Engineers are once again at the I/T Access Arm attached to the External Tank for troubleshooting, but this time it’s not to work on a leaky Ground Umbilical Carrier Plate (GUCP) seal. A problem with an ordnance cable on the ETVAS (External Tank Vent Arm System) requires repair, and holds the potential to slip STS-128’s launch date to August 25.
With the Agency Flight Readiness Review (FRR) meeting at the Kennedy Space Center (KSC) on Tuesday, several forward path options are open to managers.
The meeting will mainly discuss the risk acceptance work that has been conducted on Discovery’s External Tank (ET-132), following the numerous foam liberation events on STS-127’s tank (ET-131).
Two main areas of the tank are in focus, firstly with the LO2 Ice Frost Ramps (IFRs) – with the option to either fly as-is, or rollback to the Vehicle Assembly Building (VAB) for modifications. The second area of interest is the intertank region – which unusually shed a relatively large amount of foam during Endeavour’s ascent.
The most recent tests were carried out on the latter issue, with one final round of “pull tests” conducted on ET-132’s intertank out at the pad. Those tests – as with all previous pull tests in the VAB – showed good results.
“Orbiter: OV-103 / ET-132 / BI-139/ RSRM 107 (Pad A): “The additional 18 ET/IT plug pulls were completed on Saturday; all passed the bond adhesion test,” noted Monday processing information on L2. “The PDL pours, trimming, and closeouts are complete and the enclosures have been removed.”
Managers we also confident that the meeting will approve the risk acceptance for the IFRs, thus avoiding a rollback and a subsequent delay to October for STS-128. However, FRRs openly welcome dissenting opinion – as a safety failsafe – thus the outcome of the meeting cannot be second guessed.
Assuming the IFR flight rationale is approved, the second decision will be based on when the launch date should occur, with the August 24 NET (No Earlier Than) target placed under pressure by two issues over the past few days.
The first problem required the replacement of a Forward Power Control Assembly (FPCA) on Discovery, which resulted in the pad flow being delayed over the weekend as the vehicle was powered down for the procedure.
This impacted on the scheduled final ordnance installation/connections – known as S5009 operations.
The engineering crews successfully replaced the faulty Main Bus related box, which was followed by a trouble-free retest of the numerous associated electrical systems.
“IPR (Interim Problem Report) 56 update: Troubleshooting Friday night confirmed a bad FPCA 3. FPCA3 R&R was completed on Saturday,” processing information added. “Retest, including Reaction Jet Driver (RJD) retest, is complete to date (through Monday).”
From the point the replacement box was installed, engineers were allowed to proceed with S5009 operations. However, a problem with the ETVAS (External Tank Vent Arm System) ordnance cable – found during routine stray voltage testing – meant engineers had to back-track out of the ordnance installation/connections for the cable to be repaired.
“Ordnance installation/connections picked up early this morning (Monday) following completion of IPR 56 RJD retest. TSM (Tail Service Mast), SRB (Solid Rocket Booster) and Orbiter operations (were) complete. ETVAS is holding for IPR 63,” processing notes confirmed, before expanding on the issue.
“New IPR 63 to Pyro; During ETVAS power-off stray voltage check and connection at the GUCP, the voltage reading was 0.33V and should be less than 0.05V. This is a constraint to continuing. Trouble shooting is in work with GSE (Ground Support Equipment) Engineering on site.”
As a result S5009 ordnance disconnect operations are scheduled to begin at 23:00 Monday night, with the S5009 “run 2 pad clear” (for re-installation) now scheduled for 2200 Tuesday.
Meetings were conducted on Monday afternoon to determine the impact on the launch date, which will be discussed at the Agency FRR. It is likely, but not certain, that this will delay the launch date by one day to August 25. However, a lot will depend on how the repair – and the ordnance reinstallation – proceeds over the next 24 hours or so.
Otherwise engineers are proceeding with the flow as per normal, with the loading of hypergolics on the vehicle now complete.
“S0024, Hyper propellant load is complete: OMS/RCS fuel propellant tank load and orbiter auxiliary power unit propellant tank loading finished Friday,” added a flow update.
“S1287, Orbiter aft closeout began over the weekend and will continue today. 50-1 / 2 door installation and Aft Confidence Test are scheduled for Thursday night. S0007.100, Launch Countdown Preparations, began over the weekend and will continue this week. The GH2 storage battery burn-off, repair and recharge was completed on Saturday. The GO2 recharge is scheduled for Monday.”
Good news was also noted on what is a great achievement by the KSC engineers, specifically the replacement of several elements of hardware on Discovery’s left hand Solid Rocket Booster (SRB) – due to a problem with a Check Valve Filter Assembly (CVFA).
This resulted in a requirement for a Hydraulic Power Unit hotfire – due to its replacement as part of the troubleshooting – which all went to plan.
“LH SRB HPU update: HPU hot fire was successfully completed at 2028L Friday night. Post hot fire inspection was completed over the weekend,” pad flow information confirmed. “Hydraulic sampling, actuator system stroke, hyd bleed operations were completed yesterday (Sunday).
“Actuator pinning and final hydraulic high press leak checks, air entrainment, and aft skirt closeouts will be in work Monday.”
Only one other issue was noted on processing information, though it is deemed as minor, and holds no impact to the pad flow at this time.
“New IPR 62: During SRB aft skirt GN2 activation the GSE purge heater failed to come on. There was no constraint to continuing with the APU hotfire as temperatures were stable. The constraint will be to S0007 (Launch Countdown Operations). Troubleshooting is scheduled for throughout Monday.”
Pad flows are highly complex, especially as they draw closer to the launch countdown. Numerous issues are usually noted – especially with the associated GSE – in every flow, as engineers bring the vehicle to life for their trips to the International Space Station (ISS).
Despite the challenges, engineers have managed to keep Discovery within the previously allocated August 25 launch date – which was only advanced to the 24th a week ago – pending the required approval at the FRR.
L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.