Discovery launches after dramatic range fix late in countdown

by Chris Bergin and Chris Gebhardt

Discovery has completed her final ascent into space, following a 16:53 Eastern launch from the Kennedy Space Center (KSC). Controllers managed to launch the veteran orbiter with just seconds to spare, as the count was held at T-5 minutes to fix a range issue. A foam liberation impact on the orbiter late in ascent is highly unlikely to be of concern, as Discovery moved into Flight Day 1 of STS-133.

STS-133 Latest:

STS-133 is the 164th American manned spaceflight, the 133rd flight of the Space Shuttle, the 80th Space Shuttle flight from Pad 39A, the 39th and final flight of Discovery, the 35th Space Shuttle mission dedicated to construction and outfitting of the International Space Station, the 108th post-Challenger mission, and the 20th post-Columbia mission.

Thursday morning’s opening event was the MMT meeting for the weather brief and tanking decision, where managers opted to press ahead with the loading of LH2 and LOX into ET-137, beginning with the chill down process to avoid thermally shocking the lines. This began on time at 7:25am.

Slow fill followed, ahead of 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. As the tank entered topping, no leak detectors had tripped around the GUCP, showing the hardware was in a good condition past the point of the November scrub.

ET-137 completed tanking operations by entering stablish replenish at 10:19am Eastern. The crew have now ingressed the vehicle, following the Final Inspection Team evaluation on the condition of the tank – with no issues found.

Discovery was up to 108 Interim Problem Reports (IPR) by the start of tanking, the latest of which have been closed or are in the process of being “paper reviewed”. Only a manifold pressure issue was reviewed by controllers at the time of tanking, cleared as no constraint by way of Launch Commit Criteria (LCC).

The count was nominal with only a power imbalance on a distributor (LH2 power buss) evaluated by controllers since tanking. Ground Support Equipment (GSE) related to the buss had shorted out twice before failing. Controllers discussed affected systems, prior to clearing the issue for flight.

However, late in the countdown, the range suffered an issue, resulting in a RED. Launch Director Mike Leinbach and his team decided to take the countdown through to T-5 minutes, before holding. With only seconds remaining in the three minute launch window, the range reported a GO.

Teams in the Firing Room then quickly returned Discovery into the countdown, prior to successfully launching her on what appears to be a nominal return to space.

It can also be seen on the ET cam video that a foam liberation hit Discovery after four minutes of ascent. The liberation appears to be small by way of mass, and liberated long after the time of aerodynamic concern – as can be seen by its low velocity impact and no sign of damage on the area it struck.

Discovery and her crew then entered into Flight Day 1 operations, completing several orbital burns, opening the Payload Bay Doors (PLBDs) and checking out the Shuttle Remote Manipulator System (SRMS).

The next article will cover Flight Day 2 operations. Refer to live update pages – linked above – for up to the second information.

STS-133 Launch Issue History:

Discovery’s final flight was delayed from November, a month the fleet leader would like to forget, following a one day delay to allow evaluations of a redundant Main Engine Controller (MEC) anomaly, prior to unacceptable weather on November 4 resulting in another delay.

On the morning of the November 5, ET loading operations picked up on time and continued nominally, until the hydrogen vent valve in the ET was opened to allow boiled-off gaseous hydrogen to vent from the tank. At this time, a leak indication was detected at the GUCP.

Initially, the launch team responded by cycling the vent valve in an attempt to reseat the GUCP/ET Carrier Assembly seal. However, the leak soon breached the 44,000ppm Launch Commit Criteria limit – spiking to at least 60,000ppm: the maximum reading on the sensors at the pad.

While this incident caused the immediate scrub of STS-133’s launch attempt, a much more serious issue would present itself. During de-tanking operations, a stringer on the ET intertank structure snapped under cryogenic stress loads, thereby cracking and deforming the TPS foam on the external tank in the immediate area.

With the leak of the GUCP and the crack to the ET foam, mission managers determined that Discovery would not be able to launch before the close of the early-November launch window, and the launch was reset for NET (No Earlier Than) November 30.

STS-133 Specific – Including ET Stringer Issue – Articles:

However, post-scrub inspections and TPS external tank foam removal quickly revealed the extent of the stringer failure and sparked an inspiring and thorough investigation.

As work progressed on not only the GUCP leak but also the stringer issue, engineers removed the failed stringer and adjacent damaged stringers (which cracked under the sudden redistribution of loads), and the November 30 – December 6 launch window was ruled out.

With the failed stringers replaced and a fix to the GUCP leak found, NASA managers elected to perform an instrumented Tanking Test on Discovery’s ET-137 in mid-December. The test served two purposes: validate and verify GUCP leak resolution and monitor and determine stringer stress at the ET LOX/intertank flange area under both cryo and pressurized environments.

With the tanking test complete, NASA then pressed forward with plans to roll Discovery back to the VAB for a complete inspection of all stringers on ET-137′s intertank region. Discovery was rolled back on December 22/23 to the VAB where a complete inspection revealed three cracked stringers on the “backside” of the tank.

In January 2011, NASA engineers succeeded in determining root cause for the stringer crack issue. This information led to the decision to implement Radius block doubler installations on a vast majority of the stringers at the ET LOX/intertank flange.

Completion of these modifications allowed NASA managers to set a NET launch date of February 24th for STS-133.

Monitoring ET-137’s Flange/Stringers:

Expansive Program Requirements Control Board (PRCB) presentations have noted some the rules for the observation of issues with the flange foam, such as those seen during STS-133′s scrub due to the Ground Umbilical Carrier Plate (GUCP) leak.

“DIG (Debris Integration Group) position is that crack offset observed before MEI (Main Engine Ignition) is NO-GO for launch,” opened one such presentation. “Indication of debonded foam; no way to determine otherwise in time. In-family IT crack w/No Crack Offset is not expected to be a debris threat.”

Managers had already created a plan for camera observations of the flange’s circumference during the countdown, allowing controllers to watch out for any defects in the foam, during and after inspection by the Final Inspection Team (FIT).

“Imagery Coverage: Operational Television (OTV) and fixed Infrared (IR) assets can view majority of LO2 and LH2 flanges (some areas of both are not in view; details on subsequent charts). Existing lighting is adequate during night ops (night views in backup). All stringers are visible and not in shadow,” noted a separate presentation (L2).

“Thrust panels expected to be partially in shadow due to SRBs (Solid Rocket Boosters). Listed OTV and IR (Infrared) cameras are Ice/Debris controlled. Periodic scans of LO2 and LH2 flanges performed during tanking/post tanking.

“FIT portable assets provide a 360 degree inspection coverage of the LO2 and LH2 flanges with the following limitations. LO2 flange is not visible under cable tray and pressline. LH2 flange is not visible under LO2 feedline, cable tray and presslines.”

With this set up at the pad, managers have noted that they can be “confident can detect similar anomalies if they occur prior to lift-off.”

(Numerous articles will follow. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers – which will ramp up into full Flight Day coverage during the mission. Images used, Lead and Launch: MaxQ Entertainment/ Rest via L2 documentation).

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