Virgin Galactic announced today that it would attempt the fourth flight of SpaceShipTwo Unity as early as Thursday morning from the Mojave Air and Space Port. The launch window runs through Saturday, Dec. 15.
“We plan to burn the rocket motor for longer than we ever have in flight before, but not to its full duration,” the company said in a statement that indicated the vehicle could reach a “space altitude.”
A full duration burn of Unity’s hybrid rubber-nitrous oxide engine would take approximately 60 seconds. This week’s flight will likely include a pilot and co-pilot but no passengers.
During its most recent flight test on July 26, Unity fired its hybrid engine for 42 seconds and reached an altitude of 32.3 miles (170,800 ft/52 km). It was the longest engine burn and highest flight in the program’s 14-year history.
By space altitude, Richard Branson’s space company apparently means the 50-mile (264,000 ft/80.4 km) boundary set by the U.S. Air Force for awarding astronaut wings to X-15 pilots in the 1960’s.
The Fédération Aéronautique Internationale (FAI), which is the world governing body for air sports, sets the boundary of space at 100 km (62.1 miles/328,084 ft) . FAI recently announced it was exploring whether to lower the boundary to 80 km.
The 4.5-month long gap in powered flights is the longest for Virgin Galactic’s second SpaceShipTwo. The previous three tests came at roughly 2-month intervals.
Sources in Mojave say engineers have been grappling with several issues since July. The most serious one is a crack that was discovered in one of SpaceShipTwo’s major structural components. It’s not clear how the problem was addressed.