I quote gbregman that replied the same question some day before:

*You have to use the equatorial reference point for ISS's inclination, because you're using the *

equatorial reference point for both launch azimuth and launch latitude. It's around 51.x, which, if

you'll notice deviates about 23' from your given inclination of 74.51'. This is due to the 23.x' axial

tilt of the earth to ecliptic. To convert your value (which is ecliptic reference) to earth-equatorial

reference, just subtract 23.x' (sorry, can't remember the exact value). Then the equation should

work fine.

for Iss departure from KCS (launch on ascent node)

----------------------------------

74.51°(iss inclinaison in degree)

23.26° (equatorial inclinaison (constant in degree))

desired_orbital_inclination=51.25° (iss - equatorial)

launch_ latitude=28.34N

So:

Launch Azimuth = arcsin (cos(51.25) / cos (28.34))

Launch Azimuth= 0.789638401776836957

as the result is in radian you must convert it in degree with 180/Pi

so:

Launch Azimuth = arcsin (cos(51.25) / cos (28.34))*180/Pi

Launch Azimuth=45.24°

Dan