X Marks the Spot

Privately built rocket plane SpaceShipOne punched through Earth’s atmosphere early on Oct. 4 for the second time in a week.

Shortly after the vehicle landed, Ansari X Prize Foundation officials announced that the plane had completed their requirements for winning the $10 million X Prize: that a privately built, manned ship reach space twice within two weeks.

SpaceShipOne features an unusual hybrid rocket design. Liquid nitrous oxide is used as an oxidizer, and solid hydroxy-terminated polybutadiene (rubber) serves as the fuel. According to builder Scaled Composites, such a hybrid design combines the advantages of liquid- and solid-fuel rockets while reducing the risk of catastrophic explosion, because both substances can be stored safely without special precautions and do not react when mixed together under normal conditions. In addition, because nitrous oxide self-pressurizes at room temperature, the ship doesn’t need complicated pumps to vent oxidizer into the combustion chamber.

Founded eight years ago by aerospace engineer and physician Peter H. Diamandis, the X Prize is meant to stimulate the development of commercial space flight. It is modeled after the $25,000 Orteig Prize won by Charles Lindberg in 1927 for completing the first nonstop flight between Paris and New York City.

“Burt Rutan, Paul Allen, and the rest of the SpaceShipOne team are to be congratulated for this important achievement. They successfully demonstrated a new human spacecraft, a new propulsion system, and a new high-altitude airborne launch platform,” said National Aeronautics & Space Administration Administrator Sean O’Keefe in a statement after the ship’s flight.

SpaceShipOne was funded by Microsoft cofounder Paul G. Allen and built by Scaled Composites, an aerospace engineering company founded by noted aircraft designer Burt Rutan. It is the only vehicle to reach space out of roughly two dozen competing for the X Prize.