(Georgia Institute of Technology, 2007-03)
Johnson, Eric N.; Calise, Anthony J.; Watanabe, Yoko; Ha, Jin-Cheol; Neidhoefer, James C.
This paper describes two vision-based techniques for the navigation of an aircraft relative
to an airborne target using only information from a single camera fixed to the aircraft. These
techniques are motivated by problems such as "see and avoid", pursuit, formation flying,
and in-air refueling. By applying an Extended Kalman Filter for relative state estimation,
both the velocity and position of the aircraft relative to the target can be estimated. While
relative states such as bearing can be estimated fairly easily, estimating the range to the
target is more difficult because it requires achieving valid depth perception with a single
camera. The two techniques presented here offer distinct solutions to this problem. The
first technique, Center Only Relative State Estimation, uses optimal control to generate an
optimal (sinusoidal) trajectory to a desired location relative to the target that results in
accurate range-to-target estimates while making minimal demands on the image processing
system.The second technique, Subtended Angle Relative State Estimation, uses more rigorous
image processing to arrive at a valid range estimate without requiring the aircraft to follow
a prescribed path. Simulation results indicate that both methods yield range estimates of
comparable accuracy while placing different demands on the aircraft and its systems.
(Georgia Institute of Technology, 2006-05)
Johnson, Eric N.; Calise, Anthony J.; Curry, Michael D.
Guidance and control technology is recognized as an important aspect of the military, civil, and commercial
goal of reliable, low-cost, aircraft-type operations into space. Here, several guidance and control methods are
extended to enable integration into a single fully adaptive guidance and control system that offers a high degree
of mission flexibility, fault tolerance, and autonomy. This paper summarizes the guidance and control system and
several research issues related to use of adaptive guidance and control in reusable launch vehicles. Results that
demonstrate the ability of the integrated system to plan and fly abort trajectories are also presented.
(Georgia Institute of Technology, 2003-11)
Johnson, Eric N.; Calise, Anthony J.
In the application of adaptive flight control, significant issues arise due to limitations in the plant inputs, such as
actuator displacement limits, actuator rate limits, linear input dynamics, and time delay. A method is introduced
that allows an adaptive law to be designed for the system without these input characteristics and then to be applied
to the system with these characteristics, without affecting adaptation. This includes allowing correct adaptation
while the plant input is saturated and allows the adaptation law to function when not actually in control of the
plant. To apply the method, estimates of actuator positions must be found. However, the adaptation law can
correct for errors in these estimates. Proof of boundedness of system signals is provided for a single hidden-layer
perceptron neural network adaptive law. Simulation results utilizing the methods introduced for neural network
adaptive control of a reusable launch vehicle are presented for nominal flight and under failure cases that require
considerable adaptation.