Sierra Nevada Corporation won’t be using its own hybrid rockets for its Dream Chaser space shuttle, making it the second company in recent months after Virgin Galactic to dump the nitrous oxide-rubber motors.

Kathy Lueders, program manager for NASA’s Commercial Crew Program (CCP), revealed the change in an update during the third quarterly meeting of the Aerospace Safety Advisory Panel (ASAP) on July 24.

“SNC has also baselined a new propulsion system design (a pure liquid system design rather than a hybrid) in conjunction with their purchase of ORBITEC,” according to the meeting minutes.

Dream Chaser would have used two small hybrid motors per flight. Virgin Galactic’s SpaceShipTwo would have used one larger nitrous oxide-rubber hybrid motor.

I asked Charles Lurio, who first broke the story a few weeks back in The Lurio Report, what lay behind Sierra Nevada’s decision to abandon their own motors. He said sources told him that ORBITEC, which Sierra Nevada recently acquired, had a better engine solution.

I’m skeptical of whether that is the full story. The Virgin Galactic contract would have been quite lucrative for Sierra Nevada assuming a high launch rate for the SpaceShipTwo suborbital tourism vehicle. It also would have offset some of the fixed costs for the Dream Chaser engines, which would likely produced in much smaller numbers.

A liquid engine for Dream Chaser would be less expensive than a hybrid one assuming it could be reused multiple times. The hybrid engine would have to be replaced after each flight.