Space-Based Missile Defense: Still a Bad Idea

June 2, 2011 | 8:10 am
Laura Grego
Research Director, Senior Scientist

The House Strategic Forces Subcommittee considered the defense budget authorization in late May. In the bill passed up for the full House to consider was an amendment (HR 1540, Sec. 235) sponsored by Trent Franks (R-AZ) to add $8 million, unrequested by the defense department, for a study of space-based ballistic missile defense.

Meanwhile, Congress still awaits the results of a study of space-based missile defense by the Institute for Defense Analysis for which $5 million was appropriated in 2008. Rep Sanchez (D-CA) noted that study “has not been finalized, nor have the findings been reported to Congress.”

While $8 million is small money in this context, as Rep. Sanchez rebutted, space-based interceptors are big money. This has been established repeatedly in studies by, for example, the American Physics Society and the Congressional Budget Office, both in 2004, which show that hundreds to thousands of orbiting interceptors would be needed to provide global coverage against one or two ballistic missiles.  For the foreseeable future, each of these hundreds to thousands of orbiting interceptors would require a mass of many hundreds of kilograms, larger than an Iridium communications satellite at launch. A deployed system would be enormously expensive and challenge the U.S. launch capability.  It is unlikely to ever be deployed, and in today’s constrained budgetary environment, it is exceedingly unlikely to even be considered seriously.

Aside from the cost, a deployed system would raise significant issues for low-earth orbit crowding and space traffic management. Currently, fewer than 500 active satellites are in low earth orbits (less than about 1700 km at perigee), yet the current system managing traffic in space was unable to predict or prevent a collision between two intact satellites in 2009. (The US Air Force has stepped up its game in this respect, but tripling the number of satellites that need to be closely monitored is not a trivial upgrade.)

Why not just put up a few interceptors? A little protection is better than none, right?  The answer is a resounding no. A space-based interceptor would only be in the right place to be able to intercept a given ICBM intermittently: space-based interceptors need to keep circling Earth to stay in orbit. Because space-based interceptors (like all satellites) orbit predictably and are readily observable from the ground, a single interceptor is like a single police officer who is charged with protecting a neighborhood from mischief but required never to deviate from the precise timing of her route. She would be only a minor nuisance to determined troublemakers, who would find it easy to do what they pleased without getting caught.

In the same way that the neighborhood wouldn’t be protected until a full coterie of officers could cover the territory, space-based missile defense would be completely ineffective until a full system was deployed. Until then, the attacker could always choose her time and place to coincide with the absence of a usable interceptor.

Space-based missile defense is worse off than that, actually. In fact, even if a full system were deployed and the technology worked perfectly, an attacker could easily create such an absence by using a cheaper short- or medium-range missile either to draw out the space-based interceptor or to destroy it. Increasing the missile defense’s robustness by doubling the number of ground-based missiles such a defense could engage? This would require doubling the size of the entire interceptor constellation. Thus, this defense based on deploying hundreds to thousands of space-based interceptors can always be defeated by a handful of enemy missiles.

Rep. Franks supported his request with the statement that technology continues to change and that we should keep looking at space-based missile defense. While it’s true that interceptor technology will mature, satellite technology can be made lighter and more robust, and launch costs may eventually decrease, these gradual changes are not going to overcome the essential fact that space-based missile defense is highly vulnerable and would not be effective.

We’ve posted a fact sheet on space-based missile defense that details other reasons that testing a few space-based interceptors is a bad idea, and discuss  space-basing of interceptors in general in The Physics of Space Security’s chapter 9.