Re: Reason for FIA Radar 1/USA 215 retrograde orbit?

From: Leo Barhorst (
Date: Sat Oct 02 2010 - 00:47:08 UTC

  • Next message: Brian Weeden: "Re: Reason for FIA Radar 1/USA 215 retrograde orbit?"

    Guess 1: Possible.
    Guess 2: also possible, but the Israeli launch into a 143 degrees 
    inclination orbit in order to avoid launching over Arab countries.
    Greetings and clear skies,
    Leo Barhorst Almere The Netherlands
    Cospar 4252  52.3717 N 05.2580 E -3 m MSL
    ----- Original Message ----- 
    From: "Allen Thomson" <>
    To: "SeeSat" <>; <>
    Sent: Saturday, October 02, 2010 1:00 AM
    Subject: Reason for FIA Radar 1/USA 215 retrograde orbit?
    I've been doing a bit of head-scratching about the reason for the retrograde 
    orbit of FIA Radar 1, aka USA 215, and have only come up with a couple of 
    guesses.  If anybody can provide others or comment on the two presented 
    here, it would be appreciated.
    Guess 1:  If the satellite does in fact carry a synthetic aperture imaging 
    radar (SAR), the orbit may have been chosen to increase the doppler shift 
    returned from objects on or near the ground vs what would be returned from a 
    prograde orbit at the reciprocal inclination (57 deg). SAR processing 
    exploits doppler to encode position on the ground in one dimension, and so 
    the greater the doppler spread, the finer the spatial resolution 
    corresponding to each frequency bin.  Retrograde orbits have greater 
    velocity-over-ground than prograde ones, hence greater doppler and total 
    doppler spread.
    Guess 2: Highly retrograde orbits can give greater frequency of 
    coverage/shorter revisit times than prograde and near-polar ones. The 
    Israeli Ofeqs are a notable example of this.
    This is all very nebulous, but there has to be a reason for the retrograde 
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