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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

#61

Post by ben_w »

tonyhart7 wrote: post #60
ben_w wrote: post #45

Earlier quoted context omitted.

If you smash up your router, your router does not magically get better, it simply fails to provide any internet. The same happens with orbiting routers, e.g. Starlink satellites.

and we would fix that shit, you acting like its impossible problem

A Kessler cascade necessarily requires the density of shrapnel destroys basically everything in that orbit. Below the density where this happens, it isn't a Kessler cascade in the first place.

You would be forced by (currently around) 2000 tons worth of bullet-mass shrapnel to wait for that shrapnel to de-orbit. Depending on the orbit, this takes months to millenia, because it's determined by atmospheric drag.

The lower the orbit, the better. Starlink's orbits got lowered, this is better vs. that particular issue.

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

#62

Post by childintime »

ben_w wrote: post #38
notahacker wrote: post #33

Earlier quoted context omitted.

> 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. Hard to see how the repositioning appreciably alters this risk, since there are still thousands of satellites in the original plane to get hit by shrapnel from intentionally caused collisions, and the satellites in the lower orbit aren't invulnerable t…

> Hard to see how the repositioning appreciably alters this risk, since there are still thousands of satellites in the same plane to get hit by shrapnel from intentionally caused collisions, and the satellites in the lower orbit aren't invulnerable to it either Yes, but the lower the orbit, the faster atmospheric drag (which isn't zero, just low) cleans up a cascade.

Exactly. And this is likely to be the only valid reason for the orbit change.

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

#63

Post by notahacker »

ben_w wrote: post #38
notahacker wrote: post #33

Earlier quoted context omitted.

> 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. Hard to see how the repositioning appreciably alters this risk, since there are still thousands of satellites in the original plane to get hit by shrapnel from intentionally caused collisions, and the satellites in the lower orbit aren't invulnerable t…

> Hard to see how the repositioning appreciably alters this risk, since there are still thousands of satellites in the same plane to get hit by shrapnel from intentionally caused collisions, and the satellites in the lower orbit aren't invulnerable to it either Yes, but the lower the orbit, the faster atmospheric drag (which isn't zero, just low) cleans up a cascade.

Feel like I'm repeating myself here, but they're moving less than half of them, which is going to have a negligible impact on a state with sufficient ASAT weapons' ability to create a massive mess with the many thousands of Starlink satellites operating in their original plane. Not even like the satellites in the lowest orbit are insulated from the effects of debris cascades set off in higher reaches of LEO either

Plenty of operational reasons to want a large fraction of your constellation in a slightly lower orbit, none of them involve "terrorist states"

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

#64

Post by indoordin0saur »

spiritplumber wrote: post #21
wongarsu wrote: post #17

Earlier quoted context omitted.

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

This can't go up forever. There is only so much mass up there in orbit, and much of it is in low earth orbit so will fall back into the atmosphere quickly as it's trajectory gets knocked off course.

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

#65

Post by indoordin0saur »

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…

Very well put. It also seems like there's a limit to how bad Kessler syndrome can get. The more debris there is the more collisions, but the more collisions the quicker the debris collides with itself and de-orbits.

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

#66

Post by indoordin0saur »

perilunar wrote: post #48
tlb wrote: post #22

Earlier quoted context omitted.

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…

I guess if a collision ruptures a pressurised tank, or causes an actual explosion then you could end up with a higher-than-orbit speed?

Possibly. But more likely the thrust from escaping gas will push it in a direction to either slow the orbit down or make it more eccentric and unstable.

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

#67

Post by tlb »

indoordin0saur wrote: post #66
perilunar wrote: post #48

Earlier quoted context omitted.

I guess if a collision ruptures a pressurised tank, or causes an actual explosion then you could end up with a higher-than-orbit speed?

Possibly. But more likely the thrust from escaping gas will push it in a direction to either slow the orbit down or make it more eccentric and unstable.

Right, if there's something like a small hole in a pressure tank, it's very unlikely to be aligned exactly with the CG, so the tank will spin around and the net thrust will be near zero.

If a pressure tank splits in half, both halves will fly away but that's a very inefficient way of using the energy in the gas, so the added velocity will be a small fraction of the speed of sound in the gas, which is 1/6 of orbital speed for hydrogen, less for any other gas.

You can't really get much of a chemical explosion because the fuel and oxidizer both disperse very quickly in space.

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

#68

Post by NetMageSCW »

TOMDM wrote: post #4
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 ?

Because Kessler syndrome means you don't need to hit all 10k yourself. Lowering the orbits just means that we get back to normal faster, not that the it's impossible.

Stop trying to make Kessler syndrome a thing. Kessler syndrome isn’t a thing, and it will never be a thing.

PS The original paper expects the cascade to take decades to centuries. No one can afford to shoot down Starlink except SpaceX.

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

#69

Post by NetMageSCW »

aucisson_masque wrote: post #9
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 don’t need 10k missiles. You need just one to blow up all of starlink satellites. This is like bowling, you hit one, it hits the other one etcétéras.

That is not how it works at all.

Imagine using a rocket and blowing up one car on a highway - how many other cars will actually be affected? How many cars on other highways will be affected?

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

#70

Post by NetMageSCW »

ben_w wrote: post #43
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 ?

Looking at the price of industrial lasers, right now the only thing stoping a random 3rd world terrorist cell from being able to afford to destroy all of them is the adaptive optics to compensate for atmospheric turbulence. Well, that and the fact that so much of the stuff on Amazon etc. that's listed as "welding laser" is actually a soldering iron.

I think you severely underestimate the amount of power you would need to damage some Starlink satellites in the 4 minutes they would be visible while tracking them at ridiculous speeds.
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