Targeted Attitude Segments

You can build attitude segments for a satellite, missile, or launch vehicle that point along a specific axis at one or more targets. On the Basic Attitude page, select Override Basic attitude for selected targets under Target Pointing. Click Select Targets... to display the TargetSeg window, which enables you to:

• assign targets

• specify target slews

• choose target times

• set parameters for segment calculations

This topic provides detailed descriptions of these steps.

You can create a targeted segment as part of a multisegment profile. On the Basic Attitude page, select Multi Segment from the menu in the upper left. Then, select Target Segments and click Add/Edit segments.... Segment specification then follows the same steps as described on this page.

Assigning targets

In the TargetSeg window, select each object that you wish to assign as a target in the Available Targets list and click the right arrow () to move it to the Assigned Targets list. To move a target out of the Assigned Targets list, select it and click the left arrow button (). You can also move objects from one list to the other by double-clicking them.

Target slew

Click Target Slew... to define slews from the basic attitude to a target pointing attitude and back to the basic attitude. Select a Slew mode and enter the parameters. The table below provides descriptions of the Slew Mode options.

Mode	Description
Fixed Time	This method fixes the time required to change attitude to a constant value, defined by the Slew time field. Select Match angular velocity to account for the angular velocity (slope) at the beginning and end of the slew. If your scenario has multiple target pointing segments, the Fixed Time Slew method applies the following logic. STK calculates the duration between any two targeting segments as the stop time of one to the start of the next. If that duration is less than five times the value of Slew time, then STK will create a slew directly from the end attitude of the first target segment to the start attitude of the second target segment. If the calculated duration is more than five time the value of Slew time, then STK will create two slews. The first will start at the end of the first segment and go to the Basic attitude. The second will go from the Basic attitude to the next target pointing attitude in time for the start of that target pointing segment.
Fixed Rate	This method uses a constant slew rate to compute the time required to change attitude. This time must be no greater than the Maximum slew time value. From the Slew timing between targets box, select an event within the window of opportunity to trigger each slew. Select Optimal to change attitude whenever the slew can be performed most efficiently. Define the maximum slew rate by entering a maximum Magnitude. Select Per Axis rates to specify separate maximum rates for individual axes.
Constrained	This mode applies constraining values to both slew rate and slew acceleration to calculate the time required to change attitude. This time must be no greater than the Maximum slew time. From the Slew timing between targets box, select an event within the window of opportunity to trigger each slew. Select Optimal to change attitude whenever the slew can be performed most efficiently. From the Slew type menu, select to use a second- or third-order spline as the interpolation method of the slew's data points. Specify the maximum for slew rate and slew acceleration by entering a maximum Magnitude. Select Per Axis rates and accelerations to specify separate maximum rates and accelerations for individual axes. The slew rate and slew acceleration are the inertial angular velocity and inertial angular acceleration, respectively, during the slew. The Per Axis rate and acceleration components refer to the body components of these inertial quantities. For example, "Per Axis X" under Maximum Slew Rate refers to the body X-component of the inertial angular velocity; "Per Axis Y" under Maximum Slew Acceleration refers to the body Y-component of the inertial angular acceleration.

Target scheduling

In the TargetSeg window, click Target Times... to specify the start and stop times of target pointing intervals. For further details, see Target Times window.

Advanced

Click Advanced... in the TargetSeg window to open the Access Options window. In this window you can set parameters related to event detection, light time delay, step size control, and signal path to be used in new access computations.

Target pointing data

Click Target Pointing... in the TargetSeg window to view the Target Pointing Data window. The default target pointing attitude has the Z body axis aligned along the line-of-sight vector to the target and the X axis constrained to a minimum angle from the relative velocity vector. The defaults are specified in Cartesian coordinates, but you can choose spherical, Euler, or PR. To change the body axes associated with the Aligned Vector and Constrained Vector, enter values for the coordinate system parameters. The Constrained Vector uses the relative velocity as a default Reference. Change the Reference by clearing Use default and clicking Select... to choose another.

If you have more than one target, a check box at the top of the Target Pointing Data window gives you the option to apply this configuration to all targets.