>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 ?
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.
I think it's important to note that not all collisions are equally dangerous. Consider a sat on a polar orbit colliding with one on a equatorial orbit. Or two satellites on different directions. That is going to be spectacular. Otoh, these kind of collisions are unlikely and should be manageable by just assigning certain shells (say 5km) for every possible direction and orientation.
If two Starlink satellites collide that go roughly in the same direction, it's not exactly a huge problem.
I think the biggest issue is to coordinate this and potentially disallow some excentric orbits.
Let me see if I can. Before we go to space, let's try something on the ground. Imagine pitching a ball horizontally. What do you expect if you pitch it too slow? The ball will curve more towards the ground and meet it early, won't it? (In other words, it doesn't go very far and doesn't stay airborne for long). Going from ground to space, this action remains the same. You need to 'lower an orbit'? Reduce its forward velocity. It will curve more towards the planet and reach closer to the ground.
However, there is a bit more detail involved here. Why doesn't the satellite just fall to the Earth? (Please excuse me and disregard this part if you know this already. I'm trying to maintain conceptual continuity.) So, when something is flying horizontally (no aerodynamic forces), we know that its trajectory will curve towards the Earth due to the pull of gravity. If the ground (on Earth) curves as fast as, or even faster than the trajectory's curve, the object will never get an opportunity to even reach the ground. This is 'orbiting'.
Now assume that the satellite is initially in a circular orbit. The gravitational force acting on the satellite at any point in the orbit is perpendicular to the satellite's velocity vector and tangential to the orbit. The satellite will maintain a constant speed at this point, since its velocity and the force are always perpendicular [1]. So, what happens when we reduce the satellite's forward velocity? Just as we've seen with the ball, the satellite's trajectory (orbit) starts to curve more towards Earth. Now a subtle, but important change occurs. The velocity and the gravitational pull are no longer perpendicular! They start to align! And when that happens, the speed MUST increase. So, the satellite is now losing altitude and speeding up simultaneously [2]. At some point, the satellite will pick up enough speed again to 'straighten its curve' and avoid falling to the ground. In effect, the satellite had to compensate for the lost velocity in order to remain in orbit, and it did so by exchanging some of its altitude (gravitational potential energy) for velocity (kinetic energy) [3].
So our satellite 'fell' from where we slowed it down, until it had enough velocity again to maintain orbit. At that point, the gravity and the velocity are parallel again, since it will keep falling otherwise [4]. But since it 'fell from a higher altitude', it's speed is now too high for it to remain at that altitude. The orbital curvature is a bit 'too straight' now and it starts to curve away from Earth. So now we're in the exact opposite situation of what was explained in the last paragraph. The satellite is now climbing back up again! As it happens, the satellite actually climbs back up to the point where we slowed it down! And when at that point, its velocity is exactly the same as what it was, after we had slowed it down! [5] So the satellite did the inverse of what it did earlier - it exchanged kinetic energy to get back its altitude (potential energy). The satellite is now living in cycles juggling kinetic energy and potential energy back and forth. The final effect is that the point in orbit that's diametrically opposite to where you slowed it down, is now at a lower altitude. And thus you've effectively 'reduced the orbit'!
One more detail to pin down. How do we slow down a satellite in the first place? Easy! Push the satellite in the opposite direction of its velocity [6]. This is called 'retrograde thrusting' or 'retro burn'. But that's about as easy as it gets. Remember that unlike on Earth, you don't have a surface (a wall or the ground) to lean against. Imagine pushing something heavy on an ice rink. The good news is that you can still push things on an ice rink. The only catch is that the push force will set both the item and you in motion in opposite directions [7]. And that's exactly what we d...
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[ 2.8 ms ] story [ 36.2 ms ] thread>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 ?
The nasa is pretty scared of it, so is SpaceX.
No;, there is not, particularly in LEO.
If two Starlink satellites collide that go roughly in the same direction, it's not exactly a huge problem.
I think the biggest issue is to coordinate this and potentially disallow some excentric orbits.
However, there is a bit more detail involved here. Why doesn't the satellite just fall to the Earth? (Please excuse me and disregard this part if you know this already. I'm trying to maintain conceptual continuity.) So, when something is flying horizontally (no aerodynamic forces), we know that its trajectory will curve towards the Earth due to the pull of gravity. If the ground (on Earth) curves as fast as, or even faster than the trajectory's curve, the object will never get an opportunity to even reach the ground. This is 'orbiting'.
Now assume that the satellite is initially in a circular orbit. The gravitational force acting on the satellite at any point in the orbit is perpendicular to the satellite's velocity vector and tangential to the orbit. The satellite will maintain a constant speed at this point, since its velocity and the force are always perpendicular [1]. So, what happens when we reduce the satellite's forward velocity? Just as we've seen with the ball, the satellite's trajectory (orbit) starts to curve more towards Earth. Now a subtle, but important change occurs. The velocity and the gravitational pull are no longer perpendicular! They start to align! And when that happens, the speed MUST increase. So, the satellite is now losing altitude and speeding up simultaneously [2]. At some point, the satellite will pick up enough speed again to 'straighten its curve' and avoid falling to the ground. In effect, the satellite had to compensate for the lost velocity in order to remain in orbit, and it did so by exchanging some of its altitude (gravitational potential energy) for velocity (kinetic energy) [3].
So our satellite 'fell' from where we slowed it down, until it had enough velocity again to maintain orbit. At that point, the gravity and the velocity are parallel again, since it will keep falling otherwise [4]. But since it 'fell from a higher altitude', it's speed is now too high for it to remain at that altitude. The orbital curvature is a bit 'too straight' now and it starts to curve away from Earth. So now we're in the exact opposite situation of what was explained in the last paragraph. The satellite is now climbing back up again! As it happens, the satellite actually climbs back up to the point where we slowed it down! And when at that point, its velocity is exactly the same as what it was, after we had slowed it down! [5] So the satellite did the inverse of what it did earlier - it exchanged kinetic energy to get back its altitude (potential energy). The satellite is now living in cycles juggling kinetic energy and potential energy back and forth. The final effect is that the point in orbit that's diametrically opposite to where you slowed it down, is now at a lower altitude. And thus you've effectively 'reduced the orbit'!
One more detail to pin down. How do we slow down a satellite in the first place? Easy! Push the satellite in the opposite direction of its velocity [6]. This is called 'retrograde thrusting' or 'retro burn'. But that's about as easy as it gets. Remember that unlike on Earth, you don't have a surface (a wall or the ground) to lean against. Imagine pushing something heavy on an ice rink. The good news is that you can still push things on an ice rink. The only catch is that the push force will set both the item and you in motion in opposite directions [7]. And that's exactly what we d...
From the looks of it, you still are teaching. Very informative read!
Extra points for non-referenced footnotes! =)
Previously: https://news.ycombinator.com/item?id=46457454
Lower orbits > Increased atmospheric drag > More fuel expended to maintain orbit > Heavier sats due to more fuel > Increased launch cost per unit
Or even: Lower orbits > Increased atmospheric drag > Quicker orbit decay > Shorter lifespan of sats > More frequent launches
Forgive my Kerbal-based space knowledge here.