Published by the MIT News Office at the Massachusetts Institute of Technology, Cambridge, Mass.
Published by the MIT News Office at the Massachusetts Institute of
Technology, Cambridge, Mass.
ENGINEERING TEST Space Shuttle to Carry MIT Experiment Next Fall by Eugene F. Mallove News Office When Discovery rockets into orbit next fall on the STS-48 space shuttle mission, it will be carrying an experiment that is designed to study critical aspects of the mechanical behavior of future space structures. The experiment was crafted by a team in the Department of Aeronautics and Astronautics The experiment, called "MODE"--for Middeck 0-Gravity Dynamics Experiment--consists of special electronically-instrumented hardware that shuttle astronauts will test in the craft's pressurized middeck section. MODE will actually combine two tests of "nonlinear," gravity- dependent mechanical behavior, albeit on a small scale: the sloshing behavior of a fluid in a tank and the vibration characteristics of truss space structures. In an economy of scale, all the power, signal conditioning, and data storage facilities for the two experiments will be combined in one "Experiment Support Module" package, whose return will be eagerly awaited by Earth-bound spacecraft designers. Astronauts will control and monitor the MODE experiments through a key-pad and display unit, with the voluminous data being stored in an optical disk drive. NASA, MIT, and the McDonnell Douglas Space Systems Company are participating in MODE to bring about engineering innovation through a unique organizational effort. MODE is part of NASA's Office of Aeronautics, Exploration, and Technology In-Space Technology Experiment Program. Established in 1987, the program is designed to develop small, technologically innovative experiments from industry, academia, and government. NASA's Langley Research Center in Hampton, Virginia, is the organization responsible for managing the contract. Along with NASA Headquarters in Washington, Langley is providing technical and administrative assistance in integrating the experiment payload into the shuttle. The MODE experiment was awarded to MIT's Space Engineering Research Center in 1987, with Center Director Professor Edward F. Crawley as the principal investigator. Payload Systems, Inc., of Cambridge was selected by MIT to be the prime subcontractor responsible for fabricating and integrating the hardware elements, crew training, and mission support. McDonnell Douglas Space Systems Company of Huntington Beach, California, joined the program in 1989 on a no-cost basis, using its own funds to support the design and construction of the MODE structural test article hardware. Says Professor Crawley, "The value of this exemplary project is in the cooperation among a university research group, an industrial group that will eventually apply the technology to the Space Station, and a government laboratory--working together on a program in a synergistic way. Equally important, at MIT the project has led to involvement at all academic levels--undergraduate, graduate, and postdoctoral." This is also a new kind of experiment in its use of the space shuttle as a "shirt-sleeve" laboratory for experiments involving scale models. The shuttle cabin has of course been used for scientific experiments; MODE's innovation is that it is an engineering experiment. In the part of the experiment designed to simulate fluid behavior in large tanks aboard the space station, a small transparent plastic cylinder containing fluid will be mechanically excited to make the contents slosh about. A force-balance unit will accurately measure the forces caused by the sloshing. The Structural Test Article part of MODE, which was manufactured by McDonnell-Douglas and instrumented by Payload Systems, resembles the truss-structure of a construction crane boom. When deployed in the shuttle middeck, it is a truss beam 72 inches long with an 8-inch square cross-section. The beam structure contains various components, including a model of the Space Station solar array support structure and a prototype of the Space Station alpha joint, which allows for articulation of the sun-tracking solar arrays. All of these components are expected to behave differently in the weightless environment of orbital flight than on the ground. Eleven acceleration-measuring devices (accelerometers) and four displacement measuring units (strain gauges) will be distributed along the structure. An actuator will excite vibrations within the beam as it floats within the middeck cabin. In the course of the two-day in-orbit testing, astronauts will monitor and videotape the experiments, modifying them when necessary as unexpected conditions arise. Professor Crawley hopes that the innovative design of this relatively low-cost experiment will lead to clearer understanding of the physical phenomena that will be studied. The behavior of the alpha joint, fluid slosh, and deployable structures are among the critical dynamics issues for future space missions. The knowledge gained in MODE, says Professor Crawely, should, indeed, be applicable to a very wide range of future space activities.