US To Shoot Down Dying Satellite 429
A user writes "US officials say that the Pentagon is planning to shoot down a broken spy satellite expected to hit the Earth in early March. We discussed the device's decaying orbit late last month. The Associated Press has learned that the option preferred by the Bush administration will be to fire a missile from a U.S. Navy cruiser, and shoot down the satellite before it enters Earth's atmosphere. 'A key concern ... was the debris created by Chinese satellite's destruction -- and that will also be a focus now, as the U.S. determines exactly when and under what circumstances to shoot down its errant satellite. The military will have to choose a time and a location that will avoid to the greatest degree any damage to other satellites in the sky. Also, there is the possibility that large pieces could remain, and either stay in orbit where they can collide with other satellites or possibly fall to Earth.'"
Re:let this be a lesson to NASA/JPL (whoever) (Score:4, Informative)
Unless of course, the satellite stopped working because it's computer is bust. Then you'd have a big lump of explosives rolling around in space, and no control over it.
Re:Incompetent (Score:4, Informative)
Kind of hard to do that when the master CPU fails on boot-up, which is the whole reason why something needs to be done about it. It is literally out of control.
Re:Incompetent (Score:5, Informative)
China's debris to remain for thousands of years... (Score:5, Informative)
The two shoot-downs are not equivalent, which of course won't prevent agenda-driven comparisons...
Re:Target practice or....? (Score:5, Informative)
Longer answer: The orbit of a satellite can be determined by the position and the velocity at any time. Orbits are changed by changing the velocity of a satellite, but the old and new orbits will continue to intersect at the point where the velocity was changed.
Changing to a higher orbit will require two changes in velocity and uses a transfer orbit that intersects both orbits. One velocity change puts the satellite into the transfer orbit and one velocity change puts it into the final orbit. Usually, the two velocity changes are at opposite sides of the transfer orbit (half an orbit period apart).
I assume that this will use a warhead instead of a rocket motor for a single change of velocity, but there will only be one change of velocity. If the intercept takes place at lowest point of the current orbit then any debris will be in an orbit that will return the debris to the point of intercept. If it is already brushing the atmosphere then reentry is inevitable and the time to reentry will only depend on the ratio of the mass to air drag of the object (small heavy objects will stay in orbit longer).
Normal precautions of staying out of the temporary orbits of the debris does apply.
_Richard
Re:Our secrets are worth more than your secrets! (Score:1, Informative)
Re:let this be a lesson to NASA/JPL (whoever) (Score:1, Informative)
Re:let this be a lesson to NASA/JPL (whoever) (Score:3, Informative)
Re:Still dangerous without the shot? (Score:5, Informative)
Yes, they would. People on the ground will always be at some danger when you put an 11-ton satellite in low earth orbit.
But it's easier to predict the impact point of a body that has a well known shape and orbit than that of a body that has been torn apart and pushed in random ways by an explosion.
Re:Still dangerous (Score:4, Informative)
Sure, but how hard can you hit? It's not as if it were hitting a stone wall, it's hitting an exploding missile, that is, a fire ball. It's travelling at close to 8000 meters, or five miles, per second.
The densest parts, like batteries, fuel tanks, and possibly the main camera mirror, will go through that explosion ten times faster than a bullet. Do explosions stop bullets? Not unless it's precisely concentrated at the exact point [wikipedia.org]. There is no way the explosion could transfer enough momentum to the densest parts to significantly affect their orbit.
The flimsiest parts like, for instance, the solar panels, will be shredded to very small pieces by the explosion, of course, but those are exactly the parts that would burn first when entering the atmosphere.
Re:Land Shuttle Atlantis through LEO debris? (Score:2, Informative)
No. No matter how much energy you put into any of the pieces through this imapact, their resulting orbits will pass through the point of impact on subsequent orbits (discounting hyperbolic orbits, which won't happen, and wouldn't come back if it did). This point is so low (by definition) that these pieces will also be subject to the same significant drag that is bringing the satellite down. They will decay quickly.
* Will Atlantis be safely on the ground before LEO is polluted with the debris of this experiment for an indeterminate period of time?
Atlantis is scheduled to return on Feb 20th - well before this attempt would be made according to what I've heard. I work in this community, though not on this event - I'm absolutely sure they are taking this into consideration.
* If it falls outside the U.S. are they going to send the antisat missile into someone else's airspace?
* China, France, India, Pakistan, the shrapnel of the old U.S.S.R. all still have nuclear missile, mightn't antisats flying through/near their airspace make them a bit edgy?
Ok, give them a little credit here. It's really not the first time we've launched missiles into space.
* Didn't we sign some SALT or similar treaties against using weapons in space? If we decide to ignore this treaty, won't it be open season for satellites and space stations?
There is no ASAT treaty. The closest thing to one is the 1972 ABM treaty - which Reagan basically gutted with SDI anyway.
* If a piece of an uncontrolled satellite causes harm, we could say "sorry, it was an accident, nothing could be done." But if we intentionally break it up and a fragment causes harm, aren't we more liable?
That whole area if international law is still wide open. But I'd prefer to have smaller bits coming down then larger ones personally.
Re:Still dangerous without the shot? (Score:3, Informative)
You can minimize the danger if you inflict a sudden loss of momentum on the satellite such that it will come down in an unpopulated area, such as an ocean, with a high degree of predictability. If you can at the same time destroy the satellite's tank, which contains a highly poisonous substance, all the better. If you just let it come down on its own, it can come down anywhere (equator +/- the orbit's inclination), with the tank likely to be still intact.
But it's easier to predict the impact point of a body that has a well known shape and orbit than that of a body that has been torn apart and pushed in random ways by an explosion.
They're dealing with an out-of-control, non-aerodynamic object in orbit. Predicting the impact point of such a thing with an accuracy of less than a few thousand miles is impossible until the last one or two orbits (i.e. one our two hours before it comes down). Predicting it with an accuracy that would allow for any reasonably attempt at warning, let alone evacuating, people on the ground is well-nigh impossible.