NASA's Langley Research Center
When Sierra Nevada Corporation’s (SNC) Dream Chaser spacecraft flies through the atmosphere, it will encounter a wide variety of environmental conditions. Any spacecraft traveling at hypersonic velocities must have a robust thermal protection system (TPS) to protect astronauts and cargo from the extreme temperatures associated with ascent and re-entry.
NASA's Langley Research Center in Hampton, Va., recently conducted hypersonic testing of Dream Chaser models for SNC as part of the agency's Commercial Crew Program in order to obtain necessary data for the material selection and design of the TPS. SNC conducted wind tunnel tests to reduce risk and improve the reliability of the Dream Chaser TPS under milestone eight of the agency's Commercial Crew Integrated Capability (CCiCap) initiative.
The Dream Chaser, based on NASA's HL-20 lifting-body design, combines years of NASA analysis and wind tunnel research with SNC engineering, resulting in a reusable spacecraft that could ferry astronaut crews to and from low-Earth orbit. The HL-20 was a space plane concept studied by NASA at Langley during the early 1990s as a safe and affordable personnel launch system for trips to low-Earth orbit.
“This system, along with other Commercial Crew Program partners' systems, gets us one step closer to launching people back into space onboard American made spacecraft,” said Karen Berger, Langley aerospace engineer.
The Dream Chaser models tested were approximately 10 inches long and made of cast ceramic. They were fabricated at Langley to measure heating levels the Dream Chaser spacecraft would experience during re-entry, including the lower- and upper-body flaps, elevons and a rudder. As with all spacecraft development, the testing required attention to details, from the design of the model to the complexity of data collection and analysis.
The heating data were measured using phosphor thermography, which allowed researchers to see a global view of the surface being investigated. Each pixel in the image acts as its own data point.
“It allows us to see very complex and intricate flow patterns,” Berger said.
With this technique, an image of each model is acquired before each wind tunnel run and then multiple images are taken during the run itself.
“Using calibrations performed prior to the test and calibrating with the color change after the test run, the temperatures and heating rate for each image can be computed,” Berger said.
The temperatures and heating rate information then will be used to help determine appropriate thermal protection system materials and also will be compared with computational predictions. Hypersonic testing of the Dream Chaser spacecraft will enable NASA and SNC teams to advance their knowledge and understanding of the environments that the vehicle will encounter during ascent and re-entry.
“We can use that knowledge to better develop new vehicles in the future, whether they are NASA vehicles or we are working with our commercial partners,” Berger said.