Re: USA193 decay

From: Brian Weeden (brian.weeden@gmail.com)
Date: Fri Feb 01 2008 - 12:49:16 UTC

  • Next message: Ted Molczan: "Updated elements of USA 193"

    I think there are a couple of issues compounding the problem with
    calculating the decay rate using the flux values.  First, the flux
    values are not very good predictor of atmospheric density.  NASA is
    moving towards a different approach using atmospheric models
    calibrated using on-orbit satellites.  See the following papers for
    more info on this HASDM model:
    
    http://esa-spaceweather.net/spweather/workshops/eswwII/proc/Session2/doornbos_esaspaceweatherweek2005.pdf
    http://sol.spacenvironment.net/~JB2006/pubs/JB2006_AIAA_2002_4887.pdf
    http://www.cosis.net/abstracts/COSPAR02/03151/COSPAR02-A-03151-1.pdf
    
    Dr. Bowman's current research is into calculating better Cd curves for
    a variety of different shapes that are commonly found in the satellite
    catalog.
    
    Secondly, remember that B-star isn't just drag.  It's actually the sum
    total of all the perturbations on the object.  The General
    Perturbations model used to produce the TLEs just lumps all these
    together with drag being about 75% of B-star.  This is also why you
    might sometimes see a positive B-star - radiation pressure or other
    factors could actually boost the orbit for a very light, reflective
    object.
    
    The Special Perturbations models are much more accurate for predicting
    decay as they model most of the perturbations independently, however
    these aren't published on space-track so we are sort of screwed :)
    
    --
    Brian Weeden
    
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