Los Angeles ? After a decade of development, the Air Force this month plans to launch a robotic spacecraft resembling a small space shuttle to conduct technology tests in orbit and then glide home to a California runway.

This undated image released by the U.S. Air Force shows the X-37B spacecraft. The Air Force is preparing to launch this robotic spacecraft that resembles a small space shuttle to perform unspecified technology tests in orbit and then autonomously glide on stubby wings to a landing on a California runway.

The ultimate purpose of the X-37B Orbital Test Vehicle and details about the craft, which has been passed among several government agencies, however, remain a mystery as it is prepared for launch April 19 from Cape Canaveral, Fla.

“As long as you’re confused, you’re in good shape,” said defense analyst John Pike, director of Globalsecurity.org. “I looked into this a couple of years ago — the entire sort of hypersonic, suborbital, scramjet nest of programs — of which there are upwards of a dozen. The more I studied it, the less I understood it.”

The quietly scheduled launch culminates the project’s long and expensive journey from NASA to the Pentagon’s research and development arm and then to a secretive Air Force unit.

Hundreds of millions of dollars have been spent on the X-37 program, but the current total has not been released.

The launch date, landing sites and a fact sheet were released by Air Force spokeswoman Maj. Angie I. Blair. She said more information would be released soon, but questions on cost and other matters submitted by e-mail weren’t answered by Friday.

While the massive space shuttles have been likened to cargo-hauling trucks, the X-37B is more like a sports car, with the equivalent trunk capacity.

Built by Boeing Co.’s Phantom Works, the 11,000-pound craft is 9 1/2 feet tall and just over 29 feet long, with a wingspan of less than 15 feet. It has two angled tail fins rather than a single vertical stabilizer.

Unlike the shuttle, it will be launched like a satellite, housed in a fairing atop an expendable Atlas V rocket, and deploy solar panels to provide electrical power in orbit.

The Air Force released only a general description of the mission objectives: testing of guidance, navigation, control, thermal protection and autonomous operation in orbit, re-entry and landing.

The mission’s length was not released, but the Air Force said the X-37B can stay in orbit for 270 days. The primary landing site will be northwest of Los Angeles at coastal Vandenberg Air Force Base.