Spaceflight Now





Shuttle Discovery to undergo special fueling test Friday
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 16, 2010


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Engineers working through a modified shuttle launch countdown are preparing to pump a half-million gallons of supercold liquid oxygen and hydrogen rocket fuel into the shuttle Discovery's external tank Friday to collect data needed to assess the tank's structural integrity in the wake of cracked ribs, or stringers, found after a Nov. 5 launch attempt.

Assuming the test goes well and no other problems develop, Discovery will be hauled back to the Vehicle Assembly Building next week for additional X-ray inspections and possible modifications. NASA hopes to move Discovery back to pad 39A in mid-January for work to ready the ship for another launch attempt as early as Feb. 3.

The cracks in question are located near the top of the external tank's ribbed intertank section where a large flange supports a liquid oxygen tank. Four cracks were found in two adjacent stringers near one of the tank's two booster-attachment thrust panels. The cracks were repaired by splicing in undamaged sections and installing so-called "doublers" to add additional strength.

But engineers are still working to pin down what caused the cracks in the first place. Without a confirmed root cause, analysts cannot rule out the possibility that additional cracks could form, possibly compromising the tank's structural integrity or resulting in the loss of foam insulation that could pose an impact threat to the shuttle's fragile heat shield during ascent.

While inspections using X-ray equipment should catch any pre-existing cracks, initial results of testing using external tank hardware subjected to predicted launch day loads indicates a loss of structural safety margin if two or three adjacent stringers in critical areas were damaged enough to be considered "failed."

As a result, engineers are assessing so-called "radius-block" reinforcements that could be attached to beef up the 36 stringers on either side of the thrust panels where the shuttle's two solid-fuel boosters attach. Those stringers, nine on either side of both thrust panels -- including the two that were repaired -- experience the most stress and are most prone to assembly problems during manufacturing.

The fueling test was ordered to precisely characterize the stresses acting on the stringers before launch, when the tank is subjected to extremely low temperatures. Engineers cut away insulation and installed 21 stain gauges and 39 temperature sensors, or thermocouples, on and near the repaired stringers on the left side of the space shuttle. Another 18 strain gauges and 21 thermocouples were attached to the skin of the tank near the right-side thrust panel. Engineers then re-applied foam insulation.

The sensors will measure the stresses acting on the stringers as liquid oxygen, at minus 298 degrees Fahrenheit, is pumped into the tank along with liquid hydrogen, at minus 423 degrees. As the tanks contract in the ultra-low temperatures, the stringers will be subjected to bending stresses near the oxygen and hydrogen tank flanges. They are designed for that, but analysts want to characterize exactly how much stress might be present and map out thermal gradients in the area.

The fueling test has four primary goals:

  • Gather full-scale environmental data to help validate sub-scale testing and analysis

  • Determine if there are structural issues with the intertank that are the result of generic manufacturing issues as opposed to isolated problems with specific stringers

  • Verify that the repaired stringers perform normally during fueling

  • Verify that a gaseous hydrogen vent line attached to the side of the tank is leak free. A quick-disconnect fitting leaked during fueling Nov. 5, triggering a launch scrub
To make the fueling test as realistic as possible, the tank will be loaded with propellants following roughly the same timeline used for an actual launch:


EST........EVENT

01:00 AM...Final fueling preps
03:00 AM...Pad clear

06:00 AM...Begin a one-hour built-in hold
07:00 AM...Resume countdown

07:00 AM...Liquid oxygen/hydrogen transfer line chill down begins
07:10 AM...Liquid hydrogen slow fill begins
07:40 AM...Liquid oxygen slow fill begins
07:45 AM...Hydrogen engine cutoff sensors "wet"
07:50 AM...Liquid oxygen fast fill begins
08:00 AM...Liquid hydrogen fast fill begins
09:15 AM...Liquid hydrogen topping (98 percent full)
09:45 AM...Liquid hydrogen replenish
10:00 AM...Liquid oxygen stable replenish

10:00 AM...Begin a one-hour built-in hold
10:00 AM...Final inspection team at the launch pad
11:00 AM...Resume countdown

01:00 PM...Final inspection team departs launch pad

01:40 PM...Begin a 10-minute hold at T-minus 20 minutes
01:50 PM...NASA test director briefing
01:50 PM...Resume countdown

02:01 PM...Begin a 10-minute hold at T-minus 9 minutes
02:05 PM...NASA test director launch status verification
02:11 PM...Resume countdown

02:11 PM...Ground launch sequencer auto sequence start
02:16 PM...Terminate liquid oxygen replenish
02:18 PM...Liquid oxygen tank pressurization
02:19 PM...Liquid hydrogen tank pressurization
02:20 PM...Begin a five-minute hold at T-minus 31 seconds
02:24 PM...Fueling test ends
02:50 PM...Liquid oxygen drain begins
02:55 PM...Liquid hydrogen drain begins

Along with measuring stresses and temperatures, stereo cameras will be focused on thousands of small dots painted on the tank to document subtle changes indicative of internal components shrinking on exposure to low temperatures.

After the test is complete, cabling will be removed and Discovery will be hauled back to the Vehicle Assembly Building Dec. 21. After Christmas, engineers will carry out X-ray inspections all the way around the circumference of the tank at both the liquid hydrogen and oxygen flanges at the top and bottom of the intertank section. The instrumentation is capable of spotting even small cracks beneath the foam insulation.

Repair crews will remove the strain gauges and thermocouples and apply fresh foam insulation. And they likely will be directed to attach the radius block doublers near the thrust panels to provide an additional safety margin.

Engineers say the reinforcement hardware can be installed in time to support another launch attempt Feb. 3. But that assumes no problems emerge from the tanking test and that work to remove instrumentation and repair the tank's foam goes smoothly.

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Additional coverage for subscribers:
VIDEO: SHUTTLE DISCOVERY'S LAUNCH DELAYED TO FEBRUARY PLAY

VIDEO: INSTALLING DOUBLERS OVER STRINGERS PLAY | HI-DEF
VIDEO: GASEOUS HYDROGEN VENT ARM RETURNED PLAY | HI-DEF
VIDEO: DOUBLERS TO BEEF UP CRACKED BEAMS PLAY | HI-DEF
VIDEO: HYDROGEN FITTING IS REINSTALLED PLAY | HI-DEF
VIDEO: OPENING UP TANK'S ENTRANCE DOOR PLAY | HI-DEF
VIDEO: GUCP DETACHED AND SEALS REMOVED PLAY | HI-DEF
VIDEO: BROKEN FOAM REMOVED FROM THE TANK PLAY | HI-DEF
VIDEO: VENT ARM LETS GO FROM LEAKY GUCP PLAY | HI-DEF
VIDEO: DISCOVERY AWAITS REPAIRS TO TANK PROBLEMS PLAY | HI-DEF

VIDEO: INFORMATIVE DESCRIPTION OF TANK CRACK PROBLEM PLAY
VIDEO: DISCOVERY'S LAUNCH DELAYED TO MID-DECEMBER PLAY

VIDEO: GASEOUS HYDROGEN VENT ARM DETACHED FROM SHUTTLE PLAY

VIDEO: STS-133 MISSION PREVIEW MOVIE PLAY | HI-DEF
VIDEO: SHUTTLE DISCOVERY CREW BIOGRAPHIES PLAY | HI-DEF
VIDEO: ISS EXPEDITION 25-26 PREVIEW MOVIE PLAY | HI-DEF
VIDEO: SPACE STATION CREW BIOGRAPHIES PLAY | HI-DEF

VIDEO: POST-SCRUB NEWS BRIEFING ON LEAK PLAY
VIDEO: GASEOUS HYDROGEN LEAK SCRUBS LAUNCH PLAY | HI-DEF
VIDEO: BAD WEATHER DELAYS DISCOVERY LAUNCH PLAY
VIDEO: ELECTRICAL ISSUE NO LONGER A CONCERN FOR DISCOVERY PLAY
VIDEO: LAUNCH POSTPONED BY ELECTRICAL CONCERN PLAY
VIDEO: TUESDAY MORNING'S COUNTDOWN STATUS CHECK PLAY
VIDEO: DISCOVERY'S PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: COUNTDOWN PREVIEW BRIEFING AND WEATHER FORECAST PLAY
VIDEO: ANOTHER 24-HOUR DELAY ORDERED TO FINISH REPAIRS PLAY
VIDEO: LAUNCH DELAYED 24 HOURS BY LEAK REPAIRS PLAY

VIDEO: ASTRONAUTS ARRIVE FOR LAUNCH PLAY | HI-DEF

VIDEO: FLIGHT READINESS REVIEW SETS LAUNCH DATE PLAY

VIDEO: SHUTTLE AND STATION PROGRAM BRIEFING PLAY
VIDEO: THE STS-133 MISSION OVERVIEW PRESENTATIONS PLAY
VIDEO: PREVIEW BRIEFING ON MISSION'S SPACEWALKS PLAY
VIDEO: IN-DEPTH BACKGROUND ON ROBONAUT 2 HUMANOID PLAY
VIDEO: THE ASTRONAUTS' PRE-FLIGHT NEWS BRIEFING PLAY

VIDEO: PAYLOAD BAY DOORS CLOSED FOR LAUNCH PLAY | HI-DEF
VIDEO: CREW LEAVES KSC FOR TRIP TO HOUSTON PLAY | HI-DEF
VIDEO: ASTRONAUTS INSPECT THE PAYLOAD BAY PLAY | HI-DEF
VIDEO: SHUTTLE EVACUATION PRACTICE PLAY | HI-DEF
VIDEO: ASTRONAUTS EGRESS SHUTTLE AS SEEN LIVE PLAY
VIDEO: ASTRONAUTS BOARD DISCOVERY PLAY | HI-DEF
VIDEO: SUN RISES ON LAUNCH PAD 39A PLAY | HI-DEF
VIDEO: LAUNCH DAY REHEARSAL BEGINS PLAY | HI-DEF
VIDEO: COMMEMORATIVE WALL SIGNING IN VAB PLAY | HI-DEF
VIDEO: CREW BRIEFED ON EMERGENCY PROCEDURES PLAY | HI-DEF
VIDEO: IN SHUTTLE TRAINING AIRCRAFT'S COCKPIT PLAY | HI-DEF
VIDEO: TEST-DRIVING AN EMERGENCY ARMORED TANK PLAY | HI-DEF

VIDEO: PRE-LAUNCH INTERVIEW WITH STEVE LINDSEY PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH ERIC BOE PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH AL DREW PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH TIM KOPRA PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH MIKE BARRATT PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH NICOLE STOTT PLAY

VIDEO: PAYLOADS INSTALLED INTO DISCOVERY PLAY | HI-DEF
VIDEO: MISSION PAYLOADS ARRIVE AT LAUNCH PAD PLAY | HI-DEF
VIDEO: CANISTER HAULING PAYLOADS TURNED UPRIGHT PLAY | HI-DEF
VIDEO: MODULE HOISTED INTO SHIPPING CANISTER PLAY | HI-DEF
VIDEO: WEIGHING NEW SPACE STATION MODULE PLAY | HI-DEF

VIDEO: GANTRY PLACED AROUND DISCOVERY PLAY | HI-DEF
VIDEO: SHUTTLE ATLANTIS REACHES PAD 39A PLAY | HI-DEF
VIDEO: CROWDS WATCH DISCOVERY'S FINAL ROLLOUT PLAY | HI-DEF

VIDEO: SHUTTLE HOISTED FOR ATTACHMENT TO TANK PLAY | HI-DEF
VIDEO: CRANE ROTATES THE ORBITER VERTICALLY PLAY | HI-DEF
VIDEO: DISCOVERY DEPARTS ITS HANGAR PLAY | HI-DEF

VIDEO: TIME-LAPSE SHOWS DISCOVERY ASCENDING IN VAB PLAY
VIDEO: TIME-LAPSE SHOWS THE MOVE TO ASSEMBLY BUILDING PLAY

VIDEO: DISCOVERY'S MAIDEN FLIGHT: FIRST TRIP TO VAB PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: ROLLOUT TO PAD 39A PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: TEST-FIRING ENGINES PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: ASSORTED VIEWS OF FRF PLAY

VIDEO: THE HISTORY OF SHUTTLE DISCOVERY PLAY
VIDEO: THE HISTORY OF SHUTTLE ENDEAVOUR PLAY
VIDEO: THE HISTORY OF SHUTTLE ATLANTIS PLAY

VIDEO: INSPECTION OF THE MISSION PAYLOADS PLAY | HI-DEF
VIDEO: ROBONAUT ARRIVES AT KENNEDY SPACE CENTER PLAY | HI-DEF
VIDEO: SPACE STATION'S SPARE THERMAL RADIATOR PLAY | HI-DEF
VIDEO: BLANKETING LEONARDO WITH INSULATION PLAY | HI-DEF
VIDEO: RACK INSERTED INTO LEONARDO FOR LAUNCH PLAY | HI-DEF
VIDEO: LEONARDO RETURNS FROM ITS PREVIOUS FLIGHT PLAY | HI-DEF
VIDEO: STATION'S SPARE PARTS DEPOT ARRIVES PLAY | HI-DEF

VIDEO: ORBITER'S PAYLOAD BAY CLOSED FOR ROLLOUT PLAY | HI-DEF
VIDEO: ASTRONAUTS VISIT THEIR SPACECRAFT PLAY | HI-DEF
VIDEO: CREW INSPECTS LEONARDO MODULE PLAY | HI-DEF
VIDEO: DISCOVERY RECEIVES ITS MAIN ENGINES PLAY | HI-DEF
VIDEO: FUEL TANK MATED TO SOLID ROCKET BOOSTERS PLAY | HI-DEF
VIDEO: HOISTING FUEL TANK INTO CHECKOUT BAY PLAY | HI-DEF
VIDEO: EXTERNAL FUEL TANK UNLOADED FROM BARGE PLAY | HI-DEF
VIDEO: MISSION'S FUEL TANK ARRIVES AT SPACEPORT PLAY | HI-DEF

VIDEO: POST-FLIGHT DESERVICING: OMS POD PLAY | HI-DEF
VIDEO: POST-FLIGHT DESERVICING: OBSS BOOM PLAY | HI-DEF
VIDEO: POST-FLIGHT DESERVICING: ENGINES PLAY | HI-DEF
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