As the space shuttle approaches retirement next year, spaceplanes are surging. Unmanned hardware is being flown and dusted off while two manned concepts are vying for NASA development money and the chance to provide commercial rides to the International Space Station (ISS).

Ironically, the most successful spaceplane this year is cloaked in mystery. The Air Force’s unmanned X-37B was launched into orbit atop an Atlas V rocket in April 2010 and spent 220 days in orbit before making an automated landing on Dec. 3, at Edwards Air Force Base. 

Speculation has raged about the capabilities and intent for the X-37B, with critics suggesting it could conduct up-close investigations of satellites and even carry weapons in its payload bay, while the Air Force says the project is all about testing new sensors and systems, including the space plane’s reusability, in-orbit operations, and ability to take new sensor packages to space for a workout. A second X-37 is undergoing preparation for launch in 2011.

Two other unmanned X-named space planes built by NASA back in the '90s by Orbital Sciences (News - Alert) were pulled out of decade-long storage and are now being inspected and freshened up for possible flights, reports Wired. If one or both of the X-34 planes can be made flight-worthy, NASA will most likely make them available to private industry -- in this case, Orbital -- for engineering use.

Orbital Sciences and Sierra Nevada have declared their intentions to build space planes by putting proposals into NASA's Commercial Crew Development (CCDev) effort. The next round of CCDev is worth a $200 million award per company to more fully develop a human-rated spacecraft.

Orbital plans to build on work it did for NASA over the past decade in evolving NASA's HL-10/HL-20 lifting body work, reports Aviation Week and the company. The "blended lifting body" would initially seat four astronauts and be launched into orbit on a United Launch Alliance Atlas V rocket, but is "flexible enough" to go on other launch vehicle options. It would also be able to add more passenger seats and deliver cargo to ISS and other destinations in an unmanned mode.

Sierra Nevada's SpaceDev division is currently carrying the torch for the Dream Chaser system and in some ways could be called the brother of Orbital's proposal. Dream Chaser also traces its heritage straight back to NASA's HL-20 design work. It would hold six astronauts and also be put into orbit on an Atlas V. SpaceDev has already received $20 million from NASA to develop Dream Chaser.

Lifting bodies get brownie points among space enthusiasts for a smoother return from space -- less Gs vs. a drastic "drop" into the atmosphere -- and the ability to land horizontally on any runway.

Perhaps the most exciting thing about the current round of CCDev and spaceplane research is that NASA and the United States could end up with multiple ways and more affordable to deliver astronauts into Earth orbit after decades of dependence upon the space shuttle.