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SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

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Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#21

Post by spiritplumber »

wongarsu wrote: post #17
aucisson_masque wrote: post #7

There are so many satellites in orbit that there is a pretty good chance that if even one was to be hit by something and explode in many pieces, it would crash another one and then another one until there is nothing left. The nasa is pretty scared of it, so is SpaceX.

There are tentative signs that this is happening right now. As in: each collision causes debris that on average causes more than one additional collision, causing collision rates to go up exponentially. But so far it's not anything like in Hollywood movies, it's just a graph slowly going up. There are about 12000 satellites orbiting earth. That looks like a lot on a map, but 12000 objects spread over an area larger t…

Yep. That's the things about exponential curves, it's a graph slowly going up until it's no longer "slowly".

https://www.thefrogdoctrine.com/p/the-29th-day

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#22

Post by tlb »

_factor wrote: post #18
goku12 wrote: post #11

Earlier quoted context omitted.

That's the Kessler Syndrome. But it's better if it happens in a lower orbit, irrespective of what assets are present there. Space will be free for exploration again in a few years since all the debris there would eventually decay and deorbit. The article mentions a few months at 480 km. I'm a little skeptical about this figure though, because the last tracked piece from an NRO satellite that was shot down at ~250 km…

Two objects colliding can send debris into different orbits. Combined kinetic energy and mass differences can send debris to many different orbits. A golf ball hitting a bowling ball or basketball, both traveling at 30 units of speed can produce quite a fast golf ball. Not all of the debris will safely burn up.

At the speeds we're familiar with, basketballs and golf balls have elastic collisions. At orbital speeds, satellites are nearly inelastic. So fragment exit velocities lie between the two initial velocities, kv1 + (1-k)v2 for some k that depends on where each fragment came from. If they're colliding, the velocities must be somewhat different, so the weighted average speed has to be lower than orbital speed. So fragments usually don't survive many orbits.

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#23

Post by goku12 »

Dylan16807 wrote: post #6
lijok wrote: post #5

Earlier quoted context omitted.

Does Kessler syndrome also mean ICBMs become nonviable?

No. It's not a wall. The risk from going through a dangerous orbit is much much less than the risk from staying there.

That depends on how you define risk. If it means the probability of a collision, then you'd be correct. But if a collision does happen, the consequences will be worse than being in the same orbit. Based on an oversimplified model, debris in orbit is likely to have low relative velocities with respect to an intact satellite in the same orbit, since a large deltav would change the orbit. (It's not as simple as this, but it's good enough in practice.)

This is actually what asat weapons take advantage of. They usually don't even reach orbital velocity, just like ballistic missiles (of course, there are exceptions like the golden dome monstrosity). The kill vehicle just maneuvers itself into the path of the satellite and lets the satellite plough into it at hypervelocity.

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#24

Post by panick21_ »

tlb wrote: post #19
Jean-Papoulos wrote: post #2

From a comment : >The first move in the coming WWIII, where the emperors try to expand their empires militaril,y will be to wipe out any orbit with Starlink satellites. I find this highly unlikely, given Starlink is soon to reached 10k satellites and will continue to grow. Why expand 10 000 ballistic missiles to bring down one of many communications networks ?

You could launch some missiles, blow a few satellites into smithereens, and gradually over the next few months they would take out the others. That's a poor kind of war weapon. An effective weapon is one where you can inflict damage continuously, and are able to stop immediately upon some concession. If you can't offer to stop in return for concessions, you won't get any.

Its not really that easy, to cause such a chain reaction, specially if the other person reacts.

And its also really expensive, each sat you take down costs you far more then what you hit. So unless you can actually cause a chain reaction its a losing proposition.

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#25

Post by DrScientist »

xxs wrote: post #3
Jean-Papoulos wrote: post #2

From a comment : >The first move in the coming WWIII, where the emperors try to expand their empires militaril,y will be to wipe out any orbit with Starlink satellites. I find this highly unlikely, given Starlink is soon to reached 10k satellites and will continue to grow. Why expand 10 000 ballistic missiles to bring down one of many communications networks ?

[flagged]

It's also been used for regime change attempts - part of the internet that's harder to shutdown, though apparently jamming GPS currently appears to be quite effective.

https://www.independent.co.uk/news/world/middle-east/iran-in...

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#26

Post by RealityVoid »

tlb wrote: post #19
Jean-Papoulos wrote: post #2

From a comment : >The first move in the coming WWIII, where the emperors try to expand their empires militaril,y will be to wipe out any orbit with Starlink satellites. I find this highly unlikely, given Starlink is soon to reached 10k satellites and will continue to grow. Why expand 10 000 ballistic missiles to bring down one of many communications networks ?

You could launch some missiles, blow a few satellites into smithereens, and gradually over the next few months they would take out the others. That's a poor kind of war weapon. An effective weapon is one where you can inflict damage continuously, and are able to stop immediately upon some concession. If you can't offer to stop in return for concessions, you won't get any.

You don't take down satellites in order to force someone to negotiate, you take them down for denial of capabilities.

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#27

Post by WithinReason »

tlb wrote: post #22
_factor wrote: post #18

Earlier quoted context omitted.

Two objects colliding can send debris into different orbits. Combined kinetic energy and mass differences can send debris to many different orbits. A golf ball hitting a bowling ball or basketball, both traveling at 30 units of speed can produce quite a fast golf ball. Not all of the debris will safely burn up.

At the speeds we're familiar with, basketballs and golf balls have elastic collisions. At orbital speeds, satellites are nearly inelastic. So fragment exit velocities lie between the two initial velocities, k v1 + (1-k) v2 for some k that depends on where each fragment came from. If they're colliding, the velocities must be somewhat different, so the weighted average speed has to be lower than orbital speed. So fragm…

That's what I was thinking, Kessler syndrome should be impossible for objects in LEO since all debris orbits decay rapidly (probably 99.9% enter the atmosphere and burn up in minutes, the rest in hours)

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#28

Post by childintime »

wongarsu wrote: post #17
aucisson_masque wrote: post #7

There are so many satellites in orbit that there is a pretty good chance that if even one was to be hit by something and explode in many pieces, it would crash another one and then another one until there is nothing left. The nasa is pretty scared of it, so is SpaceX.

There are tentative signs that this is happening right now. As in: each collision causes debris that on average causes more than one additional collision, causing collision rates to go up exponentially. But so far it's not anything like in Hollywood movies, it's just a graph slowly going up. There are about 12000 satellites orbiting earth. That looks like a lot on a map, but 12000 objects spread over an area larger t…

> 12000 objects spread over an area larger than the surface of the earth isn't all that much

People keep saying this, but the only way to assure there is no collision is to have non-intersecting orbits, but that is not going to work: not enough space.

It's a tell that SpaceX is now lowering the orbits, even though their satellites mostly move in flocks that maintain a formation relative to each other: because the other ways are exhausted.

Of course if they do cause a (low orbit) Kessler syndrom, then they don't have a business any more, and SpaceX will have achieved the opposite of its stated goals.

The major reason to lower these orbits is likely the risk of a terrorist state turning these constellations into a weapon, by willingly causing the Kessler syndrome. SpaceX isn't going to tell you that, just as it doesn't tell you it's the USA's most important military asset.

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#29

Post by GuB-42 »

xxs wrote: post #3
Jean-Papoulos wrote: post #2

From a comment : >The first move in the coming WWIII, where the emperors try to expand their empires militaril,y will be to wipe out any orbit with Starlink satellites. I find this highly unlikely, given Starlink is soon to reached 10k satellites and will continue to grow. Why expand 10 000 ballistic missiles to bring down one of many communications networks ?

[flagged]

What kind of pictures can starlink would take? When I look at pictures of starlink satellites, I don't see a camera. Maybe they have one, but if we can't see it, it is most likely useless for observation, except for taking pretty pictures of the Earth, or maybe other passing satellites.

Spy satellites are more like space telescopes, but pointed at the Earth. As an example, Hubble is designed after a spy satellite, the "camera" is pretty massive and obvious.

Starlink can probably be weaponized for a variety of thing, like for communication, obviously, but I don't think earth optical observation is one of them.

Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake

#30

Post by Cthulhu_ »

goku12 wrote: post #11
aucisson_masque wrote: post #7

There are so many satellites in orbit that there is a pretty good chance that if even one was to be hit by something and explode in many pieces, it would crash another one and then another one until there is nothing left. The nasa is pretty scared of it, so is SpaceX.

That's the Kessler Syndrome. But it's better if it happens in a lower orbit, irrespective of what assets are present there. Space will be free for exploration again in a few years since all the debris there would eventually decay and deorbit. The article mentions a few months at 480 km. I'm a little skeptical about this figure though, because the last tracked piece from an NRO satellite that was shot down at ~250 km…

It's one reason why space should be regulated (but globally / internationally), the systems in place are kinda loose and more of a gentleman's agreement insofar as I understand it. A plan for decomissioning / de-orbiting stuff should definitely be mandatory. I know there's an area for geostationary sattelites to park themselves after their lifespan, for example.

But the LEO ones like Starlink will see their orbit decay in about five years (if I'm reading things correctly) even if they run out of fuel / can no longer be controlled, according to e.g. https://space.stackexchange.com/a/59560. But it's exponential, at 600 km it takes 10 years, at 700 25 years, at 800 100 years, etc. Between 500-600 km seems to be ideal for things to naturally decay in case of issues.

But also, it won't be a hard and fast "we are confined to the earth now"; the simplest model is a "the risk of being hit by debris is now x%", more advanced is "there are debris clouds in these altitudes / inclinations so best to avoid those at these times of day".

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