Its cost and mission are classified, but a first-of-a-kind reusable miniature military space shuttle is on the launch pad ready to soar into orbit on an Atlas 5 rocket Thursday evening.

The Atlas 5 rolled to the launch pad at Complex 41 Wednesday morning. Credit: Pat Corkery/United Launch Alliance

Under the cover of the Atlas 5's payload shroud, the X-37B is scheduled for launch at 7:52 p.m. EDT (2352 GMT) from Complex 41 at Cape Canaveral, Fla. The launch window extends for 9 minutes.

The 196-foot-tall booster rolled to the launch pad Wednesday morning.

"Fundamentally, this is an updated version of the space shuttle," said Gary Payton, the U.S. Air Force's top civilian leader for military space programs. "The Air Force has a suite of military missions in space. This new vehicle could potentially help us do those missions better."

Although officials are openly discussing the X-37B platform itself, the Air Force is mum on exactly what payloads the unmanned ship carries inside its cargo hold, which is about the size of a pickup truck bed.

During several weeks or months in orbit, the X-37B will be a testbed for secret new technologies.

Future flights of the reusable spaceship could approach U.S. or foreign satellites, recover old spacecraft, or test out surveillance and repair techniques. The speculation leads some to voice concerns over the militarization of space.

During a teleconference with reporters Tuesday, Payton said none of those activities are part of the X-37B's first flight. The craft launching Thursday does not carry a robot arm like the shuttle, and there are no rendezvous objectives planned for the mission, according to Payton.

New heat shield technologies, advanced guidance and navigation, a solar power generation system, and new flight control systems are at the top of the list of public goals for the test flight.

"The primary objectives of the X-37 are to [prove] a new batch of vehicle technologies for America's future, plus readying and demonstratring the concept of operations for reusable experimental payloads," Payton said.

The X-37B will return to Earth only after it completes its top secret experiments in orbit.

A mini-space shuttle

With wings and a payload bay, the spaceplane has been labeled as a miniature military space shuttle. But it is not equipped to carry people and its capabilities are significantly more limited than the real thing.

The X-37B spaceplane undergoes pre-launch processing near its Florida launch site. Credit: U.S. Air Force

It can only carry several hundred kilograms of useful payload mass to orbit, Payton said.

The X-37B, also named the Orbital Test Vehicle, is about one-quarter the size of a space shuttle orbiter.

The 11,000-pound spacecraft measures more than 29 feet long and 9.5 feet tall. Its wings span nearly 15 feet, according to the Air Force.

Instead of running on fuel cells like the shuttle, the OTV will unfurl a small solar array to produce electricity in orbit. And the X-37B uses electromechanical actuators instead of hydraulics to move its flight control surfaces.

The solar array gives the vehicle a renewable energy source, permitting the X-37B to loiter in orbit for much longer than the space shuttle, which is limited to missions lasting a few weeks.

Other technologies the OTV flight will test include advanced guidance, navigation and control, thermal protection systems, avionics, high temperature structures and seals, and conformal reusable insulations, according to an Air Force fact sheet.

Built by the Boeing Phantom Works division, the X-37B's on-board rocket propulsion system is nearly the size of the shuttle's primary orbit-changing engine, giving the spaceplane powerful capabilities to maneuver once in orbit.

The mission will be controlled by the Air Force's 3rd Space Experimentation Squadron at Schriever Air Force Base, Colo.

The Air Force says the craft's activities in space are classified, including its post-launch orbital parameters. The X-37B is designed to operate at altitudes between 110 and 500 nautical miles, or 126 to 575 miles, according to an Air Force spokesperson.

Thursday's Atlas launch will enter a news blackout after the rocket's Centaur upper stage completes its first burn about 17 minutes after liftoff. Any subsequent Centaur firings and deployment of the X-37B will not be announced.

"You can't hide a space launch," Payton said. "The main thing we want to emphasize is the vehicle itself, not so much what's going on during the on-orbit experimental phase. The vehicle itself is the piece of news here."

This artist's concept was produced when the X-37 was managed by NASA. Credit: Boeing

The length of the mission has not been determined, according to Payton. The craft can stay in orbit for up to 270 days.

At the end of the flight, the craft's main engine will fire to drop the ship from orbit. The spaceplane will re-enter the atmosphere on a computer-controlled autopilot and make a high-speed landing at nearly 300 mph on a 15,000-foot-long runway at Vandenberg Air Force Base, Calif.

"Our re-entry activity is slightly different than the shuttle because the real-time human control won't be there every single instance of de-orbit preps and de-orbit burn and entry," Payton said. "It will be relying on its own autopilot, its own gyroscopes, its own GPS receivers, eventually its own altimeter. It will be on its own all the way through entry and landing. And that's dramatically different than the way shuttle does it."

Transforming military space operations

The Air Force is building another X-37B vehicle for launch next year. Its final launch date will depend on the outcome of the first flight.

After landing, engineers will prepare the vehicles for more missions.

"The most important demonstration is on the ground," Payton said. "Once we get the bird back, we'll see what it really takes to turn this bird around and get it ready to go fly again, to learn how to do payload changeout on the ground, to learn how much it really costs to do this turnaround on the ground with these new technologies on the X-37 itself."

The Air Force hopes turnaround times and operations expenses prove faster and less costly than traditional space platforms.

"There is much to learn in the first few flights on the technologies used on this vehicle, how quickly it can be readied for a re-flight, and on the operational utility," said David Hamilton, director of the Air Force Rapid Capabilities Office. "We have started discussions with Air Force Space Command (officials) to plan for the possibility for transition to an operational capability, but the system first must prove its utility and cost effectiveness during the test program."

The program's future hinges on the outcome of test flights in 2010 and 2011.

"That all depends on the success of these first two birds," Payton said. "Can we keep the [operations and maintenance] costs low? Can we turn them around between flights easily?"

The X-37B spacecraft is encapsulated inside the Atlas 5 rocket's payload fairing. Credit: U.S. Air Force

The X-37B could bridge the divide between expensive and risky space systems and high-performance aircraft like the SR-71 spy plane.

"The OTV has the potential to revolutionize how the Air Force operates in space by making space operations more aircraft like and adding in the capability for returnable plug-and-play experiments," Hamilton said in an Air Force news article on the mission.

"If we were talking a surge of small satellites, I would like to see this X-37 handled much more like an airplane, maybe an SR-71," Payton said. "I would think handling this bird more like an SR-71 and less like a routine space launch vehicle would be a good objective. That's measured in several days, or maybe 10 or 15 days (between flights)."

Any funding for further X-37B development is classified.

The Pentagon's Operationally Responsive Space program, which is tasked with cutting space development times and costs, could be a good fit for a potential fleet of spaceplanes, Payton said in a March interview.

"We could have an X-37 sitting at Vandenberg or at the Cape, and on comparitively short notice, depending on warfighter requirements, we could put a specific payload into the payload bay, launch it up on an Atlas or Delta, and then have it stay in orbit, do the job for the combatant commander, and come back home," Payton said. "And then the next flight, we could have a different payload inside, maybe even for a different combatant commander."

Even if the X-37B demonstrates its readiness for operational missions on short notice, the availability of launch vehicles will likely impede quick re-flights.

The spaceplane can only launch on Atlas and Delta rockets, and their manifests are already full of military and NASA flights.

Long road to launch

This isn't the first time the Air Force has dabbled in reusable space technologies. But the flight is occurring as NASA retires its own reusable spaceship and turns its focus to commercial providers and expendable one-flight systems.

The craft is the manifestation of the Air Force's long-held, on-and-off again dream to operate its own space plane.

The first time the military flirted with the idea of a reusable spaceship was the Dyna-Soar project of the late 1950s and early 1960s. The Dyna-Soar, also named the X-20, was envisioned as a piloted spacecraft for anti-satellite, reconnaissance and other space weapons applications.

After Dyna-Soar's cancellation in 1963, the Air Force turned its attention to an ill-fated manned space station called the Manned Orbiting Laboratory. It was cancelled in 1969.

The military contributed to the earliest conceptual designs of the space shuttle beginning in 1971. The Air Force selected Vandenberg to host shuttle launches on polar orbit missions with classified national security payloads.

But the Pentagon scrubbed plans to launch the shuttle from Vandenberg after the Challenger accident. The military's last dedicated shuttle mission launched from Florida in 1992.

The Air Force took over the X-37B program in 2006 from the Defense Advanced Research Projects Agency, the military's research and development department.

The X-37's origins can be traced to NASA.

An atmospheric flight version of the X-37 was developed for landing tests. Credit: Boeing

"We were focused on keeping as much commonality to the prior work that NASA and DARPA had done and just assembling this vehicle and sending it through the vigorous environments so we had confidence that it would work," Payton said.

NASA selected Boeing to develop the X-37 in 1999 as a testbed for reusable launch vehicle technologies. The X-37 was later described as a demonstrator for NASA's Space Launch Initiative and Orbital Space Plane projects seeking less expensive and more reliable access to low Earth orbit.

After funding dried up, NASA transferred the program to DARPA in 2004.

"The primary reason for selecting X-37 was the need to have a demonstrator for thermal protection systems and re-entry systems," said Dan Dumbacher, NASA's former X-37 project manager. "We can do arcjet testing and other things on the ground, but you never get the right environment until you actually fly stuff back from orbit. The reason NASA stayed [with the X-37] as long as they did was because of the thermal protection system technology demonstration aspect."

NASA still works with the Air Force on the spacecraft's advanced silica thermal protection tiles and autonomous guidance system, according to Dumbacher.

"This is pretty exciting time for me, personally," Payton said. "After a tumultuous history of sponsorship, it's great to see the X-37 finally get to the launch pad and get into space."

The project's management is now concentrated in the highest levels of the Air Force under the Rapid Capabilities Office, which oversees new technological developments on the fast track for introduction into operational roles.