[amsat-bb] Re: Decoding Keps

[i8cvs]

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" <david at rushtone.com>
To: <AMSAT-BB at amsat.org>
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 AMSAT-BB at amsat.org. 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