A year ago to the day, China knocked a weather satellite out of orbit, and threw the international community into panic. Some figured the satellite-killer test was the harbinger of a future war in space -- the kind of conflict that could cripple a tech-dependent United States military. Geoffrey Forden, PhD -- an MIT research associate and a former UN weapons inspector and strategic weapons analyst at the Congressional Budget Office -- examines the possibilities of an all-out Chinese assault on American satellites. This is part one. Click for parts two and three.
High above Asia, as the bars and clubs of Beijing begin to fill up at the end of another work day, a US early warning satellite spots the tell-tale plume of a missile streaking out of the wastes of Western China. Warning bells sound all through the Pentagon. Tensions have been running high between China and the United States, as the two countries struggle to resolve the latest installment of the Taiwanese crisis. And China has had a run of unprecedented activity in space: the past two days have seen China launch four large missions into deep space, three within the last six hours.. Fortunately, a high-resolution American spy satellite will be over that second launch site within minutes, giving the US a unique ability to determine what is going on. But even though tasking orders are given to photograph the suspected launch site, none are returned. The satellite, code-named Crystal 3, no longer responds to commands. Within minutes, US Space Command reports that four NAVSTAR/GPS satellitesused to guide American drones and precision bombshave stopped broadcasting. Chinas space war against the United States has started.
For years, the American armed forces have worried about an attack on US satellites; this could be how it begins. The United States military has become increasingly dependent on space. It uses photo-reconnaissance satellites to observe potential adversaries, GPS satellites to guide munitions with pin-point accuracy, communications satellites to handle the flow of information into and out of a theater of operations, and early warning satellites to detect and track enemy missile launches to name just a few of the better known applications. Because of this increasing dependence, many analysts have worried that the US is most vulnerable to asymmetric attacks against its space assets; in their view US satellites are sitting ducks without any sort of defense and their destruction would cripple the US military. Chinas test of a sophisticated anti-satellite (ASAT) weapon a year ago, Friday -- 11 January 2007, when it shot down its own obsolete weather satellite -- has only increased these concerns. But is this true? Could a countryeven a powerful country like China that has demonstrated a very sophisticated, if nascent, ability to shoot down satellites at all altitudesinflict anything close to a knock-out blow against the US in space? And if it was anything less than a knock-out, how seriously would it affect US war fighting capabilities?
The answers to these questions should influence how the US responds to the threats Chinas ASAT represents. There is at least one way to answer these questions: war-gaming a massive Chinese attack on US satellites, where China is only limited by the laws of physics and the known properties of their ASAT, and see how much damage could be done. Such an exercise also reveals what the US could do, and what it could not do, to minimize the consequences. The results of my calculations are reported here. They assume that China launches a massive attack and that everything works exactly as planned: every ASAT launches, the US does not respond until after the attacks are launched even though it will have overwhelming evidence ahead of time, and every ASAT hits its target. Thus, this is a worst case scenario for the United States. In the end, we'll show, the US would still has sufficient space assets to fight a major conventional war with China, even after such an attack. America's military capabilities would be reduced, for a few hours at a time. But they would not be crippled. Back in 2001, a commission lead by Donald Rumsfeld warned of a "space Pearl Harbor," a single strike that could cripple America's satellite network. It turns out, there is no such thing.
Let's start with what we know about China's ASAT capabilities today. And we know quite a bit. Because there are few, if any, secrets in space. Amateurs around the world track most, if not all, of the classified US military satellites from their backyards, posting their positions on the internet. NORAD,is capable of tracking objects as small as four inches across. In fact, NORAD's measurements of the debris caused by Chinas January 2007 test were posted on the web. In the case of the Chinese test, the orbital tracks of that debris can be used to reveal the capabilities and limitations of Chinas ASAT weapon by reconstructing the collision -- much like forensic scientists reconstruct a crime scene. By backtracking the debris to the point where they all converge, we can determine the two most important aspects of the Chinese ASAT: how China destroyed that satellite, and just how capable its satellite-killer really is.
The interception was almost head on at a combined speed of almost 18,000 miles per hour. The pieces of debris wound up with the greatest speedsmuch higher than the original satellite. This means that China accomplished the most sophisticated of space maneuvers: a hit-to-kill interception, the equivalent of hitting a bullet with a bullet. This is equivalent to what the US is trying to develop in its national missile defense system and is much more sophisticated than the ASAT the Soviet Union was working in the 1980s: little more than a space mine that slowly snuck up on its target and detonated near by.
We also know that the ASAT was highly maneuverable. Yes, the target satellites orbit was known well ahead of the interception. However, that does not mean that the satellites position was known well enough that the ASAT did not need to steer itself to hit the target. In fact, it is very likely that the interceptor needed to maneuver at high speeds, perhaps as much as six times the acceleration of gravity, to hit its target.
The orbital speed of the target satellite, which is determined by its altitude, also provides us with significant insight into the interceptors capability. The closing speed of the interception, which is a combination of the target satellites orbital speed and the speed of the interceptor, determines how much time is available to make final adjustments. For instance, just one second before the collision on January 11th, the interceptor and target were five miles apart. During that one second, the interceptor had to make any final adjustments to its trajectory to hit a target smaller than six feet across. Any decrease in the closing speed makes the attack that much easier. Since orbital speeds decrease with increasing altitudes, the Chinese interceptor would find it considerably easier to hit a target in higher orbit.
Finally, the interceptor needed to track its target, so that it could determine where it should move to place itself in front of the obsolete weather satellite; we have a good sense of how that was done, too. The most likely method it employed to track the oncoming satellite was an on-board telescope using visible light. Locking onto a target this way -- as opposed to focusing on the infrared light emitted by the heat of the target, the way the US missile defense interceptor does -- imposes significant limitations on the system. In particular, until it develops a far-infrared capability, which is probably decades away, its ASAT will be forced to attack satellites while they are in bright sunlight. Indeed, even though the site from which the interceptor was launched was cloaked in darkness, the target satellite was high enough to be brightly illuminated by the sun. Until China does develop better sensors, this imposes a very severe constraint on how and when it could attack other satellites: it must wait to attack low Earth orbit satellites when they are in bright sunshine. Attacks against satellites in significantly higher orbits, such as GPS or geostationary satellites, are less constrained by this requirement since they are almost always in direct sunlight.
China has informally stated a number of times that it will never do this again. But after having paid a very high price for testing the system once, both in resources and in political capital, it seems unlikely that they would abandon it altogether. Fortunately for China, it can continue to develop the systemincluding its on board tracking, guidance, and control systemsin the guise of a missile defense system. Such interceptions could be arranged at similar, or even greater, closing speeds as the January 2007 test. Only now, China could arrange to have both the target and the interceptor collide when they are both in downward portions of their trajectories, much like the US does during its missile defense tests. That way, they can test their system again without creating orbital debris that might harm their own and other nations satellites.