TORONTO — A scaled-down version of the Dream Chaser vehicle being developed by Sierra Nevada Corp. (SNC) would fly into orbit on Stratolaunch Systems’ air-launch system as soon as the end of the decade in a concept the two companies unveiled Oct. 1.

In the proposal, which executives of the companies said has yet to be formally approved for development, SNC would build a version of Dream Chaser about 75 percent the size of the vehicle it proposed for NASA’s commercial crew program. The vehicle would otherwise look similar to the original Dream Chaser and use a similar propulsion system.

That vehicle would be attached to the two-stage Thunderbolt rocket that Orbital Sciences Corp. is building for Stratolaunch. Thunderbolt will be launched from a custom-built aircraft Stratolaunch is building at its facility in Mojave, California.

The scaled-down Dream Chaser would be able to carry two to three people into low Earth orbit, including to the international space station. 

“We took our basic design for the Dream Chaser system and adapted it for that launch capability,” Craig Gravelle, the SNC senior director who led the studies, said in a joint presentation with Stratolaunch Systems at the 65th International Astronautical Congress here.

One advantage of this concept, Gravelle said, is that air launch provides additional flexibility in arranging launches. “It can launch from pretty much anywhere to any inclination,” he said. The Stratolaunch aircraft requires a runway at least 3,800 meters long, although the smaller Dream Chaser can land on runways as short as 2,500 meters.

The Stratolaunch aircraft is more than 50 percent complete, said Chuck Beames, president of Vulcan Aerospace Corp., the holding company owned by Microsoft co-founder Paul Allen that is funding development of Stratolaunch. The company is planning initial flight tests of the aircraft in mid-2016, with initial test launches planned for 2018.

The companies declined to discuss the cost of developing this system, or per-mission prices. Beames said the smaller Dream Chaser, launched by Stratolaunch, would cost “significantly less” than the larger Dream Chaser, capable of carrying up to seven people, launched on an Atlas 5. However, he said he did not know how the prices of the two vehicles compared on a per-seat basis.

When the Stratolaunch launch system, initially proposed for the launch of medium-sized satellites, would be ready to fly a crewed vehicle is unknown. “The design is such that it doesn’t preclude human spaceflight,” Beames said in an interview after his presentation. He added it might be possible Stratolaunch would design a variant of the rocket exclusively for crewed missions.

Beames emphasized that the companies have not made a decision on whether to proceed with further development of the concept. The analysis of the concept so far involved “significant analytical work,” he said, but is not as advanced as needed for a preliminary design review in a conventional aerospace project. “We know that the design can close. We’re still thinking through, in general, the overall way ahead for what we want to do with Stratolaunch,” he said.

That decision, Beames said later, would likely be in the hands of Allen himself. “You’ll probably start seeing some decisions come out in November or December,” he said.

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Jeff Foust has more than a decade of experience writing about space policy, entrepreneurial ventures and regulatory affairs. In 2001, he established to aggregate and summarize the day's space-related news stories. In 2003, he started The...