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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

#31

Post by bagels »

est31 wrote: post #19
barbazoo wrote: post #17

Earlier quoted context omitted.

> Here's the text without having to execute arbitrary code from twitter Ok, I'll bite, what's this about? What "arbitrary" code is being executed when you visit Twitter?

You're running Javascript. It's sandboxed, which is why I have it enabled by default, but often the javascript in a website is made to spy on you and your behaviour. It's not on your side but on the side of the people who made the website. Personally I'm ok when something like discord breaks as it contains real time updates. But twitter just displays a bunch of text and pictues in a non real time manner. Even video c…

You can put a video on a page without js, but a lot of your customers would have a poor experience.

Re: Eu_sst: 20% probability for large satellite collision

#32

Post by eqvinox »

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.

Put quite simply - the energy doesn't go into destroying objects. There's only a very small amount going into heating things up from mechanical deformation [and a bit into spinning], but fundamentally, splitting something in a million pieces just means you have a million pieces that have the same total kinetic energy in orbit.

However, they also exchange kinetic energy & impulse with each other, meaning you get a mix of slower and faster pieces. This is what the Gabbard diagram shows:

https://twitter.com/EU_SST/status/1380443036862316545

Anything that is sped up in the collision (i.e. "steals" energy from another piece) has the same perigee (orbit low point) but a higher apogee (orbit high point.) The reverse happens to anything slowed down / stolen from. That's why the graph looks like open scissors.

Some pieces with lower perigee will friction against earth atmosphere and burn up, but the ones with higher apogee become a serious problem...

(also, for anyone who can't remember to distinguish apogee & perigee: think of your periphery, it's the things close to you :D)

Re: Eu_sst: 20% probability for large satellite collision

#33

Post by mnw21cam »

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.

A lot of the debris won't stay in the same orbit. It'll be like a mini-explosion, spraying out debris in every direction, but then add the existing velocity to that. So yes, the debris will be in another orbit. The question is, how much of a change occurs.

In the twitter thread, there is a Gabbard diagram that shows a prediction of the orbits that the pieces will end up in. The satellites currently have a reasonably circular orbit, with apogee (highest point) and perigee (lowest point) about 800km. After the collision, the apogee is likely to be higher and the perigee is likely to be lower, so the orbits won't be circular any more.

The way this happens is - if the debris piece is knocked directly backwards, then its apogee will be about the same, but its perigee will be lower. If it is knocked forwards (yes, that can happen), then the apogee will be raised, and the perigee will be about the same, and the piece could remain in orbit for a long time. If it is knocked up or down, then both the perigee will be lowered and the apogee will be raised. If the perigee is low enough, then the pieces will scrape through the upper levels of the atmosphere, and de-orbit eventually.

It looks like the prediction is for the lowest perigee to be about 200km. It may take a long time for even those pieces to de-orbit.

Re: Eu_sst: 20% probability for large satellite collision

#35

Post by mnw21cam »

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?

Some of the pieces will have a lower orbit, which might be low enough for them to scrape the atmosphere and bring them down. Some of the pieces will be placed into a higher orbit (although the lowest point won't be raised).

Re: Eu_sst: 20% probability for large satellite collision

#39

Post by JshWright »

eqvinox wrote: post #32
moring wrote: post #23

Earlier quoted context omitted.

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.

Put quite simply - the energy doesn't go into destroying objects. There's only a very small amount going into heating things up from mechanical deformation [and a bit into spinning], but fundamentally, splitting something in a million pieces just means you have a million pieces that have the same total kinetic energy in orbit. However, they also exchange kinetic energy & impulse with each other, meaning you get a mix…

I think of "peripheral" as being "far from the center of my vision".

Fortunately, years of Kerbal Space Program means the apo/peri prefixes are pretty solidly ingrained.

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