Space Station Stability Studies, 1980s

Manned spacecraft are generally fairly compact objects, so any changes in their shape due to what's going on inside are unimportant, or at least don't degrade the vehicle's function. The International Space Station is different, being 356 feet wide by 239 feet long by 66 feet high with a mass of about a million pounds -- the dimensions (though certainly not the form) of a tall football stadium without end-zone seating. Such a rangy object, made of the lightest-weight materials that will keep the pieces connected and sealed, is capable of "ringing" like a bell once any vibration is set up. In the vacuum of space, the only inherent damping of such vibrations is due to internal friction of the structure.

We at the Lab couldn't know the exact numbers in 1980-81, since NASA wasn't ready to specify them then. But we knew what the problems would be: aside from being tiresome to the crew, the station's arrays of sensors for observing Earth or space would work better if we could limit the wobbles. NASA asked us to study the use of computer-controlled small jets (like those that steer spacecraft) and Control Moment Gyros (CMGs) for stabilization. CMGs are familiar to many people as the active elements in gyro-stabilization of ships: much larger and heavier than a child's toy gyro, to store lots of angular momentum. They have the advantage over jets of requiring no expendable fuel, needing only enough electric power to keep them spinning and under control.

As a discipline, this was closer to the mathematics of spacecraft guidance than to the digital electronics expertise of the AGC veterans, but we brushed the dust off our calculus textbooks, groped our way through books explaining the theory, and buckled down. Some of it was fun, and it was considerate of the Lab to keep its digital people occupied in an engineering sort of way, but we had to swallow the fact that NASA wasn't interested in pushing the edges of computer technology any more.

Those of us who felt committed to computer science and engineering began looking around and drifting away. That's why I left an apparently secure lifetime career post at the Lab at the end of 1981, and jumped into the exciting though unstable world of startups.