Re: navstar

From: Bjoern Gimle (b_gimle@algonet.se)
Date: Thu Jul 27 2000 - 01:03:55 PDT

  • Next message: bruce_musson@dofasco.ca: "RE: Where was ISS ?"

    > NAVSTAR 48 (USA 151)
    > 1 26407U 00040A   00203.00016569  .00000064  00000-0  10000-3 0   158
    > 2 26407  55.0641 228.3909 0045522 273.8447  85.7199  1.99170076   175
    ...
    > NAVSTAR 48 (USA 151)
    > 1 26407U 00040A   00201.47067160  .00040912 -37353-6  44785-3 0   128
    > 2 26407  39.1123 221.1967 6078237 196.7985 127.6911  4.02681484   123
    
    > So between July 19 and July 20, this satellite quickly had a change in
    orbit.
    > This is the fatest I have ever seen a gps satellite change orbit.
    > I thought it takes a few days to change a satellite's orbit.
    > So what's going on here.
    
    ALLCOLA (or COLA) can be used to find the time of a short-impulse orbit
    change.
    Then, a prediction program like TRAKSTAR, TRACK16 or HANDE can be used to
    find the speed in the two orbits, and the position.
    ALLCOLA gives the date of manouvre 2000-07-19. With the earliest elset (11)
    :
    
    UTC Time    Range Elset Orbit separation
    12:14:25.83 423.5 13 12
    12:23:24.36 6.3   15 6.2
    12:23:27.18 9.4   14 5.2
    
    With elset 12:
    
    12:14:26.99 426.9 13 12.8
    12:23:25.69 7.5   15 6.2
    12:23:28.51 12.5  14 5.1
    
    If the later elsets had larger distances than the first, secondary or
    low-power manoeuvres could be suspected.
    Now, the likely reason is that elset 13 is inaccurate.
    
    Using the elsets 12/15 at time 12:23:25.69, Track16 XYZ xdot Ydot Zdot are:
    (-13861.32  -22020   6052.5) (1.95583 -0.52096 1.36465) before, and
    (-13866.013 -22013.6 6033.5) (2.28915 -0.62697 3.04609) after.
    
    Since the predictions differ, I ought to have picked two predictions closer
    in location, instead of the same time.
    
    The absolute speed difference is 1.42 km/s, but since there is a large
    change in inclination (39 to 55 degrees), and the apogee of the initial
    orbit was higher than the target,
    the speed difference vector (0.33332,-0.10601,1.68144) is larger, and not in
    the direction of flight.
    
    The components of the velocity change, in the direction of original motion,
    are
    1.23 km/s forward, 1.12 km/s left, and 0.44 km/s up.
    
    Since the inclination increase (dogleg to the left) occurred at 13 deg N, an
    increase of the RA of Ascending Node also occurred ( 221 to 228 )
    
    
    -- b_gimle@algonet.se (home)  http://www.algonet.se/~b_gimle --
    -- COSPAR 5919, MALMA,    59.2576 N, 18.6172 E, 23 m         --
    > So between July 19 and July 20, this satellite quickly had a change in
    orbit. This is the fatest I
    > have ever seen a gps satellite change orbit. I thought it takes a few days
    to change a satellite's
    >
    > orbit. So what's going on here.
    >
    > Thanks
    >
    > Kevin Fetter
    >
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