A new donut-shaped inflatable device designed to more effectively slow down a spacecraft upon atmospheric re-entry to Earth or other planets could not only be more economical than current methods, but also available as soon as 2020.
However, before the hardware can be fully developed for use on a spacecraft, the technology developed by NASA's Langley Research Center in Hampton, Virginia, had to undergo tests to validate its structural integrity. NASA Armstrong Flight Research Center's Flight Loads Laboratory was called on to do the job, with laboratory personnel conducting structural tests on eight different donut-shaped test articles of three different sizes. The testing occurred over a seven-month period beginning in mid-2013 and extending through early 2014.
Called the Hypersonic Inflatable Aerodynamic Decelerator, or HIAD, the concept had previously been tested under simulated flight loads, but the additional testing at NASA Armstrong helped validate models for future decelerator configurations, said Langley's Anthony Calomino, principal investigator for materials and structures for hypersonic re-entry.
"The tests have shown what we expected with the differences in test articles," he said. "The work (at Armstrong) helped us define where the structure will fail, which had been hard for us to capture.
"As an engineer, you have to know where a system will fail so that you can back off from that point and optimize a design," he added. "We now know how far we can push it. We didn't have good failure models and that's what the work [at Armstrong] allowed us to do."
The testing involved flexible sensors and hydraulic jacks that applied mechanical loads to each test article, said Tony Chen, NASA Armstrong's HIAD testing project manager. The sizes tested had diameters of roughly 11, 13 and 14.5 feet, about half the size envisioned for the functional system that would use about eight to 10 concentric rings.
A series of straps on the top and bottom of the test articles applied mechanical loads to cause the donuts to pull or twist to determine their mechanical characteristics, Chen explained. Each test article was built differently in order to find the optimal design for their construction. The test articles were also tested at different inflation pressures to see the differences in their structural integrity.
NASA Armstrong innovation also was tapped. Loads lab researchers had been looking at new strain gauges and the HIAD presented the perfect opportunity to test out those devices, said instrumentation specialist Anthony "Nino" Piazza. Strain gauges used for the HIAD tests were constructed from highly elastic material tubes, used frequently in the medical field for sensitive arterial procedures that require monitoring changes in volume. Because the sensors were flexible, they did not interfere with the tests like contemporary rigid sensors could have done, he explained.
That doesn't mean the HIAD device didn't offer challenges to obtaining the best data. While the sensors were flexible, the wires from the test equipment were not, Piazza explained. Meshing the flexible with the inflexible required some silica bonding material and careful connections in the right places to properly conduct the tests, Piazza said. The sensors were secured to 16 locations on each test object.
Once successfully developed and validated, the sensor technology could be used to provide valuable in-situ flight response data for an actual spacecraft.
In a real spacecraft, a connected stack of donut rings would be inflated before entering a planet's atmosphere to slow the vehicle for landing, Calomino said. The spaceship would look a lot like a giant cone with the space donuts assembled, similar to a child's stacking ring toy. The stacked-cone concept would allow NASA to land heavier payloads to the surface of the planet than is currently possible, and could eventually be used to deliver crews.
"The idea is that you would have something that could be packed up, put in a very small volume and then deployed into a very large size," Calomino said. "Think airbag, something we could pack into compressed volume that will fit the size limits of a launch shroud, but allow for a much larger aeroshell.
"Think of putting your hand out the window when you drive out on the highway," he explained. "The bigger the hand, the more the force you create. The bigger the aeroshell, the more you decelerate."
The HIAD structural loads effort marked the end of a three-year development funded through NASA's Game-Changing Technology program. However, a proposal is being prepared for a follow-on effort in 2016 because many researchers don't know about the new technology, Calomino said. If that proposal is successful, Langley's HIAD researchers could return to NASA Armstrong for additional testing.
Calomino suggests the HIAD decelerator system could be a good candidate for a future Mars rover mission after 2020, he added.
"We could deliver a Mars rover similar in size to Curiosity, but to a much higher elevation," he said. "The science of exploration would benefit from a system like HIAD because it would allow the investigation of the southern highlands, where it is thought that a portion of the planet was not under water when Mars had an ocean."
The test articles tested at NASA Armstrong are the size needed to enable a future Mars rover to land at a higher elevation on the Martian surface, he added.
"That size can change depending on what we do on Mars and it has beneficial application for re-entry to Earth, outer planet moons and nearly any planet with an atmosphere," Calomino said. "The system also is being examined for use in retrieving the second-stage rockets used to propel vehicles into space."
NASA photos by Ken Ulbrich
Jay Levine, editor, The X-Press
NASA Armstrong Public Affairs