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Aviation History
2003
2003 - 0322.PDF
COLUMBIA ACCIDENT INVESTIGATION NASA looks for 'missing link' The disintegration of Space Shuttle Columbia has highlighted one stark fact - even if NASA had determined that thermal-protection tile damage during launch was a safety risk, there is little the space agency could have done. This could have long- term implications for the operation of the three surviving orbiters. There is no way to repair or replace tiles in orbit, and Columbia's crew was not equipped to spacewalk outside the payload bay. Columbia did not have enough fuel to reach the International Space Station, and it was not equipped for docking. A more benign re-entry was impossi ble, says Space Shuttle programme manager Ron Dittemore. Returning to Earth on 1 February after the 16-day STS 107 Freestar sci ence mission, en route to a 09.16 landing at Kennedy Space Center, Florida, Columbia broke up over Texas just before 09.00, during the period of maximum re-entry heat ing. Tile damage has not been con firmed, but NASA believes a "ther mal event, rather than a structural event" caused the accident. Telemetry data has revealed a sequence of thermal events, affect ing the left side of the vehicle, that began as Columbia crossed the California coast (see diagram). This led NASA to re-examine the inci- dent during launch, on 16 January, when foam insulation shed from the external tank 82s after lift-off struck the underside of the left wing, potentially damaging tiles. NASA's analysis concluded the probable tile damage was "within the family" of previous debris impacts, and was "not a safety of flight issue". The "worst case" analy sis assumed a 500 x 400mm (20 x 16in) section of foam weighing 1.2kg (2.671b) and travelling at 460m/s (l,500ft/s) and concluded there was potential for damage or removal of tiles over an area 180 x 800mm - "not sufficient to cause a catastrophic event", says Dittemore. Shuttle orbiters average over 100 tile impact points per flight - "25 to 35 impacts greater than lin are well within our experience base," says Dittemore. There have been 11 flights with impacts greater than 25mm, but in the previous 112 Shu ttle flights tile damage "was never a safety of flight concern," he says. Tests are under way to determine the damage potential of the foam and tiles, but "it does not make sense that a piece [of foam] could be the root cause of the loss of Columbia and its crew," says Dittemore. The spray-on polyur- ethane insulation is fragile and lightweight, virtually waterproof, and the bipod area was checked for ice before launch, he says. "There has got to be another reason." Investigators are analysing the timeline of temperature rises and sensor losses across the left wing, to "back out to where the heat source had to be to generate the indica tions," says Dittemore. Similar "reverse analysis" is under way on the flight-control data. Reaction- control thrusters fired to help the elevons counteract increasing drag on the left side, but the rates before loss of communications indicate the flight control system "was begin ning to lose the battle", he says. Damaged or missing tiles would increase drag, while triggering tur bulent boundary-layer flow over the wing could increase drag and heat ing. But "damage to the underside of the wing would not affect han dling. It would not change the boundary layer or trip the flow over the wing," Dittemore says. NASA did not attempt to image the underside of Columbia in orbit because pictures taken in 1998 of Discovery's drag-chute compartment were "not very useful". Columbia did not have a robot arm, which could have been used to look under the orbiter. If damage had been con firmed, "there was nothing we could have done," Dittemore says. FUNDING NASA budget assumes long life for Shuttle NASA's fiscal year 2004 budget request reflects the decision taken last year to keep the Space Shuttle in service beyond 2012, and postpone development of a next-generation reusable launch vehicle. The space agency is looking at options to extend Shuttle life to 2020 and beyond. The $3.97 billion sought for the Shuttle, up from $3.79 billion in 2003, includes $379 million -$1.7 billion over five years - for the Space Shuttle Life Extension pro gramme. The budget request includes $550 million to begin development of the Orbital Space Plane, leading to an International Space Station crew return capa bility by 2010 and a crew transfer capability by 2012. The reusable OSP will be carried atop an expendable launch vehicle. NASA seeks $515 million for the Next Generation Launch Technology programme, to fund kerosene engine development and hypersonic propulsion research. A decision is due in 2010 on whether to begin full- scale development of a Shuttle replacement, leading to a first flight around 2015. Height: 265,000ft. Speed: 16,400mph. Brake-line sensors show unusual temperature rise in left wheel well. Witnesses report debris breaking away. Signals lost from four temperature sensors associated with left elevons (wiring routed via wheel well). Fourth left brake-line, strut actuator and uplock actuator temperatures rise 30-40°F over 5min. Left mid-fuselage temperature sensor indicates 60° F rise vs 15°F on right side Height: 227,000ft. Speed: 15,045mph. Maximum re-entry heating begins (c3,000°F). Fifth left brake-line sensor shows unusual temperature rise. Mission control sends message to cockpit display about temperature readings. Crew acknowledges. Flight control system counteracts higher drag on left side. Left tyre pressure and wheel temperature signals lost. Two of four left yaw thrusters fire for 1.5s to counteract increased drag. Height: 207,000ft. Speed: 12,500mph. Final transmission from mission control: "Columbia, we see your tyre pressure message but did not copy your last." Columbia responds: "Roger, uh...bluh." Communications lost, video shows breakup of orbiter. www.flightinternational.com FLIGHT INTERNATIONAL 11-17 FEBRUARY 2003 31
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