Along for the Ride
A NASA mission specialist operates SwRI’s Liquid Motion Experiment onboard a 1997 flight of the space shuttle.
SC-1 Spacecraft Computer
The Space Experiments with Particle Accelerators (SEPAC) flew aboard shuttle missions in 1982 and 1992.
The space shuttle Atlantis successfully completed its 14-day mission July 21, 2011, when it touched down at the Kennedy Space Center. That landing marked the end of the space shuttle program. During its 30-year journey, SwRI was along for the ride, providing technical expertise in everything from avionics to propellant dynamics.
A number of technologies developed by SwRI researchers for the shuttle program remain viable for today’s spacecraft as well as a host of other applications. Technology Today asked Bill Gibson, assistant vice president of the Space Science and Engineering Division, and Danny Deffenbaugh, vice president of the Mechanical Engineering Division, to offer their reflections on SwRI’s space shuttle research and how these technologies are now helping industry.
TT: In what aspects of the shuttle program has SwRI participated?
Gibson: Southwest Research Institute has been an active participant in the space shuttle program from the early 1980s to the end of the program. First, we should recognize the shuttle’s place in U.S. space history. The shuttle served as the primary heavy-lift launch vehicle, as well as the only U.S. crew-rated vehicle, for over 30 years. It is indeed an engineering marvel, albeit an imperfect marvel. No other launch vehicle had the performance needed to transport the massive components of the International Space Station (ISS) to orbit. The list of other critical launch services provided by the shuttle includes the Hubble Space Telescope along with spacecraft such as Galileo, Chandra and many others. The end of the shuttle program closes one era of U.S space flight and opens another in which transport to low Earth orbit will be provided in large part by commercial organizations using modified versions of existing vehicles. Hopefully the funding which for 30-plus years has supported the shuttle infrastructure and operational costs can now be applied to a new-generation, heavy-lift launch vehicle to take us back to the Moon and perhaps more distant locations in our Solar System.
Deffenbaugh: Our early involvement during the design and development phase of the shuttle program included propellant dynamics, shuttle main engine reliability and structural integrity. The Institute’s legacy reputation in propellant dynamics really opened the door for many of the other activities in support of this impressive launch system. During the operational phase of the program we provided payloads aboard the orbiter, as well as technology support to address various operational problems. The most high-profile involvement was of course the definitive test that confirmed that foam from the main propellant tank could indeed create a failure of the leading edge of the shuttle wing structure that resulted in the fatal accident of the Columbia orbiter. We continued to support NASA in return to flight activities as well as supporting analysis for all remaining Shuttle flights to the end of the program.
TT: When did SwRI begin working on space launch vehicles?
Deffenbaugh: The Institute’s first launch vehicle program was in the late 1950s and was an investigation of the Redstone rocket for the Army. This investigation addressed the effect of liquid dome impact when a missile lost power suddenly while still in the atmosphere. We also invested propellant liquid sloshing and a fluid-structure phenomenon, referred to as “pogo” oscillation, on many early launch vehicles. We have been involved in almost every major launch vehicle development programs since, including Jupiter, Saturn I-V, Atlas, Titan and the shuttle. One propellant project was in support of the Apollo lunar lander. During the first two Apollo missions that landed on the Moon, the module’s fuel gauge falsely read empty, but the crew members went ahead with the landings. The cause of the false reading was propellant sloshing and the solution was to limit the liquid motion.
TT: Besides the propellant dynamics work, what other programs did SwRI contribute to during the design and development of the shuttle?
Deffenbaugh: SwRI was involved in both structural integrity and main engine reliability. NASGRO®, a software program developed jointly by SwRI and NASA Johnson Space Center (JSC) for analyzing metal fatigue and fracture, was initially developed and released in the 1980s for fracture control analysis of NASA space hardware, and the space shuttle in particular. NASGRO was the standard code used for meeting fracture control analysis requirements on the space shuttle. NESSUS® (Numerical Evaluation of Stochastic Structures Under Stress) was originally developed by a team led by SwRI as part of a 10-year NASA project to produce a probabilistic analysis tool for assessing the failure probability of critical components in the space shuttle’s main engines.
TT: What SwRI science payloads have been flown aboard the shuttle?
Gibson: One of the more significant Institute projects involving the shuttle was the Space Experiment with Particle Accelerator (SEPAC). SwRI teamed with the Institute of Space and Astronautical Sciences (ISAS) in Japan to develop a 10-kilowatt electron beam accelerator and an array of diagnostic instruments in an attempt to create an artificial aurora borealis. SEPAC flew for the first time on STS-9 in 1982 and a second time on STS-45 in 1992. A significant number of scientific papers resulted from the two SEPAC flights. I should note that the SwRI-developed SC-1 computer was designed for use on SEPAC and has since seen duty on more than 50 space science and defense missions.
The Southwest Ultraviolet Imaging Spectrometer (SwUIS) instrument was another of the Institute’s space science projects using the shuttle as a platform for space science. The SwUIS was operated by the shuttle crew on orbit and used for observing comets among other targets.
Deffenbaugh: Another experiment that flew aboard the shuttle helped SwRI to improve attitude control systems for spacecraft. More than half of all on-orbit satellites spin by design, whether to obtain gyroscopic stiffness to control propellant location in the fuel tanks or to distribute solar heat loads. If a spinning spacecraft begins to wobble, the attitude control thruster must be fired. If the amplitude grows too rapidly and the thruster must be fired often, the liquid fuel is used at a faster rate and lifetime in orbit is shorter than expected. The SwRI-developed Liquid Motion Experiment (LME) was flown aboard the space shuttle STS-84 in May 1997. The results have provided validation to our predictive models for designing better attitude control systems.
TT: How did SwRI ‘s engineers contribute to problem-solving associated with the shuttle program?
Deffenbaugh: SwRI provided consultation to the NASA Engineering Safety Center (NESC) Materials Technical Discipline Team (TDT). The TDT provides in-depth peer reviews and performs technical assessments for flight-critical problems identified by the various NASA centers. Let me describe a few examples of studies that we did for NESC. A critical high-cycle fatigue cracking problem was discovered in several space shuttle liquid hydrogen flowlines, caused by flow-induced vibrations. Initial deterministic fracture mechanics analyses suggested the fatigue cracks could lead to failure. A detailed probabilistic damage tolerance analysis was then performed to demonstrate an acceptable risk margin.
Another study was to address the reinforced carbon-carbon (RCC) panels that form the leading edge of the airfoil structure of the shuttle. RCC is a composite with a three-dimensional architecture processed to form a silicon carbide (SiC) surface coating that resists oxidation during reentry into the Earth’s atmosphere. Spallation of the SiC coating can potentially expose the RCC panels to excessively high temperatures, which could lead to catastrophic events such as rapid oxidation or burning-through of RCC panels. To assure the orbiter’s integrity and safety, we were asked to develop a methodology for analyzing fiber bridging and resistance-curve behavior in cracked RCC panels with a 3-D composite architecture and a SiC surface coating.
The next study was to investigate the cause of cracking of space shuttle main engine high-pressure oxidizer turbopump knife-edge seals. SwRI performed probabilistic assessments for crack initiation and growth for different scenarios to support decisions about fleet management practices until a redesign was completed.
We have also been supporting NASA for quite a few years studying the integrity of shuttle windows that have been subjected to hypervelocity impacts (>500 m/s), low-velocity impacts (100-500 m/s) and quasistatic damage (bruising). The work is intended to support the reuse of windows and avoid replacing them after each mission.
TT: One of the biggest problem-solving exercises was probably the one that followed the loss of the shuttle Columbia. Can you discuss that?
Deffenbaugh: In 2003, the shuttle Columbia (STS-107) was lost as it re-entered the atmosphere prior to landing. The leading hypothesis was that the accident was caused by an impact during the launch phase. SwRI was called into the investigation within days of the accident. Through computational modeling, reinforced by experimental testing with a large compressed-gas gun, SwRI scientists and engineers helped prove that a piece of insulating foam for the large, exterior fuel tank had broken free and struck the leading edge of one wing of the orbiter, creating a hole that caused the fatal crash.
Early in the investigation, SwRI researchers characterized the insulating foam and thermal tiles for response far into the nonlinear, crush-up region.
In the return-to-flight program that followed that investigation, a main issue was determining risks based on potential impacts. SwRI was involved in the determination of damage to thermal tiles from impacts of a wide range of materials, including insulating foams from the external tank, the tile itself, gap fillers, fabrics and ice. Innovative testing techniques were developed to characterize these materials. Today, these impact data comprise an extensive database of impact results for foam and highly compressible material impacts.
TT: Looking into the future, what do you see as the shuttle program’s greatest legacy for SwRI?
Gibson: There already has been a considerable amount of carry-over in terms of both accumulated scientific knowledge and evolved space hardware, and these continue forward. As examples, a significant number of scientific papers resulted from the two SEPAC flights, and the SwRI-developed SC-1 computer has since flown on more than 50 space science and defense missions. The SwUIS instrument spawned a family of ultraviolet imaging spectrometers that have seen duty on missions such as Rosetta, Lunar Reconnaissance Orbiter (LRO), the New Horizons mission to Pluto and most recently, the Juno mission bound for Jupiter.
Deffenbaugh: As with many other aspects of the space program, new applications have brought shuttle-based research into areas far beyond the original purpose. Substantial recent improvements in NASGRO have made it a more valuable structural integrity analysis tool for a much larger number of potential users, including a number of major aerospace/aircraft companies, such as aircraft and rotorcraft manufacturers, turbine manufacturers and commercial space launch companies, as well as for numerous non-aerospace applications.
NESSUS is now a general-purpose, probabilistic analysis program to compute probability of failure and probabilistic sensitivity measures. It has been widely used for both aerospace and non-aerospace applications such as gas turbines, biomechanics, pipelines, defense, geo-mechanics and civil infrastructure.
Even the impact modeling and testing performed both before and after the Columbia accident have a place in future technology. This work has applications in other areas to understand dynamic crushability of impact safety materials. This potentially could increase the safety and reduce the weight of items such as cars, thus improving fuel efficiency and cutting energy usage.
Questions about this article? Contact Deffenbaugh at (210) 522-2384 or firstname.lastname@example.org.