The U.S. military relies heavily on satellites for communications, navigation, surveillance and other essential activities. To protect these satellites, some military strategists say we need to deploy defenses that include space weapons. The problem: It’s far more expensive and technologically challenging to defend a satellite than to attack one.

But if our satellites are sitting ducks, we can’t leave them undefended, can we? Yes, says physicist Richard Garwin, a national-security expert and Fellow Emeritus at IBM’s Thomas J. Watson Research Center. He and other critics of space weapons say that enemies will be deterred from attacking U.S. satellites if they know we have backup systems in place-“pseudolites” that can fill in for any satellites that are damaged or destroyed.

A pseudolite (for “pseudo satellite”) is an unmanned aerial vehicle (UAV), piloted aircraft or high-altitude balloon that performs the same functions as a satellite but over a much smaller area. For example, if an enemy were to take out one or more of the two dozen GPS satellites orbiting Earth, the Army could use GPS transmitters mounted on its Hunter UAVs to provide navigation data over a battlefield. Not only could such a system temporarily replace satellite coverage, it could also thwart attempts to jam satellite signals using ground-based equipment. A program sponsored by the Defense Advanced Research Projects Agency has already demonstrated the feasibility of pseudolites.

The advantage of pseudolites over space weapons is that they “are here now and work,” Garwin says. “It’s better to protect by making attack useless than by trying to defeat the attacker and provoking nuclear war.”