HN Reader

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...

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.

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.

tangent conspiracy thought

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