Constraining a Constellation

Constellation constraints allow you to specify the criteria to be used when constellations are combined with other objects in a chain.

Restrictions

Select one of the following from the Restriction drop-down list:

Any of

EITHER/OR criterion. The constraint is satisfied if any one object in the constellation meets the conditions for chain access. For example, if the constellation:

• is defined as a group of three ground stations A, B, and C, and
• belongs to a chain with a single satellite,

the constraint is satisfied when the satellite can access ground station A or ground station B or ground station C.

All of

AND criterion. The constraint is satisfied if all objects in the constellation meet the conditions for chain access. For example, if the constellation:

• is defined as a group of three ground stations A, B, and C, and
• belongs to a chain with a single satellite,

the constraint is satisfied when the satellite can access ground station A and ground station B and ground station C simultaneously. This is sometimes called "coincident coverage".

At Least N

AND/OR criterion. The constraint is satisfied if at least the specified number of objects in the constellation meet the conditions for chain access. In the text box to the right of the Restriction list, enter the minimum number of objects that must meet those conditions. For example, if the minimum number is set to 2 and the constellation:

• is defined as a group of three ground stations A, B, and C, and
• belongs to a chain with a single satellite,

the constraint is satisfied when the satellite can access ground stations:

• A and B or
• A and C or
• B and C or
• A and B and C

Another good example of this criterion is the Global Positioning System (GPS), for which you could specify At Least 4.

Exactly N

ONLY criterion. This constraint is satisfied if the exact specified number of objects in the constellation meet the conditions for chain access. In the text box to the right of the Restriction list, enter the exact number of objects that must meet those conditions. For example, if the exact number is set to 2 and the constellation:

• is defined as a group of three ground stations A, B, and C, and
• belongs to a chain with a single satellite,

the constraint is satisfied when the satellite can access ground stations:

• A and B or
• B and C or
• A and C

but NOT

• A and B and C

None Of

ONLY criterion. The constraint is satisfied if NO objects in the constellation meet the conditions for chain access. The results of this constraint are available only in the Complete Chain Access report or graph.

Note: Do not add a constellation with the None Of constraint as the first object in the chain.

Cross-Parent Access

Use the Disable Cross-parent Access option to constrain constellations of sensors. If the Disable Cross Parent Access checkbox is selected, a sensors on a given satellite is allowed to link only to another sensor on the same satellite. For example, if a chain consists of Facility1-Up-Down-Facility2, where Up and Down are constellations of sensors, and Disable Cross Parent Access is selected for the Down constellation, then combinations of Facility1-Up-Down-Facility2 are considered valid only where the Up sensor and the Down sensor are attached to the same satellite. The constraint excludes cases in which the uplink is to a sensor on one satellite and the downlink is from a sensor on another satellite.

Note: If you have the Communications or Radar module, the Disable Cross Parent Access option also applies to receivers, transmitters and radars.