UAV circumnavigating an unknown target using range measurement and estimated range rate

The objective of the paper is to design a control algorithm such that a UAV can circumnavigate an unknown target using range-only measurement. By assuming the availability of both range and range rate measurements, a control algorithm is proposed to accomplish the circumnavigation mission, where the associated control input is always bounded. To eliminate the requirement of range rate measurements, an estimated range rate, obtained via a sliding-mode estimator using range measurement, is used to replace the range rate measurement. By carefully choosing parameters in the estimator, range rate can be accurately estimated in finite time thanks to the boundedness of control input under the proposed control algorithm. As a consequence, the circumnavigation mission can still be accomplished using the proposed control algorithm when range rate measurement is replaced by its estimated value obtained from the estimator. This estimator-based control strategy using range-only measurement is desired for small UAVs under GPS-denied environment when limited sensing capability is allowed considering their payload restrictions.