On Sun, Jul 15, 2012 at 5:24 PM, Magnus Danielson <mag...@rubidium.dyndns.org> wrote:
> The benefit of WAAS and EGNOS is that they have a fixed location in the sky. > so you could use a highly directional antenna, like a parabolic antenna, > which would provide suppression of most jamming signal unless they are > overhead. I've seen a military GPS antenna that was a large phased array. I guess the idea was to use the almanac to track the moving GPS sats. The goal was to reject jammers by using a dozen or so synthesized pencil beams. (like a radar in a fighter jet) You could not put this in a hand held device as it was as BIG. That is the main problem with directional antenna they need to be large with respect to the wavelength. I don't know if this ever was used in a real deployed system. I think this antenna type was also the design proposed for a distributed low orbit comms system too. The current geo-sync comm-sats make for simple antenna but all of the proposed tactical "launch on an hour notice" comm-sats would be in LEO (low earth orbit) and launched with something like Pegasus or a re-purposed ICBM. The problem is that having a few dozen low power sats in LEO seriously complicates the portable ground stations, hence experiments with flat-plate phased array. THis is a very active research area. The very last payload deployed by the Space Shuttle was "pico-sat" a 5x5x10 inch satellite. It was built at the place I worked at as a test of a new pico-sized bus. This example had some sensors but really the test was if the thing could be commanded from the ground and do anything usfull at all. Look at the photo in the link. The sat is the box inside the bigger box. One of the recent innovations was to cut out patterns in sheets metal and stack many sheets to create a 3D tank and plumbing system with integrated rocket nozzles. The goal was to reduce costs by having a design that can be manufactured by robots. http://www.space.com/12354-final-space-shuttle-satellite-deployment-picosat.html So YES "everyone" knows these big satellites are targets. In a major war with a sophisticated enemy they would be gone soon. So the plan is to design systems that can be built stored and launched on VERY short notice in very large numbers. This kind of research has maybe a 25 year horizon maybe longer as you need to build up a new "eco system" of space qualified parts and engineers familiar with them and do many launches and tests. Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.