Access Defaults

Through Preferences from the Edit menu, go to the Access Defaults page to set the following access computation options:

STK always models Star objects with total (stellar) aberration, regardless of the Aberration Type and Use Light Time Delay settings.

Option Description
Maximum Step Size Use this option in new access computations. The maximum step size limits the amount of time that is allowed to elapse between samplings of the constraint functions during access computations. The value specified here is the default value for Access tool windows when they are created, and you can use the Advanced button on the Access tool to override it.
Minimum Step Size Specify the minimum step size that STK can use.
Time Convergence Specify the time tolerance for the access algorithms to use to determine the start times and stop times of access intervals. The event detection routine declares that an event is found when either the value of the access constraint converges to the desired value within eight digits or the time interval in which the event lies is within the time tolerance.
Value Tolerance

Specify the parameters controlling event detection based upon a constraint value are the following:

  • Relative: An event is considered detected when a constraint value's relative difference compared to the previous sample is within this tolerance:
     
    (value - previousValue) / value <relativeTolerance>)
     

    Values near zero use the absolute tolerance requirement instead.

  • Absolute: This is the criterion used for convergence in value for values near 0. An event is considered detected when a constraint value's difference compared to the previous sample is within this tolerance:
     
    (value - previousValue) <absoluteTolerance>)
     

    The default values have been shown to provide robust and accurate event detection over a wide variety of problems.

Use Light Time Delay Select this check box to have STK consider light time delay in access computations. If you do not select it, STK ignores aberration also.
Light Time Delay Convergence Specify the tolerance for STK to use when iterating to determine the light time delay. The iteration stops when the improvement in the value is less than this tolerance.
Aberration Type This is the model of aberration that STK uses in access computations. From the drop-down menu, choose from the following options:
  • None - STK ignores aberration.
  • Annual - STK considers annual aberration only. Thus, aberration is applied only in cases where the light time delay is computed using the solar system barycenter frame.
  • Total - STK applies the full aberration correction when it computes light time delay.
Preferred Time Sense Controls the default directionality for access computations; use the drop-down menu to choose either Transmit or Receive. Use this to set the preferred directionality for access computations in situations where no directionality is specified. For example, it affects Access, Chains, and DeckAccess but not Coverage. When Sensor Preferred Time Sense is set to No Preference (see below), this setting affects nontargeted Sensors and targeted Sensors with Track Mode set to Transpond.
Sensor Preferred Time Sense Set the preferred directionality for Sensors in access computations; use the drop-down menu to choose Transmit, Receive, or No Preference. This does not apply to targeted Sensors with Track Mode set to Receive or Transmit because, in those cases, STK uses Track Mode as the preferred directionality in access computations.
Auto Add "Access Intervals" to Timeline Select this check box to automatically have STK add Access time intervals to the Timeline View when computing Access.
Save Computed Data

Select this check box to automatically have STK save computed data. When STK creates an access, it will default its option for saving computed data to this choice.
Force Recompute on Load

When checked, this forces STK to recompute accesses when you load a scenario, even if STK saved the access computed data. STK ignores any saved computed data stored with an access.