Starlink: Collision risks

[envy887]

Regarding your numbers, I believe those are unrealistically optimistic don't you think? Most orbital collisions involve thousands of trackable debris (plus remember the huge gap between trackable >10 cm and not overly harmful <1 cm), not 100. Also, lumping all fragments into the umbrella "1e-7 POC" seems a bit arbitrary, doesn't it?

That's 1e-7 per orbit. Which implies 1e-5 per 100 orbits, which implies that every satellite needing a conjunction-avoiding maneuver about every 6 days. Prof. Lewis' data above suggests that the true rate is 20-fold lower - there are only 100 events reaching 1e-5 per week in a 2000-sat constellation. So 1e-8 to 1e-9 per orbit is more likely.

Starlinks are not large satellites, only ~300 kg. Mass is the main factor in determining how a satellite participates in a collision cascade, because it determines the size and number of fragments it can produce. Microsat-R produced 57 tracked fragments, plus probably more that size that decayed before tracking. It was estimated to produce 6500 fragments over 1 cm, BUT objects in the 1 cm range not large enough to be likely to break up a satellite. A 1 cm Al cube masses 0.0028 kg, and would eject 0.3 kg of material in a collision, on average, if Kessler's scaling of Langley research is accurate.
See: Impacts into Spacecraft Sturctures:
http://www.castor2.ca/07_News/headline_010216_files/Kessler_Collision_Frequency_1978.pdf

That implies that breaking up a second Starlink would require on average, a 2.2 kg fragment from the first, which would probably be roughly 1U cubesat sized and reasonably trackable.

If you go with 1e-8 Pc per orbit and 1000 fragments, you get the same answer. Fragments are overwhelming likely to drop through the shell without a catastrophic recollision. You might get some small-ish holes in solar arrays, or a couple unmaneuverable but mostly intact satellites that also decay, but it's quite unlikely you will get enough fragments to self-sustain the cascade. There's just way too much drag and not nearly enough targets.

Sure, but you're sidestepping from your false statement: you had just claimed 1e-5 was the upper limit for collision probability that a conjuction would ever reach during that discontinuous progression.

1e-5 is the ceiling. There will be no conjunctions above that

As you can see from the tweet kindly quoted by su27k above (ProfHughLewis/status/1436334166447173640, which I'd earlier overlooked), that's not the case - there are as many conjunctions with 1e-5 as maximum POC as there are with 1e-3 and 1e-4, excluding Starlink-on-Starlink, which supposedly (but then again, maybe not) avoid going beyond 1e-5 with their more accurate internal GNSS tracking. They will be lowered as soon as they are discovered and the actual physical conjunction will not take place, if that's what you mean - but my initial point was that 1e-5 was not conservative if looking at what long-term POCs it would give rise to if chosen any tighter. To repeat myself from my previous post: "If we consider smooth nominal operations forever, everything is and will be fine obviously - here we're talking about misjudged uncertainties, mistakes or oversights, and their consequences."

It's not false. 1e-5 is the celling at the time of the event. The Pc can vary before that, but those are just projections that feed into the decision on whether to maneuver. Only the Pc at the time of the event, after including for reductions in uncertainty due to additional observations and/or any maneuvering, matters for calculating actual collisions. If you calculate 1e-4 and maneuver so that at the event it's 1e-6, then the 1e-4 is irrelevant to whether there would actually be a collision.

And yes, this assumes the system works. But that's a fairly reasonable assumption, since the available response time (from first conjunction warning to event) is measured in days. If part of the system breaks, there is time to fix a lot of problems before satellites start crashing into each other.

[matthewkantar]

What entity has the most to lose from a collision or a cascade of them? Does this entity have any smart folks working for them?

[eeergo]

Regarding your numbers, I believe those are unrealistically optimistic don't you think? Most orbital collisions involve thousands of trackable debris (plus remember the huge gap between trackable >10 cm and not overly harmful <1 cm), not 100. Also, lumping all fragments into the umbrella "1e-7 POC" seems a bit arbitrary, doesn't it?

That's 1e-7 per orbit. Which implies 1e-5 per 100 orbits, which implies that every satellite needing a conjunction-avoiding maneuver about every 6 days. Prof. Lewis' data above suggests that the true rate is 20-fold lower - there are only 100 events reaching 1e-5 per week in a 2000-sat constellation. So 1e-8 to 1e-9 per orbit is more likely.

Now we're redefining the timescale of the POC?! The POC is instantaneous, not per orbit, not per 100 orbits, not per week. It reflects the probability of collision *at the time of the conjunction*, as you said above based on an assessment of the known uncertainties in the trajectories. You get a rate of POCs at each threshold, which can be measured in hours, days, weeks, months, years or whatever timescale you want. You get a CDM update based on new tracking of Starlinks and other trackable objects, and that gives you a set of POCs for every Starlink with respect to every other object, every time they come remotely close to each other. Most will be infinitesimal, some will time and again reach some threshold: Prof Lewis' data shows that around *once a week* they get one or two POC predictions of at most 1e-3, ten or twenty between 1e-4 and 1e-5, and about a hundred with maximum POC of 1e-5. But you can't say "well, that's for a week, so if you want the probabilities per day it's about an order of magnitude less, and per-orbit risks are off-scale low": the POC is what it is until it gets further refined at each new tracking update, and refers to the projected future time of closest approach.

Sure, but you're sidestepping from your false statement: you had just claimed 1e-5 was the upper limit for collision probability that a conjuction would ever reach during that discontinuous progression.

1e-5 is the ceiling. There will be no conjunctions above that

As you can see from the tweet kindly quoted by su27k above (ProfHughLewis/status/1436334166447173640, which I'd earlier overlooked), that's not the case - there are as many conjunctions with 1e-5 as maximum POC as there are with 1e-3 and 1e-4, excluding Starlink-on-Starlink, which supposedly (but then again, maybe not) avoid going beyond 1e-5 with their more accurate internal GNSS tracking. They will be lowered as soon as they are discovered and the actual physical conjunction will not take place, if that's what you mean - but my initial point was that 1e-5 was not conservative if looking at what long-term POCs it would give rise to if chosen any tighter. To repeat myself from my previous post: "If we consider smooth nominal operations forever, everything is and will be fine obviously - here we're talking about misjudged uncertainties, mistakes or oversights, and their consequences."

It's not false. 1e-5 is the celling at the time of the event. The Pc can vary before that, but those are just projections that feed into the decision on whether to maneuver. Only the Pc at the time of the event, after including for reductions in uncertainty due to additional observations and/or any maneuvering, matters for calculating actual collisions. If you calculate 1e-4 and maneuver so that at the event it's 1e-6, then the 1e-4 is irrelevant to whether there would actually be a collision.

Of course at the time of the event 1e-5 is the ceiling, and even lower, but only because they have maneuvered in the meantime - that's the whole point of a CAM! In fact, *at the precise time of the event* the POC will be 0 or 1, because the uncertainties will no longer be there. As I've repeated in multiple ways many times already, my message was aiming to show that 1e-5 is not conservative because tightening that threshold (say, to 1e-4) would mean they wouldn't maneuver for that threshold, and that would imply the cumulative probability numbers in my opening post -i.e. unacceptably high-, which are not conservative at all once you have more than a few thousand satellites in a shell!

This constant eye-tarring and thread-splitting is mind-numbing, and as always smears the argument my exhaustion...

[Twark_Main]

my message was aiming to show that 1e-5 is not conservative

Just out of curiosity, what number would need to be substituted instead of 1e-5 such that it would be considered "conservative," in your opinion?

[Mark K]

The "Probability of Collision" is simply the area of the future orbit paths of the satellite divided by the future orbit paths of the fragment to collide. The fact that 10 meters is used for the size of the satellite and debris already means it is a very high estimate  (Something over a hundred times high just from that) . It is a probability at a given time based on our knowledge -at that time- so it is -not- a usefully integrable property. That is, there is no reason to favor any collisions over say, a century, because 1000000 events with 1 in 100000 "POC" are happening. There might be zero if we had just better orbital measurements. Or there might be 100. It is really more a mark of our prediction than a real probability. It is making an assumption that every similar path in future movement cone of the collision object is the same probability for example.

It IS a true signal that chances are higher of a collision when the POC is higher, so it is better than precise, it is useful. That is why it is used as a flag for active action.

When models are created to mimic planned constellations, they show that there isn't  over unity feedback, that one collision causes another one. 

[dondar]

so much emotions here.

Many.

"conjunctions" are not a thing within starlink system.They are events of possible orbit intersection with other satelites (or for now between rising starlinks from different batches.)

They are as in any satellite. Between different heights and at the same height alike. They are reportedly minimized automatically based on SpaceX tracking -of which we know little or nothing about, but let's take it at face value and say they're not an issue (even if they clearly exist as shown by the SOCRATES data). There are still plenty of conjunctions <1 km with other objects as shown in the Twitter thread, and within those many that SpaceX judges worthy of executing a CAM for (~10000/year currently).

Probably you should learn what Socrat does, and how satellites operate. When SpaceX determines their satelites in the risk of collision (calculated not by Socrat) they move their sat "out of possible harm". They do it 100s times per day (sometimes). It's that simple.

SOCRAT counts also satellites in formation as a collision candidates (Because the system is simplified, read STUPID).

What are you talking about? You're calling SOCRATES stupid?\

Yes I do. So let check SOCRAT.
http://celestrak.com/SOCRATES/search-results.php?IDENT=NAME&NAME_TEXT1=&NAME_TEXT2=&ORDER=MINRANGE&MAX=10

I make search on min range to 10 satellites.
First place: TIANZHOU-2 (big surprise). 2 places ORbcomm (within one formation=>see relative speeds), 5 starlink junctions (3 of which are questionable) and one real thing.
(applause).

The probabilities even for the conjuctions with min 0.1km can be still in the range off 1e-7. And there are many of those.

They can. I did not conflate both. I did take however SpaceX's CAM numbers, and they state only events with probability >1e-5 require action, so all those CAMs are over 1e-5. All 2200 of them. Some much higher probably (continuous distribution from 1e-5 all the way to 1). I did some elementary calculations for longer times and/or satellite numbers.

They don't use SOCRAT. They do a lot of corrections indeed.
Anyway, Socrat calculates that orbcomm sats have collision probability 1.e-2., i.e. those flying within formation.... When I've checked last time they had starlinks with probability of e.-1 (within formation as well)....

Right now Starlink sit strongly under 1% per year for their system. Totally. Please don't comment, especially "doom" without proper numbers or ability to defend scientifically your opinion.

Excuse me, where are your proper numbers? You just said you'll not go into SOCRATES data? Neither basic multiplication because it's "estimated"? I explicitly showed my work, you're pulling a 1% out of your hat (seriously, where in the world do you deduce that from? By their own admission they did 2200 CAMs in 6 months when Starlink had half the satellites it has now, and now it has 1500 birds...). Where exactly are my extrapolations of their own CAM numbers and probability thresholds wrong?

Talk about emotional responses...

My numbers come from the check  of the extensive number of reports on the subject.
And the number is very conservative. (it was actually less than .01% using current "failure" rates which are reported by SpaceX to FCC). And the numbers don't take into account active collision mitigation.

I would like to mention that SpaceX made specific contract with NASA specifically concerning avoidance of the collisions between SpaceX and NASA objects. I didn't bother to search (this one was already in my collection), but I can bet SpaceX made identical contract with Air Force.  No noise from these guys. Why???

The continuous FUD about any possible possibility of some "rushed" deployment, "extensive risk" etc. is FUD.
There is no other case in the  whole FCC history of any so scrupulously analyzed project and so much bias, partizan BS and outward hostility around it. With no real basis which can be controlled, assessed and confirmed.
Get rest.

[su27k]

Viasat continues to spread FUD about Starlink:

https://twitter.com/pbdes/status/1446013178228494336

.@Viasat chairman Mark Dankberg devoted his entire keynote at Oct 6 at @SatNewsEvents Satellite Innovation conference to debris threat in LEO. No broadband, no market assessment.... If Dankberg believes what he said here -- https://bit.ly/3nzvIGG -- he had no choice.

https://twitter.com/jeff_foust/status/1445811202639032333

“The failure mode of orbital debris is effectively irreversible,” says Viasat’s Mark Dankberg at #satinnovation, a reference to the Kessler Syndrome.

Dankberg is spending his keynote going into details about models of the LEO environment, suggesting a Kessler Syndrome within a few decades of the launch of a full Starlink-type (30,000 satellites around 600 km). He adds the models may be optimistic…

[su27k]

Viasat's claim being refuted by space debris expert on twitter:

1. Refuting "“The failure mode of orbital debris is effectively irreversible,” says Viasat’s Mark Dankberg at #satinnovation, a reference to the Kessler Syndrome.":

https://twitter.com/ProfHughLewis/status/1445828422006149120

I'm not sure why this view is held so widely. Remove objects/mass to limit the growth rate and ultimately to prevent growth. #SpaceDebris #KesslerSyndrome

2. Refuting "Dankberg is spending his keynote going into details about models of the LEO environment, suggesting a Kessler Syndrome within a few decades of the launch of a full Starlink-type (30,000 satellites around 600 km). He adds the models may be optimistic…":

https://twitter.com/ProfHughLewis/status/1445829764229394432

It is not possible to say this with any certainty. Much depends on the parametrisation and model assumptions. I suspect these need to be stretched quite considerably to produce a #SpaceDebris #KesslerSyndrome outcome at low LEO altitudes.

At 1300 km altitude the time for an orbital object to decay due solely to atmospheric drag is more than 1000 times longer than the time for the same object to decay from 550 km altitude.

It is also likely that at 1300 km altitude we have already exceeded the critical number of large orbital objects required for runaway (exponential) population growth. The situation is better at lower altitudes, but is still of concern.

The assumption also being made in this statement is that a 30,000-satellite constellation cannot respond to conjunction alerts. The overall number of satellites is important but this is not the only factor. Orbit control capability is at least as important.

[Sorry for random approach to this thread] so, all other things being equal, a failed satellite at 1300 km will have an area-time product (a proxy for collision probability) approximately 1000 times greater than a failed satellite at 550 km.

Continuing the thought experiment, the lifetime risk from 300 satellites at 1300 km would be equivalent to the risk from 300,000 satellites at 550 km. It's a little simplistic, but makes the point. It also highlights the problems arising when you ignore orbit control capability

[eeergo]

SOCRAT counts also satellites in formation as a collision candidates (Because the system is simplified, read STUPID).

What are you talking about? You're calling SOCRATES stupid?

Yes I do. So let check SOCRAT[ES].
http://celestrak.com/SOCRATES/search-results.php?IDENT=NAME&NAME_TEXT1=&NAME_TEXT2=&ORDER=MINRANGE&MAX=10

I make search on min range to 10 satellites.
First place: TIANZHOU-2 (big surprise). 2 places ORbcomm (within one formation=>see relative speeds), 5 starlink junctions (3 of which are questionable) and one real thing.
(applause). [...] My numbers come from the check of the extensive number of reports on the subject.

So just over three short months after this damning assertions, here you go:

https://twitter.com/ProfHughLewis/status/1478312127198810112

The SOCRATES system was actually underestimating (!) the POC, going by the number of actual CAMs performed by Starlink S/C, as disclosed by its operator in its own reports.

Regarding the rates, there have been around 6500 CAMs this past year, and we're already well over 150 CAMs/week, or about 20 per day. By the end of 2020 (not 2021), "Starlink was responsible for 54% of the conjunction data output by the 18 SPCS" (https://amostech.com/TechnicalPapers/2021/SSA-SDA/Hiles.pdf), and that was for at least an order of magnitude less CAMs:

https://twitter.com/ProfHughLewis/status/1478315799257530371

A related assessment shows 57% of *all* trackable conjunctions <1 km are due to Starlink, in stark contrast to ominous debris clouds such as that resulting from the recent Kosmos-1408 ASAT test (8%).

For additional context, at this point in time, 1.5% of Starlinks currently on orbit are failed and decaying (this means explicitly uncontrolled - if we add those under controlled disposal, that number rises to 2%). Failure rate, including already-deorbited satellites but excluding v0.9/Tintins, is around 9%, even when including recently-launched batches with still short on-orbit lives.

[Robotbeat]

Viasat's claim being refuted by space debris expert on twitter:

1. Refuting "“The failure mode of orbital debris is effectively irreversible,” says Viasat’s Mark Dankberg at #satinnovation, a reference to the Kessler Syndrome.":

https://twitter.com/ProfHughLewis/status/1445828422006149120

I'm not sure why this view is held so widely. Remove objects/mass to limit the growth rate and ultimately to prevent growth. #SpaceDebris #KesslerSyndrome

2. Refuting "Dankberg is spending his keynote going into details about models of the LEO environment, suggesting a Kessler Syndrome within a few decades of the launch of a full Starlink-type (30,000 satellites around 600 km). He adds the models may be optimistic…":

https://twitter.com/ProfHughLewis/status/1445829764229394432

It is not possible to say this with any certainty. Much depends on the parametrisation and model assumptions. I suspect these need to be stretched quite considerably to produce a #SpaceDebris #KesslerSyndrome outcome at low LEO altitudes.

At 1300 km altitude the time for an orbital object to decay due solely to atmospheric drag is more than 1000 times longer than the time for the same object to decay from 550 km altitude.

It is also likely that at 1300 km altitude we have already exceeded the critical number of large orbital objects required for runaway (exponential) population growth. The situation is better at lower altitudes, but is still of concern.

The assumption also being made in this statement is that a 30,000-satellite constellation cannot respond to conjunction alerts. The overall number of satellites is important but this is not the only factor. Orbit control capability is at least as important.

[Sorry for random approach to this thread] so, all other things being equal, a failed satellite at 1300 km will have an area-time product (a proxy for collision probability) approximately 1000 times greater than a failed satellite at 550 km.

Continuing the thought experiment, the lifetime risk from 300 satellites at 1300 km would be equivalent to the risk from 300,000 satellites at 550 km. It's a little simplistic, but makes the point. It also highlights the problems arising when you ignore orbit control capability

Viasat looks pretty dang bad doing this. But it makes sense. Starlink is an existential threat to Viasat, at least their consumer business. Who would use lower speed and much higher latency GSO internet when you can use something better than many cable connections? And that’s going to get better over time as they blend in satellites with laser links…

The only option is lowering the price to basement bargain levels, but that’s not very sustainable.

So of course no point in Viasat doing market assessments during a keynote. The market assessment is that Viasat is all but dead, so you’ve got to spread FUD about LEO megaconstellations.

[Robotbeat]

The lower the altitude, the better for reducing space debris risk. I wonder if very low satellites might end up doing aerodynamic maneuvers with the solar panels (as I think ISS has done a little bit?), since that is faster than using electric thrusters. If designed for it, could be somewhat more efficient as well.

I also wonder if SpaceX will start investing in their own tracking capabilities for space debris in order to reduce the uncertainty and reduce the need for maneuvering.

[Robotbeat]

Also, if conjunction risk continues to be a major problem, it might be interesting if the satellites not only maneuver to minimize cross section but actually retract their solar panels before maneuvering to an edge-on orientation, flat-pack like they deployed from, maybe even with a Whipple shield in front.

Increasing survivability. Perhaps a similar maneuver could be used to minimize visibility when passing in front of Vera Rubin.

[envy887]

SOCRAT counts also satellites in formation as a collision candidates

So just over three short months after this damning assertions, here you go:

The SOCRATES system was actually underestimating (!) the POC, going by the number of actual CAMs performed by Starlink S/C, as disclosed by its operator in its own reports.

Which has nothing at all to do with SOCRATES counting Starlink-on-Starlink conjunctions. SpaceX can handle Starlink-on-Starlink conjunctions internally was far more speed and precision the the external process. Aside from producing more data to look at, those have no impacts on anyone else.

For additional context, at this point in time, 1.5% of Starlinks currently on orbit are failed and decaying (this means explicitly uncontrolled - if we add those under controlled disposal, that number rises to 2%). Failure rate, including already-deorbited satellites but excluding v0.9/Tintins, is around 9%, even when including recently-launched batches with still short on-orbit lives.

That is quite misleading. Out of the last 1,511 satellites launched, only 3 are presently failed and decaying out of control, a rate under 0.2%. The vast majority of those have been operating for 6 to 12 months, so infant mortality period has largely passed.

The other 18 failed and decaying v1.0 satellites are from the first 420 launched, a 4.3% failure rate. This is not just due to the bathtub curve (they were only launched 18-25 months ago), but pretty much what one would expect with SpaceX's iterative approach. The MTBF is markedly increasing as the design and manufacturing improve.

Satellites disposed of early are not failures for debris or collision avoidance purposes. Disposal is part of the mission for every satellite, and some of them getting there early has no impact on debris generation.

[eeergo]

The SOCRATES system was actually underestimating (!) the POC, going by the number of actual CAMs performed by Starlink S/C, as disclosed by its operator in its own reports.

Which has nothing at all to do with SOCRATES counting Starlink-on-Starlink conjunctions. SpaceX can handle Starlink-on-Starlink conjunctions internally was far more speed and precision the the external process. Aside from producing more data to look at, those have no impacts on anyone else.

Data is WITHOUT Starlink-on-Starlink (ref: ProfHughLewis/status/1478314752061358089), as should be evident since SpaceX should ideally never have to require a POC among its own satellites, which can be continuously maneuvered to avoid triggering the 1e-5 threshold. I was responding to dondar's statement that SOCRATES was stupid and grossly overestimating concerns with Starlink conjunctions, which has been proven not to be the case.

For additional context, at this point in time, 1.5% of Starlinks currently on orbit are failed and decaying (this means explicitly uncontrolled - if we add those under controlled disposal, that number rises to 2%). Failure rate, including already-deorbited satellites but excluding v0.9/Tintins, is around 9%, even when including recently-launched batches with still short on-orbit lives.

That is quite misleading. Out of the last 1,511 satellites launched, only 3 are presently failed and decaying out of control, a rate under 0.2%. The vast majority of those have been operating for 6 to 12 months, so infant mortality period has largely passed.

The other 18 failed and decaying v1.0 satellites are from the first 420 launched, a 4.3% failure rate. This is not just due to the bathtub curve (they were only launched 18-25 months ago), but pretty much what one would expect with SpaceX's iterative approach. The MTBF is markedly increasing as the design and manufacturing improve.

Satellites disposed of early are not failures for debris or collision avoidance purposes. Disposal is part of the mission for every satellite, and some of them getting there early has no impact on debris generation.

There was a similar discussion in another thread a year or so ago. The argument went that the failure rate of early launches was surely not comparable to later batches because, wait and see, not only were they *already* visibly much better, the fact that *they had just been launched* (and so didn't have time to fail yet, discounting a minor infant mortality rate) was not important.

Your statement is misleading in that it arbitrarily takes a hypothesis (new SC are more reliable) and picks a trivially biased dataset to back it up. My statement is just objective: of all Starlinks branded as "operational" that are flying at the moment, which are <2 years old (!), and discounting reportedly "experimental" ones (v0.9), 1.5% are uncontrollable, and 2% are being disposed of *at this moment in time*.

I purposely did not take into account early deorbits for that (1.3% of the 1511 subgroup you arbitrarily picked out) or semicontrolled deorbits (3%), so your last point is just a strawman.

Anyway, this point was for context, since this thread is about collision risks and not general QC. The point about SOCRATES, conjunctions and CAMs stands.

[envy887]

Data is WITHOUT Starlink-on-Starlink, as should be evident since SpaceX should ideally never have to require a POC among its own satellites, which can be continuously maneuvered to avoid triggering the 1e-5 threshold. I was responding to dondar's statement that SOCRATES was stupid and grossly overestimating concerns with Starlink conjunctions, which has been proven not to be the case.

Prof Lewis is filtering some of his data to eliminate Starlink-on-Starlink. SOCRATES otherwise includes all the Starlink-on-Starlink conjunctions, something you didn't note for these 2 claims

By the end of 2020 (not 2021), "Starlink was responsible for 54% of the conjunction data output by the 18 SPCS")
...
A related assessment shows 57% of *all* trackable conjunctions <1 km are due to Starlink, in stark contrast to ominous debris clouds such as that resulting from the recent Kosmos-1408 ASAT test (8%).

and the latter number specifically includes Starlink-on-Starlink...
https://twitter.com/ProfHughLewis/status/1478052682514452480

For additional context, at this point in time, 1.5% of Starlinks currently on orbit are failed and decaying (this means explicitly uncontrolled - if we add those under controlled disposal, that number rises to 2%). Failure rate, including already-deorbited satellites but excluding v0.9/Tintins, is around 9%, even when including recently-launched batches with still short on-orbit lives.

That is quite misleading. Out of the last 1,511 satellites launched, only 3 are presently failed and decaying out of control, a rate under 0.2%. The vast majority of those have been operating for 6 to 12 months, so infant mortality period has largely passed.

The other 18 failed and decaying v1.0 satellites are from the first 420 launched, a 4.3% failure rate. This is not just due to the bathtub curve (they were only launched 18-25 months ago), but pretty much what one would expect with SpaceX's iterative approach. The MTBF is markedly increasing as the design and manufacturing improve.

Satellites disposed of early are not failures for debris or collision avoidance purposes. Disposal is part of the mission for every satellite, and some of them getting there early has no impact on debris generation.

There was a similar discussion in another thread a year or so ago. The argument went that the failure rate of early launches was surely not comparable to later batches because, wait and see, not only were they *already* visibly much better, the fact that *they had just been launched* (and so didn't have time to fail yet, discounting a minor infant mortality rate) was not important.

Your statement is misleading in that it arbitrarily takes a hypothesis (new SC are more reliable) and picks a trivially biased dataset to back it up. My statement is just objective: of all Starlinks branded as "operational" that are flying at the moment, which are <2 years old (!), and discounting reportedly "experimental" ones (v0.9), 1.5% are uncontrollable, and 2% are being disposed of *at this moment in time*.

I purposely did not take into account early deorbits for that (1.3% of the 1511 subgroup you arbitrarily picked out) or semicontrolled deorbits (3%), so your last point is just a strawman.

Anyway, this point was for context, since this thread is about collision risks and not general QC. The point about SOCRATES, conjunctions and CAMs stands.

The rate of QC improvement is critical to discussing collision risks. And that improvement is continuous, so any cutoff is arbitrary. I use the first 420 because McDowell does. https://planet4589.org/space/stats/star/starstats.html

Support for the hypothesis that new SC are more reliable is trivially easy to show. The 420 sats from the first launch have a mean age of about 22 months, for a total operational time of 9240 sat-months. They have 18 out of control, for 1 failure per 513 satellite-months of operation. The 1511 newer sats have been in orbit on average for about 9 months, for 13600 sat-months of operation. They have 3 out of control, or one per 4,533 sat-months. That is an 8.83-fold improvement in failures per satellite-month of operations. You can fiddle with the numbers all you want, but you aren't going to twist a nearly order of magnitude improvement in MTBF down to nothing.

Going forward, the MTBF will almost certainly continue to improve as the design and manufacturing issues are sorted and newer, better satellites are launched. So your implication that the entire constellation will continue to operate at a 1.5% uncontrolled rate is at best unsupported FUD.

[eeergo]

Prof Lewis is filtering some of his data to eliminate Starlink-on-Starlink. SOCRATES otherwise includes all the Starlink-on-Starlink conjunctions, something you didn't note for these 2 claims.

By the end of 2020 (not 2021), "Starlink was responsible for 54% of the conjunction data output by the 18 SPCS")
...
A related assessment shows 57% of *all* trackable conjunctions <1 km are due to Starlink, in stark contrast to ominous debris clouds such as that resulting from the recent Kosmos-1408 ASAT test (8%).

and the latter number specifically includes Starlink-on-Starlink...

Please stop cherrypicking excerpts from my posts to twist what I quoted.

First I quoted the comparison between SOCRATES estimates for CAMs and actual CAMs executed by SpaceX. Those disproved the notion floated by dondar that SOCRATES was "stupid" and overinflating predictions. Indeed, SOCRATES is very accurate also when discounting self-conjunctions, as proven.

THEN I quoted a "related assessment" that showed 57% of all conjunctions (including self-conjunctions, as you noted, and as I quoted) in early 2022 were due to Starlink. Here the issue is not so much that there are many self-conjunctions, which SpaceX should be able to mitigate themselves, barring anomalies - but the fact that the system generates so many conjunctions in the first place, even 3x as many as an uncontrolled debris field containing about as many trackable objects.

Support for the hypothesis that new SC are more reliable is trivially easy to show. The 420 sats from the first launch have a mean age of about 22 months, for a total operational time of 9240 sat-months. They have 18 out of control, for 1 failure per 513 satellite-months of operation. The 1511 newer sats have been in orbit on average for about 9 months, for 13600 sat-months of operation. They have 3 out of control, or one per 4,533 sat-months. That is an 8.83-fold improvement in failures per satellite-month of operations. You can fiddle with the numbers all you want, but you aren't going to twist a nearly order of magnitude improvement in MTBF down to nothing.

Going forward, the MTBF will almost certainly continue to improve as the design and manufacturing issues are sorted and newer, better satellites are launched. So your implication that the entire constellation will continue to operate at a 1.5% uncontrolled rate is at best unsupported FUD.

Always refreshing to raise the good ol' "FUD" flag whenever things don't quite match up to reality. You accuse me of fiddling with numbers, but you are pulling a brutal "average" on-orbit timespan out of the hat, conflating it with significant numbers of just-launched satellites, and rubberstamping a foregone conclusion.

You're basically just employing a more mature, smaller dataset with a much larger and younger one, but treating them as equal through the "averaging" and the current fleet status. You might as well include early mortality in that, since you're leaving S/C that have already reentered in an uncontrolled fashion out, or that could easily have failed a few weeks later instead of right away. In that case:
* 18+8 = 26 S/C that will(have) reenter(ed) of the first 420 operational satellites, over 9240 months of "average operation" = 1 failure every 355 sat-months.
* 3+1+1+25 S/C that will(have) reenter(ed) of the latest 1511 operational satellites, over 13600 months of "average operation" = 1 failure every 544 sat-months.
So not quite the order-of-magnitude improvement you claim, and of course the bias of the "averaged out" relative youth remains, which is temporarily skewing the observed reliability upwards. Of course I also believe they will work obvious kinks out in their design if they keep iterating, but not so much as to offset by much the continuous tweaks for newer satellites, or the very design philosophy of cheap "disposable" S/C for megaconstellations.

[Robotbeat]

SpaceX’s Starlink satellites will likely become significantly more reliable than any other satellite bus, if they aren’t already, largely due to the large number of them that they’re producing. Smearing them as disposable (when almost all satellites are) is just FUD.

If you don’t like people using that term “FUD,” quit making it so apt.

People made similar claims about Falcon 9, now the most reliable launch vehicle flying, and perhaps of all time.

[envy887]

Support for the hypothesis that new SC are more reliable is trivially easy to show. The 420 sats from the first launch have a mean age of about 22 months, for a total operational time of 9240 sat-months. They have 18 out of control, for 1 failure per 513 satellite-months of operation. The 1511 newer sats have been in orbit on average for about 9 months, for 13600 sat-months of operation. They have 3 out of control, or one per 4,533 sat-months. That is an 8.83-fold improvement in failures per satellite-month of operations. You can fiddle with the numbers all you want, but you aren't going to twist a nearly order of magnitude improvement in MTBF down to nothing.

Going forward, the MTBF will almost certainly continue to improve as the design and manufacturing issues are sorted and newer, better satellites are launched. So your implication that the entire constellation will continue to operate at a 1.5% uncontrolled rate is at best unsupported FUD.

Always refreshing to raise the good ol' "FUD" flag whenever things don't quite match up to reality. You accuse me of fiddling with numbers, but you are pulling a brutal "average" on-orbit timespan out of the hat, conflating it with significant numbers of just-launched satellites, and rubberstamping a foregone conclusion.

You're basically just employing a more mature, smaller dataset with a much larger and younger one, but treating them as equal through the "averaging" and the current fleet status. You might as well include early mortality in that, since you're leaving S/C that have already reentered in an uncontrolled fashion out, or that could easily have failed a few weeks later instead of right away. In that case:
* 18+8 = 26 S/C that will(have) reenter(ed) of the first 420 operational satellites, over 9240 months of "average operation" = 1 failure every 355 sat-months.
* 3+1+1+25 S/C that will(have) reenter(ed) of the latest 1511 operational satellites, over 13600 months of "average operation" = 1 failure every 544 sat-months.
So not quite the order-of-magnitude improvement you claim, and of course the bias of the "averaged out" relative youth remains, which is temporarily skewing the observed reliability upwards. Of course I also believe they will work obvious kinks out in their design if they keep iterating, but not so much as to offset by much the continuous tweaks for newer satellites, or the very design philosophy of cheap "disposable" S/C for megaconstellations.

For collision purposes, why would you count satellites with inactive payloads that are still maneuvering, but not satellites with active payloads that are still actively maneuvering? As far as I can tell, those have exactly the same chance of a collision.

For example, only 1 satellite on v1.0 Launch 15 (see attached) stopped maneuvering before reentry. That is Starlink 1881, which is still in orbit and failed in Feb. 2021 at about 480 km. On that mission, 9 satellites have been disposed of (3 before reaching operation, and 6 after), and 7 more appear to be heading to their doom. But only Starlink 1881 is increasing the probability of collision. The other 16 "failures" appear to still be fully maneuverable right up to disposal.

McDowell doesn't separate out those that stopped maneuvering at low orbit from those were actively disposed of before orbit raising was complete. In most cases there is no appreciable difference, since the disposal orbit is about the same as the insertion orbit, and those largely reenter within a few days or weeks and again, have essentially no relevance to collisions because they aren't around long enough to run into anything.

I'd agree that those with lost maneuvering capability during orbit-raising, before reaching operational orbit but still high enough to hang around a while, should be counted as collision risks. But I only see one of those, Starlink 1756   on v1.0 L11 (Launch 12).

So that makes 4 out of the last 1,511 that have lost maneuvering capability at some altitude above disposal. Which still makes the newer satellites about an order of magnitude better in MTBF.

[vsatman]

In my opinion, such pictures replace the real situation  with a fictional one and mislead a person who is far from the topic.

If we try to calculate what % of the volume of space in an orbit of 560 km where StarLinks move  is occupied by the satellites themselves, then most likely it will be the same % of the volume that is occupied by two flies flying in Madison Square Garden .. with the corresponding probability of their collision ..

[abaddon]

In my opinion, such pictures replace the real situation  with a fictional one and mislead a person who is far from the topic.

If we try to calculate what % of the volume of space in an orbit of 560 km where StarLinks move  is occupied by the satellites themselves, then most likely it will be the same % of the volume that is occupied by two flies flying in Madison Square Garden .. with the corresponding probability of their collision ..

Reminds me of the Encyclopedia Brown story (yeah, dating myself here) about the guy scamming about selling a scale model of the solar system.  Sadly, it feels like Encyclopedia having to explain it to people for them to get it is as relevant today as it was back then.