The liftoff of an Atlas V rocket from Cape Canaveral this month will mark one of the most secretive U.S. Air Force spaceflights in decades. Guessing the nature of the secret has become a sport among aficionados.
"This is one odd bird," military space historian Dwayne Day told IEEE Spectrum. "They're spending an awful lot of money for a test program that seems to have no real end user."
The 6000-kilogram, 8-meter X-37B OTV-1 is often called a flying Twinkie because of its stubby-winged shape. It was built in the Boeing Phantom Works high-security facility in Seal Beach, Calif. In the flight test, the craft is supposed to orbit Earth for several weeks, maneuver in orbit, and glide its way to a landing strip at Vandenberg Air Force Base, in California.
The smart money is betting that the flight will put to the test systems that enable satellites to protect themselves from enemy attack. The most important trick in such self-protection is determining whether you are under attack at all. A clever enemy will want the attack to seem to be a mere accident. That way he'd leave no return address.
The official description of the mission talks of demonstrating "a rapid-turnaround airborne test bed." That makes sense, but there is no sign that anyone plans to fly the vehicle ever again. Official explanations also mention putting the space plane through all its steps in orbital flight—including in-orbit maneuvering, descent and landing—while demonstrating or testing 30-odd technologies, including guidance and navigation, thermal protection and power-distribution systems, and streamlined flight, all of potential use on future vehicles. The new technologies pave the way for a new White House policy under which NASA is to turn over much of its ground-to-orbit transport to commercial providers.
Most of these technologies can be seen as refinements of ideas dating back to the 1960s, but one, unmentioned idea—autonomous approach—would be truly new, if speculations are correct, and it's indeed part of this spaceflight. This is the ability to identify an attacker by electromagnetic range finding and perhaps by chemical "sniffing" for effluents that an attacker might leak while trying to match up its orbit with that of the target.
To test such capabilities properly, the mission might conceivably deploy subsatellites to impersonate enemy craft, or bogies. They'd stalk the mother ship using autonomous approach techniques tested in recent years, giving it the chance to detect clues to their presence. The X-37B has a pickup-bed-size payload bay that could carry such instruments and subsatellites.
Observers suspect that the test flight may involve observations of another space vehicle. This suspicion was fanned by the announcement in late February that a Mach-5 hypersonic glider would be launched from California toward a Pacific tracking site during the X-37B's first week in orbit.
"That is a pretty interesting coincidence," noted Brian Weeden, a Montreal-based space and missile advisor for the Secure World Foundation, a private group in Superior, Colo., that monitors space technology. "Once we get more details about when they will be on orbit and can glean info about trajectories, it might get really interesting."
Probably the best insight into the project's purpose will come after launch, as amateur (but well-equipped) satellite watchers around the world attempt to follow its orbital flight path and course changes. (You can follow their efforts at https://satobs.org.)
The degree to which the amateurs are successful, and the effort that the X-37B managers take to evade such observation, may provide a significant clue as to just how secret—and important—this mission really is.