From: wkitty42_at_gmail.com via Seesat-l <wkitty42_at_gmail.com>

Date: Wed, 09 Apr 2014 12:22:09 -0400

Date: Wed, 09 Apr 2014 12:22:09 -0400

yes, "better" is subjective but i'm curious about other's thoughts and methods... using only the data contained in a TLE, is it "better" to calculate an object's orbital period by 1. simply dividing minutes per day (1440.0) by the object's TLE mean motion OR 2. work kepler's 3rd law by calculating the semi-major axis of the orbit via the mean motion in the TLE for kepler's 3rd law, i'm currently using the WGS'72 value of 398600.8 for earth's gravitational constant... this is also the value that TS' routines use... would it be better to use a/the newer WGS values? i've not found an update for the routines that uses anything other than WGS'72 values... so, back to the orbital period calculation... there is a slight difference in the results but they generally start in the 4th or 5th decimal place of the resulting minutes... mostly the 5th... eg: COSPAR Perigee KM x Apogee KM x Inclination SemiMajorAxis KM MMPeriod SMAPeriod -------------------------------------------------------------------------------------------------------------------- 72023E 206.56106474 x 3190.47187333 x 52.09280000 8076.65146903 120.39445477 120.39447252 98067A 413.34288340 x 416.33722680 x 51.64930000 6792.97505510 92.86445208 92.86446577 granted, we're talking about only a few hundred-thousandths of a second but over time, they do add up and can lead to predictions being off by X amount of time... especially with older TLEs... in all cases, my SMAPeriods (SemiMajorAxis) are longer than my MMperiods (MeanMotion)... so, i'm curious which method(s) others use when they calculate the orbital period of an object and why they chose the method they use... FWIW: originally i decided to use both methods as a way of verifying and validating that my math was right and that i was getting the proper answers... when comparing with other's results, mine are pretty much spot on with some slight variance on some values but "close enough for gov't work" as they say ;) _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Wed Apr 09 2014 - 11:23:17 UTC

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