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    Re: Navigation using satellite doppler shift
    From: Peter Monta
    Date: 2016 Jan 30, 22:25 -0800

    EPIRBs and COSPAS/SARSAT use this in reverse for the sat to find the EPERB.

    Yes---DORIS as well.

    I know this is not exactly celestial navigation but I was wondering how accuratly you could get a fix by observing the Doppler shift as a satellite goes by. Certainly with the amateur communication satellites one can observe a significant shif in the UHF or VHF frequency, and it should be easy to automate measuring this with a cheap software defined radio dongle (like a TV dongle). I wonder how accurate the frequency is on the oscillators and how accurately we know teh emphemeris data? My guess is provided the orbit is fairly well known it should be as accurate as an EPIRB (a couple of nautical miles). 

    I think it depends on the satellite.  For example, Iridium uses OCXOs (ovenized crystal oscillators), which are good but not in the same class as the rubidiums or PHMs on GNSS satellites.  There has been some discussion on NavList of doing optical navigation with satellite photography, as they did with PAGEOS in the 1960s, and it would be helpful to have better orbits than the TLE services provide (~few hundred meters for LEO).  This is identical to doing photographic lunars, just with moons that are a lot closer and dimmer and subject to perturbations---they have high-maintenance orbits, unlike the big guy.

    A network of inexpensive receivers camped out on various ad-hoc satellite signals, and using GPS as a reference, would be just the thing, if orbits are not otherwise available.  Do the commercial LEO constellations (Iridium, Globalstar, Orbcomm, etc.) publish meter-quality orbits as a public service?  Surely they all have GPS on board.  Anyway, once good orbits are available, what you propose is then similar to TRANSIT, as you mentioned (or perhaps "assisted TRANSIT", with ephemeris information from this external source).


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