LOS ANGELES — Scaled Composites marked a dramatic increase in the test rate of Virgin Galactic’s SpaceShipTwo (SS2) by completing two glide tests over five days, including a 16-min. 7-sec. glide on April 27 that represents the longest flight to date.

The latest flight is the third in succession to increase flight time, the last one on April 22 having extended the glide to 14 min. 31 sec. The back-to-back flights tested minor aerodynamic and control system improvements to the 60-ft.-long, 42-ft.-wingspan vehicle, which is in development for suborbital space tourism and science flights.

The sudden surge in testing follows several weeks of weather-related delays, and has seen release altitudes from the WhiteKnightTwo mothership raised to 51,000 ft. and beyond. The higher altitudes provide more time to continue the flutter envelope expansion that began with the third flight in November 2010.

The flights also evaluated stability and control, and provided pilot training for the Scaled test team. Glide testing is being used to refine the vehicle’s aerodynamics and low-speed handling qualities. Building on the incremental envelope expansion approach established with SpaceShipOne (SS1), the next test phase will involve higher-speed subsonic flight with a short burst of thrust from the Sierra Nevada-developed RM2 rocket that will power all vehicles. A follow-on flight-test phase, using longer rocket burns, will open up the supersonic, higher-altitude corner of the SS2 flight envelope.

Once cleared, SS2 will move to suborbital flights. A final phase will involve extensive safety-of-flight and system robustness demonstrations for FAA Commercial Space Transportation operational approval.

Ground testing of the RM2 also is accelerating with preparations under way for a further round of hot-fire runs of the engine following a sixth full-scale flight design RM2 test in late March. The run, which was the first since a hot-fire ground test in August 2010, continued evaluation of engine systems, fuel formulation, nozzle, motor structure and valve/injector performance.

Scaled, which has a firm contract with Sierra Nevada for 50 RM2 engines, says the test met all objectives involving duration, igniter performance, oxidizer flow and pressurization systems. It also demonstrated successful collection of data-acquisition system measurements, structural evaluation, and nozzle ablation, as well as fuel regression rate and stability levels.