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 be disabled (grayed out) in the Constraints 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.
  • The Temporal Process Delay constraint can be set through Connect only.
Constraint Description Constraint used for accesses to...
Local 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; it can also be manually overwritten. For related information, see Positioning a Facility, Place or Target or Area Target Centroid. F, Pl, T, AT, LT, P, St, V
GMT Start and end GMT time constraints for when access is possible. F, Pl, T, AT, LT, P, St, V
Local Apparent 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 the satellite. Also known as Local Satellite Time (LST). F, Pl, T, AT, LT, P, St, V
Duration Minimum and maximum acceptable duration for computed accesses. If accesses whose durations are outside these limits are computed, they are discarded from the resulting list. F, Pl, T, AT, LT, P, St, V
Intervals See below for description. F, Pl, T, AT, LT, P, St, V

Interval Constraints

The Interval constraint can be used to analyze the effects of planned satellite down times on access or coverage.

To define interval constraints, enable Use in the Intervals area and select one of the following interval sources:

Enter Intervals

Selecting this source provides the following options for entering intervals:

    Add... Add default start and stop times that you can edit 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 interval data loaded from an external file is edited a new interval file will be created 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.

Select Time Component

Select this source and click the browse button to select an available time component for the selected object and click Apply. The Time Component is added to the Intervals table.

Customize Intervals. Click this button to switch to the Enter intervals source where you can edit the time component values.

     

Select Interval Files

Select this source 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... Add default start and stop times that you can edit by double-clicking a field and overwriting its contents.
  • Reload 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 interval data loaded from an external file is edited, a new interval file will be created so as not to overwrite the original.

  • 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.

    • 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.

Exclude Intervals

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

  • Enable Exclude Intervals to use the start and stop times from the specified interval files to define periods during which access is not possible.
  • Disable Exclude Intervals to use the start and stop times from the specified interval files to define periods during which access is possible

Removing and Reordering Constraints

Use the Remove and Remove All buttons to delete selected constraints or all constraints from the table.

Use the up and down arrows to reorder the constraints in the table.

Deconflict

Use the Deconflict options to resolve interval overlaps. You can choose whether the time intervals should be "deconflicted," or modified so that time periods do not overlap.

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 window 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 time interval overlaps.