Despite receiving the smallest NASA award, Sierra Nevada presses on with lifting body
. drew the short straw in 's Commercial Crew Integrated Capability (CCiCap) competition, winning only about half as much of the federal seed money to advance its Dream Chaser lifting-body crew vehicle as its two competitors received for their capsule designs.
At $212.5 million, the company's award is not exactly chump change, but the $460 million forand the $440 million for would go a lot further in wringing out the questions that remain about Sierra Nevada's unique approach to flying humans to space. The half-portion grew out of congressional fears that was spending too much to preserve competition in its commercial crew development effort (AW&ST June 18, p. 26).
In his source-selection document William Gerstenmaier, associate administrator for human exploration and operations, says the Dream Chaser design—based on the old NASA HL-20 testbed—poses “significant risks because of design complexity.”
“The winged vehicle offers a lot of advantages, even to customers, in terms of easier landing—you can land on a runway—lower gs, cross-range from deorbit, that's all called out in the document,” Gerstenmaier says. “But associated with that are more technology hurdles. You've got to look at aborts. They're a little more difficult. You've got thermal protection issues, the heat-shield kind of stuff we dealt with on shuttle protection on orbit, all those things. So there's a lot more complexity with a winged vehicle.”
As a result, the agency cut back on the milestones Sierra Nevada had proposed, commensurate with the lower funding level, and does not expect the Louisville, Colo., company to pass critical design review under CCiCap. “We kept enough in that we think we'll get really good insight into how well they can handle those technical challenges,” Gerstenmaier says.
Abort-testing is not on the new list of for Dream Chaser milestones, says Mark Sirangelo, head of Sierra Nevada's space systems unit, but the company plans to make a start anyway. The abort system uses the same hybrid-rocket engines designed for in-space maneuvering to fly off a failing Atlas V, which would be the initial Dream Chaser launch vehicle (AW&ST July 2, p. 37).
“We have plans to do a pad abort test in the coming months,” Sirangelo says. “Our vehicle has no black zones right now for abort from launch to orbit, and we can abort to a runway anywhere along the way. . . . None of the three of us has done any abort tests so far, and we need to all do that. We have that planned to retire that risk, not as one of the milestones but as work that we're doing separately.”
Those hybrid engines, also mentioned in the source-selection document as a technical risk, are based on the rockets that powered the Scaled Composites SpaceShipOne in its successful bid for the $10 million Ansari X Prize, and those planned for's SpaceShipTwo suborbital vehicle. Sirangelo says the Dream Chaser versions have been test-fired and restarted, including in vacuum, and should have no problem meeting the test-fire milestones in the CCiCap plan.
Despite the lower NASA funding, Sierra Nevada plans to go ahead with its bid to fly NASA astronauts to the International Space Station, starting before the end of the year with an autonomous drop test and landing with a full-scale engineering article that has already undergone captive-carry tests. Ultimately, Sirangelo and his corporate colleagues believe, the capabilities of their vehicle will outweigh today's risks.
“With the hybrid motors, if we don't use them on abort, they give us a tremendous capability to fly on orbit,” he says. “So we can actually go up to several hundred miles above the space station and do work. That's a really robust capability that allows us to consider potential servicing missions for things for NASA for other purposes, and to use the vehicle for other purposes.”
Also on the list of potential advantages of the Dream Chaser over the Boeing and SpaceX capsules is the high level of reuse Sierra Nevada expects from each vehicle—25-30 missions each, according to Sirangelo. The optimistic outlook for the Dream Chaser's commercial potential is shared by Gerstenmaier and the CCiCap source-selection board that advised him.
“These significant technical advantages could result in a larger customer base for [Sierra Nevada] than a capsule design and more capability for users,” Gerstenmaier writes.