STK Astrogator

STK Astrogator is a specialized analysis module for interactive orbit maneuver and spacecraft trajectory design. Astrogator acts as one of the propagators available for a satellite object. Astrogator calculates the satellite's ephemeris by executing a Mission Control Sequence, or MCS, that you define according to the requirements of your mission.

Astrogator provides the ability to model impulsive and finite maneuvers as well as high-fidelity orbit propagation. It provides targeting methods, including a differential corrector - which allows you to find the necessary values of control parameters (such as launch epoch or burn duration) to meet desired mission goals - and an optimizer - which allows you to modify control parameters to achieve an objective, while applying a set of constraints that define the problem space. Furthermore, Astrogator allows you to define automatic sequences, which represent pre-defined sets of actions that can be performed whenever a specified event occurs - such as a maneuver that occurs at every periapsis. These details highlight just some of Astrogator's many features.

Astrogator also utilizes a component catalog and editor in STK called the Component Browser. The Component Browser lets you define and customize engine models, force models, propagators, central bodies, atmospheric models, and other elements of a space mission analysis scenario. In addition, the Component Browser contains a wide array of calculation objects. All of these elements can then be used or adapted in any Astrogator scenario.

The Astrogator Orbit Properties Page

When you select Astrogator as the propagator for a satellite object, the Orbit properties page transforms to a specialized layout in which you can define the spacecraft's MCS.

The left side of the window is occupied by the MCS Tree - which lists the segments that make up the MCS and depicts their relationships to each other - and the MCS Toolbar - which contains buttons that perform various MCS and individual segment operations. By default, the MCS contains Initial State and Propagate segments which produce a low-Earth orbit. The right side of the window is occupied by the parameters of the segment that is currently selected in the MCS Tree.

Results...

Beneath the MCS Tree is the Results... button, which allows you to specify calculation objects to be reported and targeted for each segment. Clicking this button will open the User-Selected Results window, in which you can select calculation objects to include in the summary report for the currently selected segment, and to target when defining a Differential Corrector Target Sequence profile. In addition to using the button, you can open the User-Selected Results window by right-clicking a segment and selecting Results... from the drop-down menu.

Initial and Final Fields

The Initial and Final fields beneath the segment parameters area are apparent for every segment in the MCS and serve the same purpose for each; the Initial field displays the scenario time and date at the beginning of the currently selected segment, while the Final field displays the scenario time and date at the end of that segment. If a segment has not yet been run, these fields will be marked "Not Set" for that segment - since these values are not determined until the segment is run.