5 ms·

I imagined deploying a net of some sort to get close but not extremely close. But I guess the high velocities mean you need a really strong and light net and t

I imagined deploying a net of some sort to get close but not extremely close. But I guess the high velocities mean you need a really strong and light net and the rapid deceleration might damage the satellite anyway.

jiofih 6y ago
The ISS orbits at 400km altitude and 27000km/h, while many small satellites will orbit lower - I suppose this is what makes it possible to “drop” a non-propulsive satellite from the ISS like the one in the article. As their orbit decays, they would actually need tons of fuel to accelerate and raise their orbit to reach the station, it’s totally impractical. EDIT: not geostationary
- viklove 6y ago
  That doesn't make any sense. If you want to orbit at a lower speed, you need to increase your altitude. Geostationary orbit is at 35,000+ km, while the ISS orbits at ~400 km.
- madpata 6y ago
  Don't you mean much higher? Like at 36MM/36,000km?
- hnuser123456 6y ago
  Geostationary orbits are much higher altitude to achieve lower orbit speeds. Gravity is stronger closer to the surface. But they'd still need a lot of fuel to slow down, to drop lower to the ISS' orbit, and then they'd be on an elliptical, and need even more to circularize and rendezvous. edit: I'm the third one to say this in a span of a minute, sorry.
- gpav 6y ago
  Instead of geostationary, I think you mean low earth orbit (LEO). There is a link to the Wikipedia article on LEO in an adjacent comment. A circular geostationary orbit is at an altitude of 22,236 miles/35,786 kilometers. https://en.m.wikipedia.org/wiki/Geostationary_orbit https://en.m.wikipedia.org/wiki/Geostationary_orbit
- deleted 6y ago
  [deleted]
simonh 6y ago
Rifle bullet speed is a relatively small delta for orbiting craft, it goes up quite a few orders of magnitude from that. Pretty much anything you encounter that you didn't specifically try very hard to match orbits with is going to blast right through a net. There were studies on using the Shuttle to repair satellites, but aside from the maintenance mission on Hubble those plans were shelved. The cost of a new satellite was generally a lot less than the cost of a shuttle mission dedicated to repairing it, and it would often need to be dedicated due to the requirement to match orbits. Even if the ISS released a smallsat, which it does from time to time, that doesn't help you. By the time you need to do maintenance on it, the cubesat will have dropped into a much lower orbit due to upper atmosphere effects. The safest, and practically perhaps the only viable way for the ISS to do maintenance on orbital instruments is if they stay attached to the ISS.
- bzbarsky 6y ago
  > it goes up quite a few orders of magnitude from that Sorry to be pedantic, but modern rifle muzzle velocities are in the 1.2km/s range. Escape velocity in LEO is 11.2km/s, so your maximal closing speed is ~22.4kms. Which is maybe 1.3 orders of magnitude difference, not "quite a few". Orders of magnitude are big. For the rest, you are right of course: we're talking closing speeds that can easily be one order of magnitude higher than rifle bullets (or armor-piercing tank projectiles, for that matter; those are at 1.7km/s or so).
  - dheera 6y ago
    I guess it depends if you operate in base 2 or base 10.
    - hinoki 6y ago
      Naturally, you should use base e, which gives about 3 orders of magnitude.
  - db48x 6y ago
    What matters in a collision isn't velocity, it's momentum. Momentum is ½mv². There's a lot of orders of magnitude just in the mass, but the velocities add up a lot faster than you'd think too. I'd say there's around 10 orders of magnitude between the momentum of a rifle bullet and the momentum of a communications satellite at escape velocity.
LASR 6y ago
It would be like trying to catch a hypervelocity meteor with a net. It would go right through any kind of reasonable(or even extreme) net material. Keep in mind that when the atmosphere is used to "catch" a returning spacecraft, it takes several minutes of sustained deceleration over thousands of miles, and in the process the craft gets extremely hot due to compressive heating and friction with air. When you have satellites on different orbital planes, it can be twice as hard due to relative velocities.

jiofih 6y ago

The ISS orbits at 400km altitude and 27000km/h, while many small satellites will orbit lower - I suppose this is what makes it possible to “drop” a non-propulsive satellite from the ISS like the one in the article. As their orbit decays, they would actually need tons of fuel to accelerate and raise their orbit to reach the station, it’s totally impractical. EDIT: not geostationary

viklove 6y ago
That doesn't make any sense. If you want to orbit at a lower speed, you need to increase your altitude. Geostationary orbit is at 35,000+ km, while the ISS orbits at ~400 km.
madpata 6y ago
Don't you mean much higher? Like at 36MM/36,000km?
hnuser123456 6y ago
Geostationary orbits are much higher altitude to achieve lower orbit speeds. Gravity is stronger closer to the surface. But they'd still need a lot of fuel to slow down, to drop lower to the ISS' orbit, and then they'd be on an elliptical, and need even more to circularize and rendezvous. edit: I'm the third one to say this in a span of a minute, sorry.
gpav 6y ago
Instead of geostationary, I think you mean low earth orbit (LEO). There is a link to the Wikipedia article on LEO in an adjacent comment. A circular geostationary orbit is at an altitude of 22,236 miles/35,786 kilometers. https://en.m.wikipedia.org/wiki/Geostationary_orbit https://en.m.wikipedia.org/wiki/Geostationary_orbit
deleted 6y ago
[deleted]

simonh 6y ago

Rifle bullet speed is a relatively small delta for orbiting craft, it goes up quite a few orders of magnitude from that. Pretty much anything you encounter that you didn't specifically try very hard to match orbits with is going to blast right through a net. There were studies on using the Shuttle to repair satellites, but aside from the maintenance mission on Hubble those plans were shelved. The cost of a new satellite was generally a lot less than the cost of a shuttle mission dedicated to repairing it, and it would often need to be dedicated due to the requirement to match orbits. Even if the ISS released a smallsat, which it does from time to time, that doesn't help you. By the time you need to do maintenance on it, the cubesat will have dropped into a much lower orbit due to upper atmosphere effects. The safest, and practically perhaps the only viable way for the ISS to do maintenance on orbital instruments is if they stay attached to the ISS.

bzbarsky 6y ago
> it goes up quite a few orders of magnitude from that Sorry to be pedantic, but modern rifle muzzle velocities are in the 1.2km/s range. Escape velocity in LEO is 11.2km/s, so your maximal closing speed is ~22.4kms. Which is maybe 1.3 orders of magnitude difference, not "quite a few". Orders of magnitude are big. For the rest, you are right of course: we're talking closing speeds that can easily be one order of magnitude higher than rifle bullets (or armor-piercing tank projectiles, for that matter; those are at 1.7km/s or so).
- dheera 6y ago
  I guess it depends if you operate in base 2 or base 10.
  - hinoki 6y ago
    Naturally, you should use base e, which gives about 3 orders of magnitude.
- db48x 6y ago
  What matters in a collision isn't velocity, it's momentum. Momentum is ½mv². There's a lot of orders of magnitude just in the mass, but the velocities add up a lot faster than you'd think too. I'd say there's around 10 orders of magnitude between the momentum of a rifle bullet and the momentum of a communications satellite at escape velocity.

LASR 6y ago

It would be like trying to catch a hypervelocity meteor with a net. It would go right through any kind of reasonable(or even extreme) net material. Keep in mind that when the atmosphere is used to "catch" a returning spacecraft, it takes several minutes of sustained deceleration over thousands of miles, and in the process the craft gets extremely hot due to compressive heating and friction with air. When you have satellites on different orbital planes, it can be twice as hard due to relative velocities.