[Using attitude control]... > We could mount microwave antennas on a nadir-facing > surface and provide consistent, predictable, strong, > wideband signals to ground stations during a pass.
The problem with LEO satellites is that a nadir facing antenna does give great gain directly overhead ground stations, but only for about the center 2 minutes of only the one direct overhead pass a day. The problem with facing antennas "down" on a LEO satellite is that 90% of the users are not "under it", but to the side of it. For example, lets say that we put relatively high gain antennas facing down giving about a 45 degree antenna pattern (say around 10 dB). Now looking at the total time that ARISSat is above 45 degrees, turns out to be about 3 minutes a day or less than 10% of all the time it is in view to any one ground station. But as you say, it is a great advantage if the objective is to provide a 2 minute comm. window to anyone on the planet once a day, then such a design does give as much as 16 dB or so advantage over an omni antenna on a satellite. Anyway, just a thought. Bob, WB4APR _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
