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Columbia Accident Investigation Board
For Immediate Release
CAIB PA 27-03

Date: May 6, 2003
Contact: Lt. Col Woody Woodyard, 281-283-7520 or 713-301-2244
Contact: Terry N. Williams or Patricia Brach, 281-283-7565

Columbia Accident Investigation Board Releases Working Scenario

Houston, Texas - 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.

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