Starlink Thread (split from SpaceX)

[Rakaydos]

5 minutes ago, Val said:

That's not true. A point size object, can still hit something that has size, and be hit by it, if the path of point intersects the other object.

Mathematically, speaking.

If we're assuming Starlink is a point, why are we assuming other objects are not a point?

[kerbiloid]

Because the Starlink was considered as a point being compared to a much larger object (taken 20x20 m) when the Starlink size is negligible.

In Starlink-Starlink calculations one of Starlinks was considered as 1x5 m object (according to its picture), another one as a point.
If treat both ones as 1x5 m objects, things get even worse.

[Rakaydos]

17 minutes ago, kerbiloid said:

Because the Starlink was considered as a point being compared to a much larger object (taken 20x20 m) when the Starlink size is negligible.

In Starlink-Starlink calculations one of Starlinks was considered as 1x5 m object (according to its picture), another one as a point.
If treat both ones as 1x5 m objects, things get even worse.

But they arnt static objects. Hence my comment about negative feedback loops. Any deviation from synchronicity is corrected.

Likewise, anytime the chance of collision between two satelites will be greater than 1 in 10,000, ESA's standard is to correct to avoid any collision.

There's no "combinarial explosion", because the maneuvers are too minor to affect anything except the two satellites directly involved.

[kerbiloid]

8 minutes ago, Rakaydos said:

But they arnt static objects

Plays no role. While one escapes from your way, another one enters.

8 minutes ago, Rakaydos said:

anytime the chance of collision between two satelites will be greater than 1 in 10,000, ESA's standard is to correct to avoid any collision.

So, they should be maneuvering constantly. And they have fuel for just several thousand corrections.

8 minutes ago, Rakaydos said:

There's no "combinarial explosion", because the maneuvers are too minor to affect anything except the two satellites directly involved.

1200 * 1200 = 1 440 000
12 000 * 12 000 = 144 000 000

When you have 10 times more sats, you have 100 times more possibilities of collision. So, the system complexity grows "exponentially", not linearly.
As well, "exponentially" grows the collision avoidance system complexity. Until the decisions produced by the prevention system get nearly random.

Edited September 4, 2019 by kerbiloid

[Rakaydos]

8 minutes ago, kerbiloid said:

 

So, they should be maneuvering constantly. And they have fuel for just several thousand corrections.

Citation, please.

[kerbiloid]

Just now, Rakaydos said:

Citation, please.

Read the thread, please.
"10 km/s" of total delta-V
"1 m/s" per correction.
So, 10 000 corrections.
Minus deorbit, minus keeping orbit altitude, so several thousand remains.

[Technical Ben]

1 hour ago, kerbiloid said:

Didn't you read my post?
I was calculating chances (or probability if you wish) of a collision between a Starlink sat and either another one Starlink sat, or some space object 20x20 m (a big sat or an orbital ship with antennas, solar panels, possibly an upper stage) per reasonable amount of time (a day, a month, a year, a decade).

The given data from wiki describes the Starlink distribution in space.

Other starlink sats won't collide... because they are not aiming at each other. That's like saying the car in australia will collide with the one in canada... because "chances".

3 minutes ago, kerbiloid said:

Read the thread, please.
"10 km/s" of total delta-V
"1 m/s" per correction.
So, 10 000 corrections.
Minus deorbit, minus keeping orbit altitude, so several thousand remains.

Wait. That's not how this works. That's not how anything works!

The 2 sats involved move. NOT the other 1200 or 12,000. Only the two involved.

 

[kerbiloid]

8 minutes ago, Technical Ben said:

Other starlink sats won't collide... because they are not aiming at each other.

They are crossing each other's orbital plane at close altitudes.

8 minutes ago, Technical Ben said:

That's like saying the car in australia will collide with the one in canada... because "chances".

Geostationary orbits 340 km high? That's cool.

P.S.
But I mostly "worry" (actually, not - see above, why) not about Starlink self-collisions, but about their collision with non-Starlink sats.

8 minutes ago, Technical Ben said:

The 2 sats involved move. NOT the other 1200 or 12,000. Only the two involved.

Then no problem, the space is empty.

Edited September 4, 2019 by kerbiloid

[James Kerman]

Some content has been removed due to the debate becoming personal. Please keep the discussion civil.

[Technical Ben]

15 minutes ago, kerbiloid said:

They are crossing each other's orbital plane at close altitudes.

Geostationary orbits 340 km high? That's cool.

P.S.
But I mostly "worry" (actually, not - see above, why) not about Starlink self-collisions, but about their collision with non-Starlink sats.

Then no problem, the space is empty.

When? When do they cross each others orbital plane?

Could you make this in KSP? It's like a couple of mins in Hyperedit. See if it magically collides.

Could they collide with non-Starlink sats? Yes. Can anything bad happen. Yes. I don't know if it's worth our time worrying or fighting against it though. If it was down to me, I'd ban anything above running, and insist every dog be kept outside on a lead. Oh cats... I'll have to think very hard for what to do with cats... mine keeps knocking my spaceship collecting off the shelf and breaking it!

[Rakaydos]

53 minutes ago, kerbiloid said:

They are crossing each other's orbital plane at close altitudes.

Geostationary orbits 340 km high? That's cool.

P.S.
But I mostly "worry" (actually, not - see above, why) not about Starlink self-collisions, but about their collision with non-Starlink sats.

Then no problem, the space is empty.

You're REALLY having problems with this "synchronicity" concept when it comes to deconflicting orbits.

A chinook helicopter has two sets of rotors which overlap. (yes, they're different heights, but we'll assume we're talking on startup, when the blades flex downward due to gravity) Clearly this is a severe design flaw that calls for grounding every helicopter ever!

Except... they don't. Because the two rotors will never come into conflict, because they are synchronized so as to never come into conflict.

 

The same applies to orbits. Two objects can have their orbits intersect twice, but be synchronized that whenever one is crossing the point of potential collision, the other is on the entire opposite side of the planet. And vice versa when the other one reaches an intersect point. This requires a bit of orbital maintenance, and that's OK and planned for. This is normal for satellite operations, nit the end of the world as we know it.

[Elthy]

@kerbiloid You assume that satellites are chaoticaly bouncing arond like atoms in a gas, but thats not the case. In one orbital layer with different inclinations all inclinations will likely be >100m apart in height, also they can make the orbits resonant. Both variants reduce the risk of collision in the constellation itself to zero, its physicaly impossible for them to ever crash. Other individual sats can only crash if they intersect starlinks orbits, but even then its realy rare (as ive shown using your numbers), other constellations will use different orbits or resonance just like starlink itself.

Also SpaceX (and everyone else if they publish) will know the location of every sat quite precisely, they need to because they are using focused beams for transmission. Especialy coupled with laser links between the sats that results in high predictability of the orbits, greatly reducing the size of the 1/10000 collision sphere.

[mikegarrison]

I feel like I should once again post: https://en.wikipedia.org/wiki/2009_satellite_collision

We know it is not impossible for satellites to collide, because it has already happened. Both of them were in the database. One of them was being actively managed. They had been predicted to miss each other by 584 meters. They were in very different orbital inclinations. And yet....

[Guest]

That was completely different. In case of Starlink, not only are they all controlled, they are deliberately set up to be in synchronous orbits. Outside a satellite drifting out of its assigned position, it'll never even come close to any other. 600m is very close in orbital terms.

If all not-Starlink satellites keep out of the Starlink-specific plane at all phases of their flight except launch, then a collision is not possible unless one of the Starlinks goes completely out of alignment. 

[tater]

Collision probability is not zero, even for 2 Starlinks. One fails, orbit changes slightly, collision is now possible. It can none the less be very, very low. Co-orbital collisions are likely not a problem, small changes due to sats naturally deorbiting (uncontrolled) mean that the closure rate will be really small. Crossing collisions are more of an issue, I think.

The 10km/s per Starlink was a number I read someplace making assumtions about their propellant load for the krypton thrusters. It could be substantially less, that assumption might have been 100kg of props. If it's only 10kg, then they have ~1 km/s. Regardless, they have a decent dv---assuming they are functioning.

[mikegarrison]

1 minute ago, Dragon01 said:

That was completely different. In case of Starlink, not only are they all controlled, they are deliberately set up to be in synchronous orbits. Outside a satellite drifting out of its assigned position, it'll never even come close to any other. 600m is very close in orbital terms.

If all not-Starlink satellites keep out of the Starlink-specific plane at all phases of their flight except launch, then a collision is not possible unless one of the Starlinks goes completely out of alignment. 

1) we have already seen that some Starlink sats may be d.o.a. and uncontrolled from the moment they are released.

2) I do expect that actively controlled Starlink sats will be very unlikely to hit each other, but

3) They will have plenty of chances to hit other sats. I mean, you could say "if all non-Iridium sats just keep out of the Iridium plane of operations then Iridium sats can never be hit" except it was an Iridium sat that was hit. Iridium is actually quite similar to Starlink except smaller in scope (and bigger in physical size).

[tater]

4 minutes ago, mikegarrison said:

3) They will have plenty of chances to hit other sats. I mean, you could say "if all non-Iridium sats just keep out of the Iridium plane of operations then Iridium sats can never be hit" except it was an Iridium sat that was hit. Iridium is actually quite similar to Starlink except smaller in scope (and bigger in physical size).

Exactly. Also, any other sat at a higher alt that is naturally decaying at EoM could potentially cross the orbital planes used by Starlink, as well as any failed or otherwise deorbiting Starlinks.

I suppose they could put a grapple of sorts on Starlin sats, and if one fails in a concerning way they could move a neighbor to deorbit it. For huge constallations this might be a reasonable regulatory ask--make it so nearby sats in the constellation can act as tugs to deorbit one that is non-functional.

[Terwin]

17 minutes ago, tater said:

Collision probability is not zero, even for 2 Starlinks. One fails, orbit changes slightly, collision is now possible. It can none the less be very, very low. Co-orbital collisions are likely not a problem, small changes due to sats naturally deorbiting (uncontrolled) mean that the closure rate will be really small. Crossing collisions are more of an issue, I think.

You are assuming that the starlink sat thrusts in a random direction and keeps traveling in that direction.

That would mess up the constellation, it is far more likely that an avoidance maneuver will first involve moving out of the way, the moving back into position.

This process (combined with normal station-keeping) keeps the constellation in place the way it was designed, as well as ensuring that no 2 starlink satellites are ever close enough to endanger each other(except between launch and arrival at a designated position within the constellation, but that can be planned out in advance to be safe).

With hundreds of KM between any 2 starlink satellites, moving at most 10km(safe passing distance as indicated earlier in the thread) to the side before moving back into position, does not get the maneuver satellite any where near it's closest neighbor.

[mikegarrison]

11 minutes ago, Terwin said:

With hundreds of KM between any 2 starlink satellites, moving at most 10km(safe passing distance as indicated earlier in the thread) to the side before moving back into position, does not get the maneuver satellite any where near it's closest neighbor.

Yes, *active* Starlink sats seem unlikely to hit each other. But dead ones? Orbital precession could easily be a problem.

[Guest]

39 minutes ago, mikegarrison said:

3) They will have plenty of chances to hit other sats. I mean, you could say "if all non-Iridium sats just keep out of the Iridium plane of operations then Iridium sats can never be hit" except it was an Iridium sat that was hit. Iridium is actually quite similar to Starlink except smaller in scope (and bigger in physical size).

By a satellite that did not keep out of its sphere of operations (which is what I meant by "plane"). It didn't hit another Iridium sat, but a defunct Soviet one used for a similar purpose, and using a similar orbit altitude. Yes, if Iridium had an entire altitude band to itself, there would be no collisions involving it. Notice that there were zero collisions involving GPS, GLONASS or Galileo satellites. Those constellation have an entire reserved volume of space which you can pass through, but never orbit anything else in them. Now, you can't go overboard with reserving whole altitude bands, because you'd interfere with missions that require highly eccentric orbits, but Starlink is low enough for this to be a non-issue.

Edited September 4, 2019 by Guest

[mikegarrison]

Just now, Dragon01 said:

By a satellite that did not keep out of its plane. It didn't hit another Iridium sat, but a defunct Soviet one used for a similar purpose. Yes, if Iridium had an entire altitude band to itself, there would be no collisions involving it.

Perhaps I was unclear. Other satellites DO EXIST. Even dead ones like that Kosmos. There is no "clean up debris" tracking station button in Earth orbit.

So yeah, if that dead Kosmos had stayed away from the Iridium orbits then the accident would not have happened. But it didn't. It was uncontrolled and went wherever it felt like going.

[Guest]

1 minute ago, mikegarrison said:

It was uncontrolled and went wherever it felt like going.

This is where you're wrong. It didn't go wherever it felt like going. It went on a fairly predicable path, circling the Earth along its orbit while very slowly spiraling towards it. Satellites don't just change altitude at random. In particular, the Iridium sats have an orbital altitude of about 780km. Kosmos 2251 orbited, when operational, at about 780x800km. They were launched into the same altitude band. If you do that, without ensuring the sats are in synchronous orbits, then a collision is highly likely. In fact, a situation like this is a good way to get a rendezvous at the given parameters, though you'd want the orbits to be coplenar for that.

Synchronous orbits solve that problem by separating satellites in time, but this wasn't done here (in case of Starlink, it is). 

[mikegarrison]

Your faith in in the inviolability of Starlink orbital space is charming, but (IMO) misplaced.

[Terwin]

36 minutes ago, mikegarrison said:

Yes, *active* Starlink sats seem unlikely to hit each other. But dead ones? Orbital precession could easily be a problem.

If you are only talking about dead starlink sats, then you have a much smaller number than 12,000.

When launched, they start an an altitude well below the constellation where non-functional satellites will quickly de-orbit.

When running low on fuel or otherwise having a problem, they are de-orbited, and thus below the plane of the constellation and of no danger.

Even if there is a failure that kills the engines after it gets to the correct position(a much less likely event), the defunct satellite will still eventually de-orbit on it's own, so the time during which it could cause a problem is seriously limited.

(I am not sure if it will take weeks or months before it slows enough to fall out of position, but I strongly suspect that any period of risk will be less than a year long, and by the time it has slowed down enough to get close to a neighbor, it will have slowed enough to lower it's orbit.  Even then, the occurrence will be rare enough that they can track dead starlinks individually while waiting for them to de-orbit)

 

[mikegarrison]

20 minutes ago, Terwin said:

When running low on fuel or otherwise having a problem, they are de-orbited, and thus below the plane of the constellation and of no danger.

Unless the problem is not detected until it is fatal (to the sat). This has happened before, and I'm sure will happen again. Even then the odds favor that it will not hit anything. But the odds favored Iridium too.

I am not arguing that there is much risk of functional Starlink sats hitting each other. But sats do die. And they aren't out there by themselves. And we're talking 12,000 of them.

Edited September 4, 2019 by mikegarrison