David Tiller asked: > It seems that there are two parameters that are used to compute the particulars of a sun- > synchronous orbit - orbital altitude is used to derive the correct orbital inclination which > then drives the launch azimuth based on latitude. Your analysis assumes that the stated > launch altitude is correct and the launch azimuth is incorrect. > > What orbital altitude would be correct for a sun-synchronous orbit assuming that the launch > azimuth will be as the DPRK stated? The defining property of a sun-synchronous orbit is that its rate of planar precession exactly negates the -0.9856 deg/d (westward) precession due to Earth's motion about the sun. That is accomplished by taking advantage of the perturbation due to Earth's oblateness that causes an orbit's plane to precess, which is a function of its size, shape and inclination. The rate of planar precession varies in direct proportion to the cosine of the inclination; therefore, to achieve the required +0.9856 (eastward) precession requires a retrograde inclination, i.e. >90 deg. North Korea's NOTAM's for of its upcoming launch correspond to a launch azimuth of about 181 deg, which corresponds to an inclination of approximately 88.7 deg, which would not support a sun-synchronous orbit at any altitude, since it is not retrograde. The lowest orbit that would survive for at least one revolution before decay, ~140 km, requires an inclination of 96.13 deg to be sun-synchronous, which requires a launch azimuth of about 190.6 deg for a direct ascent trajectory. The 500 km orbit announced by North Korea requires a 97.42 deg inclination to be sun-synchronous, which requires an approximately 192.3 deg launch azimuth. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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