h OMS Gimbal Profile Test at approximately T-5:45, the left OMS secondary (standby) pitch and yaw actuators did not
drive with only the "enable 1" (RPC 1) command on. During prelaunch troubleshooting, both (pitch and yaw) actuators drove properly with the "enable 2" (RPC 2)
command on. An MDM BITE test was successfully performed which indicated that the most likely failure was in the Power Control Assembly (PCA) or an open wire or
connector preventing 28 VDC motor drive power from RPC 2 from reaching the motor drivers. RPC 1 and RPC 2 provide parallel power to the motor drivers.
The Left OMS Standby Actuators were considered unusable for flight because both pitch and yaw actuators are required to be driven simultaneously, and the current draw
would exceed the 13.75 amp trip-limit for a single RPC. Launch Commit Criteria (page 6.9.10-39) was invoked, which allows countdown to continue with a failure of
either the primary or secondary actuator channel for one OMS engine. The failure was confirmed in flight during a post-insertion gimbal drive test during which RPC 2
tripped off after some movement of the actuators. During the remainder of the mission the left OMS gimbal functioned normally under control of the primary actuators.
Post flight troubleshooting identified an open circuit between Aft PCA #2 and the left OMS Controller (Connector P9967, Pin NN). CONCLUSION: The OMS gimbal
drive failure was caused by an open circuit which prevented 28 VDC power from reaching the motor drivers via RPC 1. CORRECTIVE_ACTION: Launch Commit
Criteria was clarified to permit loss of either primary or secondary controller on a given OMS engine. The open circuit has been repaired.
EFFECTS_ON_SUBSEQUENT_MISSIONS: None, pending the results of failure analysis.
Tracking No
Time
Classification
Documentation
Subsystem
MER - 0

INCO-01

MET:
Prelaunch

GMT:
Prelaunch
Problem
FIAR

SPR
26RF17

IPR
None
IFA
STS-26R-V-02

UA

PR
C&T

Manager:

Page 2
Engineer:

Title:
Network Signal Processor (NSP) 1 Frame Synchronization Not Locked On Transponder 2. (ORB)

Summary:
DISCUSSION: During prelaunch checkout, NSP 1 did not indicate bit or frame synchronization when configuration was switched by uplink command from S-
band transponder 1 to transponder 2. Prelaunch troubleshooting switched back to transponder 1 and frame synchronization lock was good. All subsequent combinations of
transponders and NSP's resulted in valid frame synchronization lock. Launch mode is NSP 2 selected and configured to transponder 2 (string 2). Launch Commit Criteria
redundancy requirements were verified by placing the S-BAND PM CNTL switch from CMD to PANEL which selected NSP 1 configured to transponder 1 (string 1), and
verifying NSP 1 frame synchronization lock. Postflight troubleshooting failed to reproduce the anomaly. Any additional troubleshooting would require shipment of the
transponder to the vendor for failure analysis. Pending recurrence of this anomaly on subsequent missions, failure analysis is not considered warranted based on system
redundancy and the low probability that a specific cause could be identified.
CONCLUSION: The most probable cause of this anomaly is an intermittent malfunction of the forward link data relay in transponder 2 after which subsequent cycling
cleared the problem. CORRECTIVE_ACTION: None, pending recurrence on subsequent missions. EFFECTS_ON_SUBSEQUENT_MISSIONS: None
Tracking No
Time
Classification
Documentation
Subsystem
MER - 0

MMACS-01

MET:
Prelaunch

GMT:
Prelaunch
Problem
FIAR
WC0380

SPR

IPR
None
IFA
STS-26R-V-03

UA

PR
GFE

Manager:


Engineer:

Title:
The Mission Specialist 1 and Pilot's Suit Vent Fans Failed. (GFE)<br><b><font color=Blue><u>Summary:</U> </font></b>DISCUSSION: During
prelaunch preparation the Mission Specialist 1 and the Pilot's Personal Suit Ventilation System fans failed to operate. Subsequent investigation revealed that the 3 amp
fuses (part number ME451-0009-0003) feeding power to the fan motors had blown. At the time of suit fan motor activation, the fuel cell voltage feeding the related power
bus was reading between 30.5 and 31.0 volts. It was concluded that the 3 amp fuse, specified in the fan motor design, was marginal and would not survive the in-rush
current of a 31.0 volt buss. The 3 amp fuses were replaced with part number ME451-0009-0005 fuses which were thought to be 5 amp fuses. The fan motors then operated
nominally through the ascent phase of the mission. Later it was discovered that the -0005 fuses were in fact 10 amp fuses and would not protect the 24 gage power wiring
inside the fan motor assembly. Since the fan motor assembly is a completely sealed unit there was no hazard to the crew had a short circuit developed in the fan motor
power circuit. During ground tests, using a spare suit fan motor, it was determined that a 5 amp fuse was adequate for wire protection and fan motor operation. Page 3
Prior to entry, all suit fan motor power fuses (five) were replaced with verified 5 amp fuses that were part of the inflight maintenance kit carried onboard the spacecraft.
There was no further impact on the mission. During certification of the suit fan motor assembly, the motor power circuit was not protected by a fuse. The units were later
modified to include a 3 amp fuse, however testing at voltages greater than 28 volts was not accomplished. CONCLUSION: The 3 amp fuse in the original suit fan motor
power circuit design were underrated for the voltage levels that could be expected in the spacecraft while operating on fuel cells. CORRECTIVE_ACTION: The suit fan
motor power circuit design has been changed to reflect replacement of the 3 amp fuses with 5 amp fuses (part number ME451-0009-1021) on all units. Reference CCB
directive G2086. A spare suit fan, cables and fuses will be available for countdown operations. EFFECTS_ON_SUBSEQUENT_MISSIONS: None
Tracking No
Time
Classification
Documentation
Subsystem
MER - 0

MMACS-02, BSTR-02

MET:

GMT:
Problem
FIAR

SPR
A) 26RF07, B)
26RF20, C) 26RF08, D)
26RF18, E) 26R

IPR
None
IFA
STS-26R-V-04

UA

PR
OI - Sensors

Manager:


Engineer:

Title:
Operational Instrumentation Failures. (ORB)

Summary:
DISCUSSION: A. At liftoff, the Auxiliary Power Unit (APU) Number 3 Exhaust Gas Temperature Number 2 measurement (V46T0340A) became erratic,
cycling between 38 degrees F and 957 degrees F and failing at 44 degrees F. Postflight troubleshooting confirmed transducer failure. The transducer has been removed
and replaced. Failure analysis will be tracked by CAR 26RF07. This is a criticality 3 measurement.
B. The right Space Shuttle Main Engine (SSME) liquid hydrogen (LH2) inlet pressure measurement (V41P1300C) was erratic prior to SSME shutdown. At main engine
cutoff (MECO), the measurement went to zero. Postflight troubleshooting confirmed transducer failure. The transducer has been removed and replaced. Failure analysis
will be tracked by CAR 26RF20. This is a criticality 3 measurement. C. Approximately 5 minutes after touchdown, the APU Number 1 Exhaust Gas Temperature Number
1 (V46T0142A) became erratic, cycling between 38 degrees F and 950 degrees F. Postflight troubleshooting confirmed transducer failure. The transducer has been
removed and replaced. Failure analysis will be tracked on CAR 26RF08. This is a criticality 3 measurement. D. At 3:01:22 mission elapsed time, the hydraulic system
number 1 "B" supply pressure (V58P0115A) was biased low by approximately 60 psia. The low bias is within specification limits. No corrective action is required. This
is a criticality 1R3 measurement. E. At T-1 hour prelaunch, the hydraulic system number 3 circulation pump pressure measurement (V58P0337A) was biased low by 80
psia at operating pressure. This bias is considered acceptable. No corrective action is required. This is a criticality 3R3 measurement. F. Throughout the flight, the
number 2 SSME LH2 inlet pressure measurement (V41P1200C) oscillated with a low bias of 3-5 psia. The bias and slight oscillation is considered acceptable. No
corrective action is required. This is a criticality 1R3 measurement. G. At T+3 minutes, the Freon evaporator out temperature (V63T1407A) on Freon coolant loop number
2 lagged behind Freon coolant loop number 1 Freon evaporator out temperature (V63T1207A) by about 10 degrees F and about 5 seconds. Postflight troubleshooting
confirmed a debonded sensor. The sensor has been removed and replaced. Failure analysis will be tracked by CAR 26RF10. This is a criticality 2R3 measurement. H. At
T+70 seconds through T+127 seconds mission elapsed time, the external tank 98 percent liquid level point sensor measurement (T41X1716E) operated erratically Page 4
(flashing). Troubleshooting has been completed, no anomaly detected in orbiter system, and the problem is under evaluation. There was no impact to the flight. This is a
criticality 3/3 measurement. CONCLUSION: See above. CORRECTIVE_ACTION: See above. EFFECTS_ON_SUBSEQUENT_MISSIONS: Effects on Subsequent
Missions: None
Tracking No
Time
Classification
Documentation
Subsystem
MER - 0

EECOM-02

MET:
000:00:04

GMT:
273:15:41
Problem
FIAR

SPR
26RF11

IPR
None
IFA
STS-26R-V-05

UA

PR
Active Thermal Control
Subsytem

Manager:


Engineer:

Title:
The Flash Evaporator System Hi-Load Evaporator Froze During Ascent and Shut Down During Entry. (ORB)

Summary:
DISCUSSION: During ascent, prior to Flash Evaporator System (FES) activation, the EVAP OUT temperature dropped to 43 degrees F, indicating
water/condensate in the FES cores. After FES activation,