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July 19, 2001

John Bluck

NASA Ames Research Center, Moffett Field, CA

650/604-5026 or 650/604-9000



Technology used in laptop computers is now saving time and money by helping astronauts troubleshoot International Space Station subsystems during construction.

Rick Alena, a computer engineer at NASA’s Ames Research Center in California's Silicon Valley, and Dan Duncavage of NASA’s Johnson Space Center (JSC), Houston, engineered the computer diagnostic tool. It includes a computer card and software that can monitor status and command messages sent between onboard control computers and major space station subsystems, including solar arrays, docking ports and gyroscopes.

"For producing our on-board spacecraft troubleshooting tool, we found a suitable commercial product, flight qualified the hardware and software, and then integrated the diagnostic system with the station support computers, which are modified laptops," said Alena. "We now are using commercial computer systems to support mission and payload operations in space flight because they have the performance required and run a large range of software."

"The Databus Analysis Tool (DAT) enables engineers on the ground to analyze data during troubleshooting sessions," Alena said. The tool allows onboard monitoring of the station's nervous system, a computer control network that ties the avionics components together, he explained. Avionics are critical aviation electronics systems that control the station.

Engineers designed the tool to help solve minor problems during assembly of the space station modules. Alena explained that engineers on the ground can resolve most assembly problems using data radioed to them from station systems, but some problems require more data. "Our idea was to acquire data messages directly onboard and to provide this extra data to engineers on the ground to help analyze how station parts were interacting." Alena said.

Although engineers designed the computer tool to be a passive monitor, its first use was to issue commands for checkout of the station's gyroscope systems during the STS-92 mission in October 2000. The gyroscopes are flywheels that stabilize the station's attitude without use of propellant fuel. The attitude of a spacecraft is its tilt compared to the surface of another body in space, such as the Earth. The space station also has small jets that shoot propellant into space to slowly rotate the craft for fine attitude adjustments.

The gyroscopes spin like heavy toy tops to maintain the station's proper orientation relative to Earth, explained Alena. "Otherwise, costly propellant must be used to maintain the station's proper attitude with the control jets. The cost of stabilizing the station using propellant rather than the gyros could run into millions of dollars."

After tests in August 2000, engineers decided to use DAT to control heaters that warm the gyroscopes and to test the spin motors. Between the STS-92 shuttle mission that carried the gyroscopes to the station, and the STS-98 mission in February 2001 that delivered the U.S. laboratory module and control computers, engineers needed to check the gyroscopes' operation, Alena said.

Astronauts Bill McArthur and Leroy Chiao tested gyroscopic system operation during STS-92. The astronauts used the computer tool to activate and spin the gyroscopes on the Z1 truss to test controls and sensors. McArthur and Chiao also used DAT to test gyroscope system power, heaters and spin motors. "All four gyroscopes checked out okay," said Alena. "The detailed procedures for checking the gyroscopes were developed by Boeing engineers, in concert with the DAT team," he added.

NASA Ames and JSC partners did the initial tests of DAT in space about four years ago. "The amount of preparation and work to fly an electronic system is quite time-consuming," Alena explained. "DAT has been flown on most station assembly missions since 1998. There are two DAT flight sets, and occasionally we bring one down and test the flight hardware at JSC," he said. Duncavage and Alena hand-carried the DAT through all flight-qualification phases. The two men minimized the cost in this way and, just as importantly, the DAT was ready to fly early during space station construction, according to Alena.



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