Columbia Disaster

The loss of Columbia was a result of damage sustained during launch when a piece of foam insulation the size of a small briefcase broke off from the Space Shuttle external tank under the aerodynamic forces of launch. The debris struck the leading edge of the left wing, damaging the Shuttle's Thermal Protection System (TPS), which shields it from the intense heat generated from atmospheric friction during re-entry.

(Space Shuttle external tank is the component of the Space Shuttle launch vehicle that contains the liquid hydrogen fuel and liquid oxygen oxidizer. During lift-off and ascent it supplies the fuel and oxidizer under pressure to the three space shuttle main engines)

The enquiry conducted subsequent to the disaster revealed glaring engineering / managerial/ethical lapses. Some of these were:

       a)   NASA's original shuttle design specifications stated that the external tank was not to shed foam or other debris; as such, strikes upon the shuttle itself were safety issues that needed to be resolved before a launch was cleared. Launches were often given the go-ahead as engineers came to see the foam shedding and debris strikes as inevitable and unresolvable, with the rationale (without any concrete scientific basis) that they were either not a threat to safety, or an acceptable risk. The majority of shuttle launches recorded such foam strikes and thermal tile scarring. During re-entry of Columbia, the damaged area allowed the hot gases to penetrate and destroy the internal wing structure, rapidly causing the in-flight breakup of the vehicle.

  c) NASA's chief thermal protection system (TPS) engineer was concerned about left wing TPS damage and asked NASA management whether an astronaut would visually inspect it. NASA managers never responded.

    d)    Throughout the risk assessment process, senior NASA managers were influenced by their belief that nothing could be done even if damage was detected. This affected their stance on investigation urgency, thoroughness and possible contingency actions. They decided to conduct a parametric "what-if" scenario study more suited to determine risk probabilities of future events, instead of inspecting and assessing the actual damage. The investigation report in particular singled out NASA manager Linda Ham for exhibiting this attitude.

     e)     Damage-prediction software was used to evaluate possible tile and RCC (Reinforced Carbon-Carbon) damage. The tool for predicting tile damage was known as "Crater", described by several NASA representatives in press briefings as not actually a software program but rather a statistical spreadsheet of observed past flight events and effects.        

f)     The "Crater" tool predicted severe penetration of multiple tiles by the impact if it struck the TPS tile area, but NASA engineers downplayed this.       g)    The program used to predict RCC damage was based on small ice impacts the size of cigarette butts, not larger SOFI (Spray-On Foam Insulation) impacts, as the ice impacts were the only recognized threats to RCC panels up to that point.

      h)     Under 1 of 15 predicted SOFI impact paths, the software predicted an ice impact would completely penetrate the RCC panel. Engineers downplayed this, too, believing that impacts of the less dense SOFI material would result in less damage than ice impacts. In an e-mail exchange, NASA managers questioned whether the density of the SOFI could be used as justification for reducing predicted damage. Despite engineering concerns about the energy imparted by the SOFI material, NASA managers ultimately accepted the rationale to reduce predicted damage of the RCC panels from “possible complete penetration” to “slight damage to the panel's thin coating”.

End note: On July 7, 2003 foam impact tests were performed by Southwest Research Institute, which used a compressed air gun to fire a foam block of similar size and mass to that which truck Columbia and at same estimated speed.

To represent the leading edge of Columbia's left wing, RCC panels from NASA stock, along with the actual leading-edge panels, which were fiberglass, were mounted to a simulating structural metal frame. Over many days, tens of these blocks of foam were shot at the wing leading edge model at various angles, aimed at different specific RCC panels, most of which produced only cracks or surface damage to the RCC.

In the final round of testing, a block fired at the side of an RCC panel created a hole 41 by 42.5 centimeters (16 by 16.7 in) in the protective RCC panel. The tests clearly demonstrated that a foam impact of the type Columbia sustained could seriously breach the thermal protection system on the wing leading edge.