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Why Shoot Down a Satellite? Analyzing an Analysis
A reader, name withheld by request, writes "Writing in the IEEE Spectrum, James Oberg analyzes whether there was, in fact a significant risk to humans from the satellite which the US military shot down on 21 February, purportedly 'to head off the possibility of its splashing a half ton of toxic hydrazine fuel somewhere on Earth.' Previous experts had 'scoffed' at the rationale put forth, pointing out that there was trivial possibility that any significant amount of toxic fuel would make it to the ground intact. Oberg's analysis, titled 'the inside story,' purports to debunk this, and claims that indeed it's possible, and even likely, that there could be a danger to the ground. Unfortunately, the analysis is full of flaws and lack of rigor — indeed, lacking any sort of numerical reasoning. It seems to be too much repeating official 'spin,' and could have used a hefty dose of skepticism — and could also use a little bit of actual analysis using numbers, rather than handwaving." Read on for the rest of an interesting analysis of a topic that suddenly seems more complex.
The submitter continues:
"Here's the first number that Oberg should have quoted: 32 Megajoules per kilogram. That's orbital energy, which is how much energy has to be removed by ablation or otherwise dissipated for the hydrazine tank to enter the atmosphere and hit the ground undamaged. For reference, TNT holds about 4.6 MJ/kg.
Oberg quotes 'Hydrazine requires a tremendous amount of energy to go from solid to liquid.' This energy is known as the heat of fusion, and for hydrazine it is just a little under 400 kJ/kg. That's about 1% of the energy released by entry heating. Hardly a 'tremendous' amount of energy, compared to the entry energy that's nearly a hundred times greater.
Oberg goes on to quote 'There is a widespread notion that meteorites falling to Earth arrive red hot.' He is correct here. In fact, meteorites falling through the atmosphere typically explode, shattering into dozens or hundreds of pieces; something that occurs at the point when the dynamic pressure on the leading face exceeds the yield stress of the material. This occurs for meteoroids of all compositions, including nickle-iron meteorites that are far more robust than hydrazine tanks. If the atmospheric entry of meteorites is relevant, it hardly bolsters the case that a tank will enter intact (and if it's not relevent, why did Oberg bring it up?)
Furthermore, if you look at a typical nickle-iron meteorite, you'll see a surface pitted and mottled with holes ranging from the size of golf balls up to pits the size of baseballs. These are known as regmaglypts; they are the areas ablated away by the entry plasma. Even a single such ablation pit would, of course, destroy a hydrazine tank.
The second number Oberg should have quoted is a number called ballistic coefficient, the mass divided by the area of the tank. Basically, the smaller the ballistic coefficient, the less stressful the entry will be. Unfortunately, a full hydrazine tank has a very high ballistic coefficient. It is an empty tank, not a full one, that is likely to enter intact. Talking about empty film canisters, or even empty fuel tanks, making it intact through atmospheric entry is really about as relevant as talking about dropping a piece of paper on the floor.
The article contains a quote from Andrew Higgins, with a link to (purportedly) the research done that contains the quote. Unfortunately the link does not actually contain the quote used in the article; in fact, it seems to be mostly a discussion of a side issue. Let me emphasize this: Higgins did not say what he is quoted as saying in the place he was reported as saying it. This may merely be sloppy journalism — maybe he said it somewhere else — but I am again left with the question: if I can't even trust the simplest things he says that can be easily checked, why should I trust anything else?
In short, Oberg's article is poorly thought out, avoids even simple back-of-the-envelope calculations, and accepts uncritically information that should have been aggressively questioned. He concludes that a well-defined and thoroughly researched technological hazard assessment — of a kind that someday, for better or worse, will be needed again — has wound up buried in obscurity and obfuscation. This may be true, but no well defined nor thoroughly researched technological hazard assessment was anywhere in evidence. The analysis he gives in the article is buried in obscurity and obfuscation.
(apologies for posting as Anonymous Coward. I work in the field.)"
Oberg goes on to quote 'There is a widespread notion that meteorites falling to Earth arrive red hot.' He is correct here. In fact, meteorites falling through the atmosphere typically explode, shattering into dozens or hundreds of pieces; something that occurs at the point when the dynamic pressure on the leading face exceeds the yield stress of the material. This occurs for meteoroids of all compositions, including nickle-iron meteorites that are far more robust than hydrazine tanks. If the atmospheric entry of meteorites is relevant, it hardly bolsters the case that a tank will enter intact (and if it's not relevent, why did Oberg bring it up?)
Furthermore, if you look at a typical nickle-iron meteorite, you'll see a surface pitted and mottled with holes ranging from the size of golf balls up to pits the size of baseballs. These are known as regmaglypts; they are the areas ablated away by the entry plasma. Even a single such ablation pit would, of course, destroy a hydrazine tank.
The second number Oberg should have quoted is a number called ballistic coefficient, the mass divided by the area of the tank. Basically, the smaller the ballistic coefficient, the less stressful the entry will be. Unfortunately, a full hydrazine tank has a very high ballistic coefficient. It is an empty tank, not a full one, that is likely to enter intact. Talking about empty film canisters, or even empty fuel tanks, making it intact through atmospheric entry is really about as relevant as talking about dropping a piece of paper on the floor.
The article contains a quote from Andrew Higgins, with a link to (purportedly) the research done that contains the quote. Unfortunately the link does not actually contain the quote used in the article; in fact, it seems to be mostly a discussion of a side issue. Let me emphasize this: Higgins did not say what he is quoted as saying in the place he was reported as saying it. This may merely be sloppy journalism — maybe he said it somewhere else — but I am again left with the question: if I can't even trust the simplest things he says that can be easily checked, why should I trust anything else?
In short, Oberg's article is poorly thought out, avoids even simple back-of-the-envelope calculations, and accepts uncritically information that should have been aggressively questioned. He concludes that a well-defined and thoroughly researched technological hazard assessment — of a kind that someday, for better or worse, will be needed again — has wound up buried in obscurity and obfuscation. This may be true, but no well defined nor thoroughly researched technological hazard assessment was anywhere in evidence. The analysis he gives in the article is buried in obscurity and obfuscation.
(apologies for posting as Anonymous Coward. I work in the field.)"
The submitter is debunking an article written in IEEE Spectrum, a civilian magazine. To debunk an article written by a non-expert says very little about whether a shoot-down was actually warranted.
Nice try on the anonymity, but there's your name on the Related Stories list with the original Firehose posting...
What was the risk of shooting it down? It seems close to "none." The missile used would surely have a mechanism to self-destruct in the event of a miss, and even if it didn't, I don't see how its falling could be any more dangerous than the hydrazine. Plus, it was probably a useful training exercise, should they ever need to shoot down a "really" dangerous satellite.
Of course, since it was done months ago, it's all hypothetical anyway.
Comment of the year
The reason we shot it down was because China had just shot down one of theirs in a weapons demonstration. China was using it as propaganda about how great they were. So we chopped them down a notch by showing them that we can do it as well. And not only that, we can do it from a mobile platform (i.e. a cruiser at sea), not just from a land based stationary platform. This was simply an international pissing match. Nothing more, nothing less.
We were all warned a long time ago that MS products sucked, remember the Magic 8 Ball said, "Outlook not so good"
[1] choose your conspiracy, there are plenty to go around - you're probably closer to the truth than this article, but you already knew that.
politicians are like babies' nappies: they should both be changed regularly and for the same reasons
From the link about why the satellite was no threat:
"The hydrazine tank is a 1-meter sphere containing about 400 liters of hydrazine. The stated hazard area is about 2 hectares, something like 1/10,000,000,000 of the area under the orbit," he adds. The potential for actual harm in unbelievably small. Which means the hydrazine rationale just doesn't hold up, literally not within orders of magnitude."
That's it for any analysis - the rest of the article was devoted to analyzing the political and military reasons why the explanation was bogus. And most of the analysis seemed to be delivered with substantial chips of the speakers shoulders. As for the numbers, while they may be *statistically* insignificant, that is pretty irrelevant next to the political consequences to a military that says "Yeah, we could have shot it down, but the odds were so small it wasn't worth the money. Our bad."
Then the "analysis" with the post - sounds good, until you get to the end: "Posted anonymously". Sorry, but that's a fail right there. He could be a 13year old in his Mom's basement, or Feynman blogging from the grave, but without attribution I just can't take it seriously.
"As God is my witness, I thought turkeys could fly." A. Carlson
I think they shot it down because they decided it was a good idea. What's the problem? The US is going to get criticized by someone for any choice it could possibly make, including doing nothing. This was probably the choice with the least uncertainty.
Oberg had an earlier analysis (March 2008) on the same topic in The Space Review that covers many of the same points with a little more detail than this article.
http://www.thespacereview.com/article/1073/1
Thank you for debunking the debunking of the debunking.
The opinions stated herein do not necessarily represent those of anybody at all. Deal with it.
Actually, if there's a conspiracy, its this whole business of hydrazine being supposedly unsafe. Since I've been using hydrazine scalp cream, I've regained a full head of hair and my private assets have significantly increased in size. It's only because George Bush wants everyone to go bald, that the satellite was shot down.
This is my sig.
I got an, 'A' in rocket science. It's not nearly as hard as they make it out to be.
Most 8 year olds I know are good at making up a pretext for getting what they want.
A: I really wanna shoot down a satellite!
B: You can't do that, it'll make you look like a violent war provocateur.
A: But! But! But! What if it was a dangerous satellite. Like it was going to kill everyone or something. And we had to shoot it down to save everyone! And it had racing stripes and a turret on top and played the A-Team theme song!
B: Well.... Okay, but only if it's a dangerous satellite.
A: Yay! Mom! Dad says we can shoot down a satellite!
That may be partially true, but the Chinese shot was way more difficult (albeit messy) than ours. We, of course, had no reason to get nearly as fancy as the Chinese did when they took theirs out and it would have been silly to even try (unless we just had a fancy satellite-killer that we just wanted to try). But, to the eyes of most of the world, I'd imagine you're right. They showed that they could do it, so we did too. Despite the fact that they were radically different shots and circumstances.
He's getting rather old, but he's a good mouse.
That would be hard evidence of all the (domestic) spying that went on.
Right, because they could have flown the U.S.S. Michelle Obama (a special UFO-technology-based ship that the Evil Republicans have been hiding at Area 51) up to the wrongly-orbited sattelite, and... what? Retrieved the film? Any "domestic spying" done from orbit comes in the form data hauled down to earth... you know, satellite imagery? You're a few decades late for the satellite itself to have evidence of something like that. Anything worth talking about is on disk drives and tapes right here on the ground.
Don't disappoint your bird dog. Go to the range.
Nonsense. You guys have got it all wrong, like you can only think one layer deep.
Clearly there is no reason for the US to demonstrate an ability to shoot down satellites, as everyone knows the US can shoot down satellites. And yet, there seems to be little good practical reason to shoot down this particular satellite.
The truth is obvious. This was not a "failed" satellite, but rather a test of a satellite-based anti-missile system. In other words, the launched sat contained countermeasures against exactly this kind of missile, and the only way to test those countermeasures was to launch a missile at it.
The problem was that anybody would see such a test, and so the military needed a cover story, and thus came up with this notion of a "pissing contest" (while claiming all the while that the reason was the hydrazine tank). I'm sure that the sat was rigged to self-destruct immediately after deployment of its anti-missile system, to make it look like the cover operation was successful.
And you cannot practice simple human courtesy. WTF compels you to post that?
http://www.chomsky.info/talks/20011103.htm
I just love how someone can say "I work in the industry!", post as an AC, toss out a couple of buzzwords with no math to speak of, and scream "we're being lied to!". As the submitter of this story so clearly put it when posting his own "analysis":
Translation: "There is a conspiracy here! Trust no one! We're all being lied to!" If there's one thing I've learned over the years, there is nothing the government can say or do to convince someone who thinks like this.
Personally, I have little doubt that the satellite was shot down for exactly the official reason. We've had plenty of space junk hit the ground in recent years; as I remember, people were specifically warned not to handle debris from the space shuttle Columbia, because of concerns of hydrazine contamination. Clearly the shuttle's high ballistic coefficient didn't prevent that, did it? The hydrazine tank didn't have to reach the ground intact to cause concerns. And just imagine the headlines if nothing had been done, and debris from that spy satellite had eventually reached the ground. Russia still gets flack about the nuclear reactor debris that landed in Canada after the re-entry of COSMOS 954, and that was 30 years ago!
Of course, it was obviously an added bonus that the shoot-down was a nice demo of the military's capabilities. But if the U.S. military really wanted to test its ASAT technology, it would hardly need to hold a press conference beforehand, or issue a press release to China or Russia to inform them afterwards! China and Russia track our satellites the same as we do theirs. If one of our dead satellites conveniently "exploded", they would get the message quite clearly.
To test our new weapons and show the Chinese how we roll.
That's half of it. While there was a possibility of hydrazine rain, I think we also have to consider that this was state of the art spy satellite which was part of a much larger network of spy satellites. If this thing were to make it to the ground even partially intact, it would be a treasure trove of information concerning the US spy satellite ability and could possibly show a way to counter the shiny new spy network we spent so much money deploying.
There is no "I disagree" mod for a reason. Flamebait, Troll, and Overrated are not substitutes.
Shooting down objects in high orbit requires a 2-stage attack - They're too difficult to hit directly in spite of your greater correction time. First, a carrier rocket is sent up to get as close as practical to the target. It then launches a kill-vehicle that will track and destroy the satellite.
The US did not require that much sophistication. Since the satellite was on its way down, the attack was more akin to shooting down an ICBM when its location and velocity are both known well in advance.
1) the amount of hydrazine fuel contained was infinitesimal compared to the amount of hydrazine that spills on humans every year. The F-16 uses hydrazine in its EPU, and you can trivially find stories of people practically bathing in it as a result of EPU problems and fuel dumps. The effects are generally less than the horrific outcomes presented in the stories surrounding the shoot-down. The idea that the hydrazine presented any sort of real risk is absolutely bogus, something the articles dance around and just won't address directly.
2) the chance of the debris coming down in a populated area is very close to zero. Although underreported (see http://imca.repetti.net/metinfo/metstruck.html), there are no recorded instances of anyone being killed by anything falling from space. Now of course a 1000 lb fuel tank is much deadlier than a small stone, but 1000 lb objects have fallen from space before, and we didn't bother shooting them down (http://www.space.com/news/spacehistory/dangerous_reentries_000602.html).
3) last time I checked, when heat shields fail the aluminum structure generally fails almost immediately thereafter (http://www.columbiassacrifice.com/$A_reentry.htm). I am not aware of any unprotected structure reaching the ground intact (although that could be ignorance) but I am very much aware of many unprotected structures breaking into small parts under the same conditions. This includes tanks with frozen volatiles inside. The only really large pieces of debris to reach the ground were the insulated tanks from Skylab.
4) A nuclear reactor is MUCH more robust than this fuel tank, yet when Cosmos 954 fell to Earth it's 50 by 35 cm reactor shattered and spewed its contents over 600 km (http://gsc.nrcan.gc.ca/gamma/ml_e.php). Yes, the shaping is critical in terms of shock generation and aerodynamic loading, and it's definitely easier for a sphere to re-enter than a cylinder, but still... bologna.
5) the article Oberg's is based on claims ~8 gee loading. Again, bologna; that's what you get on a carefully controlled re-entry, uncontrolled will cause much greater loadings (again, http://www.columbiassacrifice.com/$A_reentry.htm)
6) The article links to several others that are essentially dismissive of the "publicity" cover-story angle as a conspiracy theory. However, we're talking about an administration who's history shows a well-recorded "shoot first" policy based on extremely inflated data. This case fits the pattern to a T, and I see no reason to believe it differs in any way.
I call BS. Sorry James, but the argument remains specious in my books.
Maury
Or, it's probably a combination of factors, and not just a dick-measuring competition.
Consider the following:
1. A very expensive intelligence satellite is stranded in low orbit, useless. Said satellite contains expensive, highly-classefied equipment; there's a finite chance that some of this equipment might reach the surface relatively intact (see Skylab, Columbia). Obviously, certain groups (China and Russia, especially) would love to get hold of anything that survived and analyze it. It would be nice to ensure that this equipment is rendered unusable and worthless.
2. The hydrazine tank mentioned. Yes, I know the odds of it hitting anything were very, very small... but not zero. And the public outcry had it hurt or killed anyone would have been loud and swift. The decision-makers probably figured it would be better to face the inevitable international grumbling by shooting down the satellite than to face the very small (but potentially devastating) risk of impact in a populated area.
3. The Navy ABM system is going operational, and someone realizes it has the capability to shoot down low satellites. Someone probably figured "hell, we have this satellite problem; it's going to reenter soon anyways so it's a nice convenient test target. We might as well try it while we have the chance". Besides, the additional cost is a drop in the proverbial bucket.
4. At the top levels, there probably was a bit of "let's show them" going on. But I suspect it was as much a coincidence as anything else, with #1 above leading the "rational" reasons list. The hydrazine tank story just made for the best PR.
The meek may inherit the earth, but the strong shall take the stars.
Dr. Landis implies that Andrew Higgins didn't say the quoted item.
In fact, it's easily found in the link given.
In the linked text, Higgins gives a hyperlink back to a previous letter which was in The Space Review which contains that very quote and in the context Oberg said.
Landis snipes at Oberg for poor journalism, but apparently can't follow a bloody hyperlink. Why, even Cowboy Neal could do that and on a bad day to boot.
Secondly, Landis is an expert in solar cells and solid state devices. He apparently also works on elements of spacecraft electrical power systems, lander design and operation and writes articles on a variety of subjects. Impressive, but not directly in the area.
On the other hand, Andrew Higgins is a principle investigator and an expert in the behavior of materials under extreme hypersonic conditions and computer simulation of the same. His work on materials and combustion in hypersonic ram accelerators leaves him very well equipped to comment on the dynamics of reentry and the behavior of spacecraft materials and fuels under such extreme conditions.
Landis seems to be using the very sloppy and misleading tactics that he accuses Oberg of. Pot. Kettle. Black.
(Mild disclaimer. Andy Higgins is a friend going back to undergrad days (and believe me, it's been a while). I was mildly nettled that Landis invokes the name of an old friend and then becomes selectively blind when Andy gave the link to the very quoted item in the letter that Landis read.)
Oberg goes on to quote 'There is a widespread notion that meteorites falling to Earth arrive red hot.' He is correct here. In fact, meteorites falling through the atmosphere typically explode, shattering into dozens or hundreds of pieces; something that occurs at the point when the dynamic pressure on the leading face exceeds the yield stress of the material. This occurs for meteoroids of all compositions, including nickle-iron meteorites that are far more robust than hydrazine tanks. If the atmospheric entry of meteorites is relevant, it hardly bolsters the case that a tank will enter intact (and if it's not relevent, why did Oberg bring it up?)
Perhaps he brings it up because that widespread notion is dead wrong. In fact, the parts of meteorites which make it all the way to the ground arrive quite cold, way below 'zero'. That's because of ablation. The outer part of the meteorite gets superheated by friction with the atmosphere, but before any significant portion of that heat can conduct to the inner part, the superheated part loses structural integrity and is torn away from the rest. However, the part torn away has, up until that moment, shielded the inner part from absorbing any direct friction heat.
Rinse and repeat. The end result is that whatever part does make it all the way to the ground is still at substantially the same temperature as it was when it entered the atmosphere.
Moderating "-1, Disagree" is simple censorship. Have the guts to post your opinion.
The submitter wrote:
I'm not sure why the submitter seems to have only partially quoted Oberg here (apparently out of context), and ignored the point Oberg was trying to make. Although meteorites entering the atmosphere generate a fireball, there seems to be ample evidence that the objects themselves remain cold even upon impact.
I'll cite a few articles here:
From this NASA page titled "Hot Meteors and Cold Meteorites," under the section titled "Meteorites Don't Pop Corn," we have this salient paragraph:
A slightly less assertive article on Howstuffworks is a little more reserved in its claims:
A more nuanced perspective is provided by this amateur astronomer who specializes in the study of meteors (specifically meteor spectroscopy). It's a short read, but a little too long to block quote here. Suffice it to say, there are numerous factors, including the composition and albedo (reflectivity) of the object, whether it was camping out in the Earth's shadow prior to impact (and for how long), the trajectory and velocity upon entering the atmosphere, etc.
Seems to me that the submitter is conflating two separate thoughts. Oberg brings up meteorites because they can and do impact the Earth while still cold, or only moderately warm. That's as far as the analogy goes -- he apparently wants to make the case that an object can remain cold enough that hydrazine fuel inside the container in question might not vaporize prior to impact. Whether we want to extend the analogy to the question of whether the container will shatter during re-entry is a question best asked of metallurgists or material scientists, and that I suspect depends entirely on the composition and manufacture of the fuel tank. (For that matter, whether a meteorite shatters upon re-entry would seem to be a function of the composition of the object, as well as the stresses it encounters -- and those stresses would be a function of speed and trajectory, as well as shape, would they not?)
I doubt much more was going on than the testing of space weaponry in plain sight.
But why aren't we more upset about that? Is it really just OK that our government is openly defying the treaties that prevent the weaponization of space?
This is why conspiracies bug me so much. People believe the government lies and thus focus their attentions on grandiose and outlandish possible lies and cover-ups, rather than pay attention to all of the 100% verifiable medium-sized lies that the government tells day in and day out. Rather than fabricate an entire false narrative, the way to do it these days seems to be admit to 80% of what really happened, lie your pants off even if people will call you on it, and wait for the news cycle to pass on by the 20% that didn't add up.
Seriously, we've all but caught our government in an act that is very formally (as in, it would piss off thomas jefferson and not just moveon.org) against the principles of our democracy. What more conspiracy do we need?
In Capitalist America, bank robs you!
I have a great deal of respect for Jim O , but he knows that he and I differ in our opinions regarding the destruction of 193. As one of those observers who followed this bird through 2007 and as the unfortunate soul who was , seemingly , the only person to obtain high power images of it on a number of occassions , I formed my own opinion , based on what I saw and the fact that there was no way the Pentagon was going to allow this satellite to fall any lower , let alone , re -enter. Its quite simple , at 300 km I could see the basic outline of the satellite using back yard equipment.At 200 km I would have seen "much" more detail had I had the opportunity. If I could do that , then the opposition , using much more expensive kit , and adaptive optics would have been able to discriminate the exact shape and proportions of the spacecraft , from which it could then glean a great deal of intelligence. ( See my recent images of Persona ) As I stated back in mid December 2007 "The Pentagon will not allow this bird to come much lower and will probably destroy it on orbit." Those words were , at the time , met with derision but proved to be correct. The chances of the tank making ground in tact in a densly populated area were infinitesimal. We will probably never know the truth , but for my part , I'm convinced that the toxic ice cube theory was simply fabricated to mask the real reasons for the satellite's destruction. More details on both Persona and USA 193 at http://satcom.website.orange.co.uk/