Advanced Guidance and Control for Hypersonics and Space Access
Advanced guidance and control (AGC application to hypersonic air-breathers is planned. We list the test cases used to demonstrate that the desired results are achieved, briefly describe an automated test scoring method, and display results of the tests. Some of the technology components have reached the maturity level where they are ready for application to a new vehicle concept, while others are not far along in development.
Direct Fault Tolerant RLV Attitude Control-A Singular Perturbation Approach
In this paper, we present a direct fault tolerant control (DFTC) technique, where by "direct" we mean that no explicit fault identification is used. The technique will be presented for the attitude controller (autopiiot) for a reusable launch vehicle (RLV), although in principle it can be applied to many other applications. Any partial or complete failure of control actuators and effectors will be inferred from saturation of one or more commanded control signals generated by the controller. The saturation causes a reduction in the effective gain, or bandwidth of the feedback loop, which can be modeled as an increase in singular perturbation in the loop. In order to maintain stability, the bandwidth of the nominal (reduced-order) system will be reduced proportionally according to the singular perturbation theory. The presented DFTC technique automatically handles momentary saturations and integrator windup caused by excessive disturbances, guidance command or dispersions under normal vehicle conditions. For multi-input, multi-output (MIMO) systems with redundant control effectors, such as the RLV attitude control system, an algorithm is presented for determining the direction of bandwidth cutback using the method of minimum-time optimal control with constrained control in order to maintain the best performance that is possible with the reduced control authority. Other bandwidth cutback logic, such as one that preserves the commanded direction of the bandwidth or favors a preferred direction when the commanded direction cannot be achieved, is also discussed. In this extended abstract, a simplistic example is proved to demonstrate the idea. In the final paper, test results on the high fidelity 6-DOF X-33 model with severe dispersions will be presented.
Flight Testing of Reconfigurable Control Law on the X-36 Tailless Aircraft
Piloted simulation and e ight-test results from the evaluation of a recone gurable e ight control law for the X-36 tailless e ghter aircraft are presented. The recone gurable control law, which is based on dynamic inversion in an explicitmodelfollowing framework, employs an onlineneural network to adaptively regulatetheerror in the plant inversion, which may be due to modeling uncertainties, failures, or damage. Simulated actuator failures, which causedeffectorstobelockedatprescribed positions,wereinjectedtoevaluatethestability andhandling qualitiesof therecone gurablecontrol law underfailures. Thecontrol law was not given any knowledgeof the actuator failure, and fault detection logic was not employed. Piloted simulation testing was used to compare the recone gurable control law to the X-36 dynamic inversion control laws under simulated actuator failures. The recone gurable control law showed improved handling qualities and departure resistance relative to the baseline X-36 control laws.