MEMS IN SPACE

FAYETTEVILLE, Ark. - Tiny microelectromechanical systems (MEMS) may be the key to maintaining giant space-based structures, according to U of A researchers Steve Tung and Larry Roe. Although space-based solar collectors or antenna arrays can be many square miles in size, tiny MEMS devices can keep them oriented correctly to ensure their long-term operation.

Tung, Roe and graduate student Scott Witherspoon are working with David Maynard of the Jet Propulsion Laboratory, NASA Program Manager for Space Solar power. They will present their findings today at the American Institute of Aeronautics and Astronautics Annual Structures, Structural Dynamics and Materials Conference in Seattle.

"It can cost from $5,000 to $50,000 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."

Inflatable structures have many uses, ranging from communications antennas to solar power arrays. 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.

However, such a large structure is subject to radiation damage and puncture from micrometeoriods. The flexible structures can also drift and turn away slightly from their original orientation. Constant monitoring is necessary to ensure the continued integrity and long-term performance of the structure.

That is where Tung, assistant professor of mechanical engineering, comes in. He has developed a flexible MEMS device that can be integrated into the fabric of an inflatable structure. Although it is less than 1 inch (2.5 cm) long, it can monitor both local conditions such as strain or vibration and global conditions like pressure of motion of the system.

"Traditional sensor modules are heavy, rigid and expensive," Tung said. " But a sensor module for an inflatable structure must be low mass and flexible and, just as important, it must be simple to install and of low cost."

Cost is important, since a very large inflatable structure might use several hundred of these devices. Because their device uses off-the-shelf sensors, common assembly technologies and a polyimide film base it is reliable, inexpensive to produce and easy to attach to most inflatable structures.

The MEMS devices also can be easily tailored to the needs of individual structures quickly and cheaply. It will be incorporated into a L’Garde inflatable truss at NASA Langley Research Center this summer.

Sensing a problem is one thing, but doing something about it is another. Tung and Roe are currently incorporating actuators into their MEMS device. These actuators will allow the device to take corrective action when it locates a problem. For example, they could help dampen vibration or, working together, reposition a structure that has drifted from the correct orientation.

While their MEMS device can have important applications for space-based inflatable structures, the technology also has applications a lot closer to home. It can be a low-cost, effective solution for any structure where condition, accessibility and shape are important, from land-based cell towers or television antennas to submarines.