SpaceShip Two rocket motor testing revealed

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Virgin Galactic is testing a range of fuels for its SpaceShip Two rocket motor with an eye on "whole life issues".

Testing details revealed by prime contractor Scaled Composites show three full-scale hot firings took place on 20 April, 6 and 20 May using what Scaled calls a "first-generation" motor.

Scaled's SpaceShipOne's motor used a gaseous nitrous oxide oxidiser and hydroxyl terminated polybutadiene solid fuel when it flew into space three times in 2004. But the SS2 flight rate will be at least once a week for many years.

Virgin Galactic commercial director Stephen Attenborough says: "We have asked Scaled to look at more than one fuel type. [We] anticipate that further generations [of motors] will be developed."

The SS2 engine is called Rocket Motor Two (RM2) and paraffin and asphalt-based solid fuels have been tested for it, as Scaled founder Burt Rutan said last year.

Scaled's new test log says RM2 subscale firings for fuel, igniter, injector, insulator and nozzle evaluations occurred from June 2005 to April this year. Testing was halted for at least six months after a July 2007 incident killed three Scaled employees.

The subscale work led Scaled and its Sierra Nevada subcontractor to select the first generation RM2 design now being tested. Of the three full scale firings, hot fire one evaluated the test stand, the second had the change in fuel and it and the third firing included study of fuel stability levels.

The SS1 motor had experienced low- and high-frequency combustion instability.

Virgin Galactic released video in May of the 2009 firings carried out at an Sierra Nevada facility near San Clemente, California that is leased from Northrop Grumman space and mission system's Capistrano Test Site.