I wanted a simple program that showed when target spacecraft would be above the horizon. I remembered a picture of an old program that Rob Bruninga posted on AMSAT-BB some time ago. I could not find that picture, but I built something similar and it looks like this: http://www.g0kla.com/klatrack/klatrack_dark.png
It's a simple program that plots the elevation of upcoming satellite passes as a horizontal display and then updates it in real time. It does a one time calculation to fill its buffer of positions, then its pretty efficient because it just calculates the next position it needs in the future.
The details and the download are here: http://www.g0kla.com/klatrack/index.php
Thanks again to Dave Johnson (G4DPZ) for his port to Java of John Maglicane's (KB2BD) predict library.
The is made available under the Gnu GPL and I will upload the code to github when I get a chance.
73 Chris