4 ms·

I think you heavily overstate the difficulty and cost of diverting a spacecraft, especially in the case of cubesats, which in general do not have any propulsion

I think you heavily overstate the difficulty and cost of diverting a spacecraft, especially in the case of cubesats, which in general do not have any propulsion systems to do the delta-v manuevers you state. For collision avoidance for cubesats, realistically you just change the drag profile to bring the spacecraft into a higher or lower orbit. While this can in some cases have an impact on lifetime, they're not generally going to be manuevers away from their existing orbit enough to change performance or reception characteristics as the new orbit is always going to be an orbit that the spacecraft would be expected to hit anyways. Additionally, as other comments have alluded to, part of the FCC requirements that these spacecraft have to meet is a maximum deorbit time, which is (I believe) 25 years. For satellites as low as these ones were, that period will be lower. I'm all for the FCC throwing the book at this company, but just want to make sure we don't have misconceptions as a community about what or why these things are regulated and how they work.

cbanek 9y ago
I don't think I'm overstating anything. If you don't know you're going to possibly hit something, there's nothing you can do, and lots of small objects make it more probable you'll hit something you can't detect. If you want to add some way to detect that you might hit something, it'd have to have some impressive range, as if you're in LEO going different directions with a 90 minute orbital period for each object, you have about 45 minutes to do something at best (when you just passed each other on one side of the earth, and you will collide as your orbits cross on the other side), although you can't really detect it until it's within line of sight, which brings it down to much less, maybe like 20 minutes. Radar or other detection systems also take a huge amount of mass and power to operate, which increases the cost. If your orbits go the same way, you do have some more time, and maybe multiple orbits to see that something is getting closer every pass, but then again, you can't really rely on that. I've never been good at orbital mechanics, but I'm not sure how increasing the drag would allow you to get to a higher orbit (higher meaning altitude above earth). Reducing drag just makes you slow down slower, but I don't think will let you go to a higher orbit. The height of the orbit is related to how fast you are going (for example, a geosync orbit is 3.07 km/s, whereas LEO is 1.3–1.8 km/s). Drag will never make you go faster. I think you would get a more elliptical orbit, which would also add more atmospheric drag at your new lower perigee, also decreasing the lifetime. Even a low lifetime orbit for a cubesat could easily be 10 years, and if you lose communications with it and lose track of where it is at, it could be a hazard. The amount you'd have to change the orbit also depends on the confidence of detection of the object you're trying to avoid (ie, how close you want to risk getting to it). If you're less sure where it is, you need to get further away from it in order to make sure you avoid it. To sum up, you don't know when you need to do something, your ability to do something may be limited based on the craft doing the avoiding, and you may not have a lot of time to figure out you need to do something and then do it. Why these things are regulated is because orbits around earth are basically a shared resource. How it works is very complicated. I used to work in the space industry, and I don't even pretend to be an expert.

cbanek 9y ago

I don't think I'm overstating anything. If you don't know you're going to possibly hit something, there's nothing you can do, and lots of small objects make it more probable you'll hit something you can't detect. If you want to add some way to detect that you might hit something, it'd have to have some impressive range, as if you're in LEO going different directions with a 90 minute orbital period for each object, you have about 45 minutes to do something at best (when you just passed each other on one side of the earth, and you will collide as your orbits cross on the other side), although you can't really detect it until it's within line of sight, which brings it down to much less, maybe like 20 minutes. Radar or other detection systems also take a huge amount of mass and power to operate, which increases the cost. If your orbits go the same way, you do have some more time, and maybe multiple orbits to see that something is getting closer every pass, but then again, you can't really rely on that. I've never been good at orbital mechanics, but I'm not sure how increasing the drag would allow you to get to a higher orbit (higher meaning altitude above earth). Reducing drag just makes you slow down slower, but I don't think will let you go to a higher orbit. The height of the orbit is related to how fast you are going (for example, a geosync orbit is 3.07 km/s, whereas LEO is 1.3–1.8 km/s). Drag will never make you go faster. I think you would get a more elliptical orbit, which would also add more atmospheric drag at your new lower perigee, also decreasing the lifetime. Even a low lifetime orbit for a cubesat could easily be 10 years, and if you lose communications with it and lose track of where it is at, it could be a hazard. The amount you'd have to change the orbit also depends on the confidence of detection of the object you're trying to avoid (ie, how close you want to risk getting to it). If you're less sure where it is, you need to get further away from it in order to make sure you avoid it. To sum up, you don't know when you need to do something, your ability to do something may be limited based on the craft doing the avoiding, and you may not have a lot of time to figure out you need to do something and then do it. Why these things are regulated is because orbits around earth are basically a shared resource. How it works is very complicated. I used to work in the space industry, and I don't even pretend to be an expert.