# Re: progress tle , high drag factors

From: Sebastian Stabroth (s.stabroth@tu-bs.de)
Date: Wed Aug 29 2001 - 16:28:54 PDT

• Next message: Paul Gabriel: "az/el compass"

```> If a drag factor in an elset is higher than the true drag experienced by
> the object traveling through the upper atmosphere, then if the observer
> looks for the object based on an ephemeris generated by a propagator
> using the elset, then the observer will see the object later than
> expected.

Oh, now I see that I at first incorrectly interpreted your statement. Thanks for your

> 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.

And, I forgot to multiply 'rho' by the value of Earth radius (~6378 km). So, the
ballistic parameter for Progress is around 100 kg/m^2 for this 2line elset - really
(too) high drag as you said, Walter.

Cheers,
Sebastian

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