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Can I calculate the two-line element for a new satellite using the orbital parameters? How do I calculate mean motion for a satellite?

Is BSTAR drag term in TLE same for all satellites? If not, then how do I calculate BSTAR drag term?

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  • $\begingroup$ Can you clarify which orbital elements you already have? $\endgroup$ – VolkanOzcan Jun 27 '16 at 17:47
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The mean motion is inversely proportional to the period:

$$n = \frac{1}{P}$$ This gives $n$ in as a revolutions per unit time.

The b-star is essentially empirical. One could calculate it as $$B = \frac{C_d A}{m} $$ $$B^* = B \rho / 2$$ with $m$ as mass, $C_d$ a drag coefficient one might get from CFD, $A$ the cross-sectional area, $\rho$ density of atmosphere. In practice this is determined from curve fitting with multiple observations, so it can end up incorporating multiple pertubative effects, not just drag. (In fact, it can be negative!) For a small near-earth satellite setting it to zero often suffices.

FAQ from CelesTrak

The complete details

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  • $\begingroup$ Eastrophe shows that, just like B-star, mean motion term is also not the real mean motion, but it is fit to data by Celestrak. So the formula you provided will calculate mean motion but if you put that on SGP4 code, you will get large errors. But luckily, unlike B-star, Eastrophe also shows an equation relationship between real mean motion and SGP mean motion. (Examination of the mean motion used in SGP4, Easthope, P. F., 2015) $\endgroup$ – VolkanOzcan Jun 27 '16 at 17:44

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