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Over the weekend, Shuttle engineers completed the
frequency response test that was required after the rudder/speed brake power
drive unit replacement effort. Preliminary evaluation indicates that Shuttle
Atlantis' hydraulic system is operating normally and that the PDU replacement
was a success. Shuttle engineers continue to analyze the cause of the initial
PDU failure to ensure that it was an isolated incident.
At about 1 a.m. today, engineers completed a hot
fire test of auxiliary power unit (APU) No. 1 confirming a successful hydraulic
flex hose replacement. Tomorrow, technicians will also replace a quick
disconnect located on an APU No. 2 gaseous nitrogen line. All three APUs will be
brought up to flight pressure on Wednesday as part of standard prelaunch
testing.
The minor dings located on the vacuum jacket of
two liquid hydrogen lines in Atlantis' aft engine compartment have been cleared
for flight. Thorough engineering and X-ray analysis confirmed that the
documented dings were minor in nature and did not compromise the integrity of
the internal propellant lines.
Aft compartment close-outs are in work and
ordnance installation begins tomorrow morning. Orbiter midbody umbilical unit
mating and leak checks begin today. Preparations are in work to pick up the
43-hour launch countdown on Friday at 7 p.m.
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