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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."
if they chose the eclipse date on purpose. We'll wait and see what they say AFTER it all happens.
They're shooting it down not because it might hit and blow up, but because it might hit and not blow up, and yield a lot of classified hardware/software for some enterprising person(s) to pick up.
There is also some interesting analysis done by the Federation of American Scientists that suggests this is just an excuse to test out some anti-satellite missiles. An interesting read.
http://www.fas.org/blog/ssp/2008/02/us_plans_test_of_anti-satellit.php
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I wonder what they mean by "shoot down"? It's not like an airplane, that if damaged, can't stay flying and falls to earth. If you blow up a big satellite, you end up with a bunch of little satellites, and that doesn't make them de-orbit much faster does it? I was under the understanding that blowing up stuff in space is BAD and creates a major headache more of space debris. I suppose if you really wanted to de-orbit a dead satellite you'd want to shoot a missile at it that would attach, and fire retro rockets to slow it down so it would degrade its orbit enough to hit atmosphere were it would be pulled down on its own from there.
I work for the Department of Redundancy Department.
Don't be confused by the expression "shoot down". The satellite is still very high above the Earth. The cloud of debris will continue for many orbits and alternate between daylight and nighttime every 45 minutes, like every other low-orbit satellite.
Yep, but by the time the debris orbits into the Earth's shadow, about 15 minutes after the impact if my guesstimate is right, it will be entirely dark in visible wavelengths, shining only by reflected light. At that point, the lunar eclipse hinders rather than helps things, by removing a light source. And the eclipse moves out of totality within another 15 minutes after that.
Short version: The timing relative to the lunar eclipse is pure coincidence.
Unless it's a critical part of the top secret plan to propitiate Nyarlathotep and force Great Cthulhu back into an uneasy aeons-long slumber among the cyclopean ruins of R'lyeh, the fabled city of the Old Ones, looming over the black abyssal plain that lies miles below the sparkling sunlit waters of the Pacific.
In which case, I don't want to know what's in the payload of that missile.
When all you have is a hammer, everything looks like a skull.
Are there any Slashdotters here in Hawaii?? Surely a missile zooming up to shoot down a satellite would be visible, would it not?
Yeah right... The fact that it's a two-year old, highly-classified spy satellite has nothing to do with it. The *real* reason that they're spending $60M is to make sure that some fuel doesn't contaminate an acre or so of land.
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Besides, if it's the gear (rather than the fuel) that concerns them then why haven't they bothered shooting down other de-orbiting sats in the past?
- They don't want a repeat of Skylab where parts landed in Australia and made us look bad.
- If it comes down in Russia (Russia spans 11 time zones so that's not too unlikely) they don't want the Russians to be able to figure out much from the debris.
- They want a chance to test their anti-satellite weaponry on a real target that isn't saying "Over here! I'm over here! Here I am! Yoo Hoo!"
There's actually a 4th reason - blowing stuff up is fun but they would never cop to it.Okay, forget for a minute that the orbit is decaying. Whether or not a decaying orbit is "in orbit" is kind of a philosophical question.
So imagine the satellite in a stable orbit. Then you blow it up. So some pieces go flying in all directions. If you work out the orbital mechanics, every one of those pieces will be in a different orbit, but all of those orbits will pass through the point of the explosion. Caveats: this isn't true of orbits that intersect the ground first, or bits that, as you noted, get flung out of orbit altogether - that is, they achieve escape velocity. Escape velocity is awfully fast though, so that's probably not an issue here, and if something does hit escape velocity then it's not going to be a problem for us because that chunk of satellite will be GONE.
That's the reason you can't fire things into orbit with a gun (railgun, whatever), by the way. Any "orbit" you can put it into will have a point intersecting your gun. In order to put something in orbit that way you'd have to fire it out of the gun, then have a rocket on board to fire later and put it into an orbit that doesn't intersect the ground.
You can't actually escape the gravitation of anything, much less a planet. Technically, Earth, the sun, your toothbrush, will all pull on you (very weakly) no matter how far away you get. What you're thinking of is escape velocity, the speed at which you will never fall back, but continue on (slower and slower) outward forever.
Things we send into space can go a few different ways. If it's above escape velocity (Voyager, say) then it will never come back. If it's in a nice high orbit, way above the atmosphere (like geosynchronous satellites) then it will stay up for a LONG time. It will probably eventually come down, because there are always a few stray particles and things, but not for a long, long time. Things on a suborbital trajectory will come back down without circling the planet. Like SpaceShip One. Or you can have a low orbit, like spy satellites and the space shuttle. The atmosphere at that altitude is really thin, but not non-existent, so without thrusters to boost the orbit those sats will come back down, often on a fairly short time scale. The space station is fairly high (and massive) but if I recall correctly, it's orbit will decay in something less than a year without periodic boosting.
The problem with the satellite is that they've lost control. It isn't responding to commands. So it has lots of fuel (hydrazine) but the controllers have no way to fire the thrusters.
As someone else pointed out, orbital mechanics is kind of a counterintuitive thing. You'd think you could shoot things into orbit with a big enough gun, or that blowing up a satellite could boost some bits of it into stable orbits, but it turns out not to work that way. Something else weird: when you thrust in the same direction as you're traveling you slow down. You gain altitude, but you slow down - the opposite of what we normally expect. These satellite bits are speeding up (and losing altitude) due to atmospheric friction.
But the US missile can launch from essentially any one of several Aegis-equipped cruisers, rather than needing a relatively fixed ballistic missile (like the Chinese system). The US missile is a descendant of the SM-1 Standard SAM developed to protect ships against aircraft and cruise missiles. The SM-3 version (to be used in the test) was developed specifically to intercept ballistic missiles--the only modification for this test is a software upgrade. I think it's already in regular service.
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