The Stratolaunch plane as originally depicted with the SpaceX rocket.

Stratolaunch Systems, the commercial space venture backed by Microsoft co-founder Paul Allen, has cut ties with one of its high-profile partners, SpaceX, one of the pioneers in the industry. Gary Wentz, the Stratolaunch CEO, confirmed the news Tuesday in a message to the Flight International news site.

“Stratolaunch and SpaceX have amicably agreed to end our contractual relationship because the current launch vehicle design has departed significantly from the Falcon derivative vehicle envisioned by SpaceX and does not fit well with their long-term strategic business model,” Wentz wrote.

Allen’s company is developing the world’s largest plane, with six 747 engines and a wingspan greater than the length of a football field, to launch rockets into space from 30,000 feet in the air.

The rockets were originally slated to be derivatives of SpaceX’s signature Falcon 9 rockets, which were used to launch the Dragon capsule into orbit on the first commercial supply mission to the International Space Station earlier this year. Flight International has more on the design changes that prompted SpaceX and Stratolaunch to end their partnership.

Wentz said in his message, “Moving forward, Stratolaunch has engaged Orbital Sciences Corporation to evaluate and develop alternative solutions with the objective of arriving at a design decision in the early spring timeframe. The other segment contractors will continue to proceed forward in accordance with existing plans since their interfaces have been defined.”

Previously: With Stratolaunch project, Paul Allen makes a big bet on commercial spaceflight

[Thanks to Isaac Alexander for the tip.]

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