rest of the satellites in its broadband constellation. Credit: SpaceX
TAMPA, Fla. — SpaceX called on the Federal Aviation Administration to correct a report to Congress warning that, by 2035, falling debris from U.S.-licensed constellations in low Earth orbit (LEO) could injure or kill someone every two years if they deploy as planned.

[ThatOldJanxSpirit]

A few observations:

Exec Summary p4: States F9 stage 2 mass to be >25 tons. Not a good start.

Exec summary p9: notes the predicted fatality rate to be 0.6 per annum and that >85% of the risk is from Starlink. It then notes that they should definitively evaluate if Starlink sats are fully demisable.

Annexe A is the Aerospace Corps technical evaluation.

P11: clarifies that hazard data is extrapolated from Iridium sat re-entry.

P34: acknowledges that design-for-demise will significantly lower assessed risk but that this should be independently verified.

This is a sound recommendation.

Overall the Aerospace Corp report is consistent with safety case methodology where unmitigated risks are initially assessed then measures considered to control the risk.

I don’t think this is explained well in the main FAA text and far more credit should have been given for SpaceX voluntary efforts on design-for-demise. I can understand why SpaceX are a bit upset about it, and why some commentators are seeing it as another ‘establishment’ attack on them, but I’m going to be charitable and just class it as poorly scoped, lightweight and clumsy.

[Robotbeat]

I think it’s weird to call the total demisability a “mitigation.” It’s a fundamental part of the design, as much as its mass or the number of satellites. A mitigation would be a deorbit failsafe mechanism or something.

[ThatOldJanxSpirit]

I think it’s weird to call the total demisability a “mitigation.” It’s a fundamental part of the design, as much as its mass or the number of satellites. A mitigation would be a deorbit failsafe mechanism or something.

The hazard is ‘satellite falls on head’. Mitigation is that some of it burns up so you get hit by fewer and smaller  bits. Total demisability is just an end case of that.

The key point is that it is a passive engineered safety feature, and asking for engineering substantiation of that is a reasonable requirement from a regulator.

My big problem with the report is that SpaceX have been champions of best practice in this (and on light pollution) for Starlink. There is no recognition of this in the report. The real conclusion is that SpaceX best practice need to be brought into the regulatory framework for US constellations, and promoted internationally.

[deltaV]

The key point is that it is a passive engineered safety feature, and asking for engineering substantiation of that is a reasonable requirement from a regulator.

Yep, especially since SpaceX recently had a required safety feature that failed to work properly, namely Starship's flight termination system.

[mn]

The key point is that it is a passive engineered safety feature, and asking for engineering substantiation of that is a reasonable requirement from a regulator.

Yep, especially since SpaceX recently had a required safety feature that failed to work properly, namely Starship's flight termination system.

You're comparing something that flew for the first time to something that has already worked many times over (at least as claimed by SpaceX) before the report was written.

It would be great if they actually looked at the SpaceX data regarding starlinks that have already entered and tried to verify whether they indeed completely burned up as SpaceX claims. That would be worthwhile to investigate and report on. But to act as if that doesn't exist is just blatantly incorrect, (intentional or not I don't know)

[DanClemmensen]

The key point is that it is a passive engineered safety feature, and asking for engineering substantiation of that is a reasonable requirement from a regulator.

Yep, especially since SpaceX recently had a required safety feature that failed to work properly, namely Starship's flight termination system.

A lot of Starlink satellites have de-orbited, and this is planned as an ongoing process. Is there a way to "substantiate" that no dangerous pieces reach the ground, e.g. by flying a research plane under some of these decaying satellites? Cynically, from SpaceX' perspective this would be a competitive advantage because all competitors (that need FAA approval) would be forced to do the same.

[Asteroza]

The key point is that it is a passive engineered safety feature, and asking for engineering substantiation of that is a reasonable requirement from a regulator.

Yep, especially since SpaceX recently had a required safety feature that failed to work properly, namely Starship's flight termination system.

A lot of Starlink satellites have de-orbited, and this is planned as an ongoing process. Is there a way to "substantiate" that no dangerous pieces reach the ground, e.g. by flying a research plane under some of these decaying satellites? Cynically, from SpaceX' perspective this would be a competitive advantage because all competitors (that need FAA approval) would be forced to do the same.

The real cynical take is that this is a scheme by WB-57 pilots to get more flight hours, by essentially requiring a megaconstellation to purposely launch AND reenter one satellite of every major revision so they can get a radar and IR track of the reentering sat. Which basically is pissing away the cost of one sat plus the marginal cost of launch, which ostensibly only a megaconstellation operator could dare to afford.

[jongoff]

A lot of Starlink satellites have de-orbited, and this is planned as an ongoing process. Is there a way to "substantiate" that no dangerous pieces reach the ground, e.g. by flying a research plane under some of these decaying satellites? Cynically, from SpaceX' perspective this would be a competitive advantage because all competitors (that need FAA approval) would be forced to do the same.

Almost all of their LEO constellation competitors are already doing the same "design for demisability" thing. I know OneWeb did. For instance, they required a demisability analysis for our DogTags when we were developing them. I'm skeptical that the satellite is 100% demisable -- most hall thrusters tend to have materials that are dense, and have high melting points/high heat of vaporization, so are more likely to survive. But everyone is trying to design their satellites to theoretically burn up as much as possible and minimize stuff that's likely to survive reentry.

All that said, I'd be intrigued if SpaceX had actual data to back up how well their demisability was going vs just what they theoretically expect.

~Jon

[Robotbeat]

They got rid of some of the non-demisable parts with Starlink v1 and 1.5

[edzieba]

They got rid of some of the non-demisable parts with Starlink v1 and 1.5

The Silicon Carbine mirrors, IIRC. Not sure if they just switched mirror material, or changed construction so they shattered more readily early in the entry sequence. Either way, it's why there were a bunch of 'laserless' Starlinks launched between the first laser ISL demos and laser ISL becoming the norm.

[jongoff]

They got rid of some of the non-demisable parts with Starlink v1 and 1.5

At the end of the day, I'm not totally convinced that something that has to interact with the hot plasma of a plasma thruster without melting is supposed to burn up well on reentry... Now, if that's the only non-demiseable chunk, then the odds of hitting something on the ground are likely a lot lower than the conservative assumptions the Aerospace Corp used. Just saying, I really doubt that a system using HETs is ever going to be 100% demisable...

~Jon