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

From: Brian Weeden (brian.weeden@gmail.com)
Date: Sat Oct 02 2010 - 01:36:56 UTC

  • Next message: Jim Nix: "JN 9633 Obs Oct 02"

    I concur with Leo's point about the Ofeqs.  They are retrograde because of
    the location of Israel and in what direction it can safely launch.  Being
    surrounded on 3 sides by other countries which might object to having
    missiles fired in their direction or hot rocket stages dropped on their
    territory, Israel has no choice but to launch westward across the
    Mediterranean.
    
    This is part of the reason that Israel has partnered with India to launch
    satellites on the PSLV.  TECSAR, a radar reconnaissance satellite launched
    in 2008 on a PSLV, is in a 41 deg inclination orbit.
    
    ---------------------------
    Brian
    
    On Sat, Oct 2, 2010 at 2:47 AM, Leo Barhorst <l.barhorst@upcmail.nl> wrote:
    
    > 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" <thomsona@flash.net>
    > To: "SeeSat" <SeeSat-L@satobs.org>; <hearsat@mailman.qth.net>
    > 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
    > orbit.
    >
    >
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