Scenario Basic Time

Analysis Period

The scenario analysis period defines the epoch and the start and stop times of your scenario in established units. The epoch serves as a reference for all other times in the scenario. The time and date of the epoch correspond to zero epoch seconds. The analysis period defines the general time span (a range of several hours, days or weeks) for analysis. If you change the start and stop times here, STK automatically propagates the orbits of all satellites in your scenario over the specified time period.

Note: Formats for all time-related fields are dependent upon the time units set at the scenario level.

Analysis Period Options

Option	Description
Start Time	Start date and time for the scenario analysis period.
Stop Time	Stop date and time for the scenario analysis period.
Epoch Time	Date and time in established units to represent zero epoch seconds of the scenario.
Use Analysis Start Time	Checked by default. If the Start Time is changed, the epoch is automatically updated if this checkbox is enabled. Type in the epoch time to change it and the checkbox will uncheck itself. When enabled from a disabled state, the Start Time will be copied into the Epoch Time and the field will track the Start Time until unchecked.

If you change the analysis period start time, the animation start time will also change if it falls outside the new analysis start time. If you change the analysis start time or the animation start time, the animation stop time will also change if it precedes either the new analysis start time or the animation start time.

If you change the analysis period, the waypoint times of a Mission Modeler aircraft will also change if they fall outside the new time period. Waypoint times for all other vehicles will not change even if they fall outside the new time period.

Set the start and stop times for the scenario by typing Now, Today or Tomorrow in the appropriate fields or right click on the fields to display a drop-down menu to select Set to Today, Set to Tomorrow and Set to Now options. These settings reference the current date and time based on your computer's internal clock. If you save a scenario that includes these settings, the animation time of that field is updated every time the scenario is opened to correspond to the current date and time or the next day.

The scenario's analysis period is also used as the default time period for operations involving objects that don't have an implicit sense of availability. A vehicle, for example, has an interval of availability that is defined by the span of its ephemeris, while a facility has no such time-oriented restrictions and uses the scenario time period if such an interval is needed. Finally, animation start and stop times are automatically updated to match the time period when a new one is set here.

Animation

Scenario animation properties control the animation cycle, animation step definition, and the intervals between refresh updates in the 2D and 3D windows. Enter the animation Start Time -- which defaults to the start of the scenario analysis period -- and, depending on selections made, the appropriate date and time information.

The current animation time is saved when a scenario is saved and restored when the scenario is reopened.

Time Update Mode

The following options are available for specifying the time update mode:

Time Update Mode options

Option	Description
Real Time	The scenario animates in real time in accordance with your computer's internal clock. Enter an Offset from the current time if desired.
Time Step	Enter the time interval that each animation step represents. The greater this value, the greater the distance a vehicle will move in the 2D and 3D windows each time the screen is refreshed.
X Real-Time	Enter a number specifying the multiple of real time at which you wish the scenario to animate. The Continue from current animation time after pause check box is selected by default. Deselect to have animation pick up from however much time has really elapsed since the animation was paused.

Notes

If you select Real Time, make sure that the scenario time period and the vehicle ephemeris fall within the correct time period. Otherwise, no activity occurs in the 2D and 3D windows when the scenario is animated.

If the Animation Step buttons are used while in Real Time or X Real Time, the time will be updated by the last Time Step entered.

Animation Cycle

If On, select one of the following options:

Animation cycle options

Option	Description
Stop at Time	Indicate the time at which the animation will stop.
Loop at Time	Indicate the time at which the animation loops back to the Start Time.

If Off, animation continues until you pause or reset the animation.

Animation Update

Specify the amount of time between screen refresh updates.

Animation update options

Option	Description
Update animation every	The amount of time between refresh updates. For instance, if you enter 1.0, STK attempts to refresh the screen once every second. The actual refresh rate is limited by the minimum time necessary to draw the scenario. The refresh time varies with processor performance, graphics hardware and scenario complexity.