USA193 decay and flux values clarified

From: George Roberts (
Date: Wed Jan 30 2008 - 14:58:15 UTC

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    Okay - I read what Vossinakis and Ted wrote about solar flux and decay and I 
    looked at the web page and I was very confused but I think I understand what Ted 
    is saying - I'm not really adding anything to what Ted said but I didn't 
    understand it until now and figure other people as dumb as me had just as much 
    The Flux value entered is used to determine the area to mass ratio (A/m).  This 
    needs to be known before satevo can predict how quickly a satellite will come 
    down.  This means that the Flux value entered was for *the past*.  So higher 
    values of Flux in *the past* for the same rate of decay in the past implies the 
    satellite has a high area to mass ratio (like a feather - it's gonna slow down 
    quickly).  Lower Flux values in the past result in a higher A/m (like a rock - 
    it will take longer to succumb to drag).  This (A/m) factor changes the 
    prediction more than potential future flux which has the opposite effect.
    Does that make sense?
    Again: low flux in the past implies it will come down sooner, low flux in the 
    future implies it will come down later.  The "past" affect has a stronger weight 
    in the equation.
    Maybe satevo should ask for two different flux values - past and future.
    - George Roberts
    ----- Original Message ----- 
    From: "Ted Molczan" <>
    To: <>
    > Vossinakis Andreas wrote:
    >> the bigger the value (which means strongest solar activity),
    >> the decay time moves later.
    Ted Molczan wrote:
    > The program uses the solar flux to estimate atmospheric density at the 
    > altitude of
    > the satellite at the epoch of the initial elements, then combines this
    > information with the object's rate of decay to estimate its ballistic
    > coefficient, which is its cross-sectional area divided by its mass, denoted by
    > A/m. 
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