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In a report released by NASA late last week, the agency outlined the reasons it picked Boeing’s CST-100 manned capsule over Sierra Nevada’s Dream Chaser mini-shuttle for the second contract to provide manned ferry capabilities to ISS.
Sierra Nevada’s Dream Chaser spacecraft, which would take off on top of a United Launch Alliance Atlas 5 rocket and land on a runway like the space shuttle, is not as far along in development as the competing CST-100 and Crew Dragon capsules proposed by Boeing and SpaceX, according to a source selection statement signed by Bill Gerstenmaier, head of NASA’s human exploration and operations directorate. “A winged spacecraft is a more complex design and thus entails more developmental and certification challenges, and therefore may have more technical and schedule risk than expected,” Gerstenmaier wrote in the selection statement.
NASA wants to have the commercial crew capsules operational by the end of 2017 to end U.S. purchases of astronaut seats on Russia’s Soyuz ferry craft. Before NASA permits its astronauts to fly on the CST-100 and Crew Dragon, each spaceship will go through ground testing and complete unpiloted and crewed test flights.
The reasoning seems quite reasonable. It also suggests that Sierra Nevada might have a better shot at winning a contract during the next round for cargo, as scheduling will not be as critical since NASA has other alternatives to get cargo to ISS.