[amsat-bb] Decoding Keps
David A. Rush
david at rushtone.com
Wed Sep 19 17:19:37 PDT 2012
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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