Dissapointing that the paper is full of simplifying, and seemingly unreasonable, assumptions instead of simulation based on the known orbital elements of all these tracked satellites. For example, collision cross section of 200 square meters when discussing starlink even though the satellites are about 4 x 3 meters. Assuming random distribution of trajectories. I'm also unconvinced that "how fast would a collision occur if all the electronics got fried" is a useful metric, in that scenario I'm much more worried about the situation on the ground and commercial avaition...
Need to do a full read in more depth but it looks like they used a collision cross section of A=300 m^2, which is a little conservative but not insane given that the current Starlink v2 mini has about 90-120 m^2 of total surface area on its solar arrays. [1] The solar arrays are the largest part of these spacecraft by far and what defines the “collideable” area. A combined hard-body radius of 2 x 120 = 240 is in the ballpark for starlink-on-starlink collisions.
However most of collisions of concern are going to be starlink-on-debris, which is back down at the 120 m^2 level. Starlink already self screens for collisions and uplinks the conjunction data messages over the optical intersatellite link backbone or over their global ground station network.
If they aren’t able to talk to their satellites regularly from somewhere, you’re right we have MUCH bigger things to worry about on the ground.
And wouldn’t the solar panels have less cross section than the satellite bodies, so even an apparent collision might just be a very near miss? (Honest question, not rhetorical, could be I’m wrong)
They do verify their analytical calculation using a N-body simulation, that's section 4.4
> We verify our analytic model against direct N-body conjunction simulations. Written in Python, the simulation code SatEvol propagates orbits using Keplerian orbital elements, and includes nodal and apsidal precession due to Earth’s J2 gravitational moment. [...] The N-body simulation code used in this paper is open source and can be found at https://github.com/norabolig/conjunctionSim.
The cross section isn't actually all that outrageous, it corresponds to a hardbody radius of 4.5 meters. Hardbody radius is equal to the sum of the radii of the two colliding bodies, so 2.25 meters - which seems about right for Starlink.
They did an n-body simulation based on the known Keplerian orbital elements. That's exactly what you're asking for, right?
Also, the formalism is the standard way astrophysicists understand collisions in gases or galaxies, and it works surprisingly well, especially when there are large numbers of "particles". There may be a few assumptions about the velocity distribution, but usually those are mild and only affect the results by less than an order of magnitude.
"N-body simulation" doesn't mean what it's normally taken to mean here.
And the colliding gasses models have the huge assumption of random/thermal motion. These satellites are in carefully designed orbits; they aren't going to magically thermalize if left unmonitored for three days.
Agreed. This reads more like a hit-piece than a good-faith effort to quantify the risks. They make long-tail pessimistic assumptions, explicitly ignore possible mitigating factors, and act as if this "worse than worst case" scenario is a reasonable description of the world we live in.
Yeah they seem to have gotten excited to do the probability math (with bad assumptions, conflating a 300m^2(!) cross section collision with an actual probable collision), and with no consideration that this can actually be trivially simulated.
Also, if a solar storm actually wiped out all satellites in LEO (a huge assumption), who really cares how long it takes them to collide? Realistically it's all dead space until they de-orbit in a couple years.
If the Starlink satellites all collided, the worst case is that we would have to ditch the space station (which is already planned in a few years) and wait a few years to launch more into LEO. The debris deorbits automatically due to atmospheric drag. And in the meantime we would still be able to launch through the cloud to higher orbits or escape velocity as it wouldn't be dense enough to hit something that only passes though for a couple of minutes.
IMO now that LEO communication satellites are feasible we should ban launching satellites into higher orbits. Collision debris up there is much, much worse because it's essentially permanent. It will not deorbit by itself for thousands of years or more, and there is no plausible way to clean it up even with technology much more advanced than ours.
There actually is one idea for cleaning up debris in high orbit: You launch tons of very fine powder into the orbits you wish to clear. These orbiting particles create drag on anything up there, so that their orbits degrade much faster. But the because the particles themselves are so tiny, they have a very low ballistic coefficient, and will deorbit quickly.
Hmm, seems like it would work for 800 km, but maybe not for 1000+ km? Just based on what he says there, which is that each 100 km increase is a factor of 10 in deorbit time, and it's 1 year at 800 km.
It's not just starlink up there, at minimum NRO will be sad and unable to track nuclear weapons and such, the US military will be down a satellite coms systems, and there are probably some people which use starlink for something important.
Yeah it would suck to lose Starlink for a few years. I wouldn't mourn spy telescopes. But most other satellites like weather satellites or ballistic missile detectors or GPS are in higher orbits and wouldn't be affected at all.
My point is that even the unlikely worst case scenario would be limited in time and extent. It couldn't possibly block us from reaching space or last for decades, as some people fear.
> the worst case is that we would have to ditch the space station (which is already planned in a few years)
There is more than one Space Station up there. "Tianhe space station module conducted preventive collision avoidance due to close approaches by the Starlink-1095 (2020-001BK) and Starlink-2305 (2021-024N) satellites on July 1 and Oct. 21 respectively." [1]. Wikipedia also has a long list of planned and proposed space stations.
Even though most of the satellites affected would be other Starlinks, I don't think the many entities with other spacecraft in sub 550km LEO would be particularly delighted to lose them (and the ability to safely relaunch for 5 years)
Satellites in higher orbits do a lot that can't be done in LEO and typically have much lower collision risk (though GEO is fairly crowded). There are plenty of plausible candidate technologies for cleaning up debris, just few practical demonstrations (and even tracking smaller pieces is work in progress)
> Satellites in higher orbits do a lot that can't be done in LEO
This isn't really true anymore. Yes there's a lot of legacy technology still in use and even still being launched, but there's nothing in MEO or GEO that can't be done in LEO with today's technology. Doing it in LEO requires more satellites and better radios, but you get better performance.
The risk of collisions may be lower but the consequences last thousands or millions of times longer...
It's interesting to try to create a metric of collision avoidance "stress" and resiliency to outages. I don't think this is a particularly useful one (and the title is alarmist/flamebait), but it is a first cut at something new. A more nuanced aggregate strategy for different orbital altitudes would make sense. Maybe some can suggest (or has already suggested) a comprehensive way to keep the risk of cascading debris events low (and measured) that is useful for launch planning.
Complete loss of control of the entire Starlink constellation (or any megaconstellation) for days at a time would be an intense event. Any environmental cause (a solar event) would be catastrophic ground-side as well. Starlink satellites will decay and re-enter pretty quickly if they lose attitude control, so it's a bit of a race between collisions and drag. Starlink solar arrays are quite large drag surfaces and the orbital decay probably makes collisions less likely. I would not be surprised if satellites are designed to deorbit without ground contact for some period of time. I'm sure SpaceX has done some interesting math on this and it would be interesting to see.
Collision avoidance warnings are public (with an account): https://www.space-track.org/ But importantly they are intended to be actionable, conservative warnings a few days to a week out. They overstate the probability based on assumptions like this paper (estimates at cross-sectional area, uncertainty in orbital knowledge from ground radar, ignorance of attitude control or for future maneuvers). Operators like SpaceX will take these and use their own high-fidelity knowledge (from onboard GPS) to get a less conservative, more realistic probability assessment. These probabilities invariably decrease over time as the uncertainty gets lower. Starlink satellites are constantly under thrust to stay in a low orbit with a big draggy solar array, so a "collision avoidance manuever" to them is really just a slight change to the thrust profile.
Interesting stuff in the paper, but I'm annoyed at the title. I hate when people fear-bait about Kessler syndrome against some of the more responsible actors.
By now, I'm convinced that Kessler syndrome exists solely to be fear bait. Almost no one knows what it is or what it does - people just know the stupid "space is ruined forever" media picture.
was watching a video about ICBM detection/taking them out in boost phase, and needing a lot for coverage if you had these LEO satellites ready to go but need a lot of delta v (fuel), star link... plenty of em but nah it's for internet/basic navigation/not much fuel
This is exactly what Golden Dome proposes to do for missile defense. It improves the math of missile defense a lot compared to past proposals and it’s not completely crazy but it’s still not certain if the technical capabilities would be there even with a fully operational Starship.
My first thought about that is you'd need a lot of satellites already nearly co-planar with the ICBM's inclination and there probably aren't enough Starlinks in any given inclination to make that realistic (granting secret dV and a sporty enough TWR). Boost phase is pretty short.
Readit News
However most of collisions of concern are going to be starlink-on-debris, which is back down at the 120 m^2 level. Starlink already self screens for collisions and uplinks the conjunction data messages over the optical intersatellite link backbone or over their global ground station network.
If they aren’t able to talk to their satellites regularly from somewhere, you’re right we have MUCH bigger things to worry about on the ground.
[1] https://spaceflightnow.com/2023/02/26/spacex-unveils-first-b...
Deleted Comment
> We verify our analytic model against direct N-body conjunction simulations. Written in Python, the simulation code SatEvol propagates orbits using Keplerian orbital elements, and includes nodal and apsidal precession due to Earth’s J2 gravitational moment. [...] The N-body simulation code used in this paper is open source and can be found at https://github.com/norabolig/conjunctionSim.
Also, the formalism is the standard way astrophysicists understand collisions in gases or galaxies, and it works surprisingly well, especially when there are large numbers of "particles". There may be a few assumptions about the velocity distribution, but usually those are mild and only affect the results by less than an order of magnitude.
And the colliding gasses models have the huge assumption of random/thermal motion. These satellites are in carefully designed orbits; they aren't going to magically thermalize if left unmonitored for three days.
IMO now that LEO communication satellites are feasible we should ban launching satellites into higher orbits. Collision debris up there is much, much worse because it's essentially permanent. It will not deorbit by itself for thousands of years or more, and there is no plausible way to clean it up even with technology much more advanced than ours.
More: https://caseyhandmer.wordpress.com/2019/10/25/space-debris-p...
It would not discriminate though. Everything in that orbit would be taken down - debris and any functional satellites.
My point is that even the unlikely worst case scenario would be limited in time and extent. It couldn't possibly block us from reaching space or last for decades, as some people fear.
There is more than one Space Station up there. "Tianhe space station module conducted preventive collision avoidance due to close approaches by the Starlink-1095 (2020-001BK) and Starlink-2305 (2021-024N) satellites on July 1 and Oct. 21 respectively." [1]. Wikipedia also has a long list of planned and proposed space stations.
1. https://www.n2yo.com/satellite-news/Chinas-space-station-man...
Satellites in higher orbits do a lot that can't be done in LEO and typically have much lower collision risk (though GEO is fairly crowded). There are plenty of plausible candidate technologies for cleaning up debris, just few practical demonstrations (and even tracking smaller pieces is work in progress)
This isn't really true anymore. Yes there's a lot of legacy technology still in use and even still being launched, but there's nothing in MEO or GEO that can't be done in LEO with today's technology. Doing it in LEO requires more satellites and better radios, but you get better performance.
The risk of collisions may be lower but the consequences last thousands or millions of times longer...
Complete loss of control of the entire Starlink constellation (or any megaconstellation) for days at a time would be an intense event. Any environmental cause (a solar event) would be catastrophic ground-side as well. Starlink satellites will decay and re-enter pretty quickly if they lose attitude control, so it's a bit of a race between collisions and drag. Starlink solar arrays are quite large drag surfaces and the orbital decay probably makes collisions less likely. I would not be surprised if satellites are designed to deorbit without ground contact for some period of time. I'm sure SpaceX has done some interesting math on this and it would be interesting to see.
Collision avoidance warnings are public (with an account): https://www.space-track.org/ But importantly they are intended to be actionable, conservative warnings a few days to a week out. They overstate the probability based on assumptions like this paper (estimates at cross-sectional area, uncertainty in orbital knowledge from ground radar, ignorance of attitude control or for future maneuvers). Operators like SpaceX will take these and use their own high-fidelity knowledge (from onboard GPS) to get a less conservative, more realistic probability assessment. These probabilities invariably decrease over time as the uncertainty gets lower. Starlink satellites are constantly under thrust to stay in a low orbit with a big draggy solar array, so a "collision avoidance manuever" to them is really just a slight change to the thrust profile.
Interesting stuff in the paper, but I'm annoyed at the title. I hate when people fear-bait about Kessler syndrome against some of the more responsible actors.
was watching a video about ICBM detection/taking them out in boost phase, and needing a lot for coverage if you had these LEO satellites ready to go but need a lot of delta v (fuel), star link... plenty of em but nah it's for internet/basic navigation/not much fuel
the one above and this one https://www.youtube.com/watch?v=KdPTpRfhdWM
which you know credibility who knows
edit: the "not good enough" part I mean kill vehicle trying to lock onto the right target not decoys
but I've only started looking into this, not that I really have a say in it as a civilian just along for the ride
This is the context I was thinking about https://youtu.be/XDXKRQCkvms?si=1P8eLrZcPiP_ZSHw&t=353