Last week's Pentagon operation to bring down a falling spy satellite may have been widely termed a "shootdown" of precision accuracy — but the reality is more complex, and much messier.
As military officials take stock of the event's physical and political fallout, it's worth dispelling some of the misconceptions and myths that could otherwise cloud the thinking of policymakers and the public during the debate over past and future "shootdowns."
Myth No. 1: The Navy missile shot down the satellite.
Reality: Hitting a satellite with a missile is not at all like hitting a bird with a bullet and watching it plummet to the ground. An orbiting satellite stays in orbit not because of its power or guidance, but merely because of its forward speed. An attack that does not substantially change that orbital velocity cannot drive the satellite out of orbit, no matter how much physical damage it does.
The only practical way to remove such targets from orbit is by slowing them down. 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. Breaking a big spacecraft into smaller pieces does increase the effects of air drag — as demonstrated dramatically last week — but it is the key role of air drag that makes the critical causal link between "shooting" and "downing" the target.
Myth No. 2: Falling satellites aren’t really hazardous, and since they’ve never hurt anybody before, they were unlikely to hurt anybody this time. Hence, there must have been a secret "real reason" for the missile mission.
Reality: First, counting on a string of successfully dodging bullets is no open-ended guarantee of being bullet-proof 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 disasters.
Second, it’s not true 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 have taken deliberate and expensive steps to mitigate the ground-impact hazards of satellites.
All Russian spacecraft and U.S. military satellites heavier than 15,000 pounds are deliberately steered into untraveled expanses of the far southern Pacific Ocean. NASA steered its Compton Gamma Ray Observatory into a precisely planned atmospheric re-entry in 2000, and tried (but failed) to do the same with the Skylab space station in 1978.
In last week's case, the Pentagon said it resorted to the missile-intercept option because the spy satellite's guidance system was inoperable. 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 No. 3: The hydrazine on the spy satellite was unlikely to reach the ground in any concentration worth worrying about.
Reality: Space officials were so concerned about the satellite's full tank of hydrazine fuel because they believed it had frozen solid, due to the low temperatures aboard the spacecraft. They feared that the titanium-shielded "toxic iceberg" would survive intact all the way to the ground and disperse around the crash site, not in the upper atmosphere. Safety officials had never been faced with this type of falling material before.
Slideshow: Month in Space: April 2013 How dangerous is hydrazine? The chemical is considered toxic as well as flammable. U.S. space workers have indeed survived massive short-term dosing by the chemical during fueling accidents, but they did so due to the immediate application of pre-deployed safety measures.
The U.S. might have been held legally responsible for damage following the impact of such a hazardous cargo in a region with active agricultural exports or tourism.
As with the Palomares incident 42 years ago, in which two U.S. nuclear weapons fell to earth in Spain after an aircraft accident, people outside the region might be so spooked that they stop buying the regional exports and stop visiting its recreational facilities. The lost business alone could have cost hundreds of millions of dollars — compared with the estimated $60 million cost of the missile intercept.
Myth No. 4: The missile was aimed directly at the fuel tank, in order to pierce it and let the hazardous contents leak out.
Reality: Sure, the fuel tank was the missile's main target — but the missile didn’t have to hit the tank to crack it open. It’s hard to imagine how the warhead’s guidance system could have spotted the tank anyhow, inside the blob that was the image of the entire satellite. Hitting the target dead center and thus smashing the entire satellite to smithereens was the easiest way to ensure maximum damage to the tank.
Myth No. 5: The satellite disintegrated into more than 3,000 pieces because the fuel exploded.
Reality: Some Pentagon officials seemed to imply this, as evidence that they had achieved the goal of destroying the tank. But the kinetic energy involved in the ultra-high-speed collision was more than enough to impart enough force to cause the violent shattering — it certainly was orders of magnitude greater than the chemical energy that would have been liberated from the ignition of the entire fuel supply, even assuming it wasn’t frozen. That collisional energy was also the reason that some pieces of the target satellite got thrown forward so energetically, even though the missile hit the satellite from the front.
Most of the pieces fell through the atmosphere and burned up within a couple of days of the intercept. As of Tuesday, the Air Force Space Command was reportedly tracking 17 fragments that were still in orbit.
What's the harm in just letting all these myths lie? The danger is that the topic of weapons in space is a serious one requiring serious debate, especially in this election year. Hanging onto the technical myths could lead to misconceptions on one side of the debate ("our missiles were so accurate they could make a precision strike on the fuel tank") or the other ("the shootdown created a cloud of toxic debris that's still in orbit").
If we can "shoot down" the fuzzy thinking that has frustrated a serious exchange of views on this important national security issue, that would represent a much more enduring contribution to the safety of this planet than just protecting one random spot from half a ton of plummeting poison.