Matt Melis is one of the foremost experts on the Space Shuttle program. He played a critical role in the Columbia accident investigation, and the return to flight of the Space Shuttle program. He has also worked in the ballistics laboratory at NASA Glenn Research Center, along with being an accomplished artist.
Melis gave an extensive lecture to the NASA Space Academy beginning with an overview and history of the Space Shuttle, the Columbia accident including detailed notes on what went wrong and the lessons learned, and the Space Shuttle “Return to Flight” program in which he was involved.
The Space Shuttle when fully assembled is referred to as “The Stack” and consists of the iconic Orbiter space plane combined with external tank and two solid rocket boosters. The solid rocket boosters can create 3.3 million lbs of thrust to lift the shuttle through the lower atmosphere. The external tank is a very thin (~1/8”) aluminum shell holding an upper tank of liquid oxygen, and a lower tank of liquid hydrogen. The tank is heavily insulated with closed cell urethane foam to keep the oxygen and hydrogen cold and in liquid form for approximately 8 hours between the fill and lift off.
Along with the solid rocket boosters, the Orbiter itself is capable of creating an enormous amount of thrust, creating 3,000 lbs of water vapor per second via combustion in its engines. To keep the launch pad intact during launch, the pad is flooded with water for cooling and to suppress vibration. Both the orbiter and the two solid rocket boosters are recovered after launch, but the external tank burns up in the atmosphere upon re-entry.
Due to Melis’s prior high speed ballistics work, he was recruited for the Columbia accident investigation, a three month project which turned in to 4-1/2 years of work. During takeoff, the bipod ramp section of the external tank’s insulating foam covering the liquid hydrogen and liquid oxygen intake ports broke off and impacted the left wing at approximately Mach 2.4. It was known during design that the bipod ramp could detach and impact the shuttle, but the damage estimate was unknown and underestimated. This incident was seen on the launch video and analyzed for structural damages. Unfortunately, it was determined that the damage would pose no threat to the shuttle — a fatal mistake.
During re-entry, the Orbiter experiences an enormous amount of heat generation due to atmospheric drag. The hottest parts of the shuttle (i.e. the wing leading edge) are covered with carbon fiber reinforced carbon tiles. After the Columbia broke up on re-entry, the wreckage was reassembled to investigate the exact cause of the accident.
From 3D reconstruction of the pieces of wreckage, it was found that a hole developed on the left wing of the Columbia in the location of the foam impact. The hole in the carbon heat shield allowed extremely hot plasma gasses to enter into the sensitive interior of the wing, blowing out the trailing edge.
To fully prove that the initial foam impact caused this event, Matt Melis was enlisted to perform high speed ballistic tests at Glenn Research Center’s Ballistics Laboratory utilizing the exact foam and panels used on the Space Shuttle. Small scale tests and computer models made it evident that the foam shot at high speed was fully capable of punching a hole clean through the carbon fiber reinforced carbon heat shield tiles. A full-scale test was also set up by building a large wing tip section and firing a piece of foam at high speeds at the wing. Even a glancing blow was capable of causing fatal damage to the shuttle wing.
A lot of lessons were learned from the Columbia incident. Most importantly, you cannot simply follow your intuition when it comes to high-speed travel and space flight. Nobody had the foresight to understand how dangerous impacts from soft foam could be until the experimental evidence was compiled.
After the accident, foreign object impacts were taken far more seriously. Carbon-reinforced carbon fails differently for different projectile materials and speeds (i.e., bending mode, shear mode, cracking mode). In order to fully study impact possibilities, many high speed cameras capable of nearly 30,000 frames per second are used to image high speed impacts of various shuttle materials.
It was also determined that better video needs to be taken during shuttle launches. The foam impact on the leading edge of the Columbia was extremely poor quality, and was obstructed by the top of the shuttle wing. High definition telescope video tracking stations are now used to watch every piece of the shuttle during launches.
A focused inspection arm was also added to the Space Shuttle’s Canada arm. When in space, this arm can now view all sections of the Space Shuttle and send back high resolution images to ground crews for analysis. A backwards roll is also performed before docking with the international space station, so the shuttle’s heat shield can be inspected for damage.