Spaceflight Now: STS-101 Mission Report

Failure probe, tight schedule only concerns for Atlantis

Posted: April 18, 2000

The rotating service structure swings back into position around Atlantis after replacement of a hydraulic unit last week at launch pad 39A. Photo: NASA/KSC
NASA says it remains optimistic space shuttle Atlantis will make its appointed launch date next Monday despite a continuing investigation into the failure of a hydraulics unit taken from the ship and a tight work schedule that has no room for more problems.

Engineers on Monday picked through data gathered during the so-called Frequency Response Test of Atlantis' aerosurfaces and main engine nozzles conducted over the weekend. The test was performed to check the shuttle's hydraulics after the suspect Power Drive Unit (PDU) for the rudder/speed brake was replaced late last week.

"There is no indication there were any problems," space agency spokesman James Hartsfield said of the test.

Meanwhile, a failure analysis is still ongoing to determine why pressure readings three times higher than normal were seen in the faulty PDU removed from Atlantis. NASA managers want to know what caused the high pressures and make sure there is not a larger problem with other PDUs installed across the space shuttle fleet.

Engineers say the pressure readings were actually within the acceptable range for the PDU to work properly, but officials were concerned whatever was causing the problem inside the 300-pound unit could worsen, possibly rendering it useless during the shuttle flight.

The PDU is located inside the Atlantis's tail vertical stabilizer and drives six hydraulic motors that control the rudder and speed brake to steer and slow the shuttle during landings.

Hartsfield says the analysis is expected to be completed early this week. The issue will be formally put to rest during a Mission Management Team meeting on Saturday at Kennedy Space Center.

But if engineers need more time to understand the problem, NASA will have to delay Atlantis' planned Monday launch to perform maintenance on the 16-month old International Space Station.

"The analysis will be concluded before we launch," Hartsfield said.

Pre-launch work goes on
At Kennedy Space Center's launch pad 39A, a hotfire test of Atlantis' Auxiliary Power Unit No. 1 was completed early Monday morning, confirming a successful replacement of a hydraulic flex hose last week.

Also, the minor dings located on the vacuum jacket covering two liquid hydrogen lines in Atlantis' aft engine compartment have been cleared for flight. NASA says thorough engineering and X-ray analysis confirmed that the previously-known dents were minor and did not damage the internal propellant lines.

Work to close the shuttle's three-level aft engine compartment is continuing and installation of ordnance devices on the vehicle begins Tuesday. Mating of the midbody umbilical unit mating to Atlantis and leak checks started on Monday in preparation for loading the shuttle's three fuel cells this weekend.

The seven Atlantis astronauts are slated to arrive at Kennedy Space Center on Friday at 3 p.m. EDT for launch. The three-day countdown is scheduled to start later that day at 7 p.m. EDT.

The schedule between now and Monday's planned 4:15 p.m. EDT (2015 GMT) liftoff, however, is considered tight with no extra padding left to deal with additional problems that might arise. The PDU replacement work last week used up all of NASA's "contingency" time to resolve unforeseen troubles at the launch pad.

"You always feel better if you have extra time but we are on track to make the 24th launch date," Hartsfield said.

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: 1642 GMT (12:42 p.m. EDT)
Landing site: SLF, KSC
Crew: Halsell, Horowitz, Weber, Williams, Voss, Helms, Usachev

Video vault
Workers remove the faulty Power Drive Unit from space shuttle Atlantis using a heavy-lift crane at launch pad 39A.
  PLAY (299k, 30sec QuickTime file)
A replacement Power Drive Unit is installed inside space shuttle Atlantis' tail at launch pad 39A on April 12.
  PLAY (304k, 35sec QuickTime file)
Shuttle technicians oversee the freezing of hydraulic lines leading to Atlantis' broken Power Drive Unit on April 12.
  PLAY (374k, 29sec QuickTime file)
Download QuickTime 4 software to view this file.

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