Adaptive Guidance for Hypersonic Vehicle

Introduction:
One of the overriding goals of NASA’s Next Generation Launch Technologies efforts is to develop new launch systems and space transportation architectures that are significantly safer, more reliable and less costly. NASA has recognized that these goals must be accomplished in order for the U.S. to maintain its leadership role in space. Recent interest in access to space has seeded similar goals for the Air Force.

Technology Challenges:
To address the goal of increasing vehicle safety and reliability, there is now significant interest in reconfiguration technologies for the control and avionics systems of next generation Reusable Launch Vehicles, or RLVs. On-line reconfiguration can give the vehicle the capability to account for unexpected or unforeseen changes to the dynamics, aerodynamics, or control of the vehicle, due to, for example, a control effector failure. However, RLVs typically do not possess the actuation redundancy or alternate control effectors seen in commercial or military aircraft, and this makes the reconfiguration task that much more challenging. Because of this, the reconfiguration problem will often involve not only the control of the vehicle, but also the guidance and the trajectory command functions as well.


Solution:
Barron Associates has addressed the reconfigurable guidance problem for a number of vehicles on a number of Air Force and NASA programs. Barron Associates developed initial designs and demonstrated guidance reconfiguration for Orbital Sciences Corporation’s X-34 RLV and Lockheed-Martin’s X-33 RLV. This work has led to a joint venture funded by both the Air Force Research Lab (AFRL) and Marshall Space Flight Center (MSFC) to develop a reconfigurable and adaptive guidance and control system for Boeing’s X-40A RLV. Under this program, Barron Associates just completed a detailed design of an adaptive guidance system and on-line trajectory command-reshaping algorithm that has been integrated with a reconfigurable control system designed by AFRL.

BAI's unique approach involves two main elements:
(1) Guidance gain reconfiguration: Following an effector failure, information regarding control saturation and/or inner-loop bandwidth reduction is identified on-line and delivered to algorithms that adapt the feedback gains of the guidance law. Flight path stability is then maintained in the face of degraded maneuvering capabilities.


(2) On-line trajectory command reshaping: Even with flight path stability maintained, the trajectory commands driving the guidance system may need to be continually reshaped on-line in order to achieve desired end conditions of the mission segment (e.g. on final approach, desired end conditions are characterized by a soft landing, at a certain runway touchdown point, at a certain flight speed). Here, Barron Associates’ approach is denoted as the Optimum-Path-To-Go (OPTG) algorithm. Polynomial networks describing the “best” remaining path to the end of the mission segment are interrogated on-line at regular intervals to obtain the optimal trajectory commands, given the current state and “health” of the vehicle.

Results:
This effort has been in support of the Air Force’s Integrated Adaptive Guidance & Control (IAG&C) program. Under the IAG&C program, the reconfigurable/adaptive guidance & control and trajectory reshaping systems have been successfully flight-tested using the Total In-Flight Simulator (TIFS) research aircraft. The flight tests were completed by the Flight and Aerospace Research Group, General Dynamics Advanced Information Systems (GDAIS) - formally Veridian. The flight tests were supported jointly by AFRL, Barron Associates and Boeing, Huntington Beach. The TIFS simulated approach/landings of the X-40A under a variety of single and multiple control surface failure experiments. The majority of the flight test results indicated the significant benefits of the control reconfiguration, guidance adaptation and trajectory-command reshaping, concluding in successful touchdown conditions. Although most touchdowns were simulated at an altitude of 200 feet, the pilots were comfortable enough with the system to take some of the experiments all the way to actual touchdown.

The flight test effort has resulted in a significant maturation of the guidance and trajectory reshaping technologies, and Barron Associates continues to pursue further developments in this area.

Preview a clip from the flight tests

TIFS Touchdown (159Mb - AVI)
TIFS Touchdown Nosecam (256Mb - AVI)

Links and References:
Schierman, J.D, D.G. Ward, J.R. Hull, J.F. Monaco, M.J. Ruth, "Adaptive Guidance Systems for Hypersonic Reusable Launch Vehicles," Proc. IEEE Aerospace Conference, Big Sky, MT, March, 2001.

Schierman, J.D, D.G. Ward, J.F. Monaco, J.R. Hull, "A Reconfigurable Guidance Approach For Reusable Launch Vehicles," Proc. AIAA Guidance, Navigation, and Control Conf., Montreal, Canada, Aug. 2001, AIAA Paper No. 2001-4429.

Schierman,J.D., J.R., Hull, Ward, D.G., “Adaptive Guidance with Trajectory Reshaping for Reusable Launch Vehicles,” Proc. AIAA Guidance, Navigation, and Control Conf., Monterey, CA, Aug. 2002, AIAA Paper No. 2002-4458.

Schierman, J.D., J.R. Hull, D.G. Ward, “On-Line Trajectory Command Reshaping for Reusable Launch Vehicles,” AIAA-2003-5439, Proc. AIAA Guidance, Navigation, and Control Conf., Austin, TX, Aug. 2003, AIAA Paper No. 2003-5439.