4.6 Trajectory Equations

There are three trajectory modes currently available on Ranger NBV. These are selectable using the interface described in Section 3.3.1. The open loop with latch mode simply latches the estimated quaternion as the desired quaternion when the rotational hand controller is returned to the neutral position. The last two trajectory modes (resolved rate and spacecraft dynamics) propagate the desired attitude forward as a function of rotational hand controller values and current vehicle state.
The resolved rate trajectory mode uses the rotational hand controller values to specify the desired angular velocity of the desired attitude. The first derivative of the desired angular velocity is calculated and passed to the controller. Additionally, the desired angular velocity is used to propagate the current desired attitude forward for the duration of the next time step by using a 4th order Runge-Kutta integration on (4.9). This is shown in Figure 4-8.

Figure 4-8 Resolved rate trajectory mode

The spacecraft dynamics trajectory mode is shown in block diagram in Figure 4-9. The rotational hand controller specifies the desired moment to be applied to a simulated spacecraft. The rotational dynamics (4.1) and the quaternion kinematics (4.9) equations are integrated (4th order Runge-Kutta), and the output passed to the controller as the desired trajectory.

Figure 4-9 Spacecraft dynamics trajectory mode