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http://www.youtube.com/watch?v=gYGe8jiI-II

This is a video of a bunch of students at the Georgia Tech ham radio club contacting Tony England, W0ORE in 1985 on 440 Mhz FM.

It is an opportunity for a little digression about satellite tracking. A true tracking system has multiple directional antennas all slightly offset, so that if the signal source is slightly off-axis, it will appear stronger in one antenna than the other. Therefore the antenna can be repointed. Once the original source is acquired, the tracking system is locked to it and continues to follow the source.

Real tracking systems are expensive and require a good steady signal to remain locked. See the film _The Dish_ for an example of what happens when the signal is briefly interrupted. In the days when computers were expensive, though, it was the easiest way to track a satellite source. You only needed to calculate where the satellite was at one time in the day (hopefully when it first came over the horizon) and you could stay locked once you had it.

These students did not have that degree of sophistication, but they made up for it with the staggeringly fast computational power of a Commodore 64. They downloaded keplerian elements for the shuttle from a NASA BBS. Using these constants and Kepler's equations they were able to calculate the position of the shuttle at any time; it took a few minutes to churn through all of the sines and cosines using interpreted basic on an 8-bit fixed-point machine, but that was sufficient.

The satellite antenna was on an azimuth/elevation mount with potentiometers connected to the azimuth and elevation motors. These were connected to the joystick inputs of the computer. The computer therefore could sense the direction of the antenna, calculate the direction the antenna should be pointed in, and then open and close motor switches to repoint the antenna.

Once the antenna was pointed at the shuttle it was just a matter of listening and calling and calling and listening and listening some more on the shuttle ham frequency until someone picked up the radio on the other end.

Kludge can be seen somewhere in the background but is effectively indistinguishable from all the other geeks.

shuttle (last edited 2012-11-30 19:34:45 by sauron6)