A team of undergraduate engineering students from the University of Kentucky scored a partial success in a recent test of a prototype Mars exploration aircraft whose wings would inflate to take on their aerodynamic shape once within the thin martian atmosphere.
Inflatable wings are seen as a promising solution for a vexing problem facing NASA engineers: building an aircraft that can be successfully unfurled or unfolded into its flight configuration after being stowed within the tight confines of a space capsule for the long journey to the red planet. The problem has twice abruptly halted NASA efforts to develop a glider or powered aircraft to explore Mars.
A mission featuring an aircraft with rigid but foldable wings that would move through the martian atmosphere on rocket power is among four finalists for full-scale development under NASA’s Mars Scout program. NASA will select the winning concept this August, with launch slated for 2007.
A half-scale model of the proposed Mars Scout aircraft was successfully tested this past summer off the coast of Oregon. Inflatable wings are an alternative approach to a deployable Mars aircraft, said engineering professor Suzanne Weaver Smith, principle investigator for the University of Kentucky’s Big Blue glider project.
On May 3 outside Denver, the engineering students used a weather balloon to loft their inflatable-winged glider high into the atmosphere.
At an altitude of roughly 16,666 meters, nitrogen gas was released from a canister to start filling the wings, which popped out through protective doors on the glider’s fuselage. The wings were made of a fiberglass fabric impregnated with an epoxy designed to harden when exposed to the sun’s ultraviolet light. The wings were translucent to maximize sun exposure on both sides.
As the balloon ascended past 27,000 meters, where the atmospheric density is similar to that on Mars, one of the wings inflated and took on its predicted final form. The other wing came out deformed, with waves across its surface. Still, program officials described the test as a successful first step toward an experimental free flight in early 2004.
"This technology has never been applied in an application like this," Smith said.
The inflatable wings were made by ILC Dover of Delaware, which is best known as a supplier of materials for space suits worn by U.S. astronauts and the airbags that cushioned the landing of NASA’s Mars Pathfinder spacecraft on July 4, 1997. Airbags supplied by ILC Dover also will cushion the landings of NASA’s twin Mars Exploration Rovers, which are slated for launch toward the red planet this coming June and July.
ILC Dover officials jumped at the chance to participate in the Big Blue project, and not just because of their interest in a Mars airplane. The company is in the midst of a research and development effort to build an entire new class of inflatable space components from satellite antennas to solar array supports. All would be based on the light-sensitive epoxies that were used in the Big Blue test.
"We’re trying to expand the use of this technology into inflatable structures that then become solid. The beauty of that is you have a packing and mass advantage over existing technologies," said Dave Cadogan, manager of research and development for ILC Dover.
NASA funded the Big Blue flight through an $80,000 grant administered by the Kentucky Space Grant Consortium, the local arm of the National Space Grant educational program. The Big Blue team relied on a nonprofit, volunteer-based group called the Edge of Space Sciences to loft the glider beneath one of its weather balloons. "We launched from a field next to a guy’s house," Smith said.
Cadogan of ILC Dover expressed confidence that engineers would be able to pinpoint and fix the problem that led to the deformed wing. "It’s a minor blip," he said.
For the students, the flight-test provided experience with the communications system as well as the attitude-sensing gyroscopes, motion-sensing accelerometers and pressure and temperature sensors that would feed data to the glider’s autopilot system on a free flight, Smith said. In the coming months, students will brainstorm on ways to lighten the 2-meter-long glider from its current weight of 8 kilograms to a target weight of around 5 kilograms, Smith said. The glider has a 2-meter wing span.
The students relied on atmospheric data from the U.S. National Oceanic and Atmospheric Administration to calculate the temperatures and ultraviolet intensities the plane would encounter during the wing-deployment phase. Accurately predicting those parameters was critical for ensuring that the wings would inflate and cure properly, Smith said. The curing occurred at temperatures from minus 25 degrees Celsius to minus 45 degrees Celsius, she said.
