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Meeting	ACGS Committee Meeting 93 - Colorado Springs - March 2004
Agenda Location	5 SUBCOMMITTEE A – AERONAUTIC AND SURFACE VEHICLES 5.1 VisNav: A Navigation Technology Enabling Autonomous Aerial Refueling
Title	VisNav: A Navigation Technology Enabling Autonomous Aerial Refueling
Presenter	John Junkins, John Valasek, and Declan Hughes
Affiliation	Texas A&M University
Available Downloads*	presentation
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Abstract	A novel sensor and associated navigation algorithms are discussed. The analog VisNav sensor is a cooperative vision technology. The sensor has a rise time of a few microseconds, and therefore active beacons can emit light, structured in the frequency domain – this enables matched filtering to reject spurious energy and make the approach robust with respect to off-nominal conditions. The array of LED beacons (on the receiver UAV) are commanded to emit structured light under the active control of the VisNav sensor (on the tanker UAV), with the power emitted commanded in a closed loop fashion to optimize the signal to noise of each individual measurement. Given four or more line of sight measurements, a least square algorithm has been developed to estimate the six degree of freedom solution; these geometric solutions are processed to determine a smoothed estimate accurate to .01m in position and .01 degree in orientation. A rules-based supervisory algorithm is introduced as an outer loop of the control system. This architecture uses expert rules and fault-tolerant decision logic to operate on all high level supervisory commands, all navigation information, all sensors from the re-fueling system, all sensors on the re-fueling drogue, all health-monitoring flags, and to evaluate the closed loop controlled performance of the of the proximity motion, engagement, re-fueling, and disengagement. A project is described in which the VisNav sensor and the other elements of the navigation and control architecture are being integrated in a flight test experiment. A two year project was described in which a sequence of experiments will culminate with the first fully autonomous hookup of two UAVs.