[amsat-bb] Re: Decoding Keps

[Thomas Doyle]

David,

Check this out.

http://celestrak.com/NORAD/documentation/tle-fmt.asp

73 W9KE Tom Doyle

On Wed, Sep 19, 2012 at 7:19 PM, David A. Rush <david at rushtone.com> wrote:
> I've been working on some code to decode the two-line Keplerian data like
> the ARRL sends out weekly (with a thank-you to AMSAT-NA).
>
> A couple of the values are in a somewhat cryptic format, the "BSTAR" and
> "second derivative of the mean motion".  The strings tend to be either a
> space or a + sign, five digits, usually a minus sign (but seen at least once
> as a plus sign) and finally another digit, such as:
>
> +00000-0
> +11682-3
>  00000-0
> 30767-3
>  00000-0
> 00000+0
> +00000-0
> +89689-4
>
> What I have found about this format is that it is "decimal assumed", and
> examples suggest that +89689-4 = 0.89689 * 10 ^-4 or 0.000089689, if I
> converted that correctly.
> I'm guessing that the first character is the sign (+ or -) of the number,
> where a space is assumed positive.  I've only seen one example of the 7th
> character being a plus (and all the digits were zero), so I assume that + or
> - are valid values for the exponent.  I guess the format is fundamentally
> limited to an exponent between +9 and -9.
>
> Am I interpreting it correctly?  Any other insight?
>
> David, ky7dr
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-- 

Sent from my computer.

tom ...