[amsat-bb] Re: Decoding Keps

[David A. Rush]

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" <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
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>
>