One possibility is the Technology Satellite of the 21st Century, or TechSat 21, a concept being studied by the Air Force Research Laboratory (see One System, Many Eyes," left). Instead of large satellites the size and weight of cars, TechSat 21 would use "virtual satellites"-clusters of microsatellites weighing about 300 pounds apiece. Each microsatellite would have a bistatic receiver that would not only detect radar signals bouncing off Earth from its own transmitter, but also the signals sent by its neighbors, improving the resolution of the images collected.
Researchers are convinced that mass-produced micro-satellites, working in groups, will eventually make today's bulky and more costly devices obsolete. Among the advantages: If one microsatellite fails, the entire system doesn't have to be replaced. And they'll be much more flexible, because by simply reconfiguring clusters, operators will be able to conduct different missions. For example, the same group of microsatellites could be initially widely spaced to provide worldwide radar coverage, and then within hours moved closer together to conduct fine-toothed searches of smaller areas.
Much work remains to be done before TechSat 21 will be ready. For example, researchers must figure out how to keep the microsatellites in their tight pattern of slightly different orbits without burning too much fuel. The first real demonstration of the TechSat 21 concept will occur in 2005, when the Air Force plans to launch a cluster of three identical microsatellites to see whether they can fly in a precise formation.
The marked difference between the next generation of location-finding GPS satellites, known as GPS III (see "Jam-Proof Signals"), and current models-which, besides military applications, are used for everything from crop surveys to creating digital maps in cars-is that they will have separate signals for military and civilian use. This will make it more difficult for enemies to jam military output. The importance of this capability was underscored two years ago when engineers from the Air Force Research Laboratory used instructions downloaded from the Internet to build a $7,500 homemade device that easily drowned out GPS signals in a flood of electronic noise. That demonstration stoked the fear that any enemy with little more than access to the Web could sidetrack a smart- bomb attack. To avoid this, GPS III, scheduled to be ready by the end of the decade, will transmit a higher-powered and more concentrated signal than what is provided by existing equipment. These so-called spot beams will be virtually impossible to jam without expensive and sophisticated devices.
GPS III satellites will also have improved clocks. The more precise the temporal information sent from the satellites to receivers on the ground, the better the receivers can calculate the distance traveled by the signals and then "triangulate" a position using measurements from at least three satellites. With better GPS location data, satellite-guided weapons will be able to find their targets more accurately-to within a meter, as compared to about 6 meters today.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.