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 (an old Russian rocket piece and an old US weather satellite).
But upon impact, the objects will create a large cloud of debris, that might collide with more objects, in the worst case in a chain reaction.
The danger is not falling debris, but that they will produce more damage in their orbit, maybe hitting more essential space equipment in the future.
No need to hide in a bunker.
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:
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)
Fortunately, years of Kerbal Space Program means the apo/peri prefixes are pretty solidly ingrained.
…well I guess the "center of vision" is the center of the orbit ellipse… ;D
(just trying to salvage the mnemonic aid for myself)
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.
> UPDATE: #EUSST’s network of sensors has only detected a single object or echo at passes over three radars after close approach. Most likely, the collision between SL-8 R/B and OPS 6182 did not take place. We will continue observing the objects to confirm this assessment.
(Link further in thread.)
Edit: as of 2021-04-09T20:21:00Z EUSST thinks they missed. https://twitter.com/EU_SST/status/1380601898164744199
next anticipated contact with OPS 6182 at 20:00UTC https://platform.leolabs.space/catalog/L11618#next-planned-p...
So what's that, about 90 minutes from now assuming I've got the right info?
date -d "2021-04-09T17:18:21 UTC"
It appears we have already passed the threshold at some altitudes, so a satellite collapse will happen in the future, but probably not for hundreds of years.
Active sats often do small collision avoidance maneuvers.
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 involving the maths from https://what-if.xkcd.com/13/ and whether we could push either of them out of the way...
One algorithm that is sometimes used: https://link.springer.com/article/10.1007/BF03546397
Update: according to #EUSST's latest estimates using data from its surveillance radars, the close approach between #space objects SL-8 R/B & OPS 6182 expected by tomorrow will have a miss distance under 10m and a Scaled Probability of Collision over 20%! +updates to follow soon
See the below plot for the conjunction plane at Time of Close Approach (TCA) #EUSST #spacedebris #space
Update: #EUSST simulations indicate that the potential collision between the two #space objects would generate more than 4 million fragments. This plot shows the Delta-V distribution of the whole cloud of fragments #spacedebris
More than 400 of the fragments generated by the potential collision would be larger than 20cm. Gabbard diagram shows the extent of orbital regimes that these simulated fragments would reach. #EUSST continues monitoring the probability of collision. Stay tuned for more updates.
Latest update: according to #EUSST the close approach between #space objects SL-8 R/B and OPS 6182 remains stable in geometry and in Scaled Probability of Collision. Miss distance would be ~21m and Scaled PoC over 20%. This should be the last estimate until TCA.
[Er… commit = comment… TGIF, leaving it in for fun ;D]
Also, it's 17:41 UTC now... the events of this post should be occuring now. Or not occuring.
Mine isn't publicly accessible so never gets throttled.
Ok, I'll bite, what's this about? What "arbitrary" code is being executed when you visit Twitter?
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 can be played back without any js.
True, you're right.
Well, yes and no. Narrow scope in terms of what other programming languages offer, yes. But in terms of limiting the amount of information that can leak from the user (you and your browser), it's not that narrow. And since est31 is making the privacy-argument, I'm guessing they are referring to that.
Cover Your Track by EFF showcases how much information is actually leaking and what Twitter et al could do with it: https://coveryourtracks.eff.org/
Yes it is. It's not system level, but it is indeed arbitrary code - users have no lasting visibility into what it's doing, and little ability to control it.
Browsers have had a pretty naive threat model, up until recent Firefox with its new resist fingerprinting feature. Seemingly innocuous things like reporting your window size are vulnerabilities that are being used to track you, because the groups who designed the various web APIs had no security mindset besides sandboxing. One of the chief browser makers is even an unabashed surveillance company! It's going to take a long time to close or mitigate all those holes.
Should I find a bunker?
These pieces are in orbit at many thousands of miles per hour, and have a random radar cross section, depending again, on whatever random impacts have already done to them, their orientation, composition.
The radar itself to track them must pass through the ionosphere, which itself causes variable time delays and phase shifts. Smaller objects return signals just above the noise after correlation in the receiver, most of them are just at the noise floor.
Observations only happen when the objects are in site of the tracking ground stations, which only cover a small portion of the sky, not including the expected collision volume.
All of that is just what I could recall might effect predictions off the top of my head... I'm amazed they can make predictions with any level of certainty.
And that's the difficulty with the simplifying (and wrong) assumption that that outside forces don't alter the orbit- even 2021, we have a lot of room for improvement when it comes to predicting many of the other factors that come into play, like solar activity and the Earth's climate.
Radar resolution of civil orgs might also be a limit.