http://www.caib.us/news/press_releases/pr030506.html<br /><br />Columbia Accident Investigation Board<br />For Immediate Release<br />CAIB PA 27-03<br /><br />Date: May 6, 2003<br />Contact: Lt. Col Woody Woodyard, 281-283-7520 or 713-301-2244<br />Contact: Terry N. Williams or Patricia Brach, 281-283-7565<br /><br />Columbia Accident Investigation Board Releases Working Scenario<br /><br />Houston, Texas - The Columbia Accident Investigation Board (CAIB)<br />today released their working scenario.<br /><br />After three months of intense investigation including thorough<br />reviews of hardware forensic analysis, orbiter telemetry, Modular<br />Auxiliary Data System (MADS) recorder measurements, general public<br />still and video photography, hypersonic wind tunnel testing, and<br />aerodynamic and thermal analysis, the Columbia Accident<br />Investigation Board, with the assistance of the NASA Accident<br />Investigation Team (NAIT), has reached the following preliminary<br />conclusions.<br /><br />Launch: Approximately 81 seconds after a 10:39 EST launch on<br />January 16, 2003, post launch photographic analysis determined that<br />foam from the External Tank (ET) left bipod ramp area impacted<br />Columbia in the vicinity of the lower left wing RCC panels 5-9.<br /><br />Orbit: While Columbia was on orbit for 16 days, there was no<br />indication of damage based on orbiter telemetry, crew downlinked<br />video, still photography or crew reports.<br /><br />An Air Force Space Command post flight evaluation of radar tracking<br />data indicated an object in the vicinity of the orbiter on flight<br />day two, remained on orbit for approximately two and a half days,<br />then reentered the atmosphere. Radar testing and ballistics<br />analysis of various thermal protection system items and thermal<br />blankets, along with careful inspection of downlinked orbiter<br />payload bay video, has been used in an attempt to identify that<br />object. Testing and analysis to date have eliminated from<br />consideration all but a piece of an RCC T-seal or RCC panel with a<br />rib. However, there is no conclusive evidence that either of these<br />items was the object that departed the orbiter.<br /><br />Entry: The de-orbit burn and entry targeting were accomplished<br />using well-established Mission Control Center procedures. There<br />were no problems identified with this process.<br /><br />On the morning of February 1, Columbia entered with unknown damage<br />to an RCC panel or T-seal in the left wing RCC panel 5-9 area.<br />Hardware forensic analysis and a review of MADS temperature and<br />strain measurements on the left wing leading edge structure point<br />to the RCC panel 8/9 area as the most likely area of damage. The<br />forensic evidence indicated the RCC panel 8/9 area was subjected to<br />extreme entry heating over a long period of time, leading to RCC<br />rib erosion, severely slumped carrier panel tiles, and substantial<br />metallic slag deposition on the RCC panels nearest the damaged<br />area.<br /><br />MADS data indicated the RCC cavity temperature and the temperature<br />behind the wing leading edge spar began to rise at approximately<br />8:49:00 EST. This indicates that hot gas flowed into the RCC cavity<br />between entry interface 8:44:09 EST and 8:49:00 EST. Three minutes<br />later, at 8:52:00 EST, temperature and strain measurements<br />indicated that hot gas penetrated the internal part of the wing via<br />a breach in the wing leading edge spar. Immediately, the hot gas<br />inside the wing began to heat wire bundles containing real-time<br />telemetry and MADS data. A MADS upper left wing pressure<br />measurement was the first to fail at approximately 8:52:16 EST.<br />Over the next four minutes, 164 other measurements fail, with the<br />last failure at approximately 8:56:24 EST. Most measurements failed<br />very quickly, within the first two minutes of the breach.<br /><br />Columbia's flight control system began to sense increased drag on<br />the left wing due to the damage at 8:52:05 EST. The vehicle easily<br />compensated for the initial aerodynamic disturbance. A significant<br />change in the vehicle aerodynamics was observed at 8:54:20 EST,<br />indicating a change in the damage to the left wing. At the same<br />time several very bright debris events were seen in ground-based<br />videos.<br /><br />Soon after the hot gas entered the left wing multiple debris events<br />were captured on video by observers on the ground. These video<br />images begin at 8:53:46 EST (20 seconds after California coastal<br />crossing) and end with Columbia's final break-up. The exact source<br />of the debris may never be fully understood. However, upper wing<br />skin and Thermal Protection System (TPS) parts are possible<br />candidates. Damage to the internal aluminum wing structure was most<br />probable during this timeframe as well. These debris events<br />appeared to affect orbiter communication. There were 13 unexplained<br />communication dropouts in this timeframe.<br /><br />By 8:56:16 EST hot gas had penetrated the wheel well wall as<br />indicated by an off-nominal rise in hydraulic line temperatures.<br />Another significant change in Columbia's aerodynamics occurred at<br />8:58:09 EST, accompanied by several more debris events. The vehicle<br />responded to this event with a sharp change in its aileron trim.<br />Additionally, by 8:58:56 EST all left main gear tire pressure and<br />temperature measurements were lost, indicating a rapid progression<br />of damage inside the wheel well. A continual progression of left<br />wing damage caused another abrupt change in the vehicle's<br />aerodynamics at 8:59:29 EST. Columbia attempted to compensate by<br />firing all four right yaw jets. By 8:59:32 EST the Mission Control<br />Center had lost all telemetry data. MADS recorder data was lost at<br />9:00:14 EST. Based on video imagery, main vehicle aerodynamic<br />break-up occurred at 9:00:23 EST.<br /><br />Analysis and Testing Underway to Support the Working Scenario:<br /><br />Although there is an abundance of existing evidence supporting the<br />Working Scenario described above, the CAIB and NAIT have the<br />following analyses and testing underway to refine the details of<br />the scenario:<br /><br />1) Completion of RCC and tile impact testing at Southwest Research<br />Institute.<br /><br />2) Aerothermal analyses to correlate off nominal heating trends in<br />left fuselage sidewall and left Orbiter Maneuvering System (OMS)<br />pod heating that were observed in the MADS data.<br /><br />3) Instrumentation wire burn-through arc jet tests and thermal<br />analyses to support the timing of observed instrumentation<br />failures.<br /><br />4) Instrumentation circuit analyses or testing to confirm the<br />failure signatures observed in the data.<br /><br />5) Hypersonic wind tunnel testing and aerodynamic analyses to<br />explain aerodynamic roll and yaw moments observed in flight data.<br /><br />6) Thermal analysis of RCC panel 9 clevis and spar temperature<br />sensor responses to support or refute flight data.<br /><br />7) Gas flow and heat transfer calculations internal to the wing to<br />support the MADS sensor readings in and around the wheel well.<br /><br />8) Arc jet testing and/or analysis of previous arc jet testing to<br />determine feasibility of RCC erosion observed in several key pieces<br />of RCC panel 8/9 debris.<br /><br />9) Continued forensic testing and analysis of significant recovered<br />debris.<br /><br />10) ET dissection and cryopumping tests.<br /><br />The CAIB has not reached any final conclusions and has not<br />determined the cause of the loss of the shuttle and crew. The<br />board's final report will be issued later this summer.