Intervals

Temporal Constraints

Temporal constraints enable you to impose time-based constraints on an object.

If a constraint is not available for accesses from an object, it will not appear in the Temporal constraints list on the Constraints-Active properties page for that object. The table below describes the temporal constraints and lists the objects that they can be used to constrain access to.

When an access involves a child object (i.e., sensor, transmitter, receiver, antenna, or radar), use the child object's parent or grandparent in the table below to determine whether the constraint can be used for access to that child object. For example, if a constraint can be used for accesses to all vehicles, then that constraint can also be used for any child object of a vehicle.

In the following table, abbreviations in the Constraints used for accesses to... column are:

F = facility Pl = place T = target V = all vehicles S = satellite M = missile L = launch vehicle G = ground vehicle
A = aircraft Sh = ship Sn = sensor AT = area target LT = line target P = planet St = star  

Area targets are assumed to exist within a single time zone so that there is only one local time offset from GMT. The local apparent time is computed based on the location of the centroid.

  • Intervals, Local, and GMT constraints - Intervals are defined relative to a clock colocated with the object holding the constraint. These intervals will be shifted by the light-time delay associated with a given access computation if the intervals for access are computed relative to a clock located with the other object. For example, if you specify intervals for a Mars-based facility and then compute access from an Earth-based facility to the Mars-based facility, the Mars-based intervals will be shifted by the light-time delay so that the signal will arrive at Mars during the desired intervals. This may appear to be confusing since, in this case, the interval reported by the access computation will be transmission times from the Earth-based facility.
  • Linking Transmitter/Receiver and Linked Antenna - GMT, Duration, and Intervals constraints are enabled on both the linking (transmitter/receiver) object and the linked (antenna) object. When these constraints are active on the linking and linked objects, the two resulting access intervals are combined by interval AND operation to get the final access interval result.
  • You can only set the Temporal Process Delay constraint through Connect.
Constraint Description Constraint used for accesses to...
Duration This is the minimum and maximum acceptable duration for computed accesses. Accesses with durations outside these limits are discarded from the resulting list. F, Pl, T, AT, LT, P, St, V
GMT Enter the Start and End GMT time constraints for when access is possible. F, Pl, T, AT, LT, P, St, V
Intervals See the Intervals constraint definition section below for a description. F, Pl, T, AT, LT, P, St, V
Local Apparent Time Enter the Start and End local apparent times for when access is possible. Using local apparent time, at noon the Sun is at the same longitude as a vehicle. F, Pl, T, AT, LT, P, St, V
Local Time Enter the Start and End local time constraints for when access is possible. The object local time is computed based upon the GMT of interest and the longitude of the object at that time. Local time offset from the GMT is computed automatically based on the object's position and shown as the local time offset from GMT. You can also manually overwrite it. For related information, see Positioning a Facility, Place, or Target or Area Target Centroid. F, Pl, T, AT, LT, P, St, V

Intervals constraint definition

You can use the Intervals constraint to analyze the effects of planned satellite down times on access or coverage.

To define interval constraints, select the Intervals constraint in the Active Constraints list. In the Constraint Properties below it, select one of the following for Sources:

Enter intervals option

Selecting this source option provides the following options for entering intervals:

    Add Add default start and stop times. You can edit these by double-clicking a field and overwriting its contents.

    Load... Load one or more external interval list files (*.int) containing start and stop times to indicate time periods during which access is possible, or time periods during which access is not possible.

    When you edit interval data loaded from an external file, STK will create a new interval file so as not to overwrite the original.

    Import... Add start and stop times from a Time Component by selecting an available time component for the selected object and clicking Apply.

    Use the Deconflict options to resolve interval overlaps.

    Option Description
    Automatic STK automatically modifies all time intervals during which an overlap occurs so that the intervals are further segmented, to avoid overlap.
    Manual When an overlap occurs in the interval list, an Acknowledge dialog box appears when you click OK or Apply to alert you to the fact that the overlap exists. It is then your decision whether to set the Deconflict field to Automatic so that the overlap is fixed, change the time intervals yourself by modifying the appropriate entries, or ignore the message and continue.
    None No changes are made to eliminate time interval overlaps.

Select time component option

Select this Source option and click Select... to choose an available time component for the selected object. Click OK to add the Time Component to the Intervals table.

Select interval files option

Select this source option to add one or more external interval list files (*.int) containing start and stop times to indicate time periods during which access is possible, or time periods during which access is not possible. You have the following options for entering interval files:

  • Add Files...: Click this button to load one or more external interval list files (*.int) containing start and stop times to indicate time periods during which access is possible, or time periods during which access is not possible.
  • Reload: Click this button to reload the interval files.
  • Customize Intervals: Click this button to switch to the Enter intervals source where you can edit the time component values.

    • When interval data loaded from an external file is edited, a new interval file will be created so as not to overwrite the original.

    If you loaded any interval files that also contained object data restrictions, the resulting customizable intervals will have the object data restrictions removed as well as any overlaps. Object data restrictions cannot be modified on this page; any changes must be made to the interval file itself.

Removing and reordering constraints

For the Enter Intervals and Select Interval Files options, you have these additional controls:

  • Click Remove or Remove All to delete selected constraints or all constraints from the table.
  • Use the up and down arrows to reorder the constraints in the table.

Exclude Time Intervals option

Define whether specified periods should be included in or excluded from access computations.

  • Select the Exclude Time Intervals check box to use the start and stop times from the specified interval files to define periods during which access is not possible.
  • Clear the Exclude Time Intervals check box to use the start and stop times from the specified interval files to define periods during which access is possible