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Tuesday, August 7, 2007

Invention Promises to Change the ,,Small Satellites Are Powered

Invention Promises to Change the Way
Small Satellites Are Powered
An invention developed by The Aerospace Corporation and recently patented -- the PowerSphere Nanosatellite -- could significantly enhance the way nanosatellites are powered while eliminating some technical challenges that have evolved with the miniaturization of satellite technology.

In September a research team led by Edward Simburger received the patent for the deployable geodesic solar-panel array consisting of connecting pentagon- and hexagon-shaped panels that are solar-energy-collecting cells.

Folded in a flat stack at either end of a strut attached to the payload, the panels of two halves of the PowerSphere unfurl during deployment, creating two hemispheres that interlock and encase the satellite.

Once deployed the PowerSphere becomes a 360-degree solar array that collects "a constant amount of electric power regardless of its attitude relative to the sun," Simburger said. "It eliminates the problem of providing power to nanosatellites with limited surface 'real estate.'"

The invention, co-developed by David Hinkley, Ernest Robinson, Jon Osborn and David Gilmore, also eliminates from small satellites the excess weight and bulk of solar panels and the accompanying attitude-control apparatus required to continually point them in the direction of the sun.

An added advantage, according to Simburger, is that the PowerSphere provides a controlled thermal environment for the nanosatellite electronics and battery it encases, which are subjected to extreme temperatures in space.

"The PowerSphere may find future use in providing power and thermal control for small satellites weighing from under one kilogram (one-half pound) to 60 kilograms (132 pounds)," Simburger added.

Geometry for Power
The development of the PowerSphere began in 1998, when Simburger began investigating novel methods for providing power to picosatellites, the four-by-three-by-one inch, half-pound miniatures developed by The Aerospace Corporation with Defense Advanced Research Projects Agency funding.

"I was exploring various geometries for a solar array for the picosatellites using amorphous silicon solar cells that have extremely low mass and are very flexible," he said.

A rough sketch of a Mars rover inspired Simburger to explore a spherical shape for a solar array because "the rover used three inflatable spheres as tires and a fourth sphere on an antenna mast. The fourth sphere could be a solar array that would provide power to the rover."

That prototype inflatable Mars rover eventually designed for the Jet Propulsion Laboratory ultimately used a solar array that was a deployable parasol, "but I contacted the company that designed that prototype, ILC Dover, and asked them to develop a design for an inflatable sphere for deploying an array consisting of these amorphous silicon solar cells," Simburger said.

Refining the Concept
At that point Simburger imagined the model solar array would be spherical in shape and tethered to the satellite. Testing on thermal control aspects, as well as the manner in which the solar cells of the spherical array were wired together, led the team to refine the concept even further.

"The solution to the difficulties of wiring the solar cells together was to connect them directly to the spacecraft power bus with individual DC-DC converters," Simburger said, a concept that brought the PowerSphere one step closer to encasing its payload.

Simburger received a patent in October 2000 for the method of connecting the solar cells mounted on the spherical array structure.

To verify the operation of his connection scheme, Simburger had the Aerospace machine shop fabricate a two-foot-diameter "buckeyball," which was the size he calculated would be required to produce enough power for a small satellite in low Earth orbit.

At the same time, Hinkley, lead design engineer for the picosatellites, had been working with Gilmore to come up with a thermal design for the tiny picosats.

"David Gilmore told me earlier that the interior space of the PowerSphere would provide a suitable thermal environment for the battery that would power the picosatellites during eclipse," Simburger said.

Energy, Protection
The concept quickly moved from a tethered spherical array to an array that would serve the dual purpose of collecting energy regardless of attitude toward the sun and serving as the protective thermal shell for the nanosatellite. A patent for this configuration was granted last month.

The team was next challenged to devise a deployment scheme for the PowerSphere from a flat stack of hexagon- and pentagon-shaped panels.

Simburger worked with cut-out construction cardboard hexagons and pentagons to devise a workable scheme.

Another patent for the deployment method is pending with the U.S. patent office.

The team has received funding on a proposal in response to NASA's Cross Enterprise Research Announcement, issued in March.

Aerospace, the prime contractor on the project, is working with subcontractors ILC Dover for the design and fabrication of a deployable structure and with Lockheed Martin, which will create the wiring harness for a development model of the PowerSphere.

"The program is on track to complete a preliminary design for the PowerSphere by June 2002," Simburger said.

Contract milestones call for completion of an engineering development model by June 2003 and an engineering development unit by June 2004.

Other References

  • Hinkley et al, "A Mechanical Deployment Structure for the Powersphere Concept," Energy Conversion Conference and Exhibit (IECEC) 35th Intersociety, vol. 1, (2000), pp. 659-669.

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