I am using the python SGP4 1.1 module to calculate the position and velocity of a MEO satellite. I'm noticing when compared against STK and JSatTrak that the returned values for position and velocity are incorrect. The Satellite should have a ground repeat track of roughly 6 hours, but this program is showing a ground repeat of 4:47:51. Is there something that I am doing incorrectly?
from sgp4.earth_gravity import wgs72from sgp4.io import twoline2rvfrom math import atan2, cos, pi, sin, sqrt, tanfrom datetime import datetimedef calculate(options): x = options[0] y = options[1] z = options[2] # Constants (WGS ellipsoid) a = 6378.137 e = 8.1819190842622e-2 # Calculation b = sqrt(pow(a,2) * (1-pow(e,2))) ep = sqrt((pow(a,2)-pow(b,2))/pow(b,2)) p = sqrt(pow(x,2)+pow(y,2)) th = atan2(a*z, b*p) lon = atan2(y, x) lat = atan2((z+ep*ep*b*pow(sin(th),3)), (p-e*e*a*pow(cos(th),3))) n = a/sqrt(1-e*e*pow(sin(lat),2)) alt = str(p/cos(lat)-n) lat = str((lat*180)/pi) lon = str((lon*180)/pi) #print "%s %s %s" % (lat, lon, alt) return (lat, lon, alt)line1 = '1 1U 001001 14001.00000000 .00000000 00000+0 00000+0 0 00022'line2 = '2 1 0.0891 294.8098 0002843 64.8653 0.5014 5.00115502 09'satellite = twoline2rv(line1, line2, wgs72)position1, velocity1 = satellite.propagate(2013, 3, 1, 0, 0, 1)position2, velocity2 = satellite.propagate(2013, 3, 1, 4, 47, 52)lat1,lon1,alt1 = calculate(position1)lat2,lon2,alt2 = calculate(position2)print lat1 +""+ lon1 +""+ alt1print lat2 +""+ lon2 +""+ alt2print "\n\n"print position1print position2