SS2 faces major design decisions

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SpaceShipTwo will have redesigned wing and engine, but Virgin seeks solutions to flutter and g loading

Virgin Galactic still has major design decisions to make for the SpaceShipTwo (SS2) suborbital craft, which is planned to enter service in 2008 carrying seven tourists and two pilots.

The Virgin Group company says SS2 will have wing spoilers and a redesigned hybrid rocket engine, but solutions to subsonic wing flutter and g loading are still being sought.

The UK company wants to find a way of reducing the 5g that the Scaled Composites-designed SS2 will experience during re-entry and is working with NASA and Qinetiq to achieve that.

The addition of wing spoilers will improve handling at lower speeds, while subsonic flutter must be resolved to stop it undermining SS2’s structural strength. A new hybrid rocket is needed because SpaceShipOne’s (SS1) engine had low- and high-frequency combustion instability.

This can be heard in the X Prize flight videos as a high-pitched noise. In the videos, visible shuddering which shakes pilot Mike Melville back and forth also indicates nitrous oxide feed problems. This would result from low pressure in the oxide tanks at the end of the engine burn. Nitrous oxide is the oxidiser for the engine’s solid propellant.

“There were issues with the liquid-to-gas phase of the hybrid rocket,” said Virgin Galactic operations vice-president Alex Tai at last week’s British Interplanetary Society space tourism symposium in London.

Despite the development issues, Tai still expects test flights in 2007 as the SS2 design work is almost finished. He said SS2 will probably use a nose skid for a landing brake, just as SS1 did, despite being three times larger than the X Prize-winning vehicle.

Tai expects White Knight 2, the carrier aircraft, to also be about three times as large as SS1’s carrier.

Answering questions at the symposium, Tai revealed that Virgin boss Sir Richard Branson wants to have a second launch site in the UK and that the company already has $10 million in flight bookings.