NASA mulls hydraulic problem on shuttle Atlantis
BY JUSTIN RAY
Posted: April 6, 2000
Engineers on Wednesday identified an unexplained pressure reading while reviewing data from a hydraulic system test conducted last Tuesday aboard Atlantis at Kennedy Space Center's pad 39A. The information indicated a pressure measurement three times higher than normal in the Power Drive Unit, or PDU, for the shuttle's rudder/speed brake.
The rudder/speed brake is the movable aerosurface on Atlantis' vertical tail stabilizer that is used to steer the shuttle and then to slow it down during landing. The aerosurface must operate properly for a safe touchdown.
Deciding what to do
"They now need some time -- give them a day or two -- to collect as much engineering data as they can and apply some engineering analysis and thought to this," Atlantis commander Jim Halsell said Thursday during a break in training at Kennedy Space Center. "Then they'll be able to come up with the best way of fixing the problem."
If the PDU is deemed faulty and has to be swapped, the space agency isn't sure the work could be completed at the seaside launch pad. Such a job has never been attempt in the 19-year history of the shuttle program. Besides handling the 300-pound units, engineers are also concerned about air getting into Atlantis' hydraulic lines and creating even more troubles.
For now, officials say they think the replacement could be completed at pad 39A with no impact to the scheduled April 24 launch date.
Whatever extra work is performed on the PDU likely won't start before next Monday, once a test of Atlantis' three Auxiliary Power Units is completed. The APUs provide the pressure needed to power the shuttle's hydraulic systems. Monday's test is a routine part of pre-launch preparations.
Just three April launch attempts
Officials want to dispatch Atlantis to the International Space Station as soon as possible because the 16-month old fledgling outpost is losing about 1.5-miles of altitude per week. The current orbit is 232 by 215 miles. An increase in solar activity prompted by the nearing peak of the Sun's 11-year cycle is causing the Earth's atmosphere to bulge, creating additional drag on ISS.
Besides replacing broken equipment and delivering about one ton of supplies to the station, Atlantis will also reboost the ISS orbit about 19 miles during three engine firings consuming 1,200 pounds of fuel. That should keep ISS safely aloft until the Russian-built Zvezda service module arrives in July, which is designed to maintain the station altitude.
If Atlantis is delayed or does not dock the station for some reason, the station's Zarya module can use some of its fuel to raise the ISS orbit. However, station officials don't want to use Zarya's limited fuel supply because it is the safety reserve to keep ISS in space until Zvezda arrives.
Countdown dress rehearsal
Following the test, the astronauts will unstrap and exit the shuttle. They are scheduled to leave KSC at 2 p.m. EDT and return to Johnson Space Center in Houston for final pre-flight training.
If the April 24 launch date holds, Halsell and crew are slated to head back to KSC on April 21, and the real countdown should start at 7 p.m. EDT on that day.
The mission will be the 21st for Atlantis and its first in 2 1/2 years. The $2 billion spaceplane's last flight was to the Russian space station Mir in September 1997. Since then, the Atlantis underwent a major overhaul and inspection period at Boeing's shuttle assembly plant in Palmdale, Calif.
The shuttle was outfitted with a sophisticated "glass cockpit" that replaces the 1970s-era gauges and displays and other enhancements during the year-long, $74 million tune-up.
Flight data file
Vehicle: Atlantis (OV-104)
Payload: ISS 2A.2a
Launch date: April 24, 2000
Launch window: 2012-2022 GMT (4:12-4:22 p.m. EDT)
Launch site: LC-39A, Kennedy Space Center, Fla.
Landing date: May 4, 2000
Landing time: 1523 GMT (11:23 a.m. EDT)
Landing site: SLF, KSC
Crew: Halsell, Horowitz, Weber, Williams, Voss, Helms, Usachev
STS-101 commander Jim Halsell describes Atlantis' rudder speed brake problem to reporters on Thursday at Kennedy Space Center's pad 39A.
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NASA animation with narration shows Atlantis approaching and docking to the International Space Station and later separating for return to Earth.
PLAY (249k, 1min, 04sec QuickTime file)
STS-101 Lead Flight Director Phil Engelauf describes the goals and objectives of Atlantis' mission to the International Space Station.
PLAY (269k, 38sec QuickTime file)
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