4 ms·

Speed matters a lot. You can fit a lot more walking people than speeding motorcycles in the same space. Satellites need to travel at 8 km/s to not fall down.

JumpCrisscross 9mo ago
> Speed matters a lot Not really. You're correct inasmuch as it increases collision energies. But it also increases momentum, which maintains orbital integrity within predictable bounds. Nobody is maneuvering around satellites, they–and their debris–stay where the math tells them to.
- notahacker 9mo ago
  Orbits are predictable, but they intersect and decay [at different rates] and occasionally get perturbed by space weather. This already needs periodic conjunction avoidance manoeuvres, and whilst orbits are fast satellite manoeuvres are slow, so the notice you need to avoid a conjunction is measured in hours rather than seconds. Can't imagine a scenario in which it would be sustainable for LEO to even approach the density of commercial aviation, except perhaps for a hypothetical where a single entity actually managed all the satellites. The other underestimated dimension is that satellite manoeuvres use up a finite supply of expensively-launched propellant. That's tolerable when Starlink is doing 50k conjunction avoidance manoeuvres in six months across its constellation, but once it becomes each satellite moving at least weekly you either need bigger satellites carrying more propellant or have to accept significantly higher collision risk than they currently do.
  - dylan604 9mo ago
    > and whilst orbits are fast satellite manoeuvres are slow This is something people unfamiliar tend to misconceive in their limited thinking on the subject. You can't just tap the breaks to slow down. Changing altitude of satellites is done by speeding up to increase altitude and slowing down to lower altitude. Once you change the velocity and reach the desired altitude, you have to then undo that acceleration to get back to orbital velocity. Fuel is required in both directions. The less fuel used the better for the maneuver. Most satellites EoL is defined by remaining maneuvering fuel vs functionality of the hardware. My first understanding of accelerating in space was from the old Asteroids game. To slow down, you had to rotate 180° and start accelerating in that direction. Others might learn it from Kerbal.
    - JumpCrisscross 9mo ago
      > This is something people unfamiliar tend to misconceive in their limited thinking on the subject I have a background in astronautical engineering. While you can't tap the brakes to 'slow down', you can impart miniscule amounts of impulse which, over the course of hundreds of orbits, will change your plane by an imperceptible amount from a distance, but tens or hundreds of kilometers up close. OM being OM, you can predicts these collisions in advance. I had a professor who referred to orbits not in altitude but in expected decay time. We're currently in the months to single-digit years orbits. (We will stay there for telecommunications due to latency.) If we were doing at decades or centuries what we're doing in LEO, this would be a problem. At LEO, it's a nuisance and barely more.
      - dylan604 9mo ago
        > you can impart miniscule amounts of impulse which, over the course of hundreds of orbits right. this is what is counter-intuitive for those that are not familiar with space. they don't just light the burner and boost to a new altitude. the part about stopping the acceleration with an opposite burn is often not considered. most think you can fly a space ship like a jet fighter, but in space. can't blame them since that's how sci-fi portrays it. real life space flight is really boring in comparison. jumping out of FTL to land in orbit around a planet makes me laugh every. single. time.
        deleted 9mo ago
        [deleted]
  - JumpCrisscross 9mo ago
    > whilst orbits are fast satellite manoeuvres are slow, so the notice you need to avoid a conjunction is measured in hours rather than seconds I'm not arguing against collisions becoming more likely. I'm arguing aginst it becoming commonplace to the point that it becomes a commercial concern. > satellite manoeuvres use up a finite supply of expensively-launched propellant Nobody is plane changing out of a collision. And for the foreseeable future, in LEO, the birds are not propellant constrained. (And launch is getting cheaper.) > you either need bigger satellites carrying more propellant or have to accept significantly higher collision risk than they currently do We're decades away from this being a problem. That gives ample runtime to developing e.g. magnetic station-keeping (if we go reactionless) or more-efficient engines.
    - defrost 9mo ago
      > e.g. magnetic station-keeping I've not kept up for decades now .. what's the state of solar powered magnetorquers these days? I'd quietly assumed it would be more commonplace. I dimly recall a couple of small satellites magnetically locking fifteen or so years past?
      - JumpCrisscross 9mo ago
        > what's the state of solar powered magnetorquers these days? Academic. We don't currently have a pressing need for reactionless thrust in the magnetosphere. Each of semiconductors, launch vehicles and telecommunications standards are moving faster than satellites last.
        defrost 9mo ago
        Thanks for the reply. > Each of semiconductors, launch vehicles and telecommunications standards are moving faster than satellites last. That's certainly a pragmatic cost based argument for not using them in the fast moving world of commercial magnetosphere constellations. > Academic. I feel they've moved past academic and transitioned to deployed .. at some evolution of implementation. Not commercially relevant is certainly one state of play. I guess I was more interested in the nonlinear control issue in a field of highly variable intensity.
- Gravityloss 9mo ago
  Thought experiment: Let's say you are simulating ten thousand satellites on your computer, and the simulation runs until there is a crash. Now let's say the simulation runs for an hour normally. If you increase the speed of the simulation, you get to a crash in a shorter time. Satellites move about 30x the speed of airliners. Hence, if everything else was similar, one would expect 30x the amount of collisions.
  - JumpCrisscross 9mo ago
    > Satellites move about 30x the speed of airliners. Hence, if everything else was similar, one would expect 30x the amount of collisions Not how orbital mechanics work. Planes maneuvers, get tossed around and have hubs they circle. A plane under my left wing can’t be relied on to continue in a straight line. The satellite can.
    - Gravityloss 9mo ago
      Of course. But your comment that speed is not a factor was incorrect.
      - JumpCrisscross 9mo ago
        > your comment that speed is not a factor was incorrect It would be if I had said this. Speed doesn’t matter “a lot”. (Orbits around a small object get crowded quicker. The speeds are less. But the volumes are way less. Volume absolutely dominates speed when it comes to orbital cross sections.)
- rlt 9mo ago
  Starlink and some other constellations absolutely do maneuver if a close conjunction is predicted https://starlink.com/satellite-operators https://starlink.com/satellite-operators

JumpCrisscross 9mo ago

> Speed matters a lot Not really. You're correct inasmuch as it increases collision energies. But it also increases momentum, which maintains orbital integrity within predictable bounds. Nobody is maneuvering around satellites, they–and their debris–stay where the math tells them to.

notahacker 9mo ago
Orbits are predictable, but they intersect and decay [at different rates] and occasionally get perturbed by space weather. This already needs periodic conjunction avoidance manoeuvres, and whilst orbits are fast satellite manoeuvres are slow, so the notice you need to avoid a conjunction is measured in hours rather than seconds. Can't imagine a scenario in which it would be sustainable for LEO to even approach the density of commercial aviation, except perhaps for a hypothetical where a single entity actually managed all the satellites. The other underestimated dimension is that satellite manoeuvres use up a finite supply of expensively-launched propellant. That's tolerable when Starlink is doing 50k conjunction avoidance manoeuvres in six months across its constellation, but once it becomes each satellite moving at least weekly you either need bigger satellites carrying more propellant or have to accept significantly higher collision risk than they currently do.
- dylan604 9mo ago
  > and whilst orbits are fast satellite manoeuvres are slow This is something people unfamiliar tend to misconceive in their limited thinking on the subject. You can't just tap the breaks to slow down. Changing altitude of satellites is done by speeding up to increase altitude and slowing down to lower altitude. Once you change the velocity and reach the desired altitude, you have to then undo that acceleration to get back to orbital velocity. Fuel is required in both directions. The less fuel used the better for the maneuver. Most satellites EoL is defined by remaining maneuvering fuel vs functionality of the hardware. My first understanding of accelerating in space was from the old Asteroids game. To slow down, you had to rotate 180° and start accelerating in that direction. Others might learn it from Kerbal.
  - JumpCrisscross 9mo ago
    > This is something people unfamiliar tend to misconceive in their limited thinking on the subject I have a background in astronautical engineering. While you can't tap the brakes to 'slow down', you can impart miniscule amounts of impulse which, over the course of hundreds of orbits, will change your plane by an imperceptible amount from a distance, but tens or hundreds of kilometers up close. OM being OM, you can predicts these collisions in advance. I had a professor who referred to orbits not in altitude but in expected decay time. We're currently in the months to single-digit years orbits. (We will stay there for telecommunications due to latency.) If we were doing at decades or centuries what we're doing in LEO, this would be a problem. At LEO, it's a nuisance and barely more.
    - dylan604 9mo ago
      > you can impart miniscule amounts of impulse which, over the course of hundreds of orbits right. this is what is counter-intuitive for those that are not familiar with space. they don't just light the burner and boost to a new altitude. the part about stopping the acceleration with an opposite burn is often not considered. most think you can fly a space ship like a jet fighter, but in space. can't blame them since that's how sci-fi portrays it. real life space flight is really boring in comparison. jumping out of FTL to land in orbit around a planet makes me laugh every. single. time.
      - deleted 9mo ago
        [deleted]
- JumpCrisscross 9mo ago
  > whilst orbits are fast satellite manoeuvres are slow, so the notice you need to avoid a conjunction is measured in hours rather than seconds I'm not arguing against collisions becoming more likely. I'm arguing aginst it becoming commonplace to the point that it becomes a commercial concern. > satellite manoeuvres use up a finite supply of expensively-launched propellant Nobody is plane changing out of a collision. And for the foreseeable future, in LEO, the birds are not propellant constrained. (And launch is getting cheaper.) > you either need bigger satellites carrying more propellant or have to accept significantly higher collision risk than they currently do We're decades away from this being a problem. That gives ample runtime to developing e.g. magnetic station-keeping (if we go reactionless) or more-efficient engines.
  - defrost 9mo ago
    > e.g. magnetic station-keeping I've not kept up for decades now .. what's the state of solar powered magnetorquers these days? I'd quietly assumed it would be more commonplace. I dimly recall a couple of small satellites magnetically locking fifteen or so years past?
    - JumpCrisscross 9mo ago
      > what's the state of solar powered magnetorquers these days? Academic. We don't currently have a pressing need for reactionless thrust in the magnetosphere. Each of semiconductors, launch vehicles and telecommunications standards are moving faster than satellites last.
      - defrost 9mo ago
        Thanks for the reply. > Each of semiconductors, launch vehicles and telecommunications standards are moving faster than satellites last. That's certainly a pragmatic cost based argument for not using them in the fast moving world of commercial magnetosphere constellations. > Academic. I feel they've moved past academic and transitioned to deployed .. at some evolution of implementation. Not commercially relevant is certainly one state of play. I guess I was more interested in the nonlinear control issue in a field of highly variable intensity.
Gravityloss 9mo ago
Thought experiment: Let's say you are simulating ten thousand satellites on your computer, and the simulation runs until there is a crash. Now let's say the simulation runs for an hour normally. If you increase the speed of the simulation, you get to a crash in a shorter time. Satellites move about 30x the speed of airliners. Hence, if everything else was similar, one would expect 30x the amount of collisions.
- JumpCrisscross 9mo ago
  > Satellites move about 30x the speed of airliners. Hence, if everything else was similar, one would expect 30x the amount of collisions Not how orbital mechanics work. Planes maneuvers, get tossed around and have hubs they circle. A plane under my left wing can’t be relied on to continue in a straight line. The satellite can.
  - Gravityloss 9mo ago
    Of course. But your comment that speed is not a factor was incorrect.
    - JumpCrisscross 9mo ago
      > your comment that speed is not a factor was incorrect It would be if I had said this. Speed doesn’t matter “a lot”. (Orbits around a small object get crowded quicker. The speeds are less. But the volumes are way less. Volume absolutely dominates speed when it comes to orbital cross sections.)
rlt 9mo ago
Starlink and some other constellations absolutely do maneuver if a close conjunction is predicted https://starlink.com/satellite-operators https://starlink.com/satellite-operators