Virgin Galactic Could Change SpaceShipTwo Engine Again

Nitrous nylon engine test on Jan. 16, 2014. (Credit: Ken Brown)
Nitrous nylon engine test on Jan. 16, 2014. (Credit: Ken Brown)

Here in Phoenix at the Space Access 15 Conference. Virgin Galactic Vice President Will Pomerantz spoke earlier today, revealing that after nearly 11 years of development the company still hasn’t figured out what type of engine it will use to power SpaceShipTwo.

This was a rather startling development because the matter had supposedly been settled last year. However, it does match what Parabolic Arc has been hearing for months about parallel engine development.

Readers will recall that late last May, the company announced that it was changing from a hybrid engine powered by rubber and nitrous oxide to one that would use nylon and nitrous oxide. Virgin Galactic CEO George Whitesides said the decision was made because of the better performance of the nylon engine, which would allow SpaceShipTwo to reach a higher altitude.

“Frankly, we had good performance from both of them, but as we look for the final range of test flights, we decided to go with the polyamide grain,” he said. The plastic-based fuel showed better performance by several measures, including the capability to send SpaceShipTwo higher, he said.

Pomerantz said today the company is still testing both engines, and that he was betting the rubber engine would eventually win out. He did not reveal why the company is continuing to spend money on an engine with inferior performance. Pomerantz did make a general statement about continuing to improve and test components of SpaceShipTwo.

The nylon engine was tested for the first time in flight last October when SpaceShipTwo creashed in the Mojave Desert. Although initial speculation focused on the engine as the cause of the accident, investigators and Virgin Galactic and Scaled Composites officials said the engine performed normally during the flight.

Virgin Galactic officials were very angry over the initial speculation about the engine causing the crash. They defended the engine and the team that developed it vigorously. Pomerantz repeated criticisms of those who had prematurely speculated on the cause of the crash during his talk today.

So, what happened? If the nylon engine really does have superior performance and functioned flawlessly in its only flight test, why would Virgin Galactic continue to develop an inferior rubber engine? The decision would appear to make no sense.

It does make sense if you ignore Virgin Galactic’s stated reason for the change. Sources have told that Parabolic Arc that the decision to switch to the nylon engine was a cost-saving measure that eliminated an expensive contract with Sierra Nevada Corporation, which was developing and testing the motor. The nylon engine didn’t actually perform better than the rubber one.

The lack of clarity about SpaceShipTwo’s main propulsion system is highly unusual. It’s difficult if not impossible to think of another space project that was uncertain about its primary propulsion system after nearly a decade of development.

Under the normal development process, engineers build a spacecraft around what its propulsion can accomplish. Scaled Composites designed SpaceShipTwo first, assuming engineers could scale up the rubber-nitrous oxide engine that was used on the much smaller SpaceShipOne vehicle that flew in 2004. That proved to be a bad bet as engineers struggled with oscillations and vibrations from the larger engine.

Pomerantz expressed confidence in “the engine”, presumably referring to both of them. However, he was evasive about their performance, largely dodging questions about how high SpaceShipTwo could fly and the maximum number of passengers it could carry with the different engines. These are questions that most space companies can easily answer.

[CORRECTION: Pomerantz was apparently referring to the safety of the nylon engine, which fired for about 12 seconds or so on the fatal flight. This is rather presumptuous assertion in that the engine didn’t fire all the way through to shutdown for what would have been a long burn. So the engine was performing normally a dozen seconds on its lone test fligtht. That’s good, as far as it goes. But, the would need a lot more flight and ground test data to draw deeper conclusions.]

SpaceShipTwo was designed to fly with two pilots and six passengers and to fly above the Karman Line, which is located 100 km (62.1 miles) above the Earth. This is the internationally recognized boundary of space.

Last year, Virgin Galactic officials admitted the ship could reach 50 miles (80.4 km), which is a definition of space used by the U.S. Air Force and NASA to award astronaut status. Further, sources indicated that the passenger load would be reduced to four passengers in the back using the rubber engine.