“Columbia Accident Investigation and NASA’s Return to Flight”
Dr. Matt Melis is a ballistic researcher at NASA’s Glenn Research Center. He worked on a portion of the investigation following the Columbia Space Shuttle disaster and presented us with background information on this tragic event. He also showed some of the work performed in his lab to get the shuttles safely back on the pad and NASA flying again.
As a primer, Dr. Melis discussed how the launch vehicle works. He gave an overview of the shuttle system and additional information on its three major components: the boosters, the external tank, and the orbiter. Together these three components are known as the stack.
The first component of the shuttle system is its two huge boosters pre-filled with solid rocket fuel. The boosters put out 3.3 million pounds of thrust and initial steering. As the solid fuel burns off, it loses mass at an outstanding rate, approximately the same as losing four pick-up trucks of mass per second. After burnout, the boosters are ejected from the system, coast for several more miles, and then fall into the ocean under parachute to be recovered by a diving team and boats.
The second component of the shuttle system is the external tank, which holds a section of hydrogen and a section of oxygen for fueling the shuttle engines. This capsule is spray-coated with a thick layer of insulating foam, which keeps condensation off the tank in the humid Florida air, which can cause ice crystals to form, and also keeps the fluid inside regulated and keeps it from boiling off. This tank contains fuel for the first forty minutes of flight, and then detaches. This tank is the only non-recoverable portion of the shuttle system.
The final component of the system is the orbiter, which has three main engines. The orbiter burns 750 gallons of hydrogen and 280 gallons of oxygen per second. Furthermore, the orbiter is what houses the astronauts, the space station equipment and the scientific equipment.
After this introduction, Dr. Melis discussed the events surrounding the initial damage to the Columbia, through its attempted reentry into the atmosphere, to the debris field created by the catastrophe. Dr. Melis first showed a video of the shuttle liftoff, showing the foam bipod ramp flying off and impacting the orbiter. At that time, the scientists and engineers were uncertain as to where exactly the foam hit the shuttle. They believed it was either on the leading edge of the wing, or on the foam tiles on the wing itself. The foam bipod ramp is what Dr. Melis describes as a design flaw, which is ultimately inherent within everyday life. Typically these design flaws are built in, and are only found after a disaster such as this. Dr. Melis explains that this design flaw can be beast attributed to the immaturity of the aerospace program and engineering at the time of its inception. Software and other engineering tools have since advanced, reducing the chances of such design flaws.
Several weeks were spent gathering pieces from the massive debris field stretching through several state lines. People worked together in one large room to fit together the world’s largest jig-saw puzzle. Tables were set up to reassemble the foam tiles from the orbiter, and special acrylic holders were built to reassemble the pieces of the leading edge spar of the wing. The engineers believed that the fatal damage was caused by the foam impacting either the foam tiles or the leading edge. This is why the investigation paid special attention to reassembling these sections carefully.
The leading edge of the wing was made from reinforced carbon carbon. Parts of the recovered spar were shown to have a particular wear and burn pattern that caused the scientists and engineers to conclude that the foam did in fact hit and damage the leading edge of the wing.
Dr. Melis and his team performed thousands of tests in their lab with foam material hitting pieces of this reinforced carbon carbon material. Much to their astonishment, a piece of foam weighing as much as a sheet of paper, was able to snap a coupon-sized piece of the material in half at 500mph. Based on the video evidence of the Columbia flight, a much larger piece of foam impacted the craft at 700 to 800 ft/s (500mph).
Many teams worked together to prepare an actual section of a spar to re-create the incident. High speed cameras were placed both inside and outside of the spar section to capture the impact of a large piece of foam impacting the section. The foam was shot at the spar at an angle such that it just grazed the material, traveling at 500mph. The impact, though not direct, was forceful enough to put a hole the size of a pizza box into the leading edge.
After reconstructing what had happened in the Columbia accident, Dr. Melis presented the next steps taken by his team in order to get the shuttles back into flying condition. Thousands more tests were run in their lab, making projectiles out of any type of debris that could be found near the shuttle at liftoff time, such as foam and ice. All parts of the shuttle were tested, such as the tiles, the windows, and of course the leading edge reinforced carbon carbon.
After much hard work, and some design improvements, men would return to space again on July 26, 2005. Part of Dr. Melis’ testing in the Glenn Ballistics Lab lead to new flight procedures, making it mandatory for a team to inspect the entire pad and the shuttle system just before launch to relieve it from debris. The Columbia accident was a tragic event and a severe price to pay, though many other design flaws aside from the weak bipod ramp were discovered and fixed. The lessons learned from the Columbia accident reconstruction will help to ensure safer space travel in the future of NASA.