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Mars Solar Photovoltaics Offer Earthly Hope
Sylmar, California - January 23, 2004 [SolarAccess.com] "Spirit," the first
of two NASA Mars exploratory rovers, that landed on January 4, has now
taken its first steps on the Red Planet. From beaming back high-resolution
pictures of the craft's surroundings, to doing the complex work of a geologist
in hopes of uncovering signs of life, solar photovoltaic (PV) power is
essential to the Mars rover's functions.
High-efficiency solar cells manufactured by Spectrolab,
are providing power to the NASA-built spacecraft. Spectrolab, a Boeing
subsidiary, supplied Improved Triple Junction (ITJ) solar cells for the
Spirit rover's journey to the Red Planet on a mission probing the role
of water on Mars. Spectrolab solar cells will also power NASA's "Opportunity"
rover, scheduled to land on Mars January 24.
Designing solar cells for space poses particular
challenges. The solar cells aboard Spirit and Opportunity are called triple-junction
cells because they employ a three-layered structure that more effectively
captures and converts solar energy into electricity. Each of the junctions
converts a different portion of the solar spectrum into electricity.
Designing solar cells to perform for many years
in the harsh environment of space is the most pressing challenge for designers
of space-based solar PV, said Richard Esposito, Media Relations for Spectrolab.
Whether powering Global Positioning Satellites circling
earth, or making locomotion possible for a mars rover, space-based solar
panels take a beating from the hostile environment of space where tiny
particles can constantly bombard the craft. And not only do they have be
durable, but extremely efficient for their size and weight.
"The spacecraft themselves usually afford a very
limited surface area on which to mount the cells or panels, so cell efficiency
becomes paramount," Esposito said. " However Mars' great distance from
the sun has an impact on that efficiency; cells that can attain a 26.8
percent conversion efficiency in a Geosynchronous Earth orbit would be
about 10 percent efficient on Mars due to the greater distance from sun."
While the technology of these solar cells is designed
for the heavens, it may find its way back to earth.
Esposito said Spectrolab's efforts in space-based
solar have helped the company achieve record-breaking performance for terrestrial
concentrator solar cells.
Using concentrated sunlight, these PV cells can
convert 36.9 percent of the sun's energy to electricity, a technology capability
that the company believes could dramatically reduce the cost of generating
electricity from solar energy.
"The modified cell design better suits the terrestrial
solar spectrum and opens the path for higher performance terrestrial concentrators"
said David Lillington, president of Spectrolab. "And because the terrestrial
cell we have developed is similar to our conventional space cells, it can
be implemented in production, and manufactured in very high volumes with
minimal impact to production flow."
Every advance the company makes in their space-based
solar could yield a terrestrial breakthrough. Something the entire renewable
energy industry is waiting for.
"There is considerable synergy between space and
terrestrial cells, and improvements in space cells are expected to drive
efficiency improvements for terrestrial cells," said Dr. Nasser Karam,
Spectrolab vice president for Advanced Technology. "During the last few
years, multijunction solar cells have doubled the power output of large
commercial satellites, and substantially improved their revenue-generating
capability. We believe that further optimization of the improved terrestrial
concentrator cells will yield the potential to surpass 40 percent conversion
The two Mars exploration rovers were launched in
mid-2003 to continue NASA's quest to understand the role of water on Mars.
NASA's Jet Propulsion Laboratory built the $800 million pair of robots.
Each rover's first action is to unfold its solar-array panels, allowing
the solar panels to recharge the rover's batteries. The solar panels were
folded to fit inside the rovers for the trip to Mars. Once on the Martian
surface, the solar panels deployed to form a total area of 1.3 square meters
of triple-junction solar cells. The solar cells power all the activities
and instruments of the spacecraft.
The rovers feature panoramic cameras at human-eye
height, and a miniature thermal emission spectrometer with infrared vision
to help scientists identify the most interesting rocks.
Assuming NASA is able to reestablish communication
with Spirit, the rover will extend an arm and a microscopic imager will
give scientists a close-up view of the rocks' texture and composition.
Another tool will expose the interior of the rock. The second of the two
rovers has the same capability.
Spectrolab solar cells have powered more than 500
satellites and interplanetary missions during the last 40 years. Today,
Spectrolab multijunction solar cells generate more than 325 kW of power
on orbit. Cells representing another 800 kW of power are awaiting launch.