07/22/2008 - 09:07

Can space weapons protect U.S. satellites?

Yousaf Butt

Yousaf Butt

Butt is a research professor and scientist-in-residence at the James Martin Center for Nonproliferation...

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Both presumptive presidential nominees--Arizona Republican Sen. John McCain and Illinois Democratic Sen. Barack Obama--have called for strengthening and/or increasing the number of international treaties and institutions to combat proliferation should they be elected president. An important new pact for them to consider is an agreement that restricts the weaponization of space. Not only are space weapons expensive and provocative, they're also useless: They simply cannot protect us.

Over the years, many voices in Washington have called for green-lighting space weapons as a way of neutralizing the threat to U.S. satellites. For instance, the 2001 U.S. Space Commission report warned against a "Space Pearl Harbor" and advocated that, "The [United States] must develop the means both to deter and to defend against hostile acts in and from space." It went further to suggest that the Defense Department "vigorously pursue the capabilities . . . to ensure that the president will have the options to deploy weapons in space."

Throughout this debate, it's almost taken as an article of faith that space weapons can be defensively useful. Yet, there's little technical basis to support this belief: While certainly offensively potent, space weapons are defensively ineffective.

First, let me be clear about what I mean by the term "space weapons." In my definition, I include any weapons based in space that can attack targets either in space or on the ground or any land-, sea-, or air-based weapons that can attack satellites.1

Fragile, blind, unmanned satellites are different from armored and actively piloted tanks, ships, and airplanes because they move in predictable orbits without situational awareness of their surroundings, providing an easy target for an enemy bent on interfering or destroying them. To save on launch costs, they're typically built as light as possible with minimal shielding. And the few evasive actions they can take greatly sap the limited onboard fuel.

The most optimistic incarnation of a defensive space weapon is the so-called "bodyguard satellite," which is designed to protect satellites from ground-based antisatellite (ASAT) weapons. The bodyguard would shadow the high-value satellite it's protecting by being in an identical orbit, typically trailing its "boss" by a few hundred kilometers. Once cued to a threat, it could launch an interceptor to impact and destroy the incoming ASAT kill vehicle. A single bodyguard satellite system that could intercept an incoming ASAT would have a mass of about 500 to 1,500 kilograms, including the necessary housing, solar panels, batteries, station-keeping fuel, and communication and sensor subsystems.

The problem is that a single bodyguard satellite would be insufficient to guard its "boss." Even if the bodyguard successfully intercepted an incoming ASAT, the adversary could simply try again on a successive orbit--the so-called "limited magazine" problem. Of course, a satellite could possess multiple bodyguard satellites, but the launch costs alone (about $15,000 per kilogram of payload) quickly become prohibitive for multiple bodyguards weighing about 1,000 kilograms each in orbit. At some point, the cost of having many bodyguard satellites exceeds that of the satellite being protected. It then makes more sense to simply have a backup redundant satellite ready to launch rather than multiple defensive space weapons.

More problematic still is the fact that the attacker can use simple countermeasures such as decoys and flares to fool the bodyguard's interceptor. This is the same reason why ballistic missile defense also doesn't make sense.

Directed-energy weapons such as lasers may be available in the future, but they run on chemicals as the source of the laser energy, which also are subject to the limited magazine problem if the laser is in orbit. And if the laser is ground-based, its range of lethality is limited to a small fraction of the globe in the ground-station's vicinity. Furthermore, ground-based systems must use complicated and expensive adaptive optics to compensate for the natural broadening and dimming of the laser light as it traverses the atmosphere, something that has not yet been publicly demonstrated over hundreds of kilometers for a high-power laser. Of course, the laser ground stations are hostage to conventional ground attack, and, more prosaically, cloud cover.

Thus, the much feared "Space Pearl Harbor" can happen with or without space weapons, as they provide little, if any, effective defense. In fact, introducing weapons into space that are offensively potent yet defensively ineffective may actually make a "Space Pearl Harbor" more imminent. In the eyes of potential adversaries, the only distinction between defensive and offensive space weapons would be the unknowable intention behind their use. A bodyguard satellite, for instance, could easily be reconfigured to attack other satellites instead of defending against incoming ASATs.

Fielding offensive space weapons for the sake of deterrence also doesn't make sense because the United States relies much more heavily on its satellites than any of its adversaries. A better way to deter attacks on U.S. satellites would be for Washington to make clear that any attack on its space assets would be considered an attack on U.S. soil and result in a heavy conventional retaliatory attack.

Ultimately, the protection of the capabilities facilitated by space assets is needed. For instance, having a fiber-optic backup system for certain high-value communication satellites is much smarter than maintaining many expensive, ineffective bodyguard satellites. Alternate redundant non-space systems, whenever possible, are the smartest defense. The United States could also have redundant satellites ready to replace any losses in those satellites for which no land-based backups exist. Temporary and reversible electronic countermeasures that could throw off the guidance systems of incoming ASATs are another sensible defense. Better "Space Situational Awareness" is also badly needed, if for nothing else, than to properly tell apart a satellite attack from a satellite malfunction or natural interference such as a strong solar flare or debris impact.

Most importantly, the United States should be leading the charge to have an overarching international policy that restricts the weaponization of space. The United States possesses the greatest military and civil space investment; thus, it has the most to lose in an offensive space war. And since Washington is the most reliant on its space assets, an arms race in space would be disproportionately detrimental to U.S. interests.

Instead of relying upon expensive, provocative, and defensively useless space weapons, the incoming administration would do well to invest in any of the other approaches listed above to improve our space security.

1Although exo-atmospheric ballistic missile defense (BMD) interceptors constitute de facto space weapons under this definition, a treaty restricting space weaponization would have to go beyond simple definitions. For instance, while compartmentalizing and allowing BMD, it may still specifically restrict the use of BMD interceptors against satellites. There's an important interplay between definitions, prohibitions, and verification methods for any sound set of rules to obtain space security, and this is something that will have to be negotiated carefully.