The unmanned X-37B spacecraft is scheduled for a lift into orbit later today, after a weather scrub yesteday. It will fly itself back to the runway at Edwards AFB sometime in the next nine months. This news item is breathless about the mystery plane. There's no great mystery, though: it's a technology demonstrator for military work to come ... if the US can afford it.
The Union of Concerned Scientists expresses anxiety in this statement, which warns that the X-37B is a toe in the door for the USAF's long-term designs on space domination.
Or space-based defense, at any rate. This was a theme in speculative military literature a decade ago. See this 2001 paper from an officer-student at the Air University, X-37 Space Vehicle: Starting a New Age in Space Control? on how such reusable vehicles could help the USAF establish a presence in space, or at least give it a mobile, fast-response launch and recovery capability that could be usable for anti-satellite work or to hurl kinetic projectiles before an enemy's land forces can reach its major objective or, better yet, before the attack starts. See this RAND Corporation paper on what's known to tacticians as pre-emptive attack during the halt phase. More context on the X-37B is at MilSat magazine.
Shaped like a small space shuttle, the X-37B is to ride into space inside the nose fairing of an Atlas expendable launch vehicle. This the second X-37B to be readied for launch. The first one (denoted OTV-1) went into orbit last year, using its own navigational prowess to return nine months later.
One item of historical interest is the rocket engine used for maneuvering the X-37B once in orbit, the venerable Rocketdyne AR 2/3. It runs on jet fuel and 90% hydrogen peroxide, also known as HTP for high-test peroxide. HTP is dangerous stuff if it combines with contaminants in a storage tank, but highly valued as an oxidizer for torpedoes and rocket engines.
Remember the movie The Right Stuff? The end of the story showed test pilot Chuck Yeager trying to break an altitude record in an F-104. The film used a standard model F-104G, but in reality Yeager flew a high-altitude modified version called the NF-104A, which in addition to the jet engine used for lower altitudes had a rocket engine very similar to that used on the X-37B.
The AR 2/3 rocket engine on the NF-104A, which took over at high altitude after the pilot turned off the J79 jet engine, was mounted at the base of the airplane's vertical stabilizer. A photo of the Rocketdyne in action is at this Wikipedia page.