On Tue, Jan 4, 2011 at 12:53 PM, Hal Murray <[email protected]> wrote: > > [email protected] said: >> Similar in concept to waas or tass, the satellite provides a nav signal and >> differential corrections. > >> One of the goals is to make a nav system that performs well (sub meter) in >> urban canyons, which conventional gps does not > > I thought the idea with waas was to correct for the delays through the > ionosphere by measuring the error at a known (nearby?) location and > broadcasting the correction. The idea is that a nearby location would have > similar delays and similar errors. > > I thought the problem with urban canyons was multi-path and blocked signal. > How is a correction for ionospheric delays going to help that? > > I must be missing something interesting. > > > [email protected] said: >> >As far as I know, it is a geo-synchronous polar orbiting D-GPS system. >> Duh! "Sun-synchronous" of course. > > The original crunchgear article said they needed 3 satellites to get 24 hour > coverage. > > I can't picture an orbit pattern that's going to use 3 satellites. Geosync > would work with one satellite, but Japan is fairly far north. Are they doing > something like picking the orbit height and inclination angle so that the > satellite period is 24 hours and over Japan rather than the equator at the > right time?
I think 12 hour period My guess is it is a "Molniya orbit" It is very highly eliptic with a 12 hour period. You can cover all of Japan with only two satellites. >From the point of vie of someone on the ground they tend to hover at about 63 degress N lat. You can get continous coverage with only two sats but with three you never have to have a view clear to the horizon -- ===== Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
