AUSTIN, TexasSolar cells work fine in sunshine, but do not generate electric power in the dark. That creates a special engineering problem for cells on the international space station because it is powered by solar cells on the giant set of wings recently attached to it. Engineers at The University of Texas at Austin are working to solve that problem.
The space station's orbit around the earth is 90 minutes long, cycling rapidly from the light to the shadow side of the planet.
"Every time the station is in the dark -- the equivalent of nighttime -- the solar cells do not generate electric power," explained Dr. Robert Hebner, director of UT Austin's Center for Electromechanics. "The station runs on power from batteries during these dark periods."
Hebner said batteries are very good technology "but as everyone who got a new supply of Christmas toys recently knows well, batteries wear out. Chemical batteries used currently on the space station need to be replaced about every five years."
Engineers at the Center for Electromechanics are doing research that could lead to replacing the chemical batteries needed to operate the space station when it is in the dark with flywheel batteries. Flywheel batteries store and release energy on a continuous basis.
If successful, Hebner said NASA estimates savings to the space station program of more than $200 million.
Sen. Kay Bailey Hutchison (R-Texas) recognized NASA for developing this type of program, saying: "NASA should be commended for investing in new technology to make space exploration more affordable. I am proud that The University of Texas at Austin is in the forefront of this effort."
A flywheel battery, designed to fit in the existing space provided for a chemical battery, has a greater capacity and could last the lifetime of the space station itself. Current batteries weigh about 300 pounds and fit in a box about 12 cubic feet in size. Flywheel batteries are a cleaner and more economical source of battery power than chemical models. The flywheel that would be used in the battery on the space station is about 1.5 feet in diameter and nearly three feet long.
The flywheel is a simple technology as old as the potter's wheel. It is made of a composite material, mounted on a titanium shaft and levitated on magnetic bearings. It stores the energy from solar cells by spinning faster and slows as the energy is discharged.
Flywheel battery systems are manufactured and sold commercially for power quality applications in industry. The UT Austin program not only provides trained staff and students for companies in the flywheel battery market, but it also advances the technology through its research.
A current UT Austin focus is to make the technology smaller and lighter than commercial systems, as required for space applications, by exploiting the latest advances in material research and controls.
The UT Austin program is being funded by the NASA Johnson Space Flight Center in Houston and managed by the NASA Glenn Research Center in Cleveland. UT Austin engineers hope to complete the project by the time the current space station batteries need to be replaced five years from now.
For more information, contact Dr. Joseph H. Beno, project manager, at UT Austin's Center for Electromechanics (512) 232-1627. Photos may be downloaded at: