STS-133 SCRUB: Discovery’s tanking suffers GUCP leak
Discovery was making her first real attempt to launch on Friday, as the loading of her External Tank (ET-137) picked up following approval by the Mission Management Team (MMT). Tanking had been nominal until a leak was detected on the Ground Umbilical Carrier Plate (GUCP) – causing managers to carry out testing prior to detanking – ultimately leading to a delay to November 30.
STS-133 S0007 Countdown:
Thursday’s decision was, as expected, the correct one, with unacceptable launch conditions – on several parameters – observed during the time Discovery would have been heading towards T-0. Friday’s weather conditions are deemed as more favorable, although there is still a 30 percent chance of a weather constraint.
Other than the weather, everything had aligned for Discovery to press forward with the launch attempt on Friday, with no technical issues causing the MMT any concern.
“Launch countdown operations continued to progress well per the scheduled timeline. Retraction of the Rotating Service Structure (RSS) into the parked position was completed at 20:37 (Wednesday) followed by ascent switchlist at 22:17,” noted the NASA Test Director (NTD) report (L2).
“The pre-tanking weather briefing was held at 05:30 EDT. Managers will delay Discovery’s launch for 24 hours due to weather. Managers will meet tomorrow (Friday) at 5 am to re-evaluate the weather conditions. Friday’s launch attempt would be at 3:03 pm. EDT.”
Discovery countdown was reset to the T-11 hour mark, which picked up again just prior to midnight on Thursday. Pad crews will continue walkdowns at the pad to ensure the vehicle’s configuration is as expected, while all other pre-tanking tasks have been confirmed as completed. The pad will be cleared ahead of tanking.
“Significant Processing Operations: WLE (Wing Leading Edge) and MEI (Main Engine Ignition (MEI) sensor activation and re-programming is complete. Flight Crew Systems Stow operations are complete. The SSME avionics and pneumatics checkout is complete,” added the NTD. “24 hour scrub turnaround operations are in work.”
Four additional Interim Problem Reports (IPRs) were listed by the NTD on Thursday, all of which had been cleared and would not of posed any concern to the countdown. IPR-61 related to a communications link issue associated with the Merritt Island Launch Annex (MILA), with two additional IPRs relating to the launch pad.
“IPR 0062 – Camera cable tray on zero level of MLP (Mobile Launch Platform) has corrosion – During a scheduled debris inspection per S0007, a camera cable tunnel was found to have flakes of corrosion inside a weep hole. Upon further inspection it was found that the cable tunnel had material loss due to corrosion,” noted the NTD report.
“The corrosion that was found inside of the tunnel was removed and no longer a concern. PR (Problem Report) will close MR (Material Review) accept as is.
“IPR 0063 Primary GN2 shutoff is not closing – During GVA (Gaseous Vent Arm) System Final Activation, while performing the Secondary GN2 Reg adjust, Primary heated GN2 valve 906 would not close per technician observation. Valve changed out with no resolution.
“Continued troubleshooting showed a bad orifice upstream of the valve. Orifice was cannibalized from the 906 leg, the 903 leg reg can now be adjusted. The bad orifice was cleaned and returned to operation in the 906 leg. Retest complete and good.”
IPR-64 related to a Payload Bay Circuit Particle Counter suffering from two momentary bad flow indications, no troubleshooting was required given the issue holds no Launch Commit Criteria (LCC) violations.
However, a problem with three of Discovery’s Forward Reaction Control System (FRCS) raincovers required the RSS to make an unscheduled return to the mated position late on Thursday, allowing engineers to ensure the covers – which protect against debris and water from intruding into the nozzles of the thrusters – were secure. The three covers in question were replaced.
Friday morning’s opening event was the MMT meeting for the weather brief and tanking decision, and unlike Thursday managers opted to press ahead with the loading of LH2 and LOX into ET-137, beginning with the chill down process at 6am (slightly delayed from the 5:38am start time) to avoid thermally shocking the lines.
Slow fill followed along with the required checks of the low level and Engine Cut Off (ECO) sensors via SIM checks, which ensure good readings and voltages are observed on console. A check is also carried out during the fast fill process, ahead of the transition into topping, which completes the two hour tanking operation.
UPDATE: However, prior to topping, a leak was detected on the Ground Umbilical Carrier Plate (GUCP). The leak originally peaked at 35,000 ppm – below the limit of 44,000 ppm, before peaking over 60,000ppm. The forward plan was to carry a level of testing prior to a detank, as the launch was scrubbed.
For a changeout of the GUCP seal, engineers estimate they would require a total of 96 hours until another launch attempt. Root cause and troubleshooting efforts resulted in the switch of STS-133 to the December launch window (which actually opens on November 30).
The GUCP was at the center of issues during the launch campaigns of STS-119 and STS-127. However, the issue had not repeated since, following a change of flight seal design and the associated feet which holds the hardware in place – aiding the alignment requirements.
A crack has also been noticed on the ET intertank, which requires further inspection and likely a repair.
A new article will follow based on updates, photos, presentations and engineering notes in L2’s STS-133 Special Section.
STS-133 Specific Articles: https://www.nasaspaceflight.com/tag/sts-133/
New Tracking and Communication Redundancy:
A new procedure being implemented for the launch of STS-133/Discovery will come in the form of overlapping TDRS (Tracking Data Relay Satellite) network tracking and communication redundancy.
According to the STS-133 FRR (Flight Readiness Review), the United States Air Force has moved the Remote Track Station (RTS) operations center. “The Air Force relocated the RTS operations center, and NASA chose not to relocate the NASA equipment to enable orbiter utilization of the RTS network.”
The RTS had previously been available during launch to provide a redundancy to the nominal TDRS tracking and communication abilities. Redundancy during the launch of STS-133 will now be provided via overlapping TDRS scheduling with the TDRS-E and TDRS-SPARE satellites.
The TDRS-East will “remain in ‘standby’ condition unless activated via GCMR command,” notes the FRR.
Nonetheless, the Air Force RTS was not only used to provide communication and tracking redundancy during launch but also used during the on-orbit phase of Shuttle missions to provide availability for data dumps.
“RTS were occasionally used on orbit to dump on board recorded data. On orbit use was typically infrequent (<10 times/flight).”
However, orbiter failures during flight, such as the failure of Discovery’s Ku-Band Antenna during STS-131 earlier this year, generally increase the need to use the RTS to downlink recorded data from the Orbiter.
(Photos: L2 and NASA)