The Other Guys
NASA needs a space taxi. The likely pick is SpaceX—but don’t count out Colorado-based Sierra Nevada.
- By Michael Behar
- Air & Space magazine, August 2013
University of Colorado Boulder
(Page 3 of 5)
Sänger, working under Nazi Germany, envisioned a sub-orbital bomber, known as the Silbervogel (“silver bird”), which could zoom through the stratosphere to the edge of space, from where it would drop ordnance (New York City was the intended target), then return and glide unpowered back to Earth. While the Silbervogel never got out of the wind tunnel, it inspired many future lifting bodies, including Boeing’s X-20 Dyna-Soar.
Dream Chaser’s nearest cousin is the HL-20, a craft designed at NASA’s Langley Research Center in Virginia in the early 1990s. (Langley engineers co-opted the design from a photograph of a Soviet spaceplane, revealed later to be the BOR-4.) At least in shape, the HL-20 and the Dream Chaser are nearly identical. (Lindsey says Sierra Nevada “actually brought in a couple of retirees who had worked on the HL-20 [at Langley] to help us.”)
“The only modifications we’ve made are to the wings,” says Voss. “Langley had more of a slab wing—an aerodynamic shape that worked really well in the atmosphere but would probably burn off on reentry.” Slimming the wings enhanced Dream Chaser’s inherent stability, a characteristic that allows it to naturally right itself and restore level flight.
Dream Chaser’s shape—its body providing about 50 percent of total lift—is also supposed to make for smoother reentries and cushier landings than the competing designs. During reentry and at touchdown, it reaches just 1.5 Gs. A capsule, on the other hand, can hit the water at a gut-crushing 10 Gs (or possibly twice that if a navigational glitch forces what’s known as a ballistic reentry). A low-G ride permits Dream Chaser to carry fragile scientific cargo with a greater margin of safety. “If you don’t shake, rattle, and roll as much, you get better science,” says Ed Mango, NASA program manager for Commercial Crew Integrated Capability. Drug companies are interested in growing protein crystals in microgravity, explains Lindsey. “You grow these things very carefully in orbit. If you’re putting 8 Gs on them, or [they are in a capsule that is] slamming into the water or slamming into land, you can damage that payload” if it is not sufficiently buffered.
Langley engineers got as far as a full-scale mockup of the HL-20. In 2005, SpaceDev, now a subsidiary of Sierra Nevada, licensed the technology from NASA. It was SpaceDev founder James Benson who christened the project “Dream Chaser.” (Voss, who admits he didn’t love it when he joined SpaceDev in 2007, says the name has grown on him.)
Dream Chaser is a significant advance over the HL-20, boasting numerous features the Langley group probably never could have envisaged. For example, the navigation system permits autonomous reentries and landings: The crew could be completely incapacitated and Dream Chaser will bring them home safely.
And the vehicle will be made with carbon composite—a weave of epoxy and graphite fiber—that is half the weight of aluminum and twice as strong. Though Dream Chaser would be the first manned spacecraft made of composite, Boeing’s 787 Dreamliner passenger jet employs carbon composite in nearly half its airframe and has been flying commercially since 2011. The material is also used in unmanned spacecraft. Composite is fashioned in molds, produced much like plastic. Sierra Nevada says it could stamp out duplicate spaceplanes relatively quickly and affordably, each with a 25-mission lifespan and low-cost servicing between flights.
Perhaps the most groundbreaking technology is its propulsion: two hybrid rocket engines, which burn a non-toxic mixture of synthetic rubber and nitrous oxide—yes, laughing gas. Hybrid engines propelled SpaceShipOne, and now Sierra Nevada is developing them for both Dream Chaser and Virgin Galactic’s SpaceShipTwo, which is scheduled to begin carrying paying tourists into space this Christmas. While hybrids aren’t a new idea, they have never been used on a manned spacecraft for orbital missions. Because of their simplicity, safety, and reusability, Sierra Nevada believes they are superior to liquid-fueled rockets, such as those used for the shuttle’s three main engines. The Dream Chaser’s engines work by opening a valve that allows the liquid oxidizer, in this case nitrous oxide, into a combustion chamber packed with solid propellant, the synthetic rubber. Once in the chamber, the pressurized nitrous expands and converts to vapor. When an ignition switch in the chamber fires, the rubber combusts, ejecting hot gases through the exhaust nozzle to generate thrust.