Roger M. Glaese

Finite element model-based robust controllers for the middeck active control experiment (MACE)

The middeck active control experiment (MACE) is a space shuttle flight experiment intended to demonstrate high authority active structural control in zero gravity (0-g) conditions based on analysis and ground testing. Finite element structural models are very important for the MACE program because they can be used to predict the on-orbit dynamics of the test article. However, finite element models tend to be inaccurate, requiring the use of parametric robust control techniques to achieve good performance. Several such control techniques and an overall design methodology are discussed in this paper. Experimental results from several tests are used to illustrate the feasibility of achieving good H/sub 2/ performance on the test article with robust controllers based on the finite element model. This demonstration improves confidence in the eventual on-orbit performance of this experiment and other future spacecraft.

Derivation of zero-gravity structural control models from analysis and ground experimentation

The Middeck Active Control Experiment (MACE) is a Space Shuttle flight experiment that flew on STS-67 in March 1995, to demonstrate high-authority active structural control in microgravity conditions. Because no experimental on-orbit data were available before flight, the model used to derive these controllers was obtained from a combination of analysis and openand closed-loop ground testing. A modeling approach to obtain this 0-g model is presented along with its application to the MACE test article. This approach starts with a 1-g model, which includes gravity and suspension effects. This 1-g model is improved using ground test results in a process called updating. Once updated, it is verified through a combination of structural perturbation and closed-loop control. Finally, the gravity and suspension effects are removed to arrive at a prediction of the 0-g behavior of the structure. Flight data are used to demonstrate the effectiveness of this approach.

Finite element model based robust controllers for the MIT Middeck Active Control Experiment (MACE)

The Middeck Active Control Experiment (MACE) is a space shuttle flight experiment intended to demonstrate high authority active structural control in zero gravity (0-g) conditions based on analysis and ground testing. Finite element structural models are very important for the MACE program because they can be used to predict the on-orbit dynamics of the test article. However, finite element models tend to be inaccurate, requiring the use of parameter robust control techniques to achieve good performance. Several such control techniques and an overall design methodology are discussed in this paper. Experimental results from several tests are used to illustrate the feasibility of achieving good /spl Hscr//sub 2/ performance on the test article with robust controllers based on the finite element model. This demonstration improves confidence in the eventual on-orbit performance of this experiment and other future spacecraft.

Gravity and suspension effects on the dynamics of controlled structures

The effects of gravity on the actuators, sensors and structural plant of a controlled flexible structure are investigated. These influences include gravity stiffening, gravity induced deformations, gravity influence on inertial sensors and actuators, and the interaction with the suspension system. For each of the four influences, a simplified model is derived, from which the appropriate non-dimensional parameter can be identified, and the magnitude of the influence estimated. The construction of a detailed numerical model, which includes the four gravity influences, is outlined. This modeling procedure is then applied to a simplified model of the Middeck Active Control Eperiment (MACE). The influence on the poles and input-output transfer function is examined for several variations in the plant. The modeling procedure is also applied to the MACE experimental hardware. Experimental and model-based transfer functions are compared to demonstrate the significant improvement by incorporating gravity effects.

Derivation of 0-g structural control models from analysis and 1-G experimentation

The Middeck Active Control Experiment (MACE) is a space shuttle flight experiment, manifest for launch on STS-67 on March 2, 1995, intended to demonstrate high authority active structural control in zero gravity conditions. Since no experimental on-orbit data is available before flight, the model used to derive these controllers must be obtained from a combination of analysis and openand closed-loop ground testing. A general modeling approach to obtain this 0-g model is presented along with its application to the MACE test article. This modeling approach starts with a 1-g model, which includes gravity and suspension effects on the structure. This 1-g model is improved using ground test results in a process called updating. Once the model has been updated, it is verified through a combination of structural perturbation and closed-loop control. Finally, after the model has been verified, the gravity and suspension effects are removed to arrive at a prediction of the 0-g behavior of the structure.

Flight Results from the Middeck Active Control Experiment (MACE)

The middeck active control experiment (MACE) was designed as a Space Shuttle flight experiment to demonstrate high authority active structural control in zero-gravity (0-g) conditions based on analysis, ground testing, and on-orbit control redesign. MACE is a multidisciplinary project that is at the forefront of flexible structural control. MACE was first flown on STS-67 in March 1995, and a summary of the program objectives and mission experimental results is provided.

The Middeck Active Control Experiment (MACE): using space for technology research and development

The Middeck Active Control Experiment (MACE) is a United States Space Shuttle flight experiment which flew on STS-67 in March of 1995. MACE was designed by the Space Engineering Research Center at the Massachusetts Institute of Technology, in collaboration with Payload Systems Incorporated, the NASA Langley Research Center, and Lockheed Missiles and Space Company. The goal is to explore approaches to achieving high precision pointing and vibration control of future spacecraft and satellites. In particular, MACE extends the bandwidth of conventional rigid body instrument pointing and attitude controllers to include the flexible modes of the satellite. Since the success of such control is intimately dependent upon the accuracy of the spacecraft model used for control design, MACE is essentially a spacecraft modeling validation effort where success is determined by the control performance and predictability that is achieved in Earth orbit. MACE builds upon the concept of the Middeck O-Gravity Dynamics Experiments (MODE), which flew on STS-40, STS-48 and STS-62 as a dynamics test facility to characterize fluid, Space Station structure, and crew motion dynamics in zero-gravity. MACE augments the MODE facility with real-time digital control capabilities.

A COMPARISON OF CONTROL DESIGN MODELS FOR A ONE-DIMENSIONAL STRUCTURAL-ACOUSTIC SAMPLE PROBLEM

The behavior of the simplest structural-acoustic system, namely a mass-spring piston at the end of a one-dimensional acoustic waveguide, is investigated from the perspective of closed-loop control. Three models, containing increasing levels of information about the structural-acoustic coupling, are developed. These models are a structural model only, a wave model incorporating the local acoustic coupling, and a fully coupled structural-acoustic model. Controllers are designed to reduce the acoustic pressure in the waveguide using each of these models and then implemented on the fully coupled structuralacoustic finite element model. As might be expected, the achievable acoustic reduction shows a direct correlation with model complexity. However, the intermediate model achieves 99% of the reduction of the most complex model without the features of the more complex model that make it prohibitive for use in more realistic situations.

A generalized impedance matching feedback law for structural-acoustic control

Impedance matching compensators are investigated for structural-acoustic control. The primary method for deriving these compensators is the minimization of acoustic power flow emanating from the structure-acoustic boundary. Unfortunately, due to the complexity of the solution, power flow minimization via Wiener filtering can only be used for extremely simple situations. The power flow minimization is recast in a state-space formulation that has a wealth of numerical tools, namely .the Linear Quadratic Gaussian (LQG) design technique. The equivalence between power flow minimization and the solution of the LQG problem is demonstrated on a simple one-dimensional structural-acoustic sample problem. To illustrate the LQG impedance matching derivation for more realistic systems, it is applied to a two-dimensional sample problem.

Physical model-set identification for robust control of flexible structures

An approach to dynamic system identification is presented taking into account the goal of enhancing robust control performance of flexible structures. Identification techniques are derived which take advantage of the physics of structural dynamics and can provide realistic bounds for all potential parameter uncertainties. The developed approach includes input optimization which distributes excitation energy in such a way that the influence of residual uncertainties on robust control performance is reduced.