The team at Scaled Composites have installed SpaceShipTwo's oxidizer tank, a key component that puts Virgin Galactic on track to make the spacecraft's first powered flight by the end of the year.

Spacecraft like SpaceShipTwo need an oxidizer tank because there isn't enough oxygen at the upper reaches of the atmosphere and basically none in space to allow for combustion in its rocket motor. Like the internal combustion engine in your car, SS2's solid fuel engine rocket engine need oxygen to burn the fuel it carries. So if you want some oxygen for combustion in space, it's BYOO.

Scaled Composites, which is designing and testing the ship propelling Sir Richard Branson's dream of commercial space flight, has been hard at work in recent months. The team ran into delays last year after a glide flight by SpaceShipTwo in September uncovered an aerodynamic problem with the tail surfaces. Soon after being released from its mothership, the pilot experienced a "downward pitch rate that caused a stall of the tails." The SS2 crew followed the procedure for such an event, selecting the spacecraft's unique "feather mode" that allows the pilot to regain control and land safely.

Photo: Virgin Galactic Photo: Virgin Galactic

The team spent several months analyzing the problem that led to the tail stall and developing a solution that included replacing the two small horizontal strakes on the inside of the vertical tail surface with a single larger strake. Glide flights resumed in late June. SpaceShipTwo has made six more glide flights to evaluate that new larger, single tail strake (seen on the inside of the left vertical tail below) at a variety of flight conditions including flutter tests. New thermal protection on the leading edge of the horizontal tail can also be seen in the photos.

The last SS2 glide flight on Aug. 11 lasted just over eight minutes and marked the end of envelope expansion testing for the glide flights. SpaceShipTwo now has now completed 22 glide flights.

Since the last flight, Scaled test pilots have been busy maintaining proficiency in the carrier aircraft WhiteKnightTwo. Both SS2 and WK2 share identical fuselage sections and cockpits. Pilots can configure WK2 to fly very similar to SS2, particularly for the approach to landing phase. The crew celebrated the 100th flight of WK2 on Oct. 4.

Although there is no date set for the first powered flight of SpaceShipTwo, Virgin has said it would happen by year's end. There's still no word on when the first sub-orbital space flight will occur.