It's been a long wait—in some ways, more than 50 years—but in April 2010, the U.S. Air Force is scheduled to launch an Atlas V booster from Cape Canaveral, Florida, carrying the newest U.S. spacecraft, the unmanned X-37, to orbit. The X-37 embodies the Air Force's desire for an operational spaceplane, a wish that dates to the 1950s, the era of the rocket-powered X-15 and X-20. In other ways, though, the X-37 will be picking up where another U.S. spaceplane, NASA's space shuttle, leaves off.

From This Story [×] CLOSE The X-40A test vehicle is shown making one of seven autonomous free flights at NASA’s Dryden Flight Research Center in 2001. Hoisted to 15,000 feet by a CH-47 Chinook helicopter, the X-40 points its nose down initially at a 60-degree angle before it flares near the runway and touches down at about 220 miles an hour. The X-40A provided valuable approach and landing data for the 120-percent scale X-37A vehicle that would later make its own drop tests at Dryden. Those tests paved the way for the X-37B Orbital Test Vehicle, scheduled to launch in early 2010 from Cape Canaveral. The X-37B will reach orbit atop an Atlas V booster, reenter the atmosphere autonomously, and land in California. Video: NASA Dryden Flight Research Center Video: X-40 Drop Test [×] CLOSE Photo Gallery Related Content Secret Space Shuttles

With a wingspan of 15 feet and a length of 27.5 feet, the X-37 looks like a tiny space shuttle. It has a blunt (though windowless) nose, and one rocket engine bell instead of the shuttle's three. Two cargo doors open just as the shuttle's do, revealing a four- by seven-foot bay. Like the shuttle, the X-37 was designed for low Earth orbits—in the latter's case, altitudes of 125 to 575 miles. And the craft will fly like a shuttle, reentering the atmosphere with the orbiter's 40-degree nose-high attitude. After reentry, it will change to a 20-degree nose-down glide and, flying at up to 220 mph, land at Vandenberg Air Force Base in California, with Edwards Air Force Base as an alternate.

But as for the period between launch and landing, no one, save for a select few in the Department of Defense, knows exactly what the little Boeing-built spaceplane will do, or for how long. The Air Force Rapid Capabilities Office, which is running the program, says only that the orbital test version, the X-37B, will take a suite of next-generation technologies to orbit and will break new ground in the realm of launch, recovery, and reuse, all with an unmanned twist that the shuttle never offered.

At a 2008 Space Foundation breakfast in Washington, D.C., Gary Payton, deputy under secretary of the Air Force for space programs, recalled the X-37's origins. Payton started the program while at NASA. "Then, the X-37 was intended to be a testbed for new technologies that could retrofit into the shuttle: predominantly guidance, navigation, and control, and [thermal protection system] technologies," he said. In that era, planners imagined the shuttle carrying the X-37 to space in its cargo bay and releasing it.

Now, with the shuttle's retirement looming, it appears the X-37 will have an independent, post-shuttle life. Payton envisioned such a role for the X-37, saying: "It would be really advantageous in my mind if we had a system you could launch, recover, change out the payload bay quickly, and put into a different orbit, and do all that measured in weeks instead of decades." David Hamilton, director of the Rapid Capabilities Office, says in an e-mail: "Eventually, I see the unique possibility to operate X-37B more like an aircraft and explore the needs of responsive, reusable spacecraft." Unlike a satellite, he points out, the spaceplane returns, enabling "detailed inspection and significantly better learning than can be achieved with [a satellite's] remote telemetry alone. Experiments can be modified and reflown, with the objective of shortening the technology maturation timeline."

"The space shuttle was designed to be a very heavy payload lifter, and it has performed that job extremely well," says Mark Lewis, a University of Maryland hypersonics expert who recently completed a four-year appointment as chief scientist for the Air Force. "But you don't need to send a Mack truck into space when a Toyota Celica will do."

The question is: Will do what? Lewis, whose enthusiastic speech barely keeps pace with his mind, is happy to talk about the skin-deep similarities between the shuttle and the X-37. ("A lot of the basic reentry physics is treated the same way," he says. "Blunt configurations. The shuttle has very blunt leading edges.") But when he's asked about anything more than the X-37's aerodynamics, he clams up.

So does everyone else. "While some aspects of the…program have been designated as unclassified and been released to the public; information regarding specific technical and performance capabilities will not be released at this time," writes David Hamilton. "Hide it in plain view," says one observer of the Air Force's practice of letting out just a little about the X-37, enough to make it seem like it will never be more than a research tool.

Hamilton does say that "once declared operational, the X-37B could have applications to support missions such as space situational awareness; intelligence, surveillance, and reconnaissance; on-orbit servicing and repair; and satellite deployment and/or retrieval."

It's possible the spaceplane could have a role in national security, particularly since China, India, Japan, and even Iran have begun to exploit space. In December 2007, photographs of an unmanned, classified Chinese spaceplane, the Shenlong, or "Divine Dragon," began to appear on Chinese Web sites. Though hitched to the underside of a bomber, rather than perched atop an expendable booster, the mysterious Shenlong has a blunt nose and single rocket engine bell, making its appearance strikingly similar to the X-37's.