Precision of internal calculationsΒΆ

MountWizzard4 is using for all calculations the skyfield (https://rhodesmill.org/skyfield/) from Brandon Rhodes. As for the new command set offered with 10microns FW3.x it needs to calculate the alt/az coordinates for a satellite track each second for the entire track. As you would like to follow the as precise as possible I made some comparisons between the internal calculations done in 10micron mount and the results provided by skyfield.

In skyfield there is a chapter about satellite calculations and precision: https://rhodesmill.org/skyfield/earth-satellites.html#avoid-calling-the-observe-method Despite the fact that the observe method is expensive the difference in calculation time for a 900 step track is on my computer 120ms (using more precise observe method) to 7ms (using the less precise difference).

Brandon writes about it:

While satellite positions are only accurate to about a kilometer anyway, accounting for light travel time only affected the position in this case by less than an additional tenth of a kilometer. This difference is not meaningful when compared to the uncertainty that is inherent in satellite positions to begin with, so you should neglect it and simply subtract GCRS-centered vectors instead as detailed above.

Here the charts for NOAA 15 [B] at julian date JD=2459333.26498 for the transit happening. The used TLE data was:

NOAA 15 [B]
1 25338U 98030A   21104.44658620  .00000027  00000-0  29723-4 0  9990
2 25338  98.6888 133.5239 0011555 106.3612 253.8839 14.26021970192127

You could see the alt/az of the sat track.

../_images/sat_track.png

the difference for altitude between 10micron and skyfield

../_images/sat_altitude.png

the difference for azimuth between 10micron and skyfield

../_images/sat_azimuth.png

the difference for right ascension between 10micron and skyfield

../_images/sat_ra.png

the difference for declination between 10micron and skyfield

../_images/sat_dec.png

There is a set of plots for another satellite, which shows the same behavior. The used TLE data was:

RAAVANA-1
1 44329U 98067QE  21134.29933328  .00044698  00000-0  30736-3 0  9995
2 44329  51.6342 100.9674 0004554 122.3279 237.8162 15.74179130108776

You could see the alt/az of the sat track.

../_images/sat2_track.png

the difference for altitude between 10micron and skyfield

../_images/sat2_altitude.png

the difference for azimuth between 10micron and skyfield

../_images/sat2_azimuth.png

the difference for right ascension between 10micron and skyfield

../_images/sat2_ra.png

the difference for declination between 10micron and skyfield

../_images/sat2_dec.png

For all calculations is valid:

  • they are using refraction correction with the same values.

  • the coordinates from 10micron are gathered with :TLEGEQJD#, :TLEGAZJD# commands

  • julian date is in UTC time system

  • 10micron firmware 3.0.4

  • skyfield version 1.39