Laptop Computer Tool Helps Space Station Fly Smoothly in Orbit

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.