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USA 193 intercept illustration
When the SM-3 missile hit USA 193 on February 20, it did not “shoot down” the satellite, but instead broke it apart: one of a number of misconceptions about the intercept. (credit: AGI)

Sense, nonsense, and pretense about the destruction of USA 193

I’m sorry, but I just hate the phrase “satellite shoot down”. It’s not just because, in fact, hitting a satellite with a missile—like last February 20—doesn’t really knock it out of the sky. It’s because trying to bend “earthside” words around the unearthly, unfamiliar reality of outer space is a bad fit—and if it fools us into thinking the words are proper, then our clear thinking about the events will be crippled.

“Shoot-down” implies that a physical attack has destroyed a characteristic of the target that previously had enabled it to remain aloft. For an aircraft, it could be its wings, or engine, or pilot; for a flying animal, it might be its very life. Once attacked, the object can no longer fly, and it falls to the ground.

But for a satellite in orbit around the Earth, the physical principle that keeps it “up” is not its own power or guidance, but merely its forward speed—the so-called “orbital velocity”. An attacker that does not substantially change that velocity cannot drive the satellite out of orbit. No matter how much physical damage it does, it cannot “shoot down” the target or even the fragments of it that remain after the attack.

Trying to bend “earthside” words around the unearthly, unfamiliar reality of outer space is a bad fit—and if it fools us into thinking the words are proper, then our clear thinking about the events will be crippled.

The only practical way that such targets can be removed from orbit is by slowing them down. And in practice, that occurs as a result of air drag, an effect that can take hours, weeks, or centuries depending on the thickness of the air at the satellite’s altitude. Adding to the confusion, if the target explodes from the kinetic energy of the impact, pieces fly in all directions: some into lower orbits (“down”) and some higher (“up”).

So whether or not you “shoot” at a space target, it will get “downed” mainly by air drag. Breaking a big spacecraft into smaller pieces does increase the effects of air drag—as it dramatically did for the derelict spy satellite—but it is the key role of air drag that makes the critical causal link between “shooting” and “downing” the target. Omitting consideration of this effect leads to mistaken cause-and-effect expectations.

Myths or mistakes?

Numerous other misconceptions—“space myths” might be a useful term—intruded into media reportage of the event and threaten to cloud any productive discussions (or even international diplomacy) of future replays of it. Here are some examples:

Myth #1: Falling satellites aren’t really hazardous, and since they’ve never hurt anybody before, they’re unlikely to hurt anybody this time (and hence there must be a secret “real reason” for the missile mission). This is a two-part myth that deserves two distinct refutations.

But before the debunking, let’s quote some of the bunk, and name the “bunkers”:

“The stated rationale for this shoot-down is simply not credible. There has to be another reason behind this… There has not been a single human being who has been harmed by man-made objects falling from space.” Michael Krepon, Henry Stimson Center, Washington, DC, Feb 17.

“Since 1957 hundreds of satellites [some of them three times heavier than USA 193] and pieces of debris have met the same fate… breakup and disintegration ensure. The likelihood of any of them hitting persons or buildings is very small.” Sylvestre Huet, “Pentagon’s Latest Fairy Tale”, in Liberation, Paris, Feb 21.

“In the past five years 300 satellites have fallen to Earth, and nobody has been hurt in connection with it.” Sascha Lange, German Institute for International and Security Affairs, Berlin [Sueddeutsche Zeitung, Munich, Feb 22]

“Uncontrolled reentry to Earth of space vehicles has been a repeated occurrence. Many countries use toxic fuel components. But on no occasion has this called for any extraordinary measures.” Russian Defense ministry press release, Moscow, Feb 18.

Now to the de-mythologizing of the stories. First, as space experts have learned from bitter experience, counting on a string of successfully dodging bullets is no open-ended guaranty of being bulletproof forever. The odds have a way of catching up with you, and defying them is an all-too-common fallacy called “normalization of deviance”. At NASA, this attitude laid the foundation for the Challenger and Columbia shuttle catastrophes, among other space disasters.

Secondly and more importantly, it’s absolutely false that past safe outcomes always occurred even when countries let their big satellites randomly fall to Earth. Just the opposite is true: for decades, major spacefaring powers took deliberate and expensive steps to mitigate the ground-impact hazards of satellites, especially the large satellites most likely to peel back layer-by-layer during atmospheric entry and as a result deliver large intact hunks of the structure all the way down to the surface.

Counting on a string of successfully dodging bullets is no open-ended guaranty of being bulletproof forever. The odds have a way of catching up with you, and defying them is an all-too-common fallacy called “normalization of deviance”.

All Russian spacecraft heavier than about 6,800 kilograms (15,000 pounds), and all US military satellites of similar masses, are deliberately steered into untraveled expanses of the far southern Pacific Ocean. In another example, eight years ago an expensive NASA spacecraft, the Compton Gamma Ray Observatory, was shut down over scientists’ protests, and steered into the atmosphere, when partial failures in its control system threatened a random fall to Earth that threatened a high possibility (1-in-1,000) of human injury. Here’s another: in 1978, NASA began an expensive effort to revive the shut-down Skylab in a deliberate attempt to steer it into the atmosphere over open ocean—an effort that failed in mid-1979, but was considered necessary at the time. These steps were taken specifically because allowing these massive objects to fall randomly was judged irresponsibly risky and so mitigation efforts were deemed mandatory. Nobody ignored these hazards—they acted to minimize them as they have done literally hundreds of times.

So it is incorrect to allege that this latest falling satellite could have been allowed to fall randomly since that’s what space programs had been safely doing for decades and “nobody has ever been hurt”. Now, the mix of motivations for making the missile attack can be debated, but the up-front official claim about mitigating hazard cannot be glibly dismissed.

Myth #2: The hydrazine on the spy satellite was unlikely to reach the ground in any concentration worth worrying about.

Numerous experts told the press that the tank would almost certainly disintegrate, or explode, during its fiery descent. The only expert who said different was Michael Griffin, administrator of NASA, whose experts had studied this specific situation. Not good enough, the press decided.

“There was virtually no chance it would remain intact,” attributed to Dr. Geoffrey Forden, MIT, by Robery Maginnis, Human Events, Feb. 26.

“The hydrazine tank – a hollow vessel – is unlikely to make it through the heat and aerodynamic violence of the plunge that awaits it, meaning that it will spill its contents high in the atmosphere, where it will represent barely a breath of gas that will disperse harmlessly.” Jeffrey Kluger, Time magazine science correspondent, Feb. 20, 2008.

These widespread allegations mostly ignore the first-ever special circumstances of this event, where a full tank of the chemical remained untouched by the crippled satellite, and where it had frozen solid, based on the expected low temperatures on board. Safety officials had never been faced with this type of falling material before.

These non-intuitive effects of long-term “cold soaking” in Earth orbit were dramatically illustrated in 1985 when the Soviet Salyut 7 space station lost power. After several months, a repair team of cosmonauts arrived to find the station’s water tanks frozen solid. Now, ordinary hydrazine (the kind on USA 193) freezes at a point a few degrees warmer than water, so it shouldn’t be surprising that it would freeze too. In the Russian case, that station’s thrusters used a variant form called “UDMH” (unsymmetrical dimethyl hydrazine) that has a much lower freezing point, and it did not get cold enough to freeze that fuel—but the water did.

Myth #3: Hydrazine isn’t really very dangerous anyway.

“To die from hydrazine exposure would require standing around and breathing it for hours.” Guy Raz, “All Things Considered”, National Public Radio, Feb. 14.

“The claim there was danger from the fuel is not the most preposterous thing the Pentagon has ever said. But it seemed to be a bit of a stretch.” John Pike,

“It certainly would seem that protecting people against a hazardous fuel was not what this was really all about.” Dr. Geoffrey Forden, MIT.

It might be interesting to actually perform experiments to test this claim, with the experts who made it volunteering as the test subjects. After all, FEMA emergency teams were alerted to the satellite fall with documentation describing the chemical as both toxic and flammable (imagine the damage if it fell among wooden buildings or dry woodlands). A number of American industrial and military workers have indeed survived massive short-term dosing by the chemical during fuelling accidents, but luckily they usually did so due to the immediate application of pre-deployed safety measures—a luxury that more than six billion other potential victims would have no access to.

More widespread damage (that the US is legally responsible for) could easily follow the impact of such a hazardous cargo in a region with active agricultural exports or tourism. As with the Palomares incident forty years ago (where two American nuclear weapons fell to Earth in Spain after an aircraft accident), people outside the region might be so spooked by sensationalistic press coverage that they stop buying the regional exports and stop visiting its recreational facilities. This lost business damage alone could easily reach into the hundreds of millions of dollars. And even when faltering Russian rockets fuelled by hydrazine fall back over empty deserts near the launch site in Kazakhstan, massive cleanup operations are required, and millions of dollars of reparations must be paid by Moscow—nobody treats that spilled hydrazine as “not dangerous”.

Myth #4: The satellite contained a nuclear reactor or other type of radioactive power plant.

“Moscow suspects the satellite may be carrying a nuclear power unit.” Lead story, Rossiya TV “Vesti” news program, Feb. 15, 2008.

“According to the analysis of our military people… that may be evidence that there was a nuclear power plant in it.” Igor Barinov, Deputy Chaiman of the State Duma Committee on Defense.

“The American generals are not perturbed in the least that a strike against an object with a nuclear power plant (the satellite’s lack of solar batteries led our experts to that conclusion) threatens serious consequences…” Yuriy Gavrilov, Rossiyskay Gazeta [official government newspaper], Feb. 21.

“It would have been much better if it [the nuclear power unit] had fallen down as a whole piece.” Igor Ostretsov, Russian Institute for Nuclear Engineering:, on Vesti-24 TV, which also quoted him as saying the likelihood that radioactive substances will rain down on Earth is 100% (quoted by Agenstvo Voyennikh Novostey, Feb 22.)

More widespread damage (that the US is legally responsible for) could easily follow the impact of such a hazardous cargo in a region with active agricultural exports or tourism.

One could cynically expect the Russians to want to blame other countries for threatening “nuclear contamination from space”, since it wass the USSR that really did so on such a grand and repeated scale. As for not seeing solar panels (an observation confirmed by private skywatchers), the satellite’s failure within seconds of reaching space could account for that. And had there been a powerful nuclear reactor, there should have been large heat radiators—not as easy as solar panels to notice, but readily visible had they been there.

US law prohibits nuclear power in the kind of low orbit USA 193 was launched into, and the level of inter-agency cooperation that such a system would require would guarantee leakage of the presence of such a system. This claim, widely ignored outside of Russia, can easily be dismissed as a clumsy opportunistic smear instigated within the Russian government.

page 2: fallout on Earth >>