As detailed in Technology Review, many private players are spurred by the prospect of capturing the $10 million X-Prize. This bounty, offered by a St. Louis, MO-based foundation funded by space tourism boosters, will be awarded to the first privately financed rocket craft that carries three people to the edge of space at an altitude of at least 100 kilometers, returns them safely to Earth, and does it all again within two weeks. Already, 24 players have signed up to make the attempt.

Xcor Aerospace, led by former Intel executive Jeff Greason, may have the best shot yet at actually giving the world a reusable rocket plane. Last July their lightweight craft dubbed EZ-Rocket reached a new aviation milestone when pilot Dick Rutan, who had also piloted Voyager, put its twin rocket motors through a pivotal “touch and go” maneuver: taking off, shutting down the engines, landing, firing the motors up again, and taking off without stopping. Each of Rutan’s two flights in the tiny two-seat rocketplane, which resembles a jet fighter with its tail chopped off and stubby winglets installed near its nose, lasted less than 15 minutes and never reached altitudes higher than 3,000 meters. Still, Xcor Aerospace is continuing incremental development efforts even though its EZ-Rocket does not meet the three-person criterion of the X-Prize.

Several competing companies are already pursuing the grand vision: a craft that can go all the way into orbit. One is Pioneer Rocketplane of Solvang, California which has designed a rocket-and-jet hybrid called Pathfinder. After taking off with traditional jet engines and reaching a cruising altitude of about 5,500 meters, a fuel-tanker plane will rendezvous with the Pathfinder and pump liquid oxygen into an empty tank onboard the craft. Then, propelled by a combination of liquid oxygen and kerosene, the Pathfinder will light its rocket motor and soar to an altitude of 139 kilometers, where it will release an unmanned upper stage to deliver a 2,280 kilogram payload into orbit. Pioneer’s CEO, Mitchell Burnside Clapp, (who can do more than sing) was responsible for an Air Force design of an airplane-like reusable rocket that later evolved into the Pathfinder concept. Because of that design, Pioneer Rocketplane is a leading competitor for a Defense Advanced Research Projects Agency project to develop an inexpensive rocket-propelled satellite launcher. DARPA is expected to announce the award of two final design contracts on March 1.

Development efforts of a Shuttle replacement aren’t limited to the US, either. Germany’s Astrium design is expressly leaving out human cargo. Instead, it is developing an autonomous rocket craft called Hopper, designed to provide cheap satellite launches. The first step in this direction is the Phoenix, a one-sixth-scale version of the Hopper. The Phoenix is mainly a test bed for autonomous landing technology. The craft’s designers are incorporating laser-based altimeters–altitude sensors–and digital Global Positioning System equipment together with intelligent-navigation algorithms that enable the craft to make a gliding runway landing without help from humans or equipment on the ground. The first test of the vehicle, which is under construction, is expected next year: a helicopter will drop the Phoenix from an altitude of about 1,400 meters, leaving it to land on its own. Astrium estimates that the full-size Hopper could launch satellites in 15 to 20 years, at half today’s launch costs.