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A boom in satellite engineering
by David Pescovitz
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ME professor Hari Dharan, holding one of the prototype booms, stands next to the machine used to fabricate the rolled carbon fiber tube. For three decades, Dharan has championed the use of carbon fiber composites in space vehicles. As an engineer at Ford Aerospace in the 1970s, he helped construct the 12-foot diameter carbon fiber dish antenna for NASA's Voyager 1 space probe, now the most distant human-made object in space.
DAVID PESCOVITZ PHOTO
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In October 2006, a group of five small satellites will ride a spacecraft “bus” into orbit to gather data about Earth’s magnetosphere. The satellites’ eight-foot long articulated limbs—outfitted with magnetometers, electrostatic analyzers, solid-state telescopes, and other instruments—will provide an unprecedented “bird's-eye view” of the magnetic substorms behind such phenomena as the Northern Lights.
ME professor Hari Dharan and graduate students Tien Tan, Tyler Williams, and Arezki Rahman are fabricating essential components for the mission, a $173 million NASA program known as THEMIS, or Time History of Events and Macroscale Interactions. Led by Berkeley’s Space Sciences Lab, the project’s goal is to determine how energy from solar wind is transported and explosively released, visible to us in the form of the Aurora Borealis and the Aurora Australis.
As director of the Berkeley Composites Laboratory, Dharan and his colleagues design, test, and fabricate new composite materials with high-performance properties, such as fiberglass, for use in structures from buildings to airplanes and space vehicles.
Dharan's specialty is carbon fiber composites, which combine incredible strength with very low weight and are ideal for space, where the approximate cost of launching something into orbit is roughly $15,000 per kilogram.
“In addition to being very stiff and strong, the carbon fiber structures we build have one-fifth the density of steel,” Dharan says. In his Richmond Field Station lab, the researchers are constructing prototype booms out of the new carbon fiber composite through an elaborate fabrication process that involves wrapping the carbon fiber “fabric” around a form, oven-curing it into the desired shape, machining, and assembling it. Then the booms are tested under conditions that simulate the zero gravity environment of space.
“The main challenge here is dimensional stability and stiffness,” Dharan explains. “Our carbon composites are designed to have a thermal expansion of less than 1/100th that of aluminum. Once you deploy an eight-foot long boom, you don't want it wobbling back and forth with the large temperature changes that exist in space.”
In addition to the sensor booms, Dharan's group is building part of the main body structure for each spacecraft. Once the booms, structures, and mechanisms are complete, they'll be integrated into the rest of the space vehicle at the Space Sciences Lab. Then, next fall, if all goes as planned, Dharan will watch as his research truly takes off.
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