Earlier quoted context omitted.
small price to pay for global internet
When it happens, it no longer provides global internet.
interstellar internet ???
SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
41–50 of 105 posts
Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#42Can anyone explain how does one technically lower a satellite?
Eject mass in the forward direction of its current tangent of motion. Slow down to go down.
Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#43From 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.
Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#44Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#45Earlier quoted context omitted.
When it happens, it no longer provides global internet.
interstellar internet ???
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.
Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#46Earlier quoted context omitted.
Eject mass in the forward direction of its current tangent of motion. Slow down to go down.
So, for this they have a bit of expendable extra mass on board? What material is it, would it not cause even more debris then?
https://starlink.com/technology
> Efficient argon thrusters enable Starlink satellites to orbit raise, maneuver in space, and deorbit at the end of their useful life. Starlink is the first argon propelled spacecraft ever flown in space.
And you can see "How Ion Engines Work in Under 60 Seconds" https://www.youtube.com/shorts/_MUv28Yf_4g
Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#47From 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 ?
Or why try to shoot them down when you can also go to the command center and turn them off? Or do a targeted strike on said command center. The sattelites are plentiful and redundant, but the network will collapse very quickly when they're no longer controlled from the surface.
In fact, if SpaceX can no longer do any launches due to whatever reason, Starlink will no longer be feasible after a few year - if I'm reading it correctly, the sattelites have a lifetime of only 5 years, meaning they will have to continually renew them at a rate of 2000 new sattelites a year.
Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#48Earlier 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…
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?
Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#49Earlier 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.
The periapsis will always pass through where the collision happened. To circularize at a higher orbit you would need secondary collisions on the other side of the earth.
You're right that all the fragments will pass roughly through the impact point in orbit. But it's not always the periapsis.
1. The normal or anti-normal delta-v imparted by the explosion/fragmentation (i.e, the velocity imparted perpendicular the plane of initial orbit) will cause the orbital plane of the fragment to change. The new orbit will intersect the old orbit at the impact point. Meanwhile, the eccentricity (the stretch of the orbit), semi-major axis (the size of the orbit) and displacement of periapsis from the impact point (the orientation of the orbit) remains the same as the initial orbit.
2. The prograde and retrograde delta-v (velocity imparted tangential to the orbit) will cause the diametrically opposite side of the orbit to rise or fall respectively. Here too, the new orbit intersects the old orbit at the point of impact. But since the impact point isn't guaranteed to be the periapsis or apoapsis, the above mentioned diametrically-opposing point also cannot be guaranteed to be an apsis.
3. The radial and anti-radial delta-v (this is in the third perpendicular axis) will cause the orbit of the fragment to either dip or rise radially at the point of impact. Again the impact point remains the same for the new orbit. So the new orbit will intersect the old orbit either from the top or the bottom. The new orbit will look like the old orbit with one side lowered and the other side raised about the impact point.
So none of three components of delta-v shifts the orbit from the impact point. You can extrapolate this to all the fragments and you'll see that they will all pass through the impact point. The highest chance of recontact exists there. However the perturbation forces do disperse the crossing point (the original impact point) to a larger volume over time.
Edit: Reading the discussion again, I get what you were trying to say. And I agree. The lowest possible altitude of the fragments in orbit (i.e the periapsis) is the same that of the impact point. So if the impact point is low enough to cause drag, the orbit will decay for sure. There is nothing that demonstrates this better than a Gabbard plot [1][2] - the best tool for understanding satellite fragmentation.
[1] Gabbard Plot Discussion (NASA Orbital Debris Program Office): https://ntrs.nasa.gov/api/citations/20150009502/downloads/20...
[2] Satellite Breakup Analysis (Australian Space Academy): https://www.spaceacademy.net.au/watch/debris/collision.htm
Re: SpaceX lowering orbits of 4,400 Starlink satellites for safety's sake
#50Earlier 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.
Just to elaborate the correct reply given by the others, the perigee of all fragments will be less than or equal to the altitude at impact point. If that's low enough, they will all eventually decay and deorbit. Even the fragments in elongated high-eccentricity orbits will have their orbits circularized by lowering apogee (the perigee is never going to rise) due to air drag. It will eventually spiral into the atmosphere. Here is the best visualization for this phenomenon - the Gabbard plot.
[1] Gabbard Plot Discussion (NASA Orbital Debris Program Office): https://ntrs.nasa.gov/api/citations/20150009502/downloads/20...
[2] Satellite Breakup Analysis (Australian Space Academy): https://www.spaceacademy.net.au/watch/debris/collision.htm