Rendezvous / Formation

STK Premium (Air) or STK Enterprise
You can obtain the necessary licenses for this tutorial by contacting AGI Support at support@agi.com or 1-800-924-7244.

Capabilities Covered

This lesson covers the following STK Capabilities:

  • Aviator Pro

Problem Statement

The Rendezvous / Formation strategy is a 3D strategy, operating in the wind frame, in which the aircraft uses multi-mode guidance to maintain formation with a cooperative aircraft.

This strategy differs from the Formation / Recover procedure in the fundamental manner that the route is determined. The Formation / Recover procedure assumes that the route of the leading aircraft is already known, and STK's Aviator capability plans a route using all of that knowledge. The Rendezvous / Formation strategy assumes that the route of the leading aircraft is unknown and attempts to maintain formation by responding to the leading aircraft's maneuvering as it happens.

For optimal performance, it is highly recommended to use the RK4 integrator with the Rendezvous / Formation strategy.

Sometimes certain features are not fully compatible with each other. Customers and/or post release testing uncovers incompatibilities with certain features1.

Cooperative Target

Field Description
Cooperative Target

Select an Aviator aircraft in the scenario that the aircraft will follow during the maneuver.
Pos/Vel Strategies

Position and velocity strategies for the target object. The following strategies are available:

  • NoisyBrgRng - A noisy bearing and range strategy.
  • NoisySurfTgtPosVel - A strategy that periodically generates noisy position, speed, and course updates for a constant altitude target.
Tgt Pos/Vel Resolution

The frequency of sampling of the target object's position and velocity; interpolation of the object's position will be performed between sample points.

The lowest recommended value for this property is 0.1 sec, but the lowest possible value is 0.001 sec. At the lowest value, Aviator will use the native position and velocity of the target object; this can result in dramatically slow performance when the target object is another Aviator aircraft, since STK is performing double integration calculations in such a case.
Use Counter Turn Logic

Select this check box to improve performance when flying with a target on a straight and level flight path; conversely, this option should be avoided if the target is flying a circular route.

Collision Avoidance Logic

Select the Enable check box to apply collision avoidance logic to the maneuver. In the CPA Closest Point of Approach field, specify the minimum distance between this aircraft and the reference aircraft; the guidance strategy will fly around a bubble of the specified radius, if necessary, to avoid violating the CPA. If the CPA is larger than the formation distance, then the formation distance will override the CPA.

Position

Field Description
Relative Bearing

The bearing relative to the target that the aircraft will achieve and maintain.
Relative Range

The range from the target that the aircraft will achieve and maintain.
Altitude Split

The altitude difference between the aircraft and the target.

Control Limit

Field Description
Use Performance Model Limits

Select this check box to derive the control limits of the aircraft during the procedure from the applicable performance models currently in effect; otherwise, define custom control limits for the procedure in the Altitude Rate Control, Min Load Factor G, and Max Load Factor G fields.
Altitude Rate Control The rate at which the aircraft will change altitude to achieve or maintain the Altitude Split.
Min Load Factor G The minimum load factor that the aircraft can bear while maneuvering in formation.
Max Load Factor G The maximum load factor that the aircraft can bear while maneuvering in formation.

Maneuver Factor

The Maneuver Factor defines a dimensionless factor that influences how tightly or gently the aircraft will maneuver. At its most aggressive setting, the factor will force the strategy to achieve the specified performance values; at its most gentle setting, the factor will allow the strategy to tolerate the most deviation from those values.

Airspeed Control

Field Description
Max Speed Advantage

A limit to the airspeed difference between the aircraft and the target.
Acceleration Value

Select a method to define the aircraft's acceleration performance while holding formation.

  • Acceleration performance model value - use the current acceleration performance model.
  • Override value - specify the aircraft's acceleration rate.
  • No Limit - the aircraft will accelerate according to its current performance model and its airspeed will not be constrained by the target's airspeed.
Separate Airspeed Control Select this check box to apply a dimensionless factor to the aircraft's airspeed control that provides finer control over airspeed adjustments made to maintain formation with the target. In particular, this factor can prevent oscillating behavior in which the aircraft overshoots the target, then over-corrects trying to reduce speed to match it, then over-corrects again, and so on.

Stop Condition

Select a stopping condition from the drop-down menu.

  • Normal - the basic stopping conditions will be used.
  • After Target Current Procedure - stop after the target completes the procedure that it is performing when the aircraft rendezvous with it.
  • After Target Current Mission Phase - stop after the target completes the mission phase that it is performing when the aircraft rendezvous with it.
  • When Target Performance Mode Changes - stop when the target enters a new mode of flight (e.g., it transitions from forward flight to VTOL).
  • When Target Performance Phase Changes - stop when the target enters a new performance phase (e.g., it transitions from climbing to cruising).