Time in calculus of satellite position from ephemeris data

Discussion in 'GPS Technical Discussion' started by odile, Feb 9, 2023.

  1. odile

    odile

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    Hi,
    I'm trying to determine the position of a satellite from ephemeris data but i'm facing several problems, if anyone could help :

    1. From what i can find on the internet, the first thing to do is to compute time tk as :
    tk=t−toe
    toe is time of emission given in ephemerides, i can't understand what does exactly t refer to ? is it time of transmission (also given in ephemerides) ?
    cf Navipedia :
    Code:
    gssc.esa.int/navipedia/index.php/GPS_and_Galileo_Satellite_Coordinates_Computation
    2. Second problem comes when i want to calculate satellite clock offset
    Code:
    gssc.esa.int/navipedia/index.php/Clock_Modelling
    as:
    δt~sat=a0+a1(t−t0)+a2(t−t0)^2

    first, i think t0 is the date given at the beginning of each "block" of navigation data (but i'm not sure about this)
    and once again, what is t ?? :)

    Thank you
     
    odile, Feb 9, 2023
    #1
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