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Stratolaunch engines
The Stratolaunch plane has three engines on each wing. (Stratolaunch Photo / Dylan Schwartz)

The world’s biggest airplane hit another milestone this week with the completion of the first phase of engine testing at California’s Mojave Air and Space Port, according to Stratolaunch, the space venture backed by Microsoft co-founder Paul Allen.

Stratolaunch’s CEO, Jean Floyd, reported today that all six of the plane’s Pratt & Whitney turbofan engines were started up for the first time.

“Our aircraft is one step closer to providing convenient, reliable and routine access to low Earth orbit,” Floyd said in a news release.

Allen founded Stratolaunch in 2011 with the goal of creating an air-launch system that can drop rockets from an airplane in midflight and send payloads into virtually any orbital inclination. Because the system relies on an airplane rather than a fixed launch pad, Stratolaunch theoretically could make orbital deliveries without worrying so much about the weather.

But to create the launch platform, Stratolaunch and its Mojave-based construction contractor, Scaled Composites, have to build and test a twin-fuselage airplane with an unprecedented 385-foot wingspan.

The landing gear and engines have been taken from Boeing 747 jets and added to the carbon-composite airframe. The plane was rolled out for the first time this May and is going through months’ worth of on-the-ground testing.

Floyd said the engine tests were conducted in three steps, starting with a “dry motor” phase in which an auxiliary power unit was used to charge each engine. In the second phase, fuel was introduced into the system for a “wet motor.” The third phase involved starting up each engine, one at a time, and having it idle.

“In these initial tests, each of the engines operated as expected,” he said.

Floyd said all six of the plane’s fuel tanks were filled independently to ensure proper operation and validate the tanks’ seals.

The team has also begin testing the flight control system. “So far we have exercised the full limits of motion and rate of deflection of control surfaces on the wing and stabilizers,” Floyd wrote.

Over the next few months, the engines will be tested at higher power levels and varying configurations, leading up to the start of taxi tests, Floyd said.

In March, Allen told GeekWire that he hoped the plane would be flying by the end of this year, but Floyd’s description of the test schedule suggested that getting the plane in the air could take longer than that.

Stratolaunch has said it plans to begin commercial operations by 2020. The company has a rocket partnership with Orbital ATK, which is due to be acquired by Northrop Grumman. It’s not fully clear whether that acquisition could affect Stratolaunch’s plans, but for what it’s worth, Stratolaunch development partner Scaled Composites is a Northrop Grumman subsidiary.

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