The backstory from the 1990s on the NASA shuttle flight and a Macintosh IIfx.... In partnership with the Italian Space Agency, NASA flew a mission on the Space Shuttle called the Tethered Satellite System which would deploy a spherical satellite attached to the end of a 20-km long conducting tether covered in Kevlar attached to the Shuttle for ionospheric research. That research required connecting the electrical circuit with the ionosphere by collecting electrons at the satellite end, flowing electrons down the tether, and dumping the electrons at the Shuttle end via electron guns. That was the theory, at least.
What happens when you flow a current through a wire? Why, you get a magnetic field. And the Earth is surrounded by a magnetic field of its own. These two magnetic fields can interact to cause a force on the wire (the motor effect). A really talented part of the team I was on developed a simulation on one of the most powerful computers they could get their hands on at the time - a Macintosh IIfx. Several of us acquired IIfx's so that we could run the simulation. The simulation showed that certain situations could arise where the force pushes the tether to the side in such a way to cause a reinforcing resonance. We commonly call that "skip rope." Yep, the tether could have become one giant skip rope with the satellite on one end, and the Shuttle on the other. And unfortunately that skip rope could have overwhelmed the satellite's attitude control system leading to a loss of control, leading to a bad day.
Using the simulation, we devise a way to maneuver the Shuttle end to damp the skip rope. Much like you would do on the playground, moving your hand in a certain way reinforces the skip rope, and another way can cause the skip rope to stop. That was what we devised to get rid of skip rope if it were to arise. Another key part of the simulation was detecting skip rope based on measurements from the attitude control system and scientific instruments on the satellite end, and make the information available to the team working in Mission Control. It was one of the coolest introductions I got into my now 30+ career in the space business into engineering, software development, rocket science, and teamwork.
So, what happened? The Tethered Satellite System flew on Shuttle mission STS-46 in Summer 1992, and unfortunately due to a problem in the tether deployment mechanism was only deployed to about 250m, well short of the 20 km sought, and not enough of a potential difference over that length to flow current. We tried again in early 1996 on Shuttle mission STS-75, and this time we almost made it to the 20-km point when a flaw in the tether sheathing (the Kevlar I mentioned earlier) allowed the current in the tether to arc against structure in the Shuttle payload bay that caused the tether to break. We never got the chance to put our skip rope detection and mitigation techniques originally developed on a Macintosh IIfx into play.
Here is a NASA link about the Tethered Satellite System:
https://science.nasa.gov/missions/tss
And to answer James's question, the skip rope simulation was a text-based one.
I still have a piece of the 2.54-mm diameter tether in my office desk as a treasured memory. Unfortunately the Macintosh IIfx is long gone, hence why it is on my personal grail list. Hope y'all enjoyed the backstory!
