You left out this part:

"If you want to bring something down, you slow it down. You apply a force on it which results in it being slowed down and decrease in its orbit,"

This is what I have been saying, and they weren't referring to atmospheric drag. The impactor will slow it down and it will begin to drop.

If I'm understanding ugordan's explanation of the dynamics correctly what will actually happen is that the ASAT will slow it all down a little. That situation is unstable so the debris cloud will fall lower into the atmosphere and speed up in the process as it swaps gravitational potential energy for kinetic energy.

The satellite is (believed to be) about 2600kg and is currently orbiting at around 7.8km/sec. I've no idea how the ASAT intercept is supposed to work but lets assume that they put it into a similar orbit moving in the opposite direction. The impact head of the ASAT is not likely to mass much more than 100kg and probably will mass less than 25kg if it's similar to the earlier US ASAT tests. For a perfect collision where a 100kg ASAT warhead transferred all it's momentum into the satellite the resulting object would be moving at 7.22km/sec. That's now unstable at that altitude and so it will fall until its rising velocity matches the orbital velocity at the altitude it finds itself. My [highly unreliable and full of gross simplifications] back of the envelope calculations put that at about 18 km lower down.

That alone will significantly increase the drag but the really important factor is that the end result of a successfull intercept will be a debris cloud that has a massively increased effective cross section compared to the original satellite and that is what will really bring it down fast.

I heard somewhere that the KV was only 10kg... can't find the discussion now. Some more info here:
http://blog.wired.com/defense/2008/02/the-weapon-that.html

Ahh, here it is, in the FAS anti-ASAT take:
http://www.fas.org/blog/ssp/2008/02/us_pla...ti-satellit.php

Says the interceptor is 20lb.

According to my fooling around with Orbiter, a 7.22 km horizontal velocity at 250 km altitude brings you 700 km below the surface at perigee.

Lithobraking is the word.

My back of the envelope calculation says a head-on collision with a static 100 kg impactor should give a resulting velocity of 7.5 km/s, not 7.22 km/s. If the impactor is 10 kg, that comes down to 7.77 km/s (a perfect inelastic collision). I haven't done a check for 7.77, but my gut feeling say that, too, guarantees reentry in less than half an orbit. Depending on how solid the impactor and the satellite are, the impactor might partially rip-through the satellite implying an even smaller deceleration.

A couple of things crack me up about this whole business

1. the hydrazine cover story..... as if stuff like this doesnt re-enter all the time. If anything gets decomposed
or dispersed during the entry, it'll be the hydrazine. This has to be a total non-issue that the spin doctors have
figured would be a good angle for public consumption (NB hypergolics are a problem for launch failures
where their toxicity etc sticks around, but for hypervelocity entry, I think not....)
2. the way all the TV coverage seems to use Magellan and Cassini footage or models.... I guess to a lot of
people a spaceship is a spaceship...
3. And now they are talking about delaying the shot because of weather... let's hope the Iranians/Koreans/whoever
don't play nasty and try to attack us on a cloudy day........ :-)

(I know, I know, it's for the observations to see how it all went, not for the intercept itself...)

You haven't been keeping up with things, it is solid hydrazine. Many propellant tanks (Delta II, Columbia, etc) have survived hypervelocity entry

ugordan - yeah I got a better quality envelope and it looks like the orbiter perigee is probably correct. It surprises me that even a small 10kg impactor could actually bring down a 2600kg satellite from a low earth orbit, even if there was no atmosphere involved. But it does appear to be true. Quite cool actually. Now let's see if it actually works.

But the hit isn't head on. It is around 90 degrees. the missile and warhead fly straight up into the path of the satellite. Both vehicle are destroyed by the kinetic energy into small fragments.

http://www.spaceref.com/news/viewpr.html?pid=24802

I'm not sure they'll have a good chance to hit it on February 30.

MSNBC.com and CNN.com reporting a hit.
No story, just the headline.

edit:
AP story now out: "The operation is so extraordinary that Defense Secretary
Robert Gates, not a military commander, made the final decision to pull the trigger."

CNN just ran the story about 20 minutes ago, reporting a hit. No details, and no information whatsoever about how direct the hit was. The only "information" given was that the satellite was traveling at orbital velocity (first cosmic velocity to our Russian friends), roughly 17,500 mph, and the impactor was going about 5,000 mph in the opposite direction. (Yeah, I know, it's olde English imperial units -- but it's CNN, after all.)

-the other Doug

Space/AP

Navy Hits Satellite With Heat-Seeking Missile

http://www.space.com/news/080220-satellite-hit.html

I know *empty* propellant tanks can survive entry because of their low ballistic coefficient e.g.
http://www.lpl.arizona.edu/~rlorenz/spaceball.pdf

Have any full tanks ever done so? They would surely experience much higher loads.
I wonder, can solid hydrazine detonate?

(Columbia doesnt count as it started the entry with thermal protection)

I am still waiting for the video from the missile. Don't tell me they didn't put one on it...

Hey my tax dollars paid for this, I don't think it is too much to ask for a video of said impact

They need time to clean out the aliens from the footage.

Well, Nick, looks like there have been some studies along the lines of your thoughts. I was looking at one of the sci.space.* groups and pulled this signal out of the noise --

An Overview of Demise Calculations...

You don't know half of it. You think it was a coincidence that the missile was launched exactly at the midpoint of the total lunar eclipse when the lowest level of solar radiation was reaching the moon?

How much more space debree is now orbiting Earth?

And, more importantly, anyone know if there's a possibility for updated orbital elements of the bulk of the debris cloud so we skygazers could go out and hope for reentry fireballs at certain times?

Quite a lot, but below an altitude of any active vehicle and it'll be gone within a few weeks. China's ASAT test debris, however, continues to endanger LEO vehicles (including ISS, Hubble etc) , and will do so for many years to come.

There's a Press conf. at 1200UT today I think ( http://www.defenselink.mil/news/newsarticle.aspx?id=49024 )
Doug

Immediately after the impact there was quite a lot but by now there is likely to be very little and by this time next week virtually none. The dynamics of the situation have stacked the odds very much in favour of this being a very clean strike.

Timing it to coincide with a full lunar eclpise may entirely coincidental or even have been useful for some aspects of the exercise but I can't help thinking that at some point in the planning there were a bunch of military types hovering over some Cassini (and New Horizons) Kodak Moments thinking - "Guys these are cool and all but I know how we can get an even better shot". I'm waiting for that tracking shot that shows the moment of impact against a backdrop of a red-brown lunar disc.

Apparent FEMA document outlining the satellite reentry and potential response etc.

One statement says that ninety-nine percent of the debris will renter the atmosphere within one week. The same as the original reentry timeline of the intact satellite I think.

http://88.80.13.160/wiki/US_spy_satallite_shootdown_briefing

As expected some of the British press are using the event to take some not so subtle digs at the United States....drawing attention to their criticism of the Chinese test, without realising much of the criticism of that event came from the scientific community highlighting how insanely stupid it was.

Which bits of the British Media? I've got some letter writing to do it seems

What I simply can't believe I'm reading is Chinese criticism of this. That defies belief.

Doug

It was the lead story on Newsnight last night....and the first thing the presenter asked. Sadly the press are unable to see past the politics of these events... and see how totally different they are.

LOL.. you've got to laugh at this quote from China:

The Chinese were never going to let the opportunity pass by without getting a dig or two into the US.

The 'we must protect our citizens from falling, toxic fuel soaked, shrapnel from the sky' angle seems to be part of it too.

They are going to milk it though.

Edit: How prompt was China's notice of their weapons test?

But fuel soaked shrapnel from their own failed LV's crashing into nearby villages is fine.

That's my point

Politics... I don't know whether to laugh or cry when I hear things like these... That's just insulting our intelligence on China's part.

There's a video from the military that shows the missile launch and the hit, represented in Pentagon Briefing from 21 Feb, 07:00

The BBC radio I heard in my car this morning included good info from the press conference...
http://news.bbc.co.uk/2/hi/americas/7256741.stm

Although I must say that in the recorded press conference, it sounded like they had targeted the tank specifically with the KV. *That* may have been a sort of look-what-our-ABM can do demo.

The sensor on the warhead wouldn't be able to discriminate the tank from the rest of the spacecraft. I is hard enough to just to target the spacecraft

There's more from the debris cloud right after the hit http://www.youtube.com/watch?v=vvrP1ZQrk10

I presume the tank was fairly central in the spacecraft bus. They had mentioned reprogramming the head - I presume to identify the bus, and aim for the middle of it.

Doug

I was definitely ready to believe the implication that a specific area of the satellite was targeted because of the mention in this article:
http://blog.wired.com/defense/2008/02/the-weapon-that.html
... that the kinetic warhead targets the "leathal payload area." In other words, the RV rather than the booster. Or, hopefully, decoys, clouds of chaff, etc. I can't recall the exact words used, so it may have been jumping to conclusions on my part, but the ability to discriminate the warhead from the booster and other junk *is* a key part of ABM technology, no? (well, at least post-boost-phase ABM)

If the fuel tank is one meter in diameter, and they see nothing remaining
larger than a football, wouldn't that be proof of destruction? Where would
the tank be hiding?

Where would you target the spacecraft in my avatar to hit its 1000lb propellant tank?

Definitely that bowl-shaped thigamabob on top.

Not really...you were saying that the impactor's speed was irrelevant. With such a narrow margin (in other words, such a small, fast-moving target), nothing is irrelevant. Curt little defenses are your prerogative, but you were still wrong nonetheless.

Huh? I disagree and rightly so. The destruct mechanism is the satellites velocity. The warhead only has to be fast enough to get in the way at the right time. The warhead's velocity (magnitude and direct) contribution to the destruction IS irrelevant

That's fine. The conversation was not only about velocity relative to earth. Your making the a posteriori claim that it was after ElkGroveDan's post doesn't make it so.

Now that we see that we are able to successfully de-construct a satellite with a Star
Wars projectile, I would like to suggest that this method could be a cost-effective procedure to
de-orbit other satellites when their missions have ended. The principal satellite that I have in
mind is the Hubble Space Telescope.
You may recall that NASA has planned to launch a mission, manned or unmanned, to dock
with the HST (after a docking ring is attached during STS-125) and effect a de-orbit maneuver.
This is likely to drain anywhere from $100 million to $500 million from NASA's Space Science budget.
Why not spend $25 million on a Star Wars projectile to do the job?


Another Phil

Because at Hubble's height of 600 km you would be basically doing what the Chinese did - creating a load of dangerous space junk.

Not a bad idea! It'll take a few more years then planned for HST to get low enough for a hit (and favorable debris reentry), but certainly doing so would be more cost-effective then a dedicated Shuttle mission.

Kind of a bummer to think about, though...

Might be more "cost effective", but after all the wonders she's shown us I think Hubble deserves a better end than being shot out of the sky and blown to bits by a stupid missile. Over-romantic, I know, but I'd much rather she ended her mission burning up like Enterprise did in the 3rd ST movie than being used as an orbital clay pigeon for some trainee A-SAT gunner's target practice.

Yeah...<sigh>...I feel ya, Stu, but this actually might be the best solution.

Given an unlimited budget & a choice, I'd have the Shuttle catch HST & bring it back home for permanent display in the US National Air & Space Museum. However, I don't think that the Shuttle is actually capable of returning a large payload like that (might be wrong, but IIRC there are some very stringent mass restrictions for the landing envelope), nor do I think that the cost vs. benefit vs. risk profile for such a mission would be favorable, even if it did turn out to be feasible.

Like I said: a bummer. At least we seem to have a relatively safe deorbit option available for large SVs now.

The shuttle could since HST is relatively light. The issue is that some of the servicing "mods" would have to be undone to allow it to fit in the bay

As Jim said, some mods would have to be removed, and an orbiter would have to be *significantly* modified in order for HST to fit in its payload bay (for a variety of reasons, Columbia was the only orbiter whose bay was suitable for returning HST, and plans said that it was going to be used for that task prior to its destruction).

But while landing with a significant payload in the bay can make things a little dicey under some circumstances, it's just plain impossible that a Shuttle would be allowed to lift off with a payload it can't land with. Otherwise, most all of the ascent abort modes would be worthless -- you can't take time in an RTLS abort, for example, to open the payload bay doors and dump the contents...

-the other Doug

Thanks for the clarification/feedback, guys. Bottom line: Not an insignificant effort to return Hubble, funding to do so is unlikely to say the least (and could certainly be better spent).

Argh. I hate playing the heavy, esp. in this case, 'cause I philosophically agree with Stu: by all rights, Hubble should be preserved & honored for what it really is, a revolutionary leap in our understanding of the Universe. Pragmatically, though, all things in LEO must come to an end, and with minimal damage to both the orbital environment & anything along the reentry ground track. HST has many years left, of course, but when the time comes we must accept it, and prepare for it.

HST does not have a big tank of frozen hydrazine like USA 193, so there is even less of a reason for an ASAT mission against it.