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Finding out what went wrong with the drag chute and looking forward to a new year of challenges

by: Greg Katnik
Interviewer: Brandt Secosh
January 11, l999

First, I would like to take a moment to thank all of you for being a part of the Space Team Online for 1998! 1998 was a very successful year for the space program and was highlighted by many significant events. STS-95 will be remembered as the "John Glenn" flight, but, in the bigger scheme of things, it shows that you don't have to be a 22-year-old athlete to fly into space. The STS-95 flight has brought a whole new reality on the ability of people of all ages to live and function in orbit. STS-95 rejuvenated the public interest in the space program. The number of visitors that came to see the launch of STS-95 far exceeded any other launch in the history of the space program, including the Apollo 11 launch! It captured the imagination and spirit of the world! Madeleine Albright, the United States Secretary of State, visited the Kennedy Space Center Firing Room during the STS-95 launch. She commented, "I spend all of my days mediating between countries disputing something. It was nice to come and participate in something where everybody is working together." STS-95 was a near flawless launch, and I will elaborate on that later in this journal.

1998 also began a new era with the launch of STS-88. We now have hardware components of the Space Station in space that have been successfully mated together. This was completed ahead of schedule with a record number of three incredible space walks. Being so far ahead of schedule, we were even able to do some maintenance work on the solar arrays of the Russian module that hadn't fully deployed and an antenna that hadn't deployed. This showed our ability to deal with unforeseen situations in a totally effective manner.

That leads us into 1999, which will continue to focus on delivery and construction of the International Space Station (ISS) components. The Space Shuttle Processing Facility (SSPF) is currently housing many of these components that will be delivered into space later this year. The ISS program has brought many nations together to obtain the common goal of building the space station and working together in space. It is amazing to me that nations such as Russia were once cold war enemies, and now we all work together with this common goal. Many of the people in our directorate have taken Russian language classes and several have visited Russia to interface with their engineer counterparts. This is also taking place with the 15 other nations involved with this incredible project.

shot of shuttle engines at ignition with red square showing drag chute door in normal position Although 1998 was a spectacular year, we still had situations that kept us very busy and continue to do so. As many of you may recall, during the STS-95 launch a door to the drag chute came off during the launch. Although no significant damage was noted on post flight inspection of orbiter, we are still investigating how this occurred. These photographs were taken by the launch pad cameras during launch and have been a valuable resource in the investigation of this event. Click on either image to see a larger version. In the first photograph, you will notice the red square that shows the drag chute door in its normal position. There are 22 cameras set up in the surveillance mode during each launch. During the STS-95 launch I was watching these particular cameras and at approximately T-4 seconds prior to liftoff I saw something white and rigid falling to the ground past the main engines. In real time this all happened very fast. The person sitting next to me commented, "Was that a white tile that went by?" I responded with "No, it was bigger than that. It was probably a flexible insulation blanket mounted to a carrier panel which would account for the rigidity of the object." I told everybody to keep watching the engines and watch the ascent to make sure nothing else happened. We continued to monitor the ascent and detected no further anomalies.

shot of drag chute door blowing off Although I wasn't sure, I thought the object had struck one of the main engines. My concern at the time was that if the object had struck one of the 1,080 cooling tubes on the main engine nozzle it would cause a puncture. The tubes on the main engines have hydrogen running through them at 4,000 pounds per square inch (PSI), and this is done for two reasons. First, they preheat the hydrogen and, second, they keep the main engine nozzles cool. If the object had punctured one of these tubes a potential jet of hydrogen could have been directed towards the vertical stabilizer of the orbiter. This could have ignited and become a blowtorch causing structural damage and thermal protection problems to the vertical stabilizer. Additionally, this situation could have caused improper operation of the affected main engine.

After announcing that the orbiter had safely reached orbit, we immediately reviewed the tape in slow motion. We clearly saw where the object came from and that it was the drag chute door. In photograph two you can actually see the drag chute and the pyrotechnics that are use to blow the door off to deploy the chute. We now knew what was going on, but the big question was why! The rest of the day was spent collecting video and documenting the sequence of events in preparation to brief management of the situation. The number one consideration at this point was "What does this mean on orbit and reentry?" There are no cameras available to view this area of the orbiter once it is airborne so we did not know if the drag chute was damaged or even if it was still there. The possibilities were that the nylon drag chute was gone, melted by the exhaust plume, or not reliable because of partial damage. Additionally, the pyrotechnics were an issue. The pyrotechnics may have fired already, may be defective or may be an explosion waiting to happen given the right conditions. None of this was known and that led us into exploring all the possibilities for the remainder of the mission. The re-entry plan had to be based on all the unknowns, and contingency plans had to be developed for each potential situation.

We determined that there were three possible scenarios that could give the crew problems in flight. The first one was that the drag chute could deploy during re-entry high in the atmosphere. The lack of air pressure in this mode of flight would cause the chute to just trail behind and not fully deploy. In this scenario, the chute would be jettisoned (released) by the pilot and not cause significant problems. The second scenario was if the chute deployed in the lower atmosphere where the air is more dense and the air pressure is greater. In this scenario, the chute would probably melt from air friction heating and again cause no significant problems. Our main concern was scenario three - the final approach and landing phase. Unlike scenario one and two, this scenario could cause very significant problems. The orbiter does not have the ability to add power during re-entry so the flight profile for this kind of glider is just one shot. If the chute deployed during this phase, the drag could cause the airspeed to decrease and place the orbiter in an unsafe landing profile. The possible results could be that the orbiter may not make the runway and that the airspeed would get so slow that a stall condition could occur. Additionally, the deployment of the chute would also cause the nose of the orbiter to pitch up and cause controllability problems.

The solution to this scenario was to have the pilot ready to jettison the chute if this happened. The commander would be ready to recover from the initial nose up attitude. Once the chute was jettisoned the nose of the orbiter would pitch back down and the commander would regain the correct flight profile for landing. We also had an astronaut trailing the orbiter in a Gulfstream aircraft with high power binoculars monitoring the condition of the chute. When the orbiter landed, we found virtually no damage to the chute. Nevertheless, we disconnected the pyrotechnics from the drag chute bay area and noted that the drag chute nylon holding straps were still in place with minor discoloration from the heat. Now that the orbiter was safely home, we went to the next phase of our investigation - why?

In gathering evidence and trying to piece this all together we had gone to the pad to find the drag chute door. We had found 22 pieces of the door that had shattered due to the velocity of the impact on the launch pad. The door was reconstructed for evaluation. Amazingly, no damage was noted to the main engines of the orbiter. There was only one white mark on the main engine nozzle that indicated any impact. Keep in mind that if this had hit one of the cooling tubes on the engine nozzle it could have been an entirely different situation.

Our ongoing investigation has shown that all the characteristics of the metals used for the drag chute door met all the correct criteria, the door was installed properly for launch. The shear pins to the door were fractured; however, they fractured under load and in a nominal manner. Therefore they worked properly. Since we could find no problems with the door itself or the orbiter structure, we are now looking at environmental factors, such as acoustic shock waves and vibration for the cause.

As you can imagine, being an Investigative Systems Engineer has provided me with many challenges in problem solving and provides a great example of the kind of work engineers do. When we solve this mystery I will be sure to update you right here on the Space Team Online web site. Until then, best wishes for the New Year and thanks for your support of the space program. I know this will be another great year!


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