Sun Constraints

Sun Constraints enable you to impose constraints based on the position of the Sun and Moon.

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 sun 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 AT = area target LT = line target P = planet St = star  

Constraint Description Constraint used for accesses to...
Sun Elevation Angle

Min and Max values represent the illumination angle as measured between the line of sight direction to the other object involved in the access computation and the apparent direction of the Sun relative to the constrained object.

During times when the direction between the constrained object and the sun is obstructed by the constrained object's central body, this constraint will preclude access.

Both a Min and Max value must be specified when enabling this constraint.

 F Pl T AT P St V

Sun Gnd Elev Angle Sun ground elevation angles are measured with respect to targets, places, or facilities. Min and Max values represent the Sun elevation angle that the target, place, or facility sees. V
Lunar Elevation Angle Min and Max values represent the elevation angle to the apparent position of the Moon. F Pl T AT P St V
Line Of Sight

Select the appropriate check boxes to define Solar or Lunar Exclusion Angles, as measured from the object's line of sight.

  • Solar Exclusion Angle The minimum angle between the line of sight vector to the object of interest and the Sun vector for which access is considered valid. If the line of sight vector is obstructed (for example, the Earth is between the line of sight vector and the Sun), then the exclusion constraint is not applied.
  • Lunar Exclusion Angle - The minimum angle between the line of sight vector to the object of interest and the Moon vector for which access is considered valid. If the line of sight vector is obstructed (for example, the Earth is between the line of sight vector and the Moon), then the exclusion constraint is not applied.

The Line of Sight Lunar and Solar Exclusion Angle constraints now use the main access computation to apply the correct directionality of the light time delay. If the object that holds the constraint is being used in a receive sense, then a receive sense to the obstruction central body is used; if the object is being used in a transmit sense, then a transmit sense is used. This is consistent with the Object Exclusion angle constraint which does the same thing.

F Pl T P St V

Boresight

Select the appropriate check boxes to define Solar or Lunar Exclusion Angles for sensors or their child objects, as measured from the object's boresight.

  • Solar Exclusion Angle - The minimum angle between the boresight vector and the Sun vector for which access is considered valid. If the boresight vector is obstructed (for example, the Earth is between the boresight vector and the Sun), then the exclusion constraint is not applied.
  • Lunar Exclusion Angle - The minimum angle between the boresight vector and the Moon vector for which access is considered valid. If the boresight vector is obstructed (for example, the Earth is between the boresight vector and the Moon), then the exclusion constraint is not applied.

The Boresight Lunar and Solar Exclusion Angle constraints now use the main access computation to apply the correct directionality of the light time delay. If the object that holds the constraint is being used in a receive sense, then a receive sense to the obstruction central body is used; if the object is being used in a transmit sense, then a transmit sense is used. This is consistent with the Object Exclusion angle constraint which does the same thing.

F Pl T AT P St V
Sun Specular Point Exclusion If enabled, access periods are restricted to times when the specular reflection point is at least the angle you specify from the line of sight between the constrained object and the secondary object. The location of the solar specular reflection point on the surface of the central body is computed based on the position of the constrained object. The specular reflection point does not exist for instances where the constrained object is in umbra. The specular reflection point exists when the constrained object is sunlit, regardless of whether its location is on land, sea, etc. F Pl T P St V
Lighting Indicates that access is valid under the specified lighting condition. All

Solar/Lunar Obstruction Applies only when calculating access to a star or planet. Obstruction occurs when access is blocked by the Sun or Moon. P St
FOV Specular Point Exclusion If enabled, access periods are restricted to times when the specular reflection point is outside the sensor field of view. The location of the solar specular reflection point on the surface of the central body is computed based on the position of the constrained object. The specular reflection point does not exist for instances where the constrained object is in umbra. The specular reflection point exists when the constrained object is sunlit, regardless of whether its location is on land, sea, etc.

The FOV Specular Point Exclusion constraint is only available for sensors or sensor sub-objects.

 F Pl T P St V
Additional Central Body Obstruction

To use this constraint, select Use and use the right blue arrow to assign selected central bodies as additional central body constraints.

 AT LT F Pl T P St V
LOS Sun Illumination Angle Min and Max values represent the illumination angle as measured from the object's line of sight to the apparent position of the Sun if it is not obstructed by the object’s central body. Both a Min and Max value must be specified when enabling this constraint. F Pl T P St V

If the Line of Sight constraint is off, solar and lunar exclusion angles are not accounted for when an access line intersects the local central body.

Lighting Conditions

When using the Lighting constraint select the lighting condition under which access is valid.

Lighting Condition Description
Direct Sun Total sunlight.
Penumbra or Direct Sun Partial or total sunlight.
Penumbra Partial sunlight.
Penumbra or Umbra Partial sunlight or total shadow.
Umbra Total shadow.
Umbra or Direct Sun Total shadow or total sunlight.