Launch Azimuth

The launch of a satellite into an orbit with inclination i requires launching in an azimuth direction Az defined by the formula

(11.1)

where ? ₀ is the launch site latitude. For a due east launch ( Az = 90 deg), i = ? ₀, or the orbital inclination is equal to the launch site latitude. Differentiating Eq. (11.1) and solving for d i, one obtains

(11.2)

which shows the sensitivity of inclination error d i due to an error in azimuth d Az. For range safety reasons, the azimuth may be constrained between specified limits, as is shown in Fig. 11.1, for example.

Figure 11.1: Geographic launch constraints.

In-Plane or Out-of-Plane Ascent Using a Launch Azimuth Constrained to the Nominal Value

The most efficient launch is an in-plane launch ascent characterized by a wait on the ground until the launch site lies in the mission orbit plane, which is fixed in inertial space. No plane change maneuver is then required unless the orbit inclination is less than the launch site latitude or the launch azimuth constraint is such that a "dog-leg" maneuver is needed. A direct ascent to a parking or mission orbit may be made with or without a phasing orbit to place the satellite in a specified geographic location. The phasing problem where the parking and mission orbits are not coplanar may involve excessive waiting times, which can be somewhat reduced...