Re: Q: GPS visibility

From: Wayne Hughes (hughes@dogwood.botany.uga.edu)
Date: Wed May 31 2000 - 10:32:14 PDT

  • Next message: Matson, Robert: "RE: Superbird A update flashes please?"

    "Balcewicz, Joseph F" wrote:
    
    > Has anyone reported seeing a GPS (Navstar) satellite with the unaided
    eye?
    >
    > What magnitude might they be?
    >
    
    I figure magnitude 10-12.
    
    Satellite situation report says they have radar cross sections of
    10-100,
    which is higher than many LEO satellites, but then they are also 20x
    farther
    out than LEOs.  I've constructed a little standard curve of magnitude vs
    
    rcs/d^2 function and (given all the simplifications I've made) come up
    with a
    rule of thumb of a magnitude of 7.3 for a satellite with an rcs of 1 at
    a
    distance of 1000 km.  (Yes, I know about paint, shape, angle, diffuse
    and
    specular reflectance (thanks Mike!) - I just want a ballpark figure).
    So a
    GPS with rcs of 20  and a distance of 20,000 km should be 1/20th as
    bright as
    the standard, or 3+ orders of magnitude dimmer.  Somewhere around
    magnitude
    10-11.  I *think* that's close?
    
    I've been watching for satellites with especially low rcs values (the
    tethered
    picosat has one of 0.0001!) to see how far down my 12.5" scope can
    observed
    (it can't see the tethered picosat, but it did get the CSL-04 99057AU
    fragment
    at 1100 km and rcs=0.18 last night).  I noticed in the SSR that geosynch
    
    Galaxy 5 has a rcs of 760 (suggesting magnitude 7-8) and  Glonass 36,
    the
    Russian GPS counterpart, has a rcs of 555.  Could these be right?
    
    Wayne
    
    
    
    
    
    
    
    -----------------------------------------------------------------
    Unsubscribe from SeeSat-L by sending a message with 'unsubscribe'
    in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org
    http://www2.satellite.eu.org/seesat/seesatindex.html
    



    This archive was generated by hypermail 2b29 : Wed May 31 2000 - 10:32:58 PDT