Providing Discovery’s External Tank (ET-137) can be repaired and cleared for flight in time for the upcoming launch window, managers have created a preliminary plan for a Tanking Test, built into a six day countdown. In order to avoid a slip to next February, managers are focusing on gaining confidence in the intertank’s condition, which may only come via additional inspections.
Discovery continues to track a preliminary NET (No Earlier Than) launch date of November 30 – based on the opening of the next available window – although an actual launch date is likely to remain unset until at least November 22, when a full managerial meeting on the status of Discovery’s tank is held.
Resolving the two main issues with STS-133 – both on the External Tank – will continue to drive the ability for NASA to either push forward towards the short window that runs through the first week of December, or standdown until the next window late in February, in turn delaying STS-134.
The actual repairs of the tank – as it stands – have a fair chance of being resolved in time. However, the required confidence, or Flight Rationale, on the cracks in the tank’s stringers, remains the main question which currently lacks a root cause.
At present, Discovery is enjoying the resolution of a few issues which wouldn’t of stopped the original launch, such as the Main Engine Controller (MEC) problem, which gained the required flight rationale ahead of November 5’s scrubbed attempt.
“OV-103 / SRB BI-144 / RSRM 1 112 / ET-137 (Pad-A): OV-103 (Discovery) remained powered down over the weekend in support of Panel L-4 R&R (ahead of this week’s power up and retest). Forward Mission Event Timer (MET): The forward MET was replaced last Friday. Retest will follow with power up,” noted the opening NASA Test Director (NTD) report for the week (L2).
“Main Engine Controller circuit breaker: Following replacement off all 18 circuit breakers and certification tests, panel L-4 will be re-installed back in the ship. The panel R-2 circuit breaker checkout was successfully performed last Friday.”
The Ground Umbilical Carrier Plate (GUCP) leak is likely to be the lesser of the two issues with the tank, following NASA’s previous experience with such incidents, and a potential root cause already found via concentricity measurements on the Carrier Plate – mirroring findings via STS-131’s leak.
Engineers have already begun the process of installing the replacement hardware on to the tank, starting with the flight seal, to be followed by the Quick Disconnect (QD) – although the reinstallation is being staged, with Engineering Review Board (ERB) meetings ensuring each element of hardware is fully analyzed prior to rejoining the tank.
“Ground Umbilical Carrier Plate (GUCP) leak: The replacement GUCP was installed on Friday and concentricity measurements recorded were greater than the engineering community believed they should be. The ERB on Friday afternoon gave concurrence to install the flight seal, but not the QD. The flight seal was installed on Friday night.
“In addition, the SN4 ground QD was tested in the lab with nominal results. Body seals were verified installed and no abnormalities were detected visually during disassembly. Another ERB (continues) to discuss the reassembly plan.”
For all NASASpaceflight.com articles related to the GUCP, click here: http://www.nasaspaceflight.com/tag/gucp/
The big driver on bringing ET-137 back to flight status is the four cracks observed in the two stringers, found after a crack in the Thermal Protection System (TPS) foam was noticed during detanking after the GUCP leak caused the November 5 scrub.
Four cracks, two on each stringer, were found and are at the center of managerial discussions on the forward plan. The actual repair is already underway on the first stringer to suffer from two cracks, via it’s removal and fabrication of a stringer doubler plate, ready to be installed in its place. The second damaged stringer was also being removed on Monday night.
“LO2/IT stringer crack: Two cracks have been discovered on the stringer adjacent to and left of the previous cracked stringer. The original cracked stringer has been removed. Additional foam may be removed to continue the evaluation,” added the NTD report.
So far, no additional cracks have been found under the foam, raising hopes just the two stringers were affected, a result which was expected due to the stress loads that appear to have been specific to that area of the flange.
Technically, engineers could proceed with a full repair of the area this week, with an environmental enclosure built-up over the weekend to provide the required conditions for the respray of BX foam over the doubler plates, with specialist engineers from the Michoud Assembly Facility (MAF) on site.
However, the main consideration that is being debated by managers is aimed at an assurance the rest of the intertank stringers are free from defects. In order to check the rest of the stringers, managers have been discussing the use of backscatter and x-ray techniques, performed around the circumference of the tank, which is challenging due to the restricted access at the pad.
“Two types of non-destructive evaluation (NDE), high resolution backscatter and computed radiography x-ray, were evaluated and determined to be feasible for use on ET-137 at the pad. Further discussion on these potential data gathering efforts,” noted the NTD report.
According to sources, meetings discussed whether they need to check the entire intertank, or just the orbiter facing side of the tank. Such evaluations are focusing on a scan from the outside of the tank, although requests on the ability to scan from within the intertank itself are also being discussed.
Should all go to plan, with the intertank stringer repair and GUCP reinstallation, a preliminary plan has been created for an extended countdown (S0007 operations), with a Tanking Test embedded into the preparations towards launch.
Such a Tanking Test – as last seen with STS-127 following two GUCP leak scrubs – would provide a large amount of data in the event of additional problems, or indeed a large amount of confidence, should the tanking proceed nominally.
Based on a November 30 launch attempt in the the preliminary S0007 schedule – and elaborated on within a 21 page barchart presentation (L2) of the entire “S0007.200/with Tanking Test”, the countdown would begin on Wednesday, November 24 at 0200 EST, a full six days ahead of the target T-0.
The count would then proceed in a nominal fashion with all the nominal Built In Holds (BIH) and pad operations through the T-6 hour and counting mark, at which point the Mission Management Team (MMT) would execute a full up Tanking Test on ET-137 beginning at 1841 L Friday, November 26, ending at 0011 L Saturday, November 27.
During the Tanking Test, once LH2 and L02 stable replenish have been obtained, the nominal count would deviate with the elimination of Discovery’s cabin configuration and crew ingress activities, with a scrub being declared at the end of the Tanking Test, placing the teams into the execution of a 72-hr scrub turnaround plan inside of the countdown operations.
LH2/L02 drain is expected to be completed within 4.5hrs of the initiation of the 72-hr scrub turnaround; LH2 boil off will be completed by 2000 L November 27 and the vehicle will be configured for the remainder of the S0007 count over the initial 50 hours following the end of the Tanking Test.
The countdown would then be recycled to the T-11 hours and holding mark following the 72hr scrub call, resuming from the T-11 hours mark at 1141 L on Monday, November 29 and proceed in a nominal fashion. ET tanking for launch would then commence at 1841 EST Monday, November 29, all of which targets a T-0 launch time on Tuesday, November 30 of 0401 EST.
UPDATE: A key meeting schedule has been outlined via MOD’s 8th Floor News (L2), noting a joint Shuttle Engineering Review Board (SERB)/Systems Integration Control Board (SICB) meeting that is taking place on Tuesday.
This will be followed by a Program Requirements Control Board (PRCB) meeting, which may be similar to the Special PRCB conducted for the Flow Control Valve (FCV) issue ahead of STS-119.
The result of the week’s meetings will move forward into the key Launch Status meeting on November 22.
STS-133 Specific Articles: http://www.nasaspaceflight.com/tag/sts-133/
(Further updates and articles will follow. Refer to live coverage threads linked above. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers. Images used, via L2).