Stratolaunch is making steady progress on its satellite-launching aircraft design, and intends to reach major milestones "in the summer timeframe," according to CEO Gary Wentz.

On 26 March the company announced finishing the second of two large hangars at Mojave, California, in which the one-off aircraft will largely be assembled. The massive aircraft design, to be the largest ever built, is designed to carry rockets to altitude before launch. Small parts of the wings, including the centre wing spars, are currently in production, with an eye towards full-scale production beginning in several months.

"We're going to press for a critical design review by the end of the year, so we're continuing forward," says Wentz in an interview with Flightglobal.

The aircraft design has undergone a notable change in recent weeks, with concepts showing a significantly lengthened, streamlined front end on both of its two fuselages. Wentz further cites an increase in gross takeoff weight by 100,000lb (45,000kg), to 1.3 million lb. As a result, minor changes were made to the wings and twin fuselages.

"The tails came in a little heavier than we expected, so to move the center of gravity forward on the aircraft we had to extend out the cabin," says Wentz. "I think it was just the early design estimate was lighter, it was multiple factors, the weight, and centre of gravity of the engines and where we placed them resulted in a change to our initial estimate."

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The rocket design suffered a setback when contractor SpaceX bowed out due to anticipated production difficulties. It was replaced by competitor Orbital Sciences, which has yet to establish a baseline design. The companies have yet to settle on many major issues, including whether the rocket will be solid- or liquid-fueled, or even whether to build an all-new engine versus adapting an existing design. Discussions are ongoing.

"We're not in a position to talk about the specific configurations at the moment but it's looking very promising," says Wentz "We anticipate within the next few months being able to announce settling a contractwe're really just trying to optimize their concepts, we're looking at solids and liquids."

"As late as last week I saw varied geometric configurations for the [spacecraft's] wings," he adds. The planned rocket will be capable of launching 6,100kg (13,500lb) into orbit, and requires wings to steer the rocket from its horizontal launch position and point it near-vertically towards space.

"Since we don't have a firm proposal from Orbital Sciences yet we're not sure exactly when the preliminary design review (PDR) will fall out for the launch vehicle. We'll conduct a systems design review in April, then we'll press to PDR, I suspect it will be early next year."

Source: Flight International