Thanks, Domenico. Comparing the two-line keps with the AMSAT format has been informative. Unfortunately the AMSAT data omits the two fields that I'm looking for confirmation on.
David, ky7dr
On 2012-09-19 23:45, i8cvs wrote:
Hi David, KY7DR
I suggest you to compare the 2 line NASA orbital data with the AMSAT Keplerian elements for the same day and you will get the answere to your questions.
Example for OSCAR-7
DECODE 2-LINE ELSETS WITH THE FOLLOWING KEY: 1 AAAAAU 00 0 0 BBBBB.BBBBBBBB .CCCCCCCC 00000-0 00000-0 0 DDDZ 2 AAAAA EEE.EEEE FFF.FFFF GGGGGGG HHH.HHHH III.IIII JJ.JJJJJJJJKKKKKZ KEY: A-CATALOGNUM B-EPOCHTIME C-DECAY D-ELSETNUM E-INCLINATION F-RAAN G-ECCENTRICITY H-ARGPERIGEE I-MNANOM J-MNMOTION K-ORBITNUM Z-CHECKSUM
Two line NASA orbital data for orbit KKKKK or i.e. numbar 73100
AO-07 1 07530U 74089B 12256.61218065 -.00000027 00000-0 10000-3 0 4795 2 07530 101.4099 250.4681 0012001 109.6272 250.6089 12.53591141731001
AMSAT orbital data for the same Epoch revolution i. e. the same orbit numbar 73100
Satellite: AO-07 Catalog number: 07530 Epoch time: 12256.61218065 Element set: 479 Inclination: 101.4099 deg RA of node: 250.4681 deg Eccentricity: 0.0012001 Arg of perigee: 109.6272 deg Mean anomaly: 250.6089 deg Mean motion: 12.53591141 rev/day Decay rate: -2.7e-07 rev/day^2 Epoch rev: 73100 Checksum: 262
About your calculation:
If the sign is plus like in +89689-4 your following calculation is correct:
+89689-4 = 0.89689 * 10 ^-4 or 0.000089689
73" de
i8CVS Domenico
----- Original Message ----- From: "David A. Rush" [email protected] To: [email protected] Sent: Thursday, September 20, 2012 2:19 AM Subject: [amsat-bb] Decoding Keps
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 _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb