Civil aerial refueling is a futuristic concept that was proposed for reducing the environmental impact and improving the efficiency of long-haul air transportation. It will allow a passenger aircraft (the Receiver) to take-off with much less fuel than required to fly the whole route. Dedicated Tanker aircraft will further join the Receiver along its route and transfer the required amount of fuel to complete the mission. In such scenario, the Receiver flies along its original route while the Tanker aircraft is responsible for the execution of the approach maneuver prior to the deployment of the docking equipment. To ensure smooth and safe aircraft rendezvous, automation is becoming a necessity.
In this talk, two guidance laws to achieve rendezvous between the Tanker and the Receiver will be presented. Both guidance laws were developed using linear quadratic optimal control theory to impose zero terminal relative position, zero terminal relative flight path angle, and zero terminal acceleration. The first guidance law was designed as an outer loop based on a first-order lag model of an inner closed loop airframe response. Analytic solution for this guidance law will be presented and compared to previously obtained guidance laws. The second guidance law was developed as a single loop autopilot-guidance controller, which is based on a more detailed airframe model, using full state feedback. We will demonstrate, using a detailed, nonlinear, six degrees of freedom simulation, the ability of both guidance laws to steer the Tanker aircraft to rendezvous with the Receiver. The performance of both guidance laws will be presented separately, for each plane of motion, in terms of the ability of the guidance law to shape the aircraft trajectory while inducing small variability in control surface deflections. The comparison study, carried out for a large set of design parameters using numerical simulations, indicated that the overall performance can be improved by applying each guidance law for a different plane of motion.