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Starlink (updates and concerns)


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30 minutes ago, kerbiloid said:

A spherical layer from R1 ro R2.
For the lowest orbits R1~ Rearth + 335 km, R2~ Rearth + 345 km
I take 20 km as the layer radial thickness, as they have described 3 orbit "shells" inside this layer at 5 km from each other.

Starlink satellites are uniformly distributed in this space. There is about 1.5 mln km3 per sat inside this volume.

That is sort of like saying that walking in a park has he same odds of being hit by a vehicle as walking across an interstate.

In this scenario SpaceX has 60 satellites 'driving' down each of ~200 well-known roads with a well known spacing, so that anyone who wants to cross those roads can plan months in advance and know exactly when it will be clear.  Or they can use the pedestrian bridges(aka different orbital altitude) and never even touch the roads in question.

 

I believe the process is, that whoever launches first has the right of way, and as anyone who launches later knows exactly where your satellite will be, so they are responsible for avoiding it(which is why SpaceX was supposed to avoid the ESA satellite and not the other way around).  Unless you are experimenting with aerobraking(like SpaceX is with those 3 starlinks), you should be able to calculate any potential collisions days in advance, and easily avoid it with just a couple m/s at the right time.

 

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1 minute ago, Terwin said:

That is sort of like saying that walking in a park has he same odds of being hit by a vehicle as walking across an interstate.

Poetry is nice, but what about numbers?

2 minutes ago, Terwin said:

In this scenario SpaceX has 60 satellites

12 000, and they don't driving down, they fill the space.

+ OneWab ones is madness is contagious.

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Just now, kerbiloid said:

12 000, and they don't driving down, they fill the space.

Clearly you didn't actually read the comment you were replying to.

Nor do you have any sense of scale if you think even 12,000 sats in a single orbit "fill the plane." 

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11 minutes ago, kerbiloid said:

I don't think, I have calculated, and see no opposite calculations.

Then you are blind.

Let me go over this again, one more time.

The circumference of the earth is over 40,000 km. We'll use this as an approximation of the hoop of our orbital path, which is even longer, because it's not at earth's surface.

Lets assume all 12,000 sats are in the same orbit. They arnt, but lets assume they are, just to show how ridiculus your claim is.

The sats all fit in a city bus-sized fairing. Lets be generous and call each satelite 3m by 1.5m. The solar panel folds out in the short direction about 5 times, so lets call the whole sat 3mx9m 

So we've got 12,000 satelites in 40,000 km. That's 3 satelites every 10 km, or about a sat every 2 miles. Each sat is nowhere near 2 miles long. To bring back the traffic analogy, there's plentry of room to merge with the freeway traffic.

Edited by Rakaydos
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Starlink is supposed to have (just the first few thousand?) in 24 planes, BTW. some are at 1100 km, too, so it's nothing like 12k in one plane, so maybe more like 1 every 240 km in a plane.

 

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1 minute ago, tater said:

Starlink is supposed to have (just the first few thousand?) in 24 planes, BTW. some are at 1100 km, too, so it's nothing like 12k in one plane, so maybe more like 1 every 240 km in a plane.

 

with how out of touch with reality Kerboiloid seems to be, I really wanted to drive the point home.

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@kerbiloid: Lets go with your numbers of one collision in every 80000 orbits in the lower layers. As an orbit takes about 90min thats over 13 years per necessary course correction of a single star link satellite (the one that would have collided). So for evey other sat in that layer one starlink sat (out of the whole constellation) has to do a course correction every 13 years, the others none at all. This is an incredibly low number!

Actually its way to low since orbital paths arent measured precisely, so they will maneuver even with a low chance of a collision, ESA states over 1/10000 as the limit. This would result in a course correction every 12h for one of all SpaceX sats in the layer (about 7500) -> Each one has to do a correction about every 10 years for every other sat in the same layer.

There isnt much flying around that low other than other planned mega constellations, which will propably coordinate with SpaceX, reducing the collision chance (and thus need for maneuver) drasticaly.

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9 minutes ago, Elthy said:

@kerbiloid: Lets go with your numbers of one collision in every 80000 orbits in the lower layers. As an orbit takes about 90min thats over 13 years per necessary course correction of a single star link satellite (the one that would have collided). So for evey other sat in that layer one starlink sat (out of the whole constellation) has to do a course correction every 13 years, the others none at all. This is an incredibly low number!

I'm not sure you are making the point you think you are making. Even if any individual Starlink satellite only has to adjust orbits every 13 years, that would still be about 1000 adjustments a year for the entire constellation. Three per day. One every 8 hours.

Edited by mikegarrison
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No, you are missunderstanding me (its hard to write that correctly). In this scenario, one sat had to move after 13 years to avoid a collision, the others can remain stationary. After about another 13 years another maneuver would be neccessary, propably by a different sat. If there is an imminent collision, only the affected sat has to move, not the whole constellation.

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12 minutes ago, Elthy said:

No, you are missunderstanding me (its hard to write that correctly). In this scenario, one sat had to move after 13 years to avoid a collision, the others can remain stationary. After about another 13 years another maneuver would be neccessary, propably by a different sat. If there is an imminent collision, only the affected sat has to move, not the whole constellation.

Um, you are saying there will only be one adjustment every 13 years? That's obviously not correct. They only have had 60 sats up for a few months and they have already had a conflict.

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The problem with big numbers is hard to grasp sometimes.

In the US last year, there were about 0.65 fatalities per 100 million passenger miles driven by cars. That's great, right? Except if commercial airplanes had that fatality rate, there would be over 40,000 people killed worldwide on commercial flights every year.

12000 satellites is a LOT of satellites, and even if the per satellite rate of conflicts is quite low, that's not enough. It needs to be really, really really quite low, or else there will be problems.

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30 minutes ago, mikegarrison said:

'm not sure you are making the point you think you are making. Even if any individual Starlink satellite only has to adjust orbits every 13 years, that would still be about 1000 adjustments a year for the entire constellation. Three per day. One every 8 hours.

Good thing they have like 10 km/s of dv, and those maneuvers are what, 1 m/s?

The bigger issue is knowing to do the evasions that often, and not missing any ;)

 

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Just now, tater said:

Good thing they have like 10 km/s of dv, and those maneuvers are what, 1 m/s?

The bigger issue is knowing to do the evasions that often, and not missing any ;)

That was my point. Having 10 km/s for each sat isn't important if each sat has an avoidance maneuver every 10 years. But if each sat has an avoidance maneuver every 10 years, that means roughly 3 per day for whoever is watching the constellation. They have to watch 12000 of them 24/7 and make sure that the one maneuver that happens on each shift (on average) is done correctly. Without fail. Every time.

If those numbers are correct, it means they are going to have a pretty big job that either humans or maybe computers will have to do. And do it reliably.

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1 hour ago, mikegarrison said:

If those numbers are correct, it means they are going to have a pretty big job that either humans or maybe computers will have to do. And do it reliably

Likely a big reason why they chose to go the AI route, with human oversight. It doesn’t have to be perfect, it only has to pare out a small enough number of potential collisions that the human overseers can reasonably verify and actively monitor. 

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While we have no info on how effective the Starlink satellites autonomous collision avoidance system is, I think it's not unreasonable to assume that they've at least considered the possibility of a large number of anti-collision maneuvers by the mere fact that such a feature was included. 

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1 hour ago, mikegarrison said:

That was my point. Having 10 km/s for each sat isn't important if each sat has an avoidance maneuver every 10 years. But if each sat has an avoidance maneuver every 10 years, that means roughly 3 per day for whoever is watching the constellation. They have to watch 12000 of them 24/7 and make sure that the one maneuver that happens on each shift (on average) is done correctly. Without fail. Every time.

If those numbers are correct, it means they are going to have a pretty big job that either humans or maybe computers will have to do. And do it reliably.

I think they said they plan on the constellation doing it itself---then of course we need to look at the failure rate for deciding to do THAT, and we're in the same boat, lol.

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16 hours ago, tater said:

yeah, but nuclear weapons platforms...

Iirc, there should be 432 of them or so. Definitely not 12 000.

16 hours ago, Rakaydos said:

The circumference of the earth is over 40,000 km. We'll use this as an approximation of the hoop of our orbital path, which is even longer, because it's not at earth's surface.

Lets assume all 12,000 sats are in the same orbit. They arnt, but lets assume they are, just to show how ridiculus your claim is.

The sats all fit in a city bus-sized fairing. Lets be generous and call each satelite 3m by 1.5m. The solar panel folds out in the short direction about 5 times, so lets call the whole sat 3mx9m 

So we've got 12,000 satelites in 40,000 km. That's 3 satelites every 10 km, or about a sat every 2 miles. Each sat is nowhere near 2 miles long. To bring back the traffic analogy, there's plentry of room to merge with the freeway traffic.

Are you aware of the word inclination?
Please, at last have a look at the wiki table in my calculation post to realize the picture of reality.

14 hours ago, Elthy said:

Lets go with your numbers of one collision in every 80000 orbits in the lower layers. As an orbit takes about 90min thats over 13 years per necessary course correction of a single star link satellite (the one that would have collided).

No. You can't just multiply these values.
It's like you have a new probability test every 90 min.
As in a single test the probability of crash is p, so, the probability of not crash is (1-p).
The probability of not crash in n tests is (1-p)n.
The probability to crash in n tests is 1-(1-p)n
So, if take 80 000 orbits and probability of crash, say, =10-6, you get 1-(1-10-6)80 000 ~=0.077 probability of crash, 1:13.
So, if take 10 000 orbits, you get 1-(1-10-6)10 000 ~=0.01 probability of crash, 1:100.
The dependence is not linear.

(Of course, this is a simplified calculation, as the orbiting is not discrete, so instead of 90 min long test we should integrate formulas ad so on, but it looks enough good for rough estimaton).

14 hours ago, Elthy said:

Actually its way to low since orbital paths arent measured precisely, so they will maneuver even with a low chance of a collision, ESA states over 1/10000 as the limit.

And the greater is their amount, the more often they need to do this. And the more often not one, but several of them, to avoid collisions with having just maneuvered neighbor satellite (whatever the "neighbor" means for satellites on crossing orbits).

13 hours ago, tater said:

Good thing they have like 10 km/s of dv, and those maneuvers are what, 1 m/s?

104 reserved corrections is not that much if there is ~103 potential objects to be evaded for 104 orbit turns.

Also, at 300 km and having that sail on top they need some fuel to raise orbit from time to time.
Let's recall how long do debris live in similar orbits without engine burns.

[Snip]
"He is cheating in chess!"

All my calculations are available in the post. Maybe there is a logical or calculation error, why not, but I don't see it.
So, please, feel free to find an error in the calculations and untroll their result.

[Snip]

I'm optimistic in this sense, I think this project will be cancelled after 2-3 launches more.

Edited by James Kerman
redacted by a moderator
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13 minutes ago, Wjolcz said:

Why?

Upd. to say more accurately.
Do you see a Falcon launch every two weeks, every second with Starlinks?
Do you see a Falcon launch with Starlink every two weeks, the every second launch of Falcons?
They need at least 50 Starlink launches next 4 years (see the table)

Edited by kerbiloid
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12 minutes ago, kerbiloid said:

Do you see a Falcon launch every two weeks, every second with Starlinks?

We've already seen Falcon being launched every two weeks or so, so not impossible.

13 minutes ago, kerbiloid said:

Do you see a Falcon launch with Starlink every two weeks, the every second launch of Falcons?

As I said previously: we've already seen Falcon being launched two times a month. If they can do that with customers then they can do that internally. In fact, it's probably easier to control the whole production, payload mating, etc. process internally than when you are a launch provider for someone else.

16 minutes ago, kerbiloid said:

They need at least 50 Starlink launches next 4 years (see the table)

Their current record of total rocket launches in a year is 19. Not impossible.

Now, I know it's a VERY BIG "if"at the moment, but if they use the Starship they won't need this many Falcon launches to complete the constellation.

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