Stratolaunch Systems’ effort to develop an air-launched medium-class rocket remains on schedule for a first launch in four years, with long-term plans to be able to launch crewed spacecraft as well.

“We’re still on track for a first launch in 2018,” Chuck Beames, president of Vulcan Aerospace Corp., said during a panel session at the 30th Space Symposium in Colorado Springs, Colorado, May 22. Vulcan is the holding company owned by Paul Allen, the Microsoft co-founder who is funding development of Stratolaunch.

The Stratolaunch system consists of a custom-built aircraft — the largest in the world by wingspan — and a three-stage launch vehicle. Assembly of the aircraft, at the company’s facilities at the Mojave Air and Space Port in California, is about 50 percent complete, Beames said.

The launch vehicle, which Beames said is named Thunderbolt after a spaceship toy from Allen’s childhood, is under development by Orbital Sciences Corp. The first two stages use solid-rocket motors from ATK, while the third stage will be powered by two RL10 engines from Aerojet Rocketdyne. On May 19, Aerojet Rocketdyne announced it won a contract from Stratolaunch Systems for six RL10 engines, with an option for an additional six.

Stratolaunch’s initial plans are for launching satellites “of the Delta 2 class,” Beames said, adding that Thunderbolt will comply with the Evolved Expendable Launch Vehicle Standard Interface Specification for payloads. 

However, Allen is interested in eventually using the system for human spaceflight. “His aspiration is to make this a man-rated capability,” Beames said.

Allen unveiled Stratolaunch Systems at a Seattle press conference in December 2011, but since then the company has kept a low profile. “He is a private guy. He wants to underpromise and overdeliver,” Beames said of Allen. “I can assure you that folks are working very, very hard both at Mojave and at Orbital Sciences to make progress on this project.”