The U.S. Air Force launched its X-37B space plane April 22 atop an Atlas 5 rocket to test the spacecraft’s utility as a payload carrier.

The launch was broadcast live from Cape Canaveral Air Force Station, Fla., on the Internet.

The X-37B resembles a miniature space shuttle complete with payload bay doors and landing gear. In a preflight press briefing, a top Air Force official acknowledged that the craft carries “actual experimental payloads,” but he declined to elaborate, saying “on-orbit activities” will be classified, according to a military transcript of the briefing.

The top priority is to test the “vehicle itself,” said the official, Gary Payton, deputy under secretary of the Air Force for space programs.

The Air Force has long wanted a reusable space plane to maneuver satellites to new orbits, test sensors, or deploy satellites quickly for military operations or intelligence gathering. In 2005, the Air Force tested the plane’s landing system by releasing a similar craft, called the X-37A, from the Scaled Composites’ White Night carrier aircraft, the same plane that launched the SpaceShipOne space tourism test plane.

For the X-37B experiment, tasks will include: “getting the payload bay doors open, solar array deployed, learning about on-orbit attitude control, and then bringing it all back. And so we’ll have a set of test objectives for the on-orbit activities, but the vehicle itself, proving that the vehicle itself can get up in space, do a job, get back down,” Payton said.

During the Bush administration, Air Force officials spoke openly of their desire to move conventional weapons through space, but Payton struck a different tone.

“I don’t know how this could be called weaponization of space,” he said, comparing the craft to NASA’s space shuttle orbiters. “We, the Air Force, have a suite of military missions in space and this new vehicle could potentially help us do those missions better,” he added.

The spacecraft is designed to stay in orbit for up to 270 days, but the Air Force has not said how long it plans to keep the aircraft up.

“In all honesty, we don’t know when it’s coming back for sure,” Payton said. “It depends on the progress that we make with the on-orbit experiments, the on-orbit demonstrations.”

The attraction of a reusable plane is that a satellite “could be launched into a different inclination and altitude on subsequent launches,” Payton said. A reusable plane also would be valuable in military “surge mode where you’ve got to deploy a lot of things rapidly,” Payton said. Or, new technologies could be tested for up to 270 days and then be brought back to Earth for inspection.

The spacecraft is designed to be capable of a turn-around time from landing to next flight of 10 to 15 days, according to Payton. But the Air Force hopes to learn “what it really takes to turn this bird around and get it ready to go fly again, to learn payload change-out on the ground, to learn how much it really costs to do this turn-around on the ground with these new technologies.”