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