NASA researchers pose with ROSA (Roll-Out Solar Array) technology. Photo: NASA
Over the years, the number of organizations working to crack the code for ultra-efficient solar cells have increased. Government agencies that once performed a majority of solar cell research are transitioning that science to private companies and universities through grants and student fellowships. This gives government agencies, like NASA and the Department of Defense, the resources to focus their efforts elsewhere.
For its part, NASA Glenn Research Center in Cleveland was the major hub for space solar cell research in the U.S., and the facility remains well-equipped to tinker with cell makeup. But researchers there have become increasingly concerned with how to get more solar into space within the confined area of a rocket.
Upcoming missions, like NASA’s plan to put a human on Mars, will require transporting a lot of support equipment to the red planet. One way to do it is with solar electric propulsion. But a solar array big enough to facilitate the move of human necessities—vehicles, power-making supplies, a habitat module—is larger than any rocket can accommodate.
For that reason, researchers at Glenn said the focus has moved from solar cells to solar structures. The problem for NASA now is how to get bigger, more powerful arrays to space and deploy them successfully. While a 20-kW honeycomb solar array, the predominant type of solar structure today, can fit, more powerful solar arrays will be needed for solar-electric propulsion.
An illustration of MegaFlex technology. Photo: NASA
“Up to this point, we’ve been able to improve array performance just by increasing solar cell efficiency,” said Jeremiah McNatt, electrical engineer at NASA Glenn. “Now when you’re talking about power systems that are so big, the structure is driving research. That’s why we’re talking about big solar arrays, light-weight cells, light-weight structures.”
At least two types of arrays are under research and testing at Glenn.
ROSA technology, which stands for Roll-Out Solar Array, works just like it sounds. A blanket of solar cells rolls up for transport to space. At the touch of a button, the blanket rolls out exposing the cells to sunrays.
The technology is expected be lighter and less expensive than current array designs, offering compact stowed packaging and strength and stiffness that is conducive to providing power levels from 60 kW to more than 300 kW.
Another design, called MegaFlex, is an accordion-like fanfold flexible blanket solar array. It’s made of interconnected triangular lightweight substrates, or gores. When stowed, the array is configured as a flat-pack to minimize the room it occupies. In space, a circular membrane structure stiffens much like an umbrella, resulting in an efficient, strong and stiff structure.
MegaFlex could achieve power levels of 250 kW or higher and greatly improve mass and packaging efficiency of current solar arrays.
The MegaFlex is currently undergoing testing for a variety of issues unique to space, such as hot-cold cycling and micro-meteorites, and how it could survives launch. For the latter, the array is positioned in a gigantic acoustic test bed at NASA Glenn Plum Brook Station in Sandusky, Ohio. Speakers measuring 200 feet high and as much across blast sound and rattle the array to simulate takeoff.
“We have to make sure the cells survive launch,” said McNatt. “That’s not trivial.”