Predicting When Space Junk Will Come Home To Earth

Following up on recent news of a NASA satellite falling from the sky and a German satellite that did the same, new submitter blais writes "NPR has an interesting interview about space junk falling back to Earth — and the odds of it possibly hitting someone. I thought it might be of interest to the other space nerds out there. Quoting: '... it's very difficult to know exactly when a satellite's going to come down. The Earth's atmosphere is hard to model. It's very thin up there, 100 miles or more up, but it exists. And sometimes it's a little bit denser, sometimes not, and the satellite might be tumbling, and so it makes it very difficult to know exactly when it's ... going to come down."

Comments

Zat's not my department

[Mantrid42]

Vunce ze rockets are up, who cares vhere zey come down?

Re:Zat's not my department

[perpenso]

Vunce ze rockets are up, who cares vhere zey come down?

My understanding of history is that the famous rockets scientists implied by your accent were very much concerned with where the rockets came down.

Re:Zat's not my department

[Spy Handler]

WVB: "it vill go up like a cannonball, und come down like a... cannonball, vid a parachute to spare ze life of the speceeman inside"

LBJ: "Spaceman?"

WVB: "Spe-ci-men!"

LBJ: "Well what kind of a spe-ci-men?"

WVB: "A tough one. Responsive to orders... I had in mind a jimp."

LBJ: "A Jimp? What in the hell is a jimp??"

WVB: "Jimp... a jimpanzee, senator!"

Re:Zat's not my department

[perpenso]

You might reconsider who is having the woosh moment. That satirist who penned the original was essentially making the same point as I. :-) Out of context the original intent is easily missed.

Re:Zat's not my department

[perpenso]

And you might want to reconsider as well. Lehrer wrote that when Von Braun was NASA's chief designer. It was a joke about how VB used to do the V2, and now he was working for NASA designing moon rockets.

Yes, I was aware of all that. :-)

obviously

[Hatta]

It's a non-linear dynamic system. Of course it's going to be chaotic.

Was anybody ever killed by space junk?

[mapkinase]

According to NPR, Lottie Williams of Tulsa, Oklahoma, is the only person to have ever actually been hit by space junk. In 1997, she was hit on the shoulder by a piece of what was thought to be the Delta II rocket.

The problem is weather, solar and atmospheric

[perpenso]

You run the simulation through a CFD package, compare the prediction with reality, and tweak the parameters for the upper atmosphere accordingly. Keep crashing satellites until you consistently get good results. Problem solved.

There is solar "weather" in space that can affect an orbit. There is weather and turbulence in the upper atmosphere. It is not a static environment where we can refine our parameters for greater accuracy.

Re:The problem is weather, solar and atmospheric

[jd]

The whooshing sound you hear is the incredibly large number of theoretical satellites you'd need to be able to model the upper atmosphere (plus the fact that you can't treat the extreme upper atmosphere as a fluid).

Yes, the space weather affects things, but we monitor that increasingly. It can be modeled. Not in fine detail, but in aggregate, as indeed can the weather. You may not be able to compute the exact trajectory (you can actually prove you can't, since it's a chaotic system) but you can improve your estimation of the probability of any individual trajectory.

Re:There is a reason...

[jd]

Never quite understood the idea of remotely switching a satellite off when de-orbiting it. You'd want to switch off any non-command channel transmitter, sure, as that could interfere with other satellites, but there's no obvious reason to switch off any command channel stuff and this isn't the sort of crash you want to be able to reboot from. Now, I'll throw in one proviso in there - you DO want the computer system switching off once the thermal conditions go out of range, as you don't want a partially-functioning system sending random messages that could mess with the trajectory. But you absolutely want to have the satellite on a controlled descent for as long as possible (ideally via a mix of ground control and on-board computer, since you don't want control lost if the link is lost).

Re:Design for it

[mjr167]

I think the problem is that all the space junk is ALREADY in space. There is far more crap orbiting the planet than operational satellites. AGI has a nice plugin for Google Earth that plots all the space junk and it looks like a swarm of bees attacking the planet.