Gossamer Spacecraft
Inflatable structures can reduce the cost of communication antenna arrays, solar collectors, sun shields and other space-based structures. The mechanisms for initial inflation and subsequent maintenance of these structures are a critical part of mission planning. University of Arkansas researcher Larry Roe details these inflation systems in a new book published by the American Institute of Aeronautics and Astronautics.
Roe’s work appears in Gossamer Spacecraft: Membrane and Inflatable Structures Technology for Space Applications, which is edited by C.H.M Jenkins. Roe served as an associate editor of the book and wrote the section on inflation systems.
“It can cost from $5,000 to $10,000 per pound to put an object into space,” explained Roe, associate professor of mechanical engineering. “Because inflatable structures minimize mass and volume, they are far less expensive and will become increasingly important in near-term and future space missions.”
An object that can be folded and compressed to the size of a desk can, when inflated, be a solar collector 1 miles (1.6 km) wide. Because of this, inflatable structures reduce launch costs.
Inflatable structures have been developed for space missions for nearly 40 years. Gossamer Spacecraft brings together experts in mechanics, materials, optics and a host of other fields to discuss the great strides that have been made in this field.
It begins with an overview and historical review of membrane/inflatable applications for space by A.B. Chmielewski, manager of the Jet Propulsion Laboratory Large Telescope Systems Office. Although inflatable structures have been deployed since the 1950s for antennas and sunshades, he points out that new materials and inflation systems will greatly expand their use in both near-term and far-term missions.
Subsequent sections focus on the fundamental underpinnings of the technology, including the mechanics and physics of membrane structures, as well as issues related to materials, processing, testing and deployment. The final sections deal with applications, which range from radar, solar arrays and solar shades to gossamer sailcraft and inflatable habitats.
Some space structures, such as solar arrays and solar shields, are rigidized inflatables (RI) that require inflation only during deployment. After that, the materials become rigid. However, continuously inflated (CI) systems like data collection antennae are subject to damage and leakage and require a system for monitoring and replenishing inflation gases.
“One example of an RI-class structure is the sunshield for the Next Generation Space Telescope,” Roe said. “A prototype is scheduled for 2001 as the ISIS (inflatable Sunshield in Space) mission. Here, the inflatable structure is limited to booms that deploy and extend a membrane for spacecraft thermal control.”
Because the actual inflated volume is relatively small (about 3 cubic meters) , ISIS will use a tanked-gas system for inflation. Although the mass of the container is a disadvantage of tanked-gas systems, their simplicity and extensive use aboard spacecraft give them an advantage for small structures.
Other inflation systems for near-term missions will include chemical-reaction gas generation systems, some combination of tanked-gas and chemical-reaction-gas systems or, in some instances, phase-change systems. Long-term missions, such as Martian surface missions, could use other systems, such as local atmospheric gas expanded by solar heating to be lighter than air.
When selecting a system, engineers must evaluate total wet mass of gas and/or feedstock, tanks, reactors, valves, fittings and regulators. Engineers are working to reduce the mass by integrating inflation and propulsion systems.
Propulsion/inflation system integration is particularly promising in two areas, according to Roe. Hydrazine decomposition has already been identified as a promising gas-generation approach and the use of cryogenic hydrogen for both inflation and propulsion may be effective for larger single-inflation systems.
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CONTACT: Larry Roe, associate professor of mechanical engineering, (501) 575-3750; lar@engr.uark.edu
Carolyne Garcia, science and research communication officer,
(501) 575-5555; cgarcia@uark.edu
