SS2 Breaks Sound Barrier On First Powered Flight

By Guy Norris
Source: Aviation Week & Space Technology
May 06, 2013
Credit: Virgin Galactic

Powered flight tests of Virgin Galactic's SpaceShipTwo (SS2) suborbital spaceplane are expected to resume by early June following the vehicle's first rocket-propelled flight over Mojave, Calif., on April 29.

Although only 16 sec. of SS2's 13-min. flight were powered by its hybrid RM2 rocket motor, the event was hailed by Virgin Galactic founder Richard Branson as the “single most important flight test to date.” Coming 2.5 years after the first glide flight of SS2, the powered test also marks the start of the final envelope-expansion phase and the “very realistic goal of full spaceflight by the year's end,” he adds.

Whether that is achievable will depend on the success of the forthcoming flights that will end with a maximum apogee demonstration flight to 361,000 ft. At that point, SS2 developer Scaled Composites will turn the vehicle over to Virgin Galactic, which plans to begin commercial suborbital services from Spaceport America, N.M., in 2014. Tests will follow a “methodical build-up” to the maximum apogee flight says Scaled President Kevin Mickey, gradually expanding the supersonic aerodynamic flight envelope, launch weight and structural loads.

Scaled is optimistic tests will remain on track partly because of experience gained during flight tests of the SpaceShipOne (SS1) vehicle during the build-up to winning the Ansari X-Prize almost a decade ago. “We learned a tremendous amount on SS1, which will minimize any test surprises,” says Mickey. The 17-flight SS1 test program included just six rocket-powered flights in 2003-04, and uncovered several issues with directional stability, flight control and avionics systems.

“With SS1, we leapt to the ultimate goal fairly quickly. The goal of this program is different to SS1. It is our job to help Virgin and The Spaceship Co. mature this into a commercial operation, and we'll take steps to ensure the vehicle's safety and robustness,” he adds. The Spaceship Co. (TSC) is Scaled Composites' wholly owned manufacturing sister business .

Although Mickey acknowledges that “with any testing, you don't know what you don't know,” he says the overall level of maturity of the SS2 design and systems makes the upcoming test effort more predictable. For example, maximum dynamic pressure (Max q) testing, which is the next major target, was almost completed on the rocket-powered April 29 flight. “That will be an important data point,” Mickey says.

The powered test flight began when SS2, mounted below the wing of the WhiteKnightTwo carrier aircraft, took off from Mojave at 7.03 a.m. local time. Launch occurred 45 min. later from an altitude of almost 47,000 ft. Following release from the carrier aircraft, Scaled test pilots Mark Stucky and Mike Alsbury “lit the rocket almost immediately,” says Mickey. The rocket boosted the vehicle to Mach 1.22 and an apogee of 56,200 ft. following rocket burnout after 16 sec.

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