Discovery/ET-137 Tanking Test complete – Flight Rationale data drive

by Chris Gebhardt

Engineers have gathering detailed data on the thermal and stress environments of the External Tank’s intertank stringers at the LOX flange and LH2 flange areas, NASA managers completed fueling Discovery’s External Tank with nearly 535,000 gallons of liquid hydrogen and liquid oxygen, with a smooth Tanking Test is culminating in a GLS (Ground Launch Sequencer) cutoff at the T-31sec mark at 14:24 EST.

Tanking Test Countdown Milestones and Requirements:

To ensure that all the necessary information can be collection during the test, controllers conducted an engineering briefing with the Launch Director, FR2 (Firing Room 2), “2P20” representatives, and the Design Center at ~0600 EST to verify that all of the newly installed instrumentation affixed to the ET (External Tank) are functioning properly.

This included verifying thermocouple reading quiescent temperatures, output readings from the strain gauges, and verification of Design Center specified minimum required instrumentation to begin tanking.  

Based on this review, the Launch Team and the Design Center made a recommendation to the Launch Director and Launch Integration Manager to proceed with the Tanking Test.  This recommendation occured during the planned 0630 EST Tanking Weather Briefing.

With no weather concerns and all instrumentation is working properly, the Mission Management Team (MMT) gave the Launch Director a “go” to proceed with tanking operations.

Should any issue with the instrumentation occur during the test, “ET instrumentation issues will be integrated between Integration Console, FR 2, the instrumentation team in 2P10, MAF (Michoud Assembly Facility), and the Design Center per normal S0007 (Launch Countdown) protocols.”

Following a “go” to begin tanking, the Launch Team transitioned to chill down operations, thermally preparing the LH2 (Liquid Hydrogen) and LOX (Liquid Oxygen) transfer lines and Discovery’s aft MPS (Main Propulsion System) plumbing for the flow of cryogenic propellants.

Once chill down is complete, the launch team began loading Discovery’s External Tank will over 535,000 gallons of LH2 and LOX. The NET (No Earlier Than) start time for tank loading is set for 0700 EST.

With the on-time 0700 EST start time (and no significant leaks of the GUCP), both LH2 and LOX commodities reached stable replenish just prior to 1000 EST.

The countdown then entered a 1-hr built in hold at the T-3hrs mark (1000 EST) – during which the Final Inspection team began scouring Discovery’s tank for ice build up, foam cracks, and thermal irregularities (a process they undertake before every single Shuttle launch).

For this Tanking Test, a minimum of four hours of LO2 stable replenish was be required.

The countdown resumed at 1100 EST and proceed to the T-20min mark (1340 EST), where the standard 10-minute built in hold will be observed. During this built in hold, the NTD (NASA Test Director) conducted the standard NTD briefing. 

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

The launch team then continued the countdown to the T-9min mark where the countdown entered a planned 10-minute built in hold at 1401 EST. During this hold, the Launch Team verifoed all systems, command the Engine Cut Off (ECO) sensors, and conducted a launch status verification and “go/no go” poll to proceed with the count.

“In hold at T-9 minutes, Integration will poll FR2, MAF, and the Design Center to ensure all goals have been satisfied. Once given a GO, the launch team will execute remainder of countdown.”

Unlike a standard Shuttle launch countdown, however, several nominal terminal count procedures were not performed during the Tanking Test’s terminal count.

These standard items that will not be performed include: retraction of the Orbiter Access Arm, pre-start and start of Discovery’s three APUs (Auxiliary Power Units), Orbiter Aerosurface profile test, SSME (Space Shuttle Main Engine) gimbal test, fuel cell transition to internal reactants, FES (Flash Evaporator System) heater reconfiguration, and closure of the L02 and LH2 outboard fill and drain valves.

Nonetheless, ET-137 was pressurized for flight – just like it would in a nominal terminal count.

Termination of LO2 replenish for the ET occured at T-4mins 55secs and counting, and LO2 tank press for flight commenced – as always – at T-2mins 55secs and counting. This was followed by the retraction of the Gaseous Oxygen vent arm (a process which began at T-2mins 55secs and culminates with full retraction of the vent arm by T-1min 30secs). Lastly, the LH2 tank was pressurized to flight levels at T-1min 57secs.

The countdown then proceeded to the T-31secs mark, where the countdown entered a 5-minute built in hold at 1419 EST. The T-31secs mark is usually the point in the terminal count where the GLS hands off control of the countdown to the Orbiter’s GPC (General Purpose Computers).

As noted by the STS-133 S0037 Instrument Tanking Test: Vehicle Configuration Review and Readiness presentation, “Once we have satisfied Tanking Test data gathering requirements, Vehicle and ground will count down and hold at T-31 seconds for the ET GO2 pressurized generic certification time of 5 minutes.”

Following the cutoff, the launch team began securing the vehicle immediately. Critical safing and recycle lasted ~15minutes, and LOX stable replenish was restored to the ET by ~1440 EST.

Then, following 10 minutes of LOX stable replenish, the launch team began draining the LOX/LH2 commodities from the ET. The LOX and LH2 ECO sensor were expected to go “dry” ~95minutes after the start of ET drain.

According to the Tanking Test specifications document, “Data recording will be terminated at a point when overall skin temperature is approximately Temp (start) or configuration is released by Design Center and KSC Chief Engineers. Post-processing of data to 2 samples/second will be done at KSC and files sent (for analysis).”

Post Tanking Test inspection and securing teams will be allowed preliminary access to the FSS (Fixed Service Structure) and MLP (Mobile Launch Platform) No Earlier Than 1710 EST. ET post-drain walk-down will begin around 1830 EST.

See also:
Tanking Test Overview 1
Tanking Test Overview 2

Tanking Test Vehicle Configuration:

For this Tanking Test, the vehicle will not be placed into the standard launch configuration and several nominal launch countdown steps/procedures will not be performed.

In terms of Discovery, her Navaids components, Star Trackers, Air Revitalization and Pressure Control System will be powered down; her MADS system, Solid State Recorders, and Solid State Mass Memory cards will be powered up but will not record data; her Fuel Cells will be powered up and configured to “load share” but will not transition to internal reactants at T-2mins 35secs; her PRSD (Power Reactant Storage Distribution) system tanks will be loaded to provide one hour of recovery time should a ground power supply failure occur.

All pyros will remained installed but most disconnected and safed “via resistive safing plugs or Faraday caps with firing circuits terminated in NSI simulators – Drag Chute, RMS/OBSS (Remote Manipulator System/Orbiter Boom Sensor System) MPMs, and ODS (Orbiter Docking System) pyros will be connected and safed via breakers.”

Avionics bay fire extinguisher functionality and smoke detectors will remain activated throughout the Tanking Test; hydraulics will remain in “recirculation mode;” the crew module O2/N2 air system will be turned off as will the ammonia boilers; PCMMU (Pulse Code Modulator Master Unit) 2 will be the active PCMMU; MPS Helium tanks will be pressurized to “standby pressure (1800 – 2200 psia);” only MEDS (Multi-Electronic Display System) IDP/CRT 1, 2, and 3 will be powered up; PASS GPCs 1-4 will be configured into redundant set while GPC 5 will be configured to Ops 0 standby.

Likewise, the SSMEs will have their TVC systems in flight configuration, their main fuel valve heaters deactivated, and their GN2 purges active throughout the Tanking Test. The SSMEs will remain in PSN 3 and combustion chamber polishing will not be performed.

Moreover, all “ET umbilicals will remain attached by pyro bolts with switch guards/lockout tags installed. Pyro bolt firing circuit will be connected to NSI simulators and safed using Faraday caps.”

ET intertank purge will remain active throughout the test, but ET nose cone purge will be terminated. The ET LOX feedline camera will not be activated at its nominal activation time in the terminal count, and “ET Bipod heater system will be turned off but dead facing will not be verified.”

Furthermore, the SRBs (Solid Rocket Boosters) will NOT be powered up and their ignition Safe and Arms will not be rotated to the ARM position. All pyros will either be safed with NSI simulators and shorting plugs or Faraday caps and NSI simulators. All SRB joint heaters and igniter heaters will not be powered up; SRB aft skirt GN2 will be maintained a “low pressure.”

Additionally, the GSE (Ground Support Equipment) configuration will see all blast shields configured for flight; the sound suppression water system will not be activated; FIREX capability will be maintained and available if needed; the ET intertank access arm may remain extended during the test; the TSM (Tail Service Mast) retract system will be deactivated and all pyro bolt pressure cartridges safed with Faraday caps and firing lines “terminated with NSI simulators.”

In terms of the countdown configuration: the crew module will remain unmanned during cryo loading and will be configured per Tanking Test specific switch list; PASS/BFS/SSME software will be configured in the flight version.

 “Ground software will be in launch configuration except S0037 GLS Mask, Bypass list; Flight software will transition from GNC 9 to OPS 1 at T-20 minutes; BFS preflight uplink loading will not be performed; Horizontal situation configuration will not be verified; MPS He isolation switch reconfiguration will not be performed; and APU heaters will not be terminated,” added documentation.

(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, Lead: Larry Sullivan, MaxQ Entertainment/ Within the article: via L2 acquired PRCB presentations and NASA KSC).

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