USA 193 Shootdown Set For Feb 21, 03:30 UTC

An anonymous reader writes "Amateur satellite watcher Ted Molczan notes that a "Notice to Airmen" (NOTAM) has been issued announcing restricted airspace for February 21, between 02:30 and 05:00 UTC, in a region near Hawaii. Stricken satellite USA 193, which the US has announced plans to shoot down, will pass over this area at about 03:30. Interestingly, this is during the totality of Wednesday's lunar eclipse, which may or may not make debris easier to observe."

Comments

Good coverage

[BWJones]

Bruce is a fellow satellite spotter also with some degree of background and in the subject matter and has good coverage here.

Re:Good coverage

[everphilski]

Now, instead of one big vaguely predictable chunk of technology falling down, we're going to have hundreds if not thousands of smaller chunks that are going to be absolutely impossible to predict their trajectory.

As someone whose day job is re-entry of large objects from near-orbital velocities I feel pretty qualified to respond to this. "vaguely predictable" is pretty generous. For the upper stage of a launch vehicle re-entering under an hour after launch (read: we know precisely where it is coming from, have the trajectory modeled, etc), there are thousands of miles in the "footprint" of the debris. And while most of it will come down in one or several big chunks, there will be a lot of scatter debris over that footprint. Now, think of something that's been in orbit for a number of years. Sure, we can observe it for a few months and try and nail the orbital parameters, but any way you slice it, it's an uncontrolled re-entry. We don't know with high precision the injection orientation, velocity, orientation, etc. That baby could have an uncertainty of 10,000 miles or more on it's footprint.

Also another note: big, dense, heavy things tend to break up very little on re-entry. They soak a lot of heat and come down hard and heavy. Big, light things like expended stages tear apart into little pieces and essentially dissipate in the atmosphere, leaving very little debris. And what debris remains, slows down very quickly, reducing scatter versus heavy pieces that just keep on flying. So there is a distinct advantage to breaking this thing into pieces. It will tear itself to shreds, versus coming down like a rock.

there's even the risk that the explosion might send pieces of debris upwards in the atmosphere, and it may even reach an altitude that will not allow it to fall back down for a very long time.

Don't believe everything you read on slashdot. What goes up must come down. The only way it will stay in orbit is if you give it the appropriate energy tangential to the surface of the earth to sustain an orbit, or more. That's it. I could shoot a bullet up into the sky right now at M=10,000, and it's either escaping the gravitational grasp of the earth or coming back to hit it. The chances of random pieces entering a stable orbit for the long term is slim. The chance of a few random pieces extending their stay? Granted, maybe for a few months to a year.

Moon hiding behind megameters of solid rock

[isomeme]

Since that time interval occurs during daylight hours near Hawaii, with the eclipsed moon (necessarily) below the horizon, I doubt the eclipse will have much effect on visibility. :)

Re:Nothing to see here, move along

[Rei]

At least they never dared launch anything as crazy as Starfish Prime.

We are not the immaculate custodians of space that you seem to be picturing. Why, do you think, did we not shoot down the Delta II second stage that reentered in 1997 with a large amount of residual hydrazine and nitrogen tetroxide onboard? We have stages with signficant amounts of toxic residual fuel reenter all the time. Why, in the same year, when we had a Delta II explode *full* on liftoff, did the Air Force tell people in the *immediate area* that the smoke posed no danger? This was a *full launch vehicle*, not just a satellite's orbital maneuvering system. Do you have any idea how much beryllium we've had reenter? We sit by as large amounts of toxic materials enter all the time. As for the hydrazine itself, what do you think happens *on its own* to pressurized tanks of highly flammable fluids on reentry? I can't think of a *single* sizable object that's survived reentry still pressuretight.

The argument is completely bogus.