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Eu_sst: 20% probability for large satellite collision

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Re: Eu_sst: 20% probability for large satellite collision

#21

Post by scanny »

undecisive wrote: post #6

In summary, a rocket body and an old weather satellite want to have a nice big hug. At high speed. Producing a cloud of 4 million fragments. 400 of which will bigger than 20cm. Except that they'll probably miss (by about 10m). Probably. Really interesting how much of this is statistical probabilities, and how much we can model about this. Right down to particle sizes. And yet, I still have so many questions. Mostly i…

I’m curious as to how they get those sizes and quantities! Too they have cad models of both objects or are they just taking the radar returns and material and making an estimate?

Re: Eu_sst: 20% probability for large satellite collision

#23

Post by moring »

AlphaGeekZulu wrote: post #13

The two satellites involved are: OPS 6182 (10820, 1978-042A): https://www.n2yo.com/satellite/?s=10820 SL-8 R/B (12443, 1981-041B): https://www.n2yo.com/satellite/?s=12443 They are on head-on course. With a probability of about 80 percent they will miss each other. With a probability of more than 20 percent they will impact at a speed of more than 50000 km/h in an altitude of 780 km. The two objects are not important…

Can somebody give a layman explanation why the debris would stay in the same orbit? I would expect a lot of energy to go into destroying both objects, especially in a head-on collision.

Re: Eu_sst: 20% probability for large satellite collision

#24

Post by stonesweep »

AlphaGeekZulu wrote: post #13

The two satellites involved are: OPS 6182 (10820, 1978-042A): https://www.n2yo.com/satellite/?s=10820 SL-8 R/B (12443, 1981-041B): https://www.n2yo.com/satellite/?s=12443 They are on head-on course. With a probability of about 80 percent they will miss each other. With a probability of more than 20 percent they will impact at a speed of more than 50000 km/h in an altitude of 780 km. The two objects are not important…

Does the debris have a degrading orbit and eventually get pulled earthward and burn up on entry? Or is that chaff out there floating around forever just outside the gravitational pull?

Re: Eu_sst: 20% probability for large satellite collision

#26

Post by bagels »

scanny wrote: post #21
undecisive wrote: post #6

In summary, a rocket body and an old weather satellite want to have a nice big hug. At high speed. Producing a cloud of 4 million fragments. 400 of which will bigger than 20cm. Except that they'll probably miss (by about 10m). Probably. Really interesting how much of this is statistical probabilities, and how much we can model about this. Right down to particle sizes. And yet, I still have so many questions. Mostly i…

I’m curious as to how they get those sizes and quantities! Too they have cad models of both objects or are they just taking the radar returns and material and making an estimate?

For well known objects like these, the mass and approximate size is known. You can Google them to find values even. The positional uncertainty and lack of data about attitude lead to modelling the objects as spheres as not so bad a choice.

One algorithm that is sometimes used: https://link.springer.com/article/10.1007/BF03546397

Re: Eu_sst: 20% probability for large satellite collision

#27

Post by toomuchtodo »

stonesweep wrote: post #24
AlphaGeekZulu wrote: post #13

The two satellites involved are: OPS 6182 (10820, 1978-042A): https://www.n2yo.com/satellite/?s=10820 SL-8 R/B (12443, 1981-041B): https://www.n2yo.com/satellite/?s=12443 They are on head-on course. With a probability of about 80 percent they will miss each other. With a probability of more than 20 percent they will impact at a speed of more than 50000 km/h in an altitude of 780 km. The two objects are not important…

Does the debris have a degrading orbit and eventually get pulled earthward and burn up on entry? Or is that chaff out there floating around forever just outside the gravitational pull?

In the case of these objects, at ~800km, the time for orbital decay is often measured in decades.

Re: Eu_sst: 20% probability for large satellite collision

#28

Post by bagels »

undecisive wrote: post #6

In summary, a rocket body and an old weather satellite want to have a nice big hug. At high speed. Producing a cloud of 4 million fragments. 400 of which will bigger than 20cm. Except that they'll probably miss (by about 10m). Probably. Really interesting how much of this is statistical probabilities, and how much we can model about this. Right down to particle sizes. And yet, I still have so many questions. Mostly i…

It would probably take longer than the notice you might get of a potential collision (5-7 days)

Re: Eu_sst: 20% probability for large satellite collision

#29

Post by hn_throwaway_99 »

moring wrote: post #23
AlphaGeekZulu wrote: post #13

The two satellites involved are: OPS 6182 (10820, 1978-042A): https://www.n2yo.com/satellite/?s=10820 SL-8 R/B (12443, 1981-041B): https://www.n2yo.com/satellite/?s=12443 They are on head-on course. With a probability of about 80 percent they will miss each other. With a probability of more than 20 percent they will impact at a speed of more than 50000 km/h in an altitude of 780 km. The two objects are not important…

Can somebody give a layman explanation why the debris would stay in the same orbit? I would expect a lot of energy to go into destroying both objects, especially in a head-on collision.

Conservation of momentum. All of the teeny little bits of the two colliding objects still have the exact same average momentum of the two original objects, now there are just hundreds of thousands of them flying off in slightly different directions. The movie Gravity actually gives a fairly good, if overly dramatized, example of what happens when objects collide in space.

Re: Eu_sst: 20% probability for large satellite collision

#30

Post by the_duke »

Buttons840 wrote: post #18

Do near misses (hopefully) like this happen without us knowing, or do we track almost everything in orbit?

The current tracking infrastructure detects pieces down to 10cm. All of those are catalogued, get identification numbers, and are tracked.

Active sats often do small collision avoidance maneuvers.

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