That’s what Ambassador James Jeffrey’s called the decision to use an an Aegis SM-3 to try to shoot down USA 193 in the next 3-12 days. (Transcript should be posted here ; video at the Pentagon Channel.)
Holding the aside the politics of this — which are terrible — the briefing on debris risk left me cold. I have to say that I am very, very uneasy about this decision — our missile defense tests have been heavily scripted to minimize debris creation and modeling of debris creation isn’t an exact science.
The burden of proof really should be on these guys to demonstrate that the risks to the ISS and other objects in space are minimal.
General Carwright, to his credit, provided enough technical information to model the intercept. David Wright is working on that right now — for those of you who can’t wait, the important numbers are:
1. The intercept will occur at 240 kilometers (130 nautical miles)
2. The mass of the satellite is 2,300 kg (5,000 pounds)
3. The mass of the interceptor is 20 kg. (From CBO)
4. The closing velocity will be 9.8 km/s (22,000 mph), suggesting a virtually head-on collision.
Other pertinent observations. At 240 km, the satellite should be traveling 7.8 km/s; the SM-3 has a burnout velocity of 3 km/s.
I am very worried about the debris creation — particularly the debris that the light-weight interceptor will kick into higher orbits when it hits the massive (bus-sized) satellite. Thnk, as Geoff Forden suggested, of a ping pong ball hitting a superball.
Virtually all the debris should come down quickly. Cartwright said 50 percent would come down within two orbits, with the rest coming down in weeks and months. That seems plausible, at first blush.
But those two orbits could be hairy and some of the debris will remain in orbit. Michael Griffin, NASA Administrator, said there are “good times and bad times” to conduct the intercept, based on the position of the ISS but that “bad times are not all that bad” comparing the risk to an order of magnitude lower than flying the shuttle.
Last I checked, the PRAN for the shuttle was 1 in 100. Extrapolating, there would be only a 1 in 1000 chance of wiping out the ISS.
Great.
Anyway, we should be able to get some real numbers in the next 24 hours.
I can’t believe we’re going to do this after going ape shit over the Chinese ASAT test last year, where the Chinese did basically the same thing we’re planning to do. This, at a time when we’re already taking flak at the CD from Beijing and Moscow on space weapons. Incredible.
I’m curious to hear what techies out there think about this question: What are the best technical arguments for conducting this operation? Will it result in new performance data on Aegis? Does USA 193 have such sensitive technology that the military is taking no chances that pieces of it survive reentry and land someplace unfriendly? Or is the only reason to do this to prevent it from coming down on a population center?
A question for the debris modelers:
Is there a possibility that an interceptor can reach a slightly higher altitude, then intercept the bird by striking it ‘downward’ instead of a strike from ‘below’ in order to lower the long term debris count?
Does it have to be a hard impact or is there a chance for a softer strike / push that de-orbits the bird with a minimum of debris?
Do the US have an interceptor that have an ability to execute such a maneuver? Is the proposed plan the only game in town?
Wouldn’t it be a supreme irony if debris from this shoot down ended up destroying another American spy satellite?
I am kind of partial to the Aviation Week comment about the reason why this satellite has to be shot down —- to prevent pieces from coming down where other parties (read Chinese, Russian, Indian, French, etc.) can recover and learn details about how the bird is built.
The Columbia shuttle crash shows that many, many pieces can survive reentry and yield useful intelligence information.
The stated reason for doing this strikes me as very, very bogus. The figure of “two football fields” was mentioned a couple of times as the hazard area for hydrazine exposure. Two football fields is two hectares, or 1/50 of a square kilometer. That’s less than one ten-amerobillionth (1/10,000,000,000) of the area of the planet under the orbit of USA-193.
Not, to my mind, a threat to life and health that would warrant “taking the shot.”
At the moment, I’d say this looks a lot like a political exercise meant both to send a message to the ChiComs and to bolster missile defense.
Our actions differ from China’s in several ways. 1) The degree of risk (from orbital debris) associated with an intercept at 240 km vs 850 km (the altitude of the FY-1C) is significantly diminished. 2) The US has notified other nations’ governments through diplomatic channels and other means before the intercept. Much of the criticism directed at the Chinese was about how they conducted the test, their reluctance to discuss it afterward, and the stark contrast between their actions on 11 Jan 07 and their rhetoric in Geneva. 3) The Pentagon is offering a compelling reason (arguably) to conduct the intercept (i.e., human safety, although I suspect tech control too).
Having said that, I too am concerned about the political fall-out. China and Russia have long criticized our BMD program because of its dual-use qualities (i.e., inherent anti-satellite capability). We appear to be making their point. Is BMD a space weapon? It just became one.
Is it just one shot? No multiple launches, no time for a second shot if we miss? Better yet, what are the odds that we could hit the target, but off center— clipping it, but leaving a big enough chunk left that the original concerns over dangerous debris and tech control were still valid? Or is it expected that vaporized parts from the two bodies will create enough of a blast that the whole will be shattered regardless of the location of impact? Do we know whether the target will present head-on, side-on, or tumbling? There’s a big difference between hitting an RV-sized body hard enough to render it nonfunctional and hittting a body ten times larger hard enough to reduce it to fragments.
I’d have to agree with Allen: the stated risk doesn’t come close to justifying the action which means some significant part of this is a big BS happy pill for the world public. Either something significantly bad is coming down or we’re showing off for effect.
Stupid question, maybe, but I’ll ask it. The hit is supposed to take place at the upper limit of the interceptor’s capability, correct? So we have a large target in a near decay orbit essentially running into a small target that has little or no vertical velocity at the apex of a suborbital trajectory, and any horizontal velocity is in the opposite direction of our target’s already decaying orbit. I don’t understand where the energy would be coming from that accelerates anything into a higher, longer lasting orbit.
I don’t see that they are making an effort to keep the debris down at all. To me, it seems like they just want to test their kill vehicle.
The impact shock is strong enough to vaporize steel on steel and still leave over enough kinetic energy to be supersonic in steel for secondary impacts on the satellite. USA 193 is just going to turn into steel marbles. It’s crazy.
If Jeffrey’s numbers are right, the included angle of impact is 124 degrees. That’s got to be just about right for a maximum information intercept path given the differing speeds of the objects. Why not pick a closing angle where the intercept speed is small like a few hundred km/s, but the intercept is more finicky to do. I mean, a 5,000 pound satellite has got to be a bigger target than a ballistic missile, right?
That is, if you are serious about minimizing debris…
My question is, the closing velocity of this attempt is gonna be 9.8 km/sec. My understanding of recent successful Aegis BMD tests is that the closing velocity for those was somewhere around 6 km/sec.
Anybody still confident that Aegis BMD can actually shoot the doggone thing down?
I agree that the risks of being hit by a hydrazine tank are very, very small. Of course, the chances of actually hitting the satellite are probably quite small too! Most of the SM-3 engagements have taken place with closing speeds of 4 km/s or less (I think they go up to maximum of 6 km/s if you use the LEAP’s third stage; but that is the maximum and chances are they less when the geometry of the collisions is taken into account. (Thanks to George Lewis for helping me track down these numbers!)
The largest speed piece of debris the Chinese ASAT test created was 600 m/s more than the original satellite’s speed. If you add 600 m/s to the USA 193’s speed, a piece of debris from the engagement might go out as far as 2700 km altitude. But its perigee would still be at 210 km so while I dont know how fast it will decay, it will decay fairly quickly. Id say that the chances of it hitting another satellite are probably about the same as the USA 193 hitting somebody on Earth, ie several million to one against a hit.
Is there a military equivalent of a NASA Safety Standard 1740.14, “Guidelines and Assessment Procedures for Limiting Orbital Debris? The NASA version requires a 1-in-10,000 odds (or higher) for human casualty per re-entry event. Does the military used this value as their baseline?
One tool I know of for sort of a rough cut is the Debris Assessment Software, which from which I’ve read tends to be overly-conservative for small satellites. A more refined and accurate model is called ORSAT (which is used internally by NASA as far as I know).
I’m still wondering if the satellite had a redundant flight system. If it didn’t, shame on the NRO; a classic dollar-wise megabuck foolish mentality.
Lao Tao Ren-
The difference is that the Columbia was designed to re-enter the atmosphere, and did so successfully before it disintegrated.
The problem (as far as I recall) was bad panels, that failed, eventually causing it to break apart, during the descent following re-entry. I think it was during the glide or S-turn phase (but, just going from memory here)
Point is, the satellite wouldn’t survive like the Columbia shuttle did. Not to say that even fragments of debris might not still pose a security risk.
I’m with Jeff in worrying about debris patterns, because the way I understand hypervelocity impact, the two impactors instantaneously disintegrate into shrapnel clouds that expand radially relative to their original vector — some objects moving ahead, some behind, others in all other directions. The direction of the impactor seems to have little relation to the debris distribution from the impactee. So I’ve been told.
Fortunately, all objects will have such a low perigee that they will all clear out pretty quickly. But some could indeed temporarilly wind up in higher-apogee orbits — hundreds of km higher than the parent satellite’s apogee pre-impact.
As stated by Chachi, there is an enormous difference between this and the Chinese ASAT test last year. (Debris, notification, purpose).
The area affected by hydrazine contamination would indeed be very small, compared a large nuclear detonation. However if one were unfortunate enough to be affected, there would be little comfort in that you were just unlucky. Remember there is no way to “aim” this satellite to a increase the probability that it strikes a remote area.
Any reasonably knowledgeable person understands that intercepting a ballistic missile and its (possibly maneuvering) warheads is a far harder task than intercepting a satellite subject to Kepler’s law. (Yes Virginia, they really are laws.) Given this, any ballistic missile interceptor with enough “legs” to reach a satellite and a sensor system capable of finding the target has an inherent antisatellite capability. The Russians, Chinese, and a whole host of other countries understand this. Does this make the use of a BMD system to down your own satellite in a human safety scenario any less embarrassing? Probably not. With this mind, exactly how does taking the shot “…bolster missile defense”? And what message would it send to the Chinese? OMG, the US has BMD systems that have the inherent capability to hit some satellites! DUH!
Is there a potential that this event will add more fuel to the debate on space weapons? Yes. However, the proposal announced by Sergei Lavrov, the Russian foreign minister, at the UN conference on disarmament in Geneva discussed “Weapons deployment in space…” By this definition, space weapons would only include space-based weapons. Any weapon based elsewhere would not fall into this narrow definition of “space weapon”.
As for the possibility that technology protection is the real reason for taking the shot, give me a break. (Where’s CSM {Chain Smoking Man}? Wait, wasn’t that him standing just off camera at the press conference today?) Unlike the shuttle, this satellite was not designed to reenter intact or (relatively) unscathed. The aerodynamic stress and extreme heat of an uncontrolled reentry will reduce the high tech components to little more than dust. Here size (mass) matters. Large structures, like a 1000+ lb tank of hydrazine, are truly more likely to survive than small ones, like an 8-oz digital electronics board.
The ‘technical argument’ for this is that if successful it will demonstrate the Navy’s continued relevance to funders.
The biggest political drawback I can see is that, even if the shot is wildly successful and all the debris burns harmlessly, every on-orbit hiccup for the next ten years will be blamed on us.
Would there be some cause for being unusually confident that the SM-3 will intercept the satellite? Griffin seemed to be managing expectations by discussing the potential for a miss or a glancing blow, but after China’s recent hit, a miss would seem embarrassing at the very least. This seems like an unusual move for an organization that has been reluctant to test its wares in the past.
30 mentions of the word ‘Hydrazine’ in the transcript! sounds like subliminal messaging.
I argue that this is a big “Fuck you” from Cheney to Russia and China who had the audacity to introduce a new anti-space-weapon initiative at the UN two days ago.
http://www.moonofalabama.org/2008/02/the-space-weapo.html
Is there opportunity in this problem? Evacuate the ISS, redesign the intercept, and rid ourselves of that costly and unproductive albatross so we can proceed with some real science in space?
Regarding the hazards, I think you’re all missing (and I know, I missed it too) the issue that the hydrazine in the full tank is now frozen. Griffin pointed out — correctly, I believe — that this nearly guarantees the tank, intact and still mostly full, reaches the surface.
See
Heading off a toxic iceberg from space
Concern about hydrazine fuel leads to Pentagon’s satellite intercept plan
http://www.msnbc.msn.com/id/23166344/
By James Oberg, NBC News space analyst // Special to MSNBC
updated 5:56 p.m. CT, Thurs., Feb. 14, 2008
and
Q&A: Destroying a broken spy satellite
What will happen when missiles are fired from Navy cruiser
By James Oberg, NBC News space analyst // Special to MSNBC
updated 1:41 p.m. CT, Thurs., Feb. 14, 2008
b is right. Gen. Cartwright and the DoD press release both emphasized that the decision was made by the President, with as little as 3 days notice before the deed is done. It’s FY not just to Russia and China but to Congress, all arms controllers and the whole world.
I am very disappointed at the non-reaction from the funded arms control community. There should have been angry press conferences yesterday and today. There should be action in Congress dissenting from the position taken by Tauscher & Co. on the HASC, or at least questioning the BS rationale given for this unarguable ASAT shot.
The issue is that President Bush is making an intemperate, ill-considered decision as a demonstration of his power to do so in the last year of his presidency, historically reaffirming American commitment to reject arms control and assert its right to develop and retain capabilities for war in space as well as anywhere else.
The risk of debris creation from the shot is as much a nonissue as the risk of injury to someone from falling hydrazine. The latter is a finite risk of some people being exposed to a small risk. The most effective way to mitigate that risk is to watch the reentry, alert whoever the object might fall on and educate people to get away as quickly as possible if it falls near them. Yes, a successful intercept would eliminate even this minor danger (and possible public relations disaster). But Gen. Cartwright tried to pretend the shot would give some control over where the debris was coming down, while conceding that most of it would be coming down over several orbits, pretty much anywhere.
Technical reasons for such a test? The SM-3 as is cannot be considered an ASAT weapon due to its low ceiling, but a simple booster upgrade would make it a sea-based, globally mobile LEO ASAT if they can show the seeker works in this role. Its closing velocity in TMD roles is typically half or less the 9.8 km/s for this shot but the target is larger and probably brighter as well as fatter, which partially offsets the added stress of the high closing speed. Besides, if MDA can do it with the GMD system, the same technology base should be available for the latest generation of the SM-3.
They have 3 missiles ready and they say they’ll take one shot at a time, with an 11-day window for assessing and correcting any problems. Oh boy, they are a brave bunch, out there taking their best shot at this thing, this monster gone rogue that they created (remind you of anything?) that now menaces the Homeland.
JimO, it is hard to argue with Michael Griffin’s claim that modeling “as certain as any like this can be” shows the tank will (with emphasized certainty) come down intact but breached and full of hydrazine slush. What Griffin couldn’t say with any certainty was that anyone would be hurt. Cartwright almost shot himself down when he described what would happen should people be exposed to the resulting “two football field” sized cloud, which will only happen if the satellite misses the ocean and hits a populated area. Obviously, it is unlikely (or very unlikely) that anyone will be killed or even seriously injured. The risk is distributed over most of the world and its population. The cost of attempting to mitigate the risk by blasting apart the satellite is in nine figures, and is in addition to the cost of ground-awareness and response measures that will be mobilized in any case both as a fallback if the intercept fails and to support the public rationale for the ASAT test.
No way is safety the real motive for this outrageous act.
this satellite is very low in oribt, so low that in a few weeks it’s going to break up in re-entry. it’s going to produce a few large chunks. if we break it up at this point, the debris must stay in the very lower regions of earth orbit 300 miles below the ISS. the missile doesn’t have any where near the energy to change the debis orbit enough to damage anything and even if it did, the closing velocity is 22,000 mph while the satellite is going 18,000 mph- that means the missile needs to be going in the opposing direction to the orbit of the satillite. any energy imparted to debris would slow them down moving them into a lower orbit not a higher one (that is if the angle is correct) I know it’s profitable to scream that the sky is falling and doom for us all because saying that there isn’t any risk from this won’t generate the page views that paranoia does.
The motivation nobody’s mentioned so far is classified stuff that the President has been convinced needs to be protected.
Mark, I see you have the firm faith of your convictions and don’t need facts, so I’ll decline to bother you with them in the future.
But Timmy, you are still thinking in earthside collison analogies that don’t work in space — they mislead you, in space [the General made the SAME mistakes, as someone perceptively noted, above].
The energy transfer is hardly at all dependent on the original collider vectors — it creates a kinetic energy omnidirectional explosion of both colliders, each cloud more or less ‘on average’ moving in the original direction of the collider, but with debris expanding in all directions from that center. On the China impact a year ago, at least one piece was blasted into an orbit with an apogee 1000 (t-h-o-u-s-a-n-d, not a typo) kilometers higher… from a front-on collision!
This effect is mitigated in the current case because of the extremely low apogee — but some pieces ARE going to fly a LOT higher for at least a few days.
I’m checking the figures, but it seems to me that the frozen nature of the full hydrazine tank — a first-ever entry of such an object — raises the hazard to humans above a pre-set threshhold.
Recall the fuss back in early 2000 when NASA decided to deorbit the still-working Compton Gamma Ray Observatory because its degrading control system might fail before a controlled entry could be made. Its particularly dense structural elements created a hazard above this same threshhold. Astrophysicists howled (and I did too, in several UPI articles), but NASA stuck with the prescription when the present threshhold gets broken and splashed the bird. Same standards here, it seems, with somebody else’s satellite.
“No way is safety the real motive for this outrageous act.”
I concur, it is not normal procedure for the government to spend this much money to ameliorate a risk this small, especially since alternative procedures (e.g. last orbit tracking and notification, global alert hazmat teams, etc.) are likely to be much cheaper and possibly even more effective.
In addition to “demonstrate the wonderful Aegis technology” I would have to place a high degree of likelihood on “destroy as much classified technology as possible”.
Carey Sublette
Here’s a question for those more knowledgeable about space systems. If hydrazine is really the problem, why not just burn it off with the thrusters before reentry?
SQ – the NRO lost control of the satellite right after launch. You can’t turn on the thrusters if the bird can’t receive the signal.
I suspect Carey is right: this seems to be in part an opportunity seized for a demonstration and in part an export-control shot. Even if there is only a small chance that sensitive technology would survive re-entry intact, that may be a larger chance than what a decision maker somewhere along the line is prepared to accept.
(To answer my own question about burning off the hydrazine, the satellite is out of communication.)
Recalling Cosmos 954 over at http://whirledview.typepad.com
JimO, my intent is not to trade insults with you in this forum, but I believe if you review my comments you will see that I have taken full account of your facts.
I think some perspective is in order here. Yes, the international politics of this *potentially* suck (more on this in a sec). But this decision makes much more sense if you put yourself in the shoes of a politician-policymaker with the responsibility of making the call here. You basically have two choices:
1) Do nothing and thereby knowingly accept the risk, however small, that a spy satellite-turned-chemical bomb drops on some population center and kills or hurts people; or
2) Try and take the satellite out, knowing full well that its going to piss off lots of committed arms controllers and maybe even the Chinese and the Russians but do your best to manage the international fallout.
No politician in a democracy is ever going to choose the first option. Period. “Mr.President, when did you first become aware of this risk?” “Mr. President, what do you have to say to the families of the victims?” “Mr. President, let me make sure I understand this properly: 8-year old little Suzy Jones and her adorable puppy are dead because you didn’t want to upset China and Russia?” You get the idea.
China and Russia may even empathize with this decision. As far as I can tell their response so far has been muted. I’m limited to English-language Chinese and Russian news sources, but as of this writing Pravda and ITAR-TASS, for instance, have no story on this posted on their front pages.
Xinhua has a very short story buried further down on the page. The text is worth reproducing in whole:
U.S. to shoot down defunct spy satellite
WASHINGTON, Feb. 14 (Xinhua)
The Pentagon said Thursday it plans to shoot down a defunct spy satellite expected to hit the Earth in early March, agencies reported.
An option on the table is to use a sea-based missile to do the job, before the satellite falls into the Earth’s atmosphere, Pentagon officials told reporters.
Last month, Gordon Johndroe, spokesman for the National Security Council said a defunct U.S. spy satellite is falling from orbit and could hit the Earth in late February or March.
The satellite, which has lost power and propulsion, could contain hazardous materials, he said.
Because the satellite could not be controlled any longer, it is unknown where the Earth it might hit.
In 1979, Skylab, a 78-ton abandoned NASA space station fell from orbit in an uncontrolled manner.
Its debris eventually dropped into the Indian Ocean and across a remote section of western Australia harmlessly.
Sorry, JimO, but as a supporter of this action, maybe you could answer the question I would most like to ask Gen. Cartwright, Amb. Jeffrey and Director Griffin. Namely, if this is such an innocent and responsible action on behalf of the United States, intended solely to minimize risk to human life on Earth below, is it then a good example for other spacefaring nations to follow, when and if they have the capability? If a Chinese satellite, for example, should fail in this way and threaten to rain hydrazine or some other noxious substance on some unfortunate village somewhere, should China then use one of its ASAT interceptors or another missile to shoot it down in this same manner? Would or should the US applaud such an action? How about France, or Iran, say? Would you accept the explanations offered for this intercept if they came from the North Koreans?
With regard to remarks by Mark Gubrund and JimO above:
It would be worthwhile to discover what risk models were run if safety really is the motivating factor. Those presumably involve decay/ reentry models, population density maps, etc. The end product, I’d think, would be something like “There is an X% chance that at least one person will receive injuries requiring medical attention.” Presumably X was greater than an action threshold.
I remain extremely dubious that safety was the reason for the decision but if it was, opening the risk analysis to examination would be very much in the government’s interests.
How can this test possibly be designed to test the wonderful AEGIS/SM-3 technology, as Carey said? This is a totally different task for the SM-3, one much, much more complicated than what the SM-3 normally does. If this action succeeds, normative issues aside, it will be an engineering marvel. There is a high probability of failure.
Given that this is a brand new task the SM-3 was not designed to do, it seems unlikely this action is designed to demonstrate the greatness of AEGIS.
Andy,
There are all kinds of improbable events of this sort that could be framed in just such an alarming way. Some of them would be far more consequential, were they to occur. (For example, the chance that crazies will get ahold of a Pakistani nuclear weapon.) So the real question might be why advisers would be motivated to present the choice to the President in the first place, framed the way you suggest it is framed. And that brings us straight back to the question of whether this really is about public safety.
Put another way, it seems like many people here have been using the “Jump to Conclusions” mat from Office Space. Shouldn’t we step back and think about it a bit before assuming we absolutely positively have all of the necessary information on this and can perfectly read the motives of the administration?
If NASA really requires 1 in 10,000 chance of hitting a person, then perhaps they should shoot it down. We really need to understand the chances of the hydrazine tank making down to Earth. The average number of people killed by the satellite is about 7% if the tank makes it to Earth. (That is, the average number of people killed is 0.07.)
well . it took the time to research everything possible written on whats available on the satellite, the weapon planned to “score the hit” and all other factors involved. i also read each and every comment from every brilliant mind on this forum (and that was a pleasure, mind you , so, here are my conclusions. 1) its a great chance to see if this wonderful aegis tech actually functions 2) the sensitive nature of whats in the bird must not fall into the wrong hands 3) it is a “fuck-you” to both russia and china. if we succeed, what a great notch on our gun,in view of recent developments
http://rutube.ru/tracks/464280.html?v=ca6edbbd593f016aeed89c0f1f3607ca
This is the latest report on space from Russia’s equivilant of the Pentagon Channel. They mention the satellite as the second half of a 42 second report on space in general. The first half is about Atlantis and the International Space Station. The report notes that a similar Chinese shot last year “caused an international scandal” and that the satellite “might contain a radioactive source, according to experts.”
Given that the Ministry of Defense’s own TV network devoted 20 seconds of airtime to it, it doesn’t sound like they want to make too big a deal of it.
Now that it is public that the shoot down is going to cost something around $40 to $60m….
If the real issue is just danger from a measly 1,000lbs of Hydrazine (Specific gravity of .797 @25C), then here are some other approaches:
a) take out an insurance policy from Lloyds of London for say, $500m of coverage against claims. It would probably be cheaper than the shoot down.
b) Contract it out to the Russians or Chinese to shoot down the bird for something south of $20m. I am sure the Chinese would jump at the chance!
Sometimes, trying to do PR can have the effect of drawing attention to the real reasons why the shoot down is being done.
Andy, the issue isn’t that the shot will “upset China and Russia”, it’s that the shot signals not merely American rejection of space arms control but American intent to forge ahead with testing and deployment of space war technology and weapons. This in time to serve as a response to the resurgent worldwide interest in space arms control and renewed Russian-Chinese proposals, which despite their inadequacies have widespread support in the absence of any American counterproposals. This as a parting shot of the Bush space warriors in their last year of little power.
Bush is taking the opportunity to commit a violent act on behalf of the United States and its arms-control rejectionist policy. Your narrative of a presidential decision to act in protection of “8-year old little Suzy Jones and her adorable puppy,” essentially the Bush gang’s narrative, is belied by the fact that the same risk has been run many times before, without catastrophe, and any fatal outcome in this case is very unlikely. Even if I can imagine Bush assuming the mindset of a protector in authorizing this action, it only goes to show what an intemperate fool he is, and a dishonest one at that, since his true motive is to show that he has the power to commit this act.
I’ve got your motive right here:
The Heritage Foundation, “The Next Steps for Missile Defense”, April 07 (http://www.heritage.org/Research/NationalSecurity/bg2028.cfm):
“the Bush Administration and congressional supporters of missile defense need to take the following steps…
– Formulate a strategy involving missile defense supporters in Congress and President Bush to protect missile defense programs in defense authorization and appropriations legislation,
– Maintain robust funding for the missile defense program,
– Support the construction of a “space test bed” for missile defense;
– Rebut charges that the testing and fielding of missile defense systems will cross a threshold by “weaponizing” space,
– Support the deployment of sea-based defenses to protect U.S. coastal areas against short-range ballistic missiles launched from ships,
– Oppose efforts to deny the military the option of putting developmental missile defense systems on operational alert, and
– Shift responsibility for sea-based missile defense systems from the Missile Defense Agency to the Navy.”
And here’s the aimed-for end point:
“Arms control advocates are currently focused on preventing the weaponization of space. They base their proposals on the assertion that space is not already weaponized,23 which is valid only if properly defining the term “space weapons” is irrelevant to the exercise of controlling them.24
The fact is that space was weaponized when the first ballistic missile was deployed, because ballistic missiles travel through space on their way to their targets. The threat that these weapons pose to U.S. security and the U.S. population is undeniable. The superior effectiveness of space-based interceptors in countering ballistic missiles is based on the fact that ballistic missiles transit space. As a result, space-based interceptors are ideally located to intercept ballistic missiles in the boost phase.
Congress needs to reject the charge that space-based ballistic missile defense interceptors would constitute an unprecedented move by the U.S. to weaponize space. It can do so by adding a preamble to the amendment to provide more robust funding for construction of a space test bed.
This preamble should take the form of a congressional finding that the deployment of ballistic missiles weaponized space and that the government has a fundamental obligation to protect the U.S. population and territory against ballistic missile attack. The preamble should go on to state that space-based interceptors will likely be the most effective defense against ballistic missiles precisely because ballistic missiles are space weapons. The preamble should conclude by stating that the construction of the space test bed and eventual deployment of space-based interceptors is a response to the weaponization of space brought about by the deployment of ballistic missiles.
President Bush and missile defense supporters in Congress should also be prepared to counter proposals in defense authorization and appropriations bills calling for the U.S. to enter into an international agreement that imposes sweeping prohibitions on space weapons, including by implication all forms of anti-satellite weapons”
If this shot fails, it will be used as an argument for space-based interceptors instead. If it suceeds, it will be used as an argument for space-based interceptors as well.
Regards, Cernig
Andy: “I don’t think anyone anticipated the breach of the [hydrazine tanks].”
A large-scale natural disaster in which many people died occurred in a major US city a few years ago—despite ample advance notice of a high probability of occurrence. And ultimately, there wasn’t much fallout. Now, you might say they’ve learned their lesson, but somehow the government spending tens or hundreds of millions solely to prevent a million to one chance of collision—not even convincingly demonstrated to be a fatal collision—doesn’t ring true. It’s not the possibility of accident that spurs us to action, it’s the repeat nature of such; you normally see a response (overreaction?) of this magnitude after there’s already been a similar incident and paranoia is running high.
Andy
The point here is that they did not give probability of casualties. I don’t think it is very difficult to calcuale that for U.S. military.
Do tax payer think it is worth to spend 60 million U.S. dollor, if the probability of casualities is 1 in billion?
Without that number, this action can just be viewed as excuse for doing ASAT test.
Actually, it was the biggest news in http://www.sina.com(Yahoo in China). The comment is that this is a ASAT Test.
“I am very worried about the debris creation — particularly the debris that the light-weight interceptor will kick into higher orbits when it hits the massive (bus-sized) satellite. Thnk, as Geoff Forden suggested, of a ping pong ball hitting a superball.”
The laws of orbital mechanics dictate that, regardless of what happens at impact, any debris generated will be in a new orbit that must still pass back through the same altitude as the point of impact, which will be 240 km. Due to the geometry of the impact, the impactor will only likely decelerate the fragmented NRO satellite, further lowering the orbit. However, even if the impact event were to magically transfer a huge boost in kinetic energy and greatly raise the apogee (high point) of the debris’ orbit, the perigee (low point) will still be at 240 km or lower. This is a law of orbital mechanics.
Any impact fragment in such a low orbit will reenter and burn up in a matter of days. Orbital debris on this time scale is not a realistic concern.
Thus, we can state with certainty that there will be no generation of long-term orbital debris from this planned event. This is in contrast to the orbital debris generated by last year’s Chinese ASAT test, which will remain in orbit for centuries.
Whether the planned intercept attempt is a good or bad policy decision is a valid (different) issue, but please avoid confusing this with the physics.
Andrew:
You should take another look both at what I wrote, ast ASAT intercepts and debris models.
Having now looked at a debris model from a colleague who I think is about the best in the business, 50 percent will be down in a day and 95 percent will reenter in 10 days. 1-2 percent, however, will remain in orbit for some longer period than 30 days.
Moreover, some of these debris may be in much higher orbits. As we saw in the Chinese test, some of the resulting debris had apogees as high as 3,500 km. General Carwright indicated that the closing velocity of the intercept will be 9.8 km per second.
My worry stems from the very large gap between the size of the interceptor and the size of the satellite, more than 100:1. I don’t think we’ve ever seen a collision disparity like this.
The NASA breakup model underestimated the debris from the Chinese test by a factor of 3 to 4. I wonder how well anyone can actually understand and quantify the risk to ISS. This is a big science experiment. Chances are, it will be fine. But then again, you could say that about letting the hydrazine tank reenter.
“I am kind of partial to the Aviation Week comment about the reason why this satellite has to be shot down —- to prevent pieces from coming down where other parties (read Chinese, Russian, Indian, French, etc.) can recover and learn details about how the bird is built.”
[and many similar comments]
This just doesn’t add up for me. Since the earliest spysats (e.g., Corona), every component that could reenter had clever passive countermeasures to ensure that nothing sensitive could fall into less-than-friendly hands. Corona’s reentering film capsules, for example, were rather ingeniously designed to sink if not recovered in 24 hours after ocean splash down. See: <http://www.vectorsite.net/tamrc_06.html#m2>
Surely, the NRO satellite was design with the possibility in mind that it might someday reenter in an uncontrolled fashion and land somewhere that would be less-than-desirable for national security interests. For example, standard practice for sensitive military electronics is to build them on a substrate of Pryofuze, an energetic reacting Pd/Al alloy that can be triggered to “burn” (exothermally alloy), generating over 2000 K and melting circuits, etc. Recall reports of the “puff of smoke” that was observed when the EP-3 spy plane opened its doors after being forced down in China. These are examples of active devices (i.e., they need to be triggered), but I can’t conceive that a similar passive self-destruct mechanism is absent from the more sensitive NRO satellite components.
The official story—that they did not expect to lose control of the satellite immediately after arrival on orbit, with the hydrazine tank still full—appears to hold more water. Whether this justifies the shoot-down, or is being used as justification for some ulterior motive, is another question.
Thanks, Andrew, for making the clarifying point that the new orbit of any debris must pass through the same altitude as the intercept. In addition, the higher the apogee the lower the perigee, and atmospheric drag increases exponentially below about 160 km. Therefore only debris that remains near the original satellite circular orbit will persist for weeks and months. The high-apogee debris Jeffrey is talking about is debris that will come down cleanly in the first orbit, unless it should impact something else on that first arc.
Gen. Cartwright promised that they would try to schedule the shot to minimize that last risk. He says that because they ought to, but apart from minimizing risk to the ISS and a few other targets, it may be hard for them to schedule around all traffic in LEO.
I am not clear on the significance of the satellite/interceptor size ratio. It seems to me that the interceptor will accomplish the goal of fragmenting the satellite and a larger target/interceptor size ratio ought to mean fewer fragments if anything.
The fact that the target is more than twice as large in linear dimension as the TBM warhead the interceptor is intended to home on partially mitigates the challenge posed by the twice-higher closing speed.
Wouldn’t a THEL be safer?
Heating the hydrazine tank may explode it.
Outstanding comments thread. A pleasure to read.
Jeffrey Lewis wrote: `Moreover, some of these debris may be in much higher orbits. As we saw in the Chinese test, some of the resulting debris had apogees as high as 3,500 km. General Carwright indicated that the closing velocity of the intercept will be 9.8 km per second. My worry stems from the very large gap between the size of the interceptor and the size of the satellite, more than 100:1. I don’t think we’ve ever seen a collision disparity like this.’
There is a subtle but important point that people seem to be missing here:
When the faster object (the satellite) hits a slower object (the kinetic-kill interceptor), the faster object or any fragments from it must be decelerated by the impact. There is simply no physical mechanism I can think of that will result in fragments of the satellite leaving the impact with a greater longitudinal velocity than it had originally. (I hate to role out my credentials at this point, but I have been working as a university professor & researcher in the field of shock waves and hypervelocity physics for 20 years. If anyone can explain the mechanism by which the initially faster object is accelerated by the impact, please inform me.)
Now, the slower object (impactor) or fragments of it may actually be expelled from the impact at a greater velocity. Think of Geoffrey Forden’s ping-pong ball analogy for a moment: a heavy, dense superball (the satellite) hits a light ping-pong ball (the interceptor). See Geoff’s illustartion here. It is possible for the ping-pong ball to be sped-up by the impact, but the superball must slow down, albeit only slightly if it is very massive.
This analogy is highly idealized: impacts at these speeds are certainly not elastic, and the relative acceleration/deceleration of the bodies involved is governed by impact and transmission of shock waves, which in turn depends on their acoustic impedance (product of density times sound speed). However, the “superball impacting ping-pong ball” analogy will work for now to illustrate that only the initially slower object can be accelerated to a higher speed. The terminology is also a bit confusing here, since the “interceptor” is actually the slower body that is impacted by the faster target satellite in the earth-fixed reference frame.
The significance of this point is absolutely critical: in the Chinese ASAT test, the interceptor was almost equal in mass to the satellite (Geof Forden’s numbers are 600 kg vs. 880 kg, respectively). All of the debris tracked leaving the impact with an increase in longitudinal velocity (by as much as 600 m/s, as Goeff Forden’s analysis of the tracking data shows) must have been mass from the interceptor.
For the proposed intercept of USA 193, the mass of the interceptor is only 20 kg, compared to the mass of the satellite (2300 kg). Thus, the maximum mass of material that could be kicked into a significantly higher apogee orbit is only 20 kg.
David Wright’s comment: This satellite is about two-and-a-half times as massive as the Chinese satellite destroyed last year, so you would expect to get a lot more debris is true. However, by the argument above, none of this mass can be kicked into a significantly higher apogee orbit. Only the mass of the interceptor (20 kg) can have a significantly increased longitudinal velocity. Thus, the potential amount of high-apogee debris generated by the proposed intercept of US193 is much, much less than the Chinese ASAT test.
Don’t be bashful about rolling out your credentials.
If all you are arguing is that the amount of mass that will be kicked into higher orbits is constrained by the mass of the interceptor, well, yes.
I think the problem is that you are conflating — or assuming that I am conflating — two separate concerns: 1. This will create a massive amount of short-term debris and 2. a very small amount of the debris will be long lived, with a small portion of that in higher altitudes.
The issue of the ‘small portion ‘ of debris that will be in higher altitudes is an issue for the following reasons:
a) space debris that remain in orbit for any length of time (arbitrarily say more than 1 year), cumulatively add up.
b) debris that are too small to be tracked, if it were in the right place at the right time, can damage not only other spacecraft, but also more sensitive things like instruments and sensors. A speck of paint, too small to pick up by ground based radar, can just about ruin the day for an optical sensor if it hit it just right.
A certain amount of increase in space debris from normal activities is unavoidable. The point is, shouldn’t activities that increase (often substantially) the debris load, and thus, everyone and everythings’ risks be limited to the extent practical?
Just because the USA 193 debris is in lower orbits than the Chinese ASAT test does not mean that there is no danger from the debris and no long term increase in debris orbiting earth.
Spacecraft that are launched (and ending up in higher orbits or beyond) have to transit the lower altitudes where USA 193 debris will be around.
True, the chance of a strike may be exceptionally low… and I am sure someone with a rusty slide ruler can crank out odds that look real good. I mean, some Chinese engineer also did the same calculations for their ASAT test that showed how low the odds of their debris striking a satellite are!!!!
That is great until one of YOUR birds mysteriously malfunctions or explodes possibly because it struck debris.
A statistically low risk does not equal NO risk.
At a certain point, it is necessary to have the engineer talk squelched and the policy wonk talk amplified.
The optics and politics of this American ASAT test look awful from the point of view of long term American interests in space.
Let me also raise the economic losses possible from what I call the ‘Palomares Effect’. If this tank falls in any economically active zone, it could cripple export traffic from that zone for years, as people outside the zone become too frightened by news reports, to buy food or other materials from the zone. And say goodbye to any local tourist industry. Didn’t the USG pay out millions to spanish enterprises that suffered business lossses from public fear of radiation from those two lost H-bombs?
The Russians aren’t fooled. (http://news.bbc.co.uk/2/hi/americas/7248995.stm)
Russia has accused the US of using a plan to shoot down a broken spy satellite as a cover for testing an anti-satellite weapon.
The US said last week that it would use a missile to destroy the satellite, to stop it from crash landing.
Officials say the satellite contains hazardous fuel which could kill humans.
But Russia’s defence ministry said the US planned to test its “anti-missile defence system’s capability to destroy other countries’ satellites”.
…“Speculations about the danger of the satellite hide preparations for the classical testing of an anti-satellite weapon,” a statement reported by Itar-Tass news agency said.
…Such testing essentially means the creation of a new type of strategic weapons,” it added.
“The decision to destroy the American satellite does not look harmless as they try to claim, especially at a time when the US has been evading negotiations on the limitation of an arms race in outer space,” the statement continued.
The Russian defence ministry argued that various countries’ spacecraft had crashed to Earth in the past, and many countries used toxic fuel in spacecraft, but this had never before merited such “extraordinary measures”.
From http://www.mda.mil/mdaLink/html/delta_team.html
It could be that there is a similar “rare” combination of circumstances in play. Dr. Griffin under these circumstances might not be the best spokesman to represent the interests of the civilian space program.
Does anyone have any data on the satellite’s orbit at the point of proposed interception? Is it circular, or is this the apogee or perigee of a more elliptical orbit?
It was noted by behindthefall over at emptywheel that according to the Shanker 2/14 NYT article (http://tinyurl.com/27xrk3), this satellite is 5,000 lbs. This is a lot less than most reconnaisance satellites, which run 15-30k. Anyone know what gives?
(Apologies to our host—this is the second iteration of this comment, I put the first one in the wrong thread.)
“Does anyone have any data on the satellite’s orbit at the point of proposed interception? Is it circular, or is this the apogee or perigee of a more elliptical orbit?”
Wikipedia has the orbit presently being very nearly perfectly circular:
Apoapsis 268km, as of 2008-02-11
Periapsis 255km, as of 2008-02-11
Lao Tao Ren: “Just because the USA 193 debris is in lower orbits than the Chinese ASAT test does not mean that there is no danger from the debris and no long term increase in debris orbiting earth.”
Yes, it does mean that there is no long-term danger of debris orbiting earth. The fact that the intercept is occurring at such a low altitude means there will be no fragments left in orbit after a month.
To make an analogy: the intercept of USA193 is walking through a smoky hotel bar. The Chinese ASAT test last year was the equivalent of being a chain smoker for life. Both may be unpleasant, but only one of these is high-risk behavior.
The only straw man argument would be if a fragment from the USA193 intercept were to result in another, higher-orbit impact within the few days after the shot, that then resulted in the generation of high perigee debris. I.e., an upward cascade of debris generation. But the odds of this happening in just a few days after the first impact are truly astronomical (we are talking one in billions—or more—here). Like getting lung cancer from a single dose of second hand smoke. If you worry out things like this, you don’t get out of bed in the morning.
Yossi: “Wouldn’t a THEL be safer? Heating the hydrazine tank may explode it.”
Ground-based lasers have been proposed to deal with smaller orbital debris, by vaporizing a tiny bit off the debris to decelerate slightly and lower its orbit, thereby bringing it down sooner. In particular, see the study done by Ivan Bekey, (also, here and here).
However, we are nowhere near having lasers powerful enough to cause structural damage to a large satellite in orbit or significantly heat something as big as a half-ton hydrazine tank.
Jeffrey Lewis : “I think the problem is that you are conflating — or assuming that I am conflating — two separate concerns: 1. This will create a massive amount of short-term debris and 2. a very small amount of the debris will be long lived, with a small portion of that in higher altitudes.”
My two points are:
1. All of the debris generated will be short-lived (days or weeks at most), since it must have a perigee of 240 km or less.
2. Only a tiny fraction of the debris generated (the 20 kg kill vehicle) has even the theoretical potential to be accelerated to faster than the satellite’s original velocity and get kicked into a higher apogee orbit (the perigee of even these faster fragments will still be 240 km or less, as I explained in a prior post).
“the intercept is occurring at such a low altitude means there will be NO [emphasis added] fragments left in orbit after a month”
My oh my, that is like saying there is NO risk in having unprotected sex with a panda.
“Only a tiny fraction of the debris generated (the 20 kg kill vehicle) has even the theoretical potential [emphasis in original] to be accelerated to faster than the satellite’s original velocity and get kicked into a higher apogee orbit (the perigee of even these faster fragments will still be 240 km”
Now, that is wonderful Engineer Speak.
Q.E.D.
Jeffrey… Wonk Speak PLEASE.
Tell us about the optics and politics of this thing!
FYI, the limits of detection of space debris via ground based radar and optical sensors, is something like 1cm for the Haystack Radar and roughly the same for optical. Objects smaller than 1 cm can be detected, but with exponentially increasing difficulty. Spacecraft Surface Examinations, of course, find plenty of evidence of smaller particles.
It would be fair to say particles that are smaller than 1cm but troubling —- like the ones that cause the average of 2 windows to be replaced per Space Shuttle mission, are beyond the abilities of the present detection system to economically find. If a particle is smaller than the sensor’s normal detection limit, it doesn’t mean that it doesn’t exist or that there is no risk from a particle of that size.
These sub 1cm particles in lower orbits can cause plenty of damage to a space craft transiting the orbits.
To say the deliberate destruction of USA 193 poses NO risk is an impressive statement that could have come out of a PQ rally!!! Je me souviens.
So it seems we have two camps here: those who see the odds of harm from a hydrazine tank’s fall to earth as vanishingly small, and those who see the odds of harm from post-intercept debris as vanishingly small.
Somehow, I doubt the administration’s choice of a course of action was based on weighing one set of odds and consequences against the other.
“We really need to understand the chances of the hydrazine tank making down to Earth.”
I am sure that codes exist for modeling reentry heat and momentum transfer. I am also sure that the parameters for the fuel tank (size, wall thickness, etc.) and the hydrazine are well known. So is the current temperature of the satellite. The difficult part might be modeling how the rest of the satellite might come apart around it.
It’s hard to believe that the hydrazine, if exposed to the atmosphere on reentry, wouldn’t combust. The question is how much heat transfer would take place to take it out of its frozen state and burst the container, or what other events might open up the container.
But overall I would be extremely surprised if nobody were running those simulations even as I type.
Andrew Higgins is correct. The only risk in space created by the intercept will be from the very small amount of debris from the interceptor that will climb to a high apogee before crashing back to Earth in less than one orbit. Little or no debris will be scattered forward into a high apogee orbit with perigee at the intercept altitude. No debris will persist significantly longer than the satellite would have, since perigee for all debris will be the intercept altitude or lower.
Debris is not the issue.
> Jeffrey… Wonk Speak PLEASE.
Another topic that might stand some wonkification is the BMD aspects of this. Although people (Garwin IIRC) have noted that the SM-3 has some anti-ICBM capability, the numbers that have come out of this event might help sharpen up the analysis.
For example, hitting USA-193 at 240 km altitude is pretty much like hitting an ICBM RV ~600 km uprange of the target, isn’t it? And since the Navy, I’d think, is trying for a co-planar intercept, that constrains where the ship can be (on the ground track of the satellite/RV downrange of the intercept point).
Etc.
On the chances of someone being killed by the satellite if nothing is done, there are, on average, about 0.01 persons within 30 yards of any point on Earth’s land surface within the latitude band covered by the satellite’s orbit, and about a third of the surface is land, which leads to an expectation value of 0.034 for the number of people who will be close enough to the impact to be potentially killed by the hydrazine.
That’s not a 3.4% chance of someone being killed. The actual chance of anyone being within the potential kill radius is closer to 1% due to clustering of people.
The chance of any of those people being killed is smaller still. If a satellite chunk weighing a ton crashed within 30 yards of you and emitted a noxious cloud that burned your lungs, would you be more likely to hang around huffing the hydrazine or to run screaming from the site, or perhaps first try to rescue anyone not able to get out on their own?
Even if you can’t get out, the hydrazine cloud will disperse and if you breathe it for some minutes you might get sick but in most cases you would survive, particularly with medical and rescue workers rushing to the scene.
If we estimate as much as a 10% chance that someone within 30 yards of the impact is actually killed, we are down to one chance in a thousand of a fatality, or 99.9% likelihood that no one dies.
All this assumes Michael Griffin is right to assert that the hydrazine tank “will” come down intact, breached, and full of hydrazine slush.
The worst-case scenario, which is extremely unlikely, is that the tank hits a building or a densely populated area, and maybe a dozen get killed. The intercept will do little to mitigate this risk, since its likelihood of failure is at least 10% (many analysts say more), and since there may still be large pieces of debris that could hurt someone.
Thanks Mark, etc.
The NO. 1 issue, from the moment the shoot down was proposed, is the optics and politics of this thing.
It is worst than proposing to seat the Michigan and Florida delegates based on the primary results there.
I have learned a lot reading this. But what do people think about the probability of a successful intercept? The NYT seems to think this will be easier than other things SM-3 has done:
http://www.nytimes.com/2008/02/16/washington/16satellite.html?ref=us
The relevant sentence is: “So it should be easier for the Standard Missile 3, a Navy weapon launched from an Aegis cruiser in the northern Pacific, to find and strike a satellite almost the size of a school bus making orbits almost as regular as bus routes around the globe, 16 times a day.”
Is this true?
It seems to me that a successful intercept of a satellite might be easier, in theory, if the system was designed to do so from the beginning, but quickly trying to shift what the SM-3 does in such a short period will not necessarily end in success.
Many of you know the engineering problems here much better than I do. What do you think are the chances of a successful intercept?
p.s. Dr. Wonk — so is Andrew Higgins right about the debris issue or not?
You are comparing an intercept of a 1 m target at 5 km/s with intercept of a 3-10 times larger target in linear dimension at 10 km/s closing speed. How will the various systems of an interceptor designed for a 5 km/s intercept be stressed by the higher closing speed?
First, 10 km/s is very fast. One second before the impact, the target is 10 km away. The interceptor has to aim a telescope at it and adjust its own course during that last second with precise puffs of its thrusters. When the target is 100 m away, there is only 10 msec until the collision.
So everything is happening very fast. However, if the aim is better before the last moments, less has to happen in the last moments.
Since the satellite target is larger, the interceptor can track it from farther away and begin to correct its own velocity sooner. This relieves some of the stress on the thrusters of having to make large, fast corrections. In addition, the interceptor can miss the aimpoint by more and still score a kill. However, the expected total velocity correction is still proportionally greater, which stresses the divert fuel supply of the interceptor.
Weighing these various factors is a sufficiently heavy task that even the mighty David Wright has shrugged, and I tend to agree: It’s 50-50, i.e. no information about a binary outcome.
Lao Tao Ren: please remember that the really high stuff will be cleared in a single pass – high apogee means low perigee. So when Andrew is laying out the worst-case scenario (a high orbit collision) it requires that this collision happen in the day or two after the collision. Maybe if this timescale was over a period of years it might get into the realms of possibility, but the chances of getting such an impact in just a day or two is so utterly minute that it’s not worth worrying about. Might as well worry that the fuel tank will hit the White House or a Uranium shipment if they don’t shoot the thing down.
And when Andrew says there will be no fragments after a month, that is absolutely certain: it’s not possible for any objects’ perigee to be any HIGHER than 240km. Can’t happen. So everything, every single piece of debris, is decaying from a perigee of (at most) 240km.
Atmosphere doesn’t care what your apogee is.
Andrew Higgins: “There is simply no physical mechanism I can think of that will result in fragments of the satellite leaving the impact with a greater longitudinal velocity than it had originally.”
A possibly naive question: Suppose the larger and heavier object has a cavity pointing towards the approaching impactor. The impactor passes the entrance and hits the bottom of the cavity. Now, the material near the entrance of the cavity will be hit from the inside by an expanding hot gas cloud (evaporated material from both the impactor and the heavier object), won’t it? Can’t this accelerate some fragments of the larger object in the direction of its original motion? Or am I misunderstanding something?
I particularly like “Atmosphere doesn’t care what your apogee is.”
Mike, Andrew is correct with the following potential point of disagreement: The last estimate I saw that 1 or 2 percent in orbit longer than a month.
I agree with the general point that the debris risk will be short-lived is correct and the potential for higher orbit debris constrained by the mass of the interceptor.
Even very small risks, though, are not the same as “zero” — something the Administration highlights when it talks about hydrazine, if not debris.
Kusigrosz: “A possibly naive question: Suppose the larger and heavier object has a cavity pointing towards the approaching impactor. The impactor passes the entrance and hits the bottom of the cavity. Now, the material near the entrance of the cavity will be hit from the inside by an expanding hot gas cloud (evaporated material from both the impactor and the heavier object), won’t it? Can’t this accelerate some fragments of the larger object in the direction of its original motion? Or am I misunderstanding something?”
Yes, ricochet and other secondary events are possible, and these are taken into account in more sophisticated debris generation models.
The question you have to ask is: how effective is this mechanism at generating a significant amount of debris that will have just the right orbital characteristics to keep it in orbit longer than the original satellite and raise its orbit sufficiently to threaten other satellites? Essentially, only impact fragments that have undergone pure prograde delta-v from the original satellite are a threat; every other velocity vector fragment will have a perigee lower than the original 240 km and will likely burn up within a few orbits.
Remember we are starting with just a 20 kg kill vehicle. For your scenario, this impactor first has to strike one part of the spacecraft directly behind another part of the spacecraft (not very likely, but let’s be sporting and say it’s a 1 in 10 chance). Yes, there will be a ejecta cloud that is generated, of similar mass to the impactor. However, this ejecta spreads outward roughly hemispherically. Only a fraction of that cloud will strike the spacecraft structure in front of it; let’s be generous a call it 1 kg. Only a fraction of material hit in that secondary impact is in turn accelerated, since being hit with an impact spray is really not that bad (that the whole idea behind multi-wall Whipple bumpers) and is not very efficient at accelerating the structure hit, but, again, let’s be charitable and say that 100 g is launched from this secondary impact. Of this, only a fraction (say, 10 g) will again move in the prograde direction, since this cloud is expanding hemispherically as well. And only a fraction of that has picked up sufficient prograde velocity to threaten other satellites (remember, there is nothing else in orbit at 240 km). Now we are down to just 1 g.
Start multiplying all these fractions together, and very quickly you are talking about a one in 10 chance of generating a single 1-cm-sized fragment that could be a threat to higher-orbiting satellites.
I think the numbers above were quite generous. Realistically, you are statistically talking about the overwhelming likelihood of less than a fragment (i.e., odds are, no threatening fragment is generated at all) via the mechanism you suggested above.
There are more likely scenarios for generation of fragments moving faster than the original satellite, such as direct ricochet of the impactor from the spacecraft and the “ping-pong ball” scenario discussed previously. The key thing in dealing with in issue like this is to try to be quantitative. Even if there are huge uncertainties in your models and you have to crudely estimate efficiencies and factors, the exercise of trying to discipline a hypothesis with numbers can quickly sort out the feasible from the irrelevant.
Forgive me for being naive, Professor Doctor Higgins, would you be kind enough to give a lecture to us here about how the NASA model so badly underestimated the debris generated from the Chinese ASAT test? You must have a better model than NASA. I bet your model is probably not as good as President Sarkozy’s!
Please also give us an exposition on how the impact vehicle and the target’s internal structure is being modeled by yours truly. As I understand it, neither of these are solid bodies, but contain real interesting internal innards made of different materials of varying physical properties, and upon impact, presumably there will be some plastic deformation and interaction between the components before it explodes. Let’s see how it is factored into your infallible model.
As an example, think of how we do analysis of what happens to occupants in an auto crash and how a properly designed internal structure can make the difference between a ‘dead’ or ‘alive’ crash dummy. The models used by the bigger car companies are real good, and guess what, in real live tests, lots of things show up that the model didn’t quite get right.
While you are at it, would you be kind enough to upload to this site detailed blueprints and documentation on the structure and mechanical properties of USA 193 and the kill vehicle? Pretty hard to do that kind of modeling without the blueprints and a good bill of materials with details as to the properties of the innards. So let’s share what you must have laying around with the rest of us.
BTW, if you intend on showing us the blueprints… be aware that there is a big market in China for that knowhow!
Correct me if I am wrong, but I think this is the largest object to be intercepted by a kill vehicle ever —- so there really isn’t a database to fall back on to see what was ‘irrelevant’ last time.
As for calculations of risk —- the best and boldest way to do it is to ask Lloyd’s of London to sell the US Government an insurance policy. You can pretty much guarantee that if they will sell one, the world’s best actuarial minds gave decent odds that are overwhelmingly in their favor.
A- I hope it works, now that we said we’re gonna do it.
B- Does this became the standard way of handling errant vehicles threatening re-entry? The Rooskies will have to demonstrate they can do it next…Who’s after them?
b2
How can this test possibly be designed to test the wonderful AEGIS/SM-3 technology, as Carey said? This is a totally different task for the SM-3, one much, much more complicated than what the SM-3 normally does. If this action succeeds, normative issues aside, it will be an engineering marvel. There is a high probability of failure.
Given that this is a brand new task the SM-3 was not designed to do, it seems unlikely this action is designed to demonstrate the greatness of AEGIS.
My passing reference (others have covered the point in more depth) to the ASAT/ABM test role of the satellite shot was a little flip, but the points you make actually support the contention that this is in part a technology test shot to extend the Aegis system’s capability and role.
No, I don’t think it is a PR effort in the sense that it is an “easy kill.” I think it is a development test of a deployable ASAT/ABM capability. I expect a great deal of R&D has gone into to preparing Aegis for these roles, and that this was a stroke of luck for the program, giving them a test shot at no additional cost to the program and PR cover to boot.
Lao Tao Ren, I find Andrew Higgins’s main arguments to be correct, particularly these points:
1) None of the debris can have perigee higher than the intercept altitude and only debris which is scattered forward and right or left but not upward or downward of the satellite’s velocity vector at the intercept can possibly have a higher apogee without also a lower perigee.
2) Debris that has a higher apogee, with perigee at intercept altitude, can possibly persist slightly longer than the satellite itself would have, but not much longer.
3) Very little of the debris will be in this category. Nearly all will be scattered somewhat upward or downward, or more backward than forward, so that it will reenter sooner than the satellite would have, both due to the lower perigee orbits and due to the lower ballistic coefficient of smaller particles.
You ask some interesting questions, but I don’t know why Andrew needs to answer them. If you disagree with the technical arguments people have actually offered, please tell us why.
If you want to see a video on the plan of the shoot down of the satellite.? I have one on my site http://www.jhwireless.com > on the Join/Members Page of the site.
Mark et. al.
I do not disagree with the technical arguments —- and by this time, if there were an outside chance of larger consequences than fore casted —- we would have heard about it.
I did express my concern about the tentative nature of the debris modeling —- having spent a decade working in another area of simulation modeling (factory optimization)and seeing how often outputs from the model can be wrong.
My greater concern is the politics and optics of this test —- which I will address in another post.
Thank you, and all the other contributors for throwing light on the technical issues.
Donning my tinfoil hat for a moment, I have to ask, do we have any evidence that the satellite is in fact a failed recon satellite and not a dummy sent up specifically for this test?