Re: progress tle , high drag factors

From: Sebastian Stabroth (s.stabroth@tu-bs.de)
Date: Wed Aug 22 2001 - 13:52:37 PDT

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    Walter Nissen wrote:
    > PROGRESS M-45   oig
    > 1 26890U 01036A   01233.77072885  .00199884  25346-4  70872-3 0    56
    > 2 26890  51.6382 118.5983 0014078 346.5632  91.3524 15.88457051    60
    >
    > If a drag factor is too high, the object will arrive late.
    
    Hmm, it should exactly be the opposite in orbital motions. If an object loses height
    because of high drag, it travels faster and arrives sooner at your point of
    observation.
    
    Btw: Can someone explain how to derive the ballistic coefficient B (mass/(drag
    factor*cross-sectional area)) from the Bstar drag term in the 2line elsets? The
    Spacetrak report says something like: B=rho/(2*Bstar) with rho=2.461*10^-5
    kg/m^2/Earth radii. But with the Progress TLE above (Bstar=0.70872*10^-3 in 1/Earth
    radii) I realy don't think that B=0.017.. kg/m^2 is right! The ballistic coefficient
    of a Progress freighter should be around 200 kg/m^2 in the worst case.
    
    Cheers,
    Sebastian
    
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