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.'"
Target practice or....? (Score:5, Interesting)
Re:Target practice or....? (Score:5, Interesting)
A bit of both I suppose. It's not every day you get to do a live-fire exercise of your satellite-attacking technologies... Not to mention it's not every day you get a real live test of just how good your satellite's anti-missile technologies are! Either way somebody in the military wins :P
Big chunks will no doubt re-enter the atmosphere relatively quickly, and they should be small enough that they will burn up completely in upon re-entry, which I think was the whole point of this exercise...
Not the same as Chinese Test (Score:5, Interesting)
Controlled de-orbit? (Score:2, Interesting)
There is far too much space junk up there already. Blowing the satellite into a million pieces doesn't seem like the smartest thing to do. I suspect the US simply wants to demonstrate and test its own anti-satellite system.
let this be a lesson to NASA/JPL (whoever) (Score:4, Interesting)
Re:Oh bullshit. (Score:5, Interesting)
The reson we are doing this is obvious - to demonstrate to the world (and the Chinese) that was have functional ASAT capability.
I think the reason is more because various agencies are worried that the satellite will end up falling in someplace while Russia or China and the intact pieces will give these countries examples to reverse engineer or clues as to US capabilities. I believe the satellite is supposed to be the newest generation of spy sats so it's probably full of interesting little tech.
They are spinning the media with a scare story (Score:3, Interesting)
Looks like a great chance for the Bush regime to pull off an ASAT test, with a ready-made cover story to deflect blame for all the space junk it will create.
Re:Ulterior motive? (Score:5, Interesting)
And from TFA (again, emphasis mine):
It doesn't seem as if "shooting down" the satellite is really going to cause much more damage than re-entry and impact will...for this reason, my money's on either target practice for our benefit, or, more likely, a not-so-subtle demonstration of our space superiority.
Re:Target practice or....? (Score:5, Interesting)
Re:ASAT (Score:3, Interesting)
Both the original ASAT system and the Aegis are only useful for low orbiting targets. So it's probably more useful to have it as part of a theater defense setup more than something you need to have enough warning to launch an F-15 at.
But, yah, the smart money's on it being a demonstration to Russia and China.
A better idea... harpoon interceptor missle (Score:1, Interesting)
Major differences (Score:3, Interesting)
- The solar max does not have much in way of secret equipment. Nearly all is known. OTH, the spy bird is highly secret (though it appears that a number of leaks have been occurring over the last couple of decades).
- The solar max is STILL UNDER CONTROL. OTH, the spy bird is not. There is no way to tell it to plunge into the atmosphere at such and such a place and such and such an angle.
Keep in mind, that America (as does Russia, China, UK, France, and others) de-orbits spy sats regularly. There have been some that have also been put into much higher orbits due to issues with spreading contaminates (read radiation).Re:Ulterior motive? (Score:5, Interesting)
Heh, or not. One of the things Britain did during WW II was to leave bits of busted machinery (electronics) that not only never worked, but were designed to be deliberately misleading, at the occasional aircraft crash site in German-occupied territory. The idea was to keep German radar scientists, etc, busy chasing down wrong paths if/when they recovered the equipment. (Which they did; recovering any kind of radar-related gear from Allied aircraft was a high priority for them.)
Don't assume that the sat failed (Score:1, Interesting)
Re:Still dangerous (Score:1, Interesting)
If they don't hit it, it will still break up on re-entry, and still create a debris field. But likely much larger pieces will survive to impact. You may have been working satellite control systems for 24 years - but I've been working re-entry physics for at least 5 years and satellite operations for 14.
And yes, hydrazine is nasty stuff. The references I've seen don't show it to be quite that nasty (1 drop = fatal), but that's splitting hairs - it's bad stuff. I certainly wouldn't want half a metric ton of it breaking open in my back yard. If you want to increase the odds that the tank full of this stuff makes it to the ground intact (to break up on impact), then by all means, let the satellite re-enter intact so that the rest of the structure can shield it from re-entry forces and heat.
Re:Still dangerous (Score:4, Interesting)
Since you've got 8 km/s of orbital velocity and probably around 3 km/s on the interceptor, you're probably talking about 10 km/s at the intercept. The heat of vaporization of iron is 250 kJ/kg and this thing has a mass of 11 tons, so we can assume 2.7 GJ will do quite a number on this satellite. Sure, it's not made of iron, but you don't really need to liquify it to destroy it. Satellites are usually only built to survive launch stresses, not impacts.
Anyhow at an impact velocity of 10 km/s 2.7 GJ would require a impactors with a total mass of 50 kg, probably in the form of lead or depleted uranium for compactness. To be thorough in your destruction, you probably want multiple small impactors, say 500 of them at 100 grams each. The total mass of the warhead depends upon how close you can get to the target. If you could be ensured a direct hit, 50kg would suffice. But it's likely that this won't be a direct hit, so you'll need to cover a larger area than the satellite itself.
We'll assume the satellite projects an aspect of 600 square meters (say about 60 meters by 10 meters) and that our shot cloud covers a circular area. Once your impact parameter exceeds 14 meters your warhead size goes up as the square of the distance. At 25 meters, you need 160 kg. At 50 meters you need 650 kg. At 100 meters you need 2.6 tons. At a kilometer you need 260 tons.
The only thing determined by the yield of the charge that scatters these impactors is the timing. How long before impact do you need to set it off and how accurate does your timing need to be? These are left as an exercise for the reader. If I were designing the thing I'd keep the scattering charge as small as possible. The bulk of the constraints are set by the trajectory. In a head on trajectory, there is nothing wrong with scattering the impactors 5 seconds or more before impact. For an interceptor that travels vertically, the maximum timing probably depends upon atmospheric properties.
Given the geometry of the likely impacts, it is unlikely there would be significant amounts of ejecta inserted into long lasting orbits. The worst cases would be insertions into elliptical orbits, but they would circularize quickly at low altitude due to the low perigee. It should be possible to choose in impact point that will minimize risk to other vehicles.
FWIW, I do not design space weaponry, and I do not know the actual capabilities of U.S. anti-satellite weaponry. I just know how to break things in a practical and sometimes dramatic manner.
Re:Target practice or....? (Score:3, Interesting)