Flying high above the Mojave, Calif., desert, the X-37, an unpiloted, reusable space plane, made its first captive-carry flight June 21 under the wings of Burt Rutan’s White Knight, the same plane that carried SpaceShipOne on the initial phase of its historic flight into suborbital space on the exact same date a year ago.

Scaled Composites’ White Knight carrier plane previously had taken the X-37 for repeated runs down the runway at the Mojave Spaceport — all in preparation for the June 21 flight test and return landing of the twosome.

Tagged by the Defense Advanced Research Projects Agency (DARPA) as an Approach and Landing Test Vehicle , the X-37 will undergo captive-carry flights, followed by high-altitude drop tests throughout the summer, said DARPA spokeswoman Jan Walker.

The X-37, a project of Boeing, DARPA and NASA, is intended to explore the potential applications such as on-orbit satellite repair for commercial and military users and possible applications for future reusable launch systems.

Designed by Scaled Composites, the multi-purpose White Knight was used to haul that firm’s SpaceShipOne to altitude for release. The rocket plane made a series of piloted suborbital flights last year — the first on June 21, 2004 — and eventually won the $10 million Ansari X Prize after conducting back-to-back suborbital flights.

The X-37 has been billed as an unpiloted, autonomously operated vehicle designed to conduct on-orbit operations and collect test data in the Mach 25 (re-entry) region of flight.

The Boeing-built X-37 is intended to be a test bed for airframe, propulsion and operation technologies designed to make space transportation and operations significantly more affordable.

Late last year, NASA transferred its X-37 technology demonstration program to DARPA .

The Approach and Landing Test Vehicle has been at the Mojave airport since mid-April, Walker said.

NASA’s involvement in the X-37 dates back to 1998, when the project was selected as the first of a planned series of flight demonstrators dubbed Future X. At the time, NASA agreed to share the X-37’s projected $173 million cost with Boeing and the U.S. Air Force. After the Air Force announced in 2001 that it would stop funding the project, NASA told Boeing that the company would have to submit a new proposal for the X-37 to be eligible for additional funding.

After persistent prodding from U.S. Rep. Dana Rohrabacher (R-Calif.), NASA in 2002 awarded Boeing a $301 million contract for two X-37 vehicles instead of one. One of those vehicles would conduct a series of drop tests within the atmosphere, paving the way for the flight of the orbit and re-entry vehicle in 2006.

But NASA advised Boeing in late 2003 to throttle back on development of the orbit and re-entry vehicle and directed Boeing to stop work on that part of the program altogether. X-37 was dealt a further setback last year when a NASA review concluded that the program was not a good fit with the agency’s new space exploration agenda.

Staff writer Brian Berger contributed to this article.

Leonard David has been reporting on space activities for nearly 50 years. He is the 2010 winner of the prestigious National Space Club Press Award and recently co-authored with Apollo 11’s Buzz Aldrin the book “Mission to Mars — My Vision for Space...