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.

IMAGE CAPTION: [http://www.aero.org/news/newsimages/powerball.gif (59KB)]
Ed Simburger poses with an early prototype model of a spherical solar
array that embodies the concept of the PowerSphere patented by researchers
at The Aerospace Corporation. (Eric Hamburg photo)