The glide flight, which took place in the skies above the Mojave Air and Space Port in California, was the fourth free flight of the second SpaceShipTwo, named VSS Unity, all performed without a rocket engine on board. The previous glide flight was Feb. 24.
On this test, SpaceShipTwo pilots Mark Stucky and Mike Masucci engaged the vehicle’s “feather” system, which raises the spaceplane’s twin tail booms, after release from its WhiteKnightTwo carrier aircraft. The pilots then lowered the tail booms into their regular configuration and glided to a runway landing in Mojave.
“Full analysis of the data from today’s flight will, as always, take time; but initial reports from the pilots and from mission control are extremely encouraging,” the company said in a post-flight statement.
The feather test is the latest milestone in the testing program for the vehicle. “The feather will be raised at lower altitudes — and consequently thicker atmosphere — than would be the case during a full mission to space,” the company said before the flight. “This will provide a rigorous test of the feather system in the air, complementing extensive testing already completed on the ground.”
The feather system, designed to provide a stable configuration during reentry, was also linked to the October 2014 accident that destroyed the first SpaceShipTwo, VSS Enterprise, during a powered test flight. On that flight, vehicle co-pilot Michael Alsbury prematurely unlocked the feather system while the vehicle was accelerating through the sound barrier. The aerodynamic forces on the vehicle cased the feather to deploy, leading to the vehicle’s breakup. Alsbury was killed in the accident and vehicle pilot Peter Siebold was injured.
An investigation by the National Transportation Safety Board concluded that Scaled Composites, which built the first SpaceShipTwo, failed to consider the possibility that a pilot might prematurely unlock the feather and thus took no steps to prevent it. The new SpaceShipTwo includes a locking system that prevents the feather from being unlocked during the early phases of powered flight.
Virgin Galactic has not disclosed a detailed test flight schedule, but company officials said they expect to need on the order of ten glide flights to meet all their test objectives before moving on to powered test flights. The exact number of glide flights will depend on how quickly they reach those test objectives.
Once the glide flights are complete, the company will move ahead to powered test flights, using the hybrid rocket motor on the spaceplane. “We have started the glide flight program, and we will continue that for the next few months, and then we’ll get into powered flight over the course of the year,” George Whitesides, chief executive of Galactic Ventures, which includes Virgin Galactic, said at a February conference. “We aspire to push far into the test flight program during the course of 2017.”
If all goes well, that’s expected to permit commercial flights to begin in 2018. However, in an April 28 on-stage interview, Virgin Galactic founder Sir Richard Branson declined to commit to a schedule for beginning commercial flights. “I’ve made the mistake of giving dates before and being wrong,” he said.