STS-107 Debris Impacting Orbiter Wing
Preliminary Debris Transport Assessment of Debris Impacting Orbiter Lower Surface in STS-107 Mission
January 21, 2003

In a report prepared by Boeing Aerospace on the impact of debris during launch, the contractor indicated there was indeed cause for concern. The summary, below, indicates engineers really had no idea of the exact nature of the damage caused when insulating foam impacted the underside of the orbiter's left wing. They were forced to hypothesize.

Debris Impacts Orbiter Lower Surface

• Issue

– At about 82 seconds into the flight, a large piece of debris was seen emanating from the ET bipod area and later seen impacting the Orbiter lower surface tiles

• Background

– Preliminary assessment of debris impact conditions predicted an impact to the Orbiter lower
surface at location XO1049, YO185 (results provided on January 17, 2003)

• Impact Velocity estimated to be 750 ft/sec.

• Impact Angle estimated to be less than 20 degrees

– Refinement of the results show reduction of impact angle and impact velocity

– Analysis methodology and results were presented to the Aero Panel on January 21, 2003

• Aero Panel concurrence was obtained

• Aero Panel recommended sending results to Orbiter Program for damage assessment

Debris Impact Conditions to Be Evaluated for Area on Orbiter Lower Surface

• Actions Taken

– Defined impacts area based on film observations and debris trajectory modeling

• Large uncertainty in trajectory computation does not allow a good prediction of the
impact area

– Performed debris trajectory computations to define impact conditions inside impact area.

• Debris particle emanates from bipod ramp area (XO 389, YO 50)

• Two debris sizes analyzed:

– 20” x 10” x 6” (representing flange foam)

– 20” x 16” x 6” (representing bipod ramp)

• Debris material considered to be foam (density = 2.4 lb/ft3)

• Particle subjected to initial lateral motion to simulate lateral loading of bipod ramp

– Impact conditions inside predicted impact area was derived as follows:

• Actual Impacts: Particle impact information as computed by the debris trajectory
program

• Near Impacts: Particle velocity obtained for specific points in particle trajectory

• Debris Database: to define particle impact angles at locations in the landing gear wheel
well

Results Show Low Impact Angles on the Orbiter Lower Surface

• Results -

– Completed evaluating results for trajectory analysis of foam debris of size = 20”x10”x6”

• Impact velocity inside predicted impact area range between 650 and 730 ft/sec.

– Impact velocity at wing RCC may vary between 700 and 720 ft/sec.

– Impact velocity at Landing wheel well varies between 650 and 730 ft/sec.

• Impact angles can be expected to be larger near wing leading edges because of wing
curvature

– RCC impacts can be as high as 22 degrees in some regions

• Impact angles at the landing wheel well are expected to be less than 10 degrees

– Results for trajectory analysis of foam debris of size = 20”x16”x6” are currently under
evaluation

Summary and Conclusion

Impact analysis (“Crater”) indicates potential for large TPS damage

– Review of test data shows wide variation in impact response

– RCC damage limited to coating based on soft SOFI

- Thermal analysis of wing with missing tile is in work

– Single tile missing shows local structural damage is possible, but no burn through.

– Multiple tile missing analysis is on-going M/OD criteria used to assess structural impacts of tile loss.

– Allows significant temperature exceedance, even some burn
through

- Impact to vehicle turnaround possible, but maintains safe return capability

Conclusion

-Contingent on multiple tile loss thermal analysis showing no violation of M/OD criteria, safe return indicated even with significant tile damage.

FMI: http://spaceflight.nasa.gov