7 ms·

Given that starlink is in LEO does that mean there is enough friction to deorbit fragments of a collision in a relatively short time frame? Does anyone know? K

Given that starlink is in LEO does that mean there is enough friction to deorbit fragments of a collision in a relatively short time frame? Does anyone know? Kessler syndrome is scary because it could render certain orbits unusable for a long time and starlink ups the risk by having a huge constellation but I've wondered how much of the risk is mitigated by being in LEO.

wongarsu 6y ago
If a Starlink satellite fails the drag alone will deorbit it within five years or so. (this actually happens, they used to have 5% failure rate) Of course a collision event is chaotic. The debris is catapulted in all directions, changing the orbit. But because of how orbital mechanics works their new orbit will still pass through their old orbit, so every piece of debris will deorbit eventually (unless it impacts something else first). Being so low reduces the risk considerably, and even with a couple thousand satellites more we are talking about mostly empty space.
nabla9 6y ago
Not all of them. Practically all space debris collisions in LEO will be hypervelocity collisions (the kinetic energy of the impact is greater than the explosive energy released by the same mass of TNT) When collision happens in LEO, some fragments gain more velocity than the colliding satellites. They may end up in higher orbits where they can stay for a very long time.
- Gwypaas 6y ago
  That is not correct. To actually end up in an orbit with both higher apoapsis and periapsis another collision would need to happen higher upp, which then would raise the periapsis. Otherwise it would simply be an elliptic orbit still passing through the altitude which the collision happened at. An elliptic orbit may slow the decay though, but contrast this with the larger surface to weight ratio of smaller pieces and it should not really matter.
  - nabla9 6y ago
    How come? If the satellites collide close to 90 degree angle the horizontal velocity of some fragments can be more than 10 km/s and the orbit increases.
    - Gwypaas 6y ago
      See the regular Hohmann transfer [0]. Adding Δv at one point causes the orbit to become elliptic and will still pass through the same altitude, the yellow line in the picture. To increase the lower altitude, also called the periapsis, you need to add Δv higher up, which is the opposing side of the orbit for 100% efficiency and through that you create the circular red line. [0]: https://upload.wikimedia.org/wikipedia/commons/thumb/d/df/Hohmann_transfer_orbit.svg/440px-Hohmann_transfer_orbit.svg.png https://upload.wikimedia.org/wikipedia/commons/thumb/d/df/Ho...
      - nabla9 6y ago
        Ah. The lowest point of the orbit is the previous orbit. The fragments can still have more energy and decay slower than the original satellite. Especially when they don't have drag generating solar panels anymore.
    - modeless 6y ago
      The perigee of an orbit originating from a collision cannot be higher than the collision point and is very likely to be lower. Apogee could be higher, but it won't be for most of the debris. And even if it is, the low perigee will still cause the orbit to decay. And as Gwypaas points out, the pieces will in general decay faster than the whole satellite would due to higher surface area to mass ratio.
    - LeifCarrotson 6y ago
      Orbits in LEO are nearly circular. By giving a fragment a single instantaneous change in velocity, you change that orbit to an ellipse, which could have a higher apogee, but will always return to the initial altitude. To turn that ellipse into a circle with a larger radius than the LEO orbit, you need an additional maneuver when it is at that larger radius.
- deleted 6y ago
  [deleted]
mlindner 6y ago
Just to make sure you realize. SpaceX was not at fault here at all. They went out of their way to help OneWeb even though their satellites normally maneuver automatically.

wongarsu 6y ago

If a Starlink satellite fails the drag alone will deorbit it within five years or so. (this actually happens, they used to have 5% failure rate) Of course a collision event is chaotic. The debris is catapulted in all directions, changing the orbit. But because of how orbital mechanics works their new orbit will still pass through their old orbit, so every piece of debris will deorbit eventually (unless it impacts something else first). Being so low reduces the risk considerably, and even with a couple thousand satellites more we are talking about mostly empty space.

nabla9 6y ago

Not all of them. Practically all space debris collisions in LEO will be hypervelocity collisions (the kinetic energy of the impact is greater than the explosive energy released by the same mass of TNT) When collision happens in LEO, some fragments gain more velocity than the colliding satellites. They may end up in higher orbits where they can stay for a very long time.

Gwypaas 6y ago
That is not correct. To actually end up in an orbit with both higher apoapsis and periapsis another collision would need to happen higher upp, which then would raise the periapsis. Otherwise it would simply be an elliptic orbit still passing through the altitude which the collision happened at. An elliptic orbit may slow the decay though, but contrast this with the larger surface to weight ratio of smaller pieces and it should not really matter.
- nabla9 6y ago
  How come? If the satellites collide close to 90 degree angle the horizontal velocity of some fragments can be more than 10 km/s and the orbit increases.
  - Gwypaas 6y ago
    See the regular Hohmann transfer [0]. Adding Δv at one point causes the orbit to become elliptic and will still pass through the same altitude, the yellow line in the picture. To increase the lower altitude, also called the periapsis, you need to add Δv higher up, which is the opposing side of the orbit for 100% efficiency and through that you create the circular red line. [0]: https://upload.wikimedia.org/wikipedia/commons/thumb/d/df/Hohmann_transfer_orbit.svg/440px-Hohmann_transfer_orbit.svg.png https://upload.wikimedia.org/wikipedia/commons/thumb/d/df/Ho...
    - nabla9 6y ago
      Ah. The lowest point of the orbit is the previous orbit. The fragments can still have more energy and decay slower than the original satellite. Especially when they don't have drag generating solar panels anymore.
  - modeless 6y ago
    The perigee of an orbit originating from a collision cannot be higher than the collision point and is very likely to be lower. Apogee could be higher, but it won't be for most of the debris. And even if it is, the low perigee will still cause the orbit to decay. And as Gwypaas points out, the pieces will in general decay faster than the whole satellite would due to higher surface area to mass ratio.
  - LeifCarrotson 6y ago
    Orbits in LEO are nearly circular. By giving a fragment a single instantaneous change in velocity, you change that orbit to an ellipse, which could have a higher apogee, but will always return to the initial altitude. To turn that ellipse into a circle with a larger radius than the LEO orbit, you need an additional maneuver when it is at that larger radius.
deleted 6y ago
[deleted]

mlindner 6y ago

Just to make sure you realize. SpaceX was not at fault here at all. They went out of their way to help OneWeb even though their satellites normally maneuver automatically.