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.
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.
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.
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...
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 the context I was thinking about https://youtu.be/XDXKRQCkvms?si=1P8eLrZcPiP_ZSHw&t=353
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
Checking out Perun
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.
TGower•1mo ago
philipwhiuk•1mo ago
M3L0NM4N•1mo ago
deddy•1mo ago
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...
brookst•1mo ago
deddy•1mo ago
It’s a conservative definition in the field. It’s generally defined as the hard body radius: take the smallest sphere centered at the center of mass that would entirely enclose the object, then use the maximum cross section of that sphere to define the potential “area” of the colliding object.
Maybe put more simply, it’s the worst case area size / orientation you could be looking at. So yes. Solar arrays have a narrow cross section from the side but looking at them head-on (which is the angle used for Pc calculations) they’ll be very large.
HPsquared•1mo ago
deddy•1mo ago
Generally people really don't want collisions due to cascading effects, so they take the worst-case probability of collision found with bounding assumptions. Additionally, while often all these vehicles have active attitude (orientation) control, sometimes they go into safe mode and are spinning (often spin stabilized to point at the sun), so it will clear the entire potential radius while rotating.
Also how do you define the probabilistic average area for a space object that you don't know how it's control system works or what it's been commanded to do / point at. Yes we can make some pretty good assumptions for things like Starlink, but even those do take safemodes occasionally.
So It's an engineering judgement call on how to model it. It's hard to get a probabilistic average for attitude that you can confidently test and say is "right", it's a lot easier and conservative to take the worst-case upper-bound. That's at least not-wrong.
notahacker•1mo ago
The papers assumptions lead to the conclusion that with no manouevres, we'd see a catastrophic crash between two or more satellites in LEO within 2.8 days. To be on the safe side, Starlink did over 144000 in the first six months of the year (and based on historical doubling rate, will probably be doing 1000 per day by now)...
rzimmerman•1mo ago
MarkusQ•1mo ago
hughes•1mo ago
schiffern•1mo ago
Why did this need to be a (badly done) acronym at all? It's a countdown to a collision, a collision clock, but of course "crash" (in all caps no less) sounds worse, and science writing needs sciencey acronyms don't ya know...
Sanzig•1mo ago
bpodgursky•1mo ago
queuebert•1mo ago
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.
MarkusQ•1mo ago
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.
Sanzig•1mo ago
Solar flares cause atmospheric upwelling, so drag dramatically increases during a major solar flare. And the scenario envisioned in the paper is basically a Carrington-level event, so this effect would be extreme.
queuebert•1mo ago
SiempreViernes•1mo ago
MarkusQ•1mo ago
https://www.scribd.com/document/883045105/SpaceX-Gen1-Gen2-S...
It also notes that the collision odds on which SpaceX triggers such maneuvers is 333 times more conservative than the industry standard. Were that not the case (and they were just using the standard criterion) one might naively assume that they would only be doing a maneuver every ten hours or so. But collision probabilities are not linear, they follow a power law distribution so in actuality they would only be doing such maneuvers every few days.
It is disingenuous to the point of dishonesty to use SpaceX's abundance of caution (or possibly braggadocios operational flex) as evidence that the risk is greater than it actually is.
SiempreViernes•1mo ago
> 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.