Virgin Galactic's Rocket Motor Two (RM2) propulsion system for its SpaceShipTwo suborbital vehicle has successfully completed hot firing tests.

With the SS2 experimental prototype's construction more than 75% complete, Virgin Galactic is planning flight-testing before the end of the year. Trials will begin with carrier flight tests using the rocket glider spacecraft's mothership, WhiteKnightTwo, which made its maiden flight on 21 December 2008.

"There is a programme under way with RM2 to mirror rapid progress on the [WK2] flying programme and SS2 final construction, but we are saying no more than that," Virgin Galactic president Will Whitehorn told Flight International. The spaceline's latest quarterly newsletter revealed that tests of a rocket motor had taken place.

Whitehorn declined to provide any more detail. "We don't give out details like this for potential competitors beyond what is said on the newsletter website," he said.

The SS2 prime contractor Scaled Composites' founder Burt Rutan said in July 2008 that paraffin- and asphalt-based solid fuels had been tested, for what is now known as RM2.

California based-space technology company Spacedev has been contracted by Scaled Composites to assist the company in developing RM2. The last newsletter for 2008 of the commercial spaceflight news website The Lurio Report said that Spacedev had conducted nitrous oxide flow tests. But the technology company was not available to confirm this.

In 2004 the Scaled Composite-designed SpaceShipOne's rocket motor used gaseous nitrous oxide as its oxidiser and hydroxyl terminated polybutadiene as its solid fuel, to carry its pilot, and ballast representing two more people, for two flights into space, one in September and one in October.

The RM2 oxidiser and fuel has been the subject of speculation given the larger, eight-person SS2's energy needs to reach space.

If SS2's test-flight programme emulates the SS1's, it will first be carried by its carrier aircraft WK2, then air dropped so it can glide back to the runway, then launched for horizontal rocket-powered supersonic flights and, finally, make a maiden ascent into space. Virgin Galactic is aiming for a late 2010 first commercial flight.

Source: Flight International