Spaceflight Now





Special fueling test could be ordered for Discovery's tank
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 2, 2010


Bookmark and Share

NASA managers and engineers met Thursday to discuss the potential root cause of cracks in the shuttle Discovery's external tank, what additional tests might be needed and what, if any, modifications might be required before another launch attempt can be made.


Credit: Justin Ray/Spaceflight Now
 
Despite around-the-clock work to assess the problem, engineers still do not understand what caused cracks in structural ribs, or stringers, during fueling for a Nov. 5 launch attempt, a critical element in the development of an acceptable flight rationale, or engineering justification, for making another launch attempt.

"The one thing they don't have is root cause," said one NASA official. "They're just not there yet."

NASA is still holding open the possibility of a launch between Dec. 17 and 20. But the amount of work required to get there does not appear to fit in the available time. The schedule will be compressed even more by a decision late Thursday to carry out a fueling test to collect more data on how the tank's structural components respond to ultra-low temperatures.

It is not yet known when such a test could be carried out. In one option, sensors would be attached to the skin of the tank prior to fueling to precisely measure the stresses in the structure.

But installing such instrumentation and cabling at the launch pad, which would require cutting away more foam insulation, is a challenge in itself. Some engineers favor carrying out a fueling test without any additional sensors, loading the tank and pressurizing it for launch. Any cracks in the tank's foam insulation would be seen and X-ray analysis could find any cracks in the underlying metal.

Sources said Wednesday the requirements of an instrumented tanking test likely would rule out any attempt to launch this month. But they held open the possibility of a near-term launch if an un-instrumented test shows no problems and the on-going engineering analysis shows the tank has enough safety margin to withstand any credible failures.

During a four-hour program requirements control board meeting Thursday, engineers did not even get to a discussion of fueling test options or potential launch dates. The analysis will continue and in the meantime, the "no-earlier-than" Dec. 17 launch date placeholder is "still in play," an official said.

NASA originally hoped to launch Discovery on its 39th and final mission Nov. 1, but a series of technical problems caused repeated delays. After a gaseous hydrogen leak in an external tank vent arm derailed a launch attempt Nov. 5, engineers discovered cracks in two adjacent stringers making up the ribbed intertank compartment that separates the tank's liquid oxygen and hydrogen sections.

The vent line has since been repaired, but the crack issue has proven much more difficult to resolve. Engineers believe normal shrinkage due to ultra-low-temperature propellants, coupled with stresses built into the tank, caused the two stringers to crack near the top of the intertank.

What might have caused the presumed built-in stress, or pre load, is not yet known. But before Discovery can be cleared for another launch attempt, engineers must show the tank can withstand the rigors of fueling and launch without developing similar, or worse, cracks that could lead to the loss of foam insulation or compromise the structural integrity of the tank.

As of this writing, sources say the most likely scenario is an instrumented fueling test followed by a roll back to the Vehicle Assembly Building where platforms can be put in place to give engineers better access to the entire circumference of the intertank. Using sophisticated scanners, technicians then could closely inspect all of the stringers and their connections to other structural components to make sure no new cracks formed during exposure to low temperatures.

At the same time, structural braces called doublers are being prepared that could be attached to beef up any suspect or damaged stringers. But a roll back to the VAB would delay launch to the next window in February and NASA managers have not yet officially taken that step.

The official embroidered crew patch for shuttle Discovery's final flight is available in our store. Free shipping to U.S. addresses!
U.S. SHOPPERS | WORLDWIDE


Spaceflight Now Plus
Additional coverage for subscribers:
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
SUBSCRIBE NOW