Middeck Active Control Experiment Research Articles

Advanced smart structures flight experiments for precision spacecraft

This paper presents an overview as well as data from four smart structures flight experiments directed by the U.S. Air Force Research Laboratory's Space Vehicles Directorate in Albuquerque, New Mexico. The Middeck Active Control Experiment $ ̄ Flight II (MACE II) is a space shuttle flight experiment designed to investigate modeling and control issues for achieving high precision pointing and vibration control of future spacecraft. The Advanced Controls Technology Experiment (ACTEX-I) is an experiment that has demonstrated active vibration suppression using smart composite structures with embedded piezoelectric sensors and actuators. The Satellite Ultraquiet Isolation Technology Experiment (SUITE) is an isolation platform that uses active piezoelectric actuators as well as damped mechanical flexures to achieve hybrid passive/active isolation. The Vibration Isolation, Suppression, and Steering Experiment (VISS) is another isolation platform that uses viscous dampers in conjunction with electromagnetic voice coil actuators to achieve isolation as well as a steering capability for an infra-red telescope.

On-Orbit Closed-Loop Control Results for the Middeck Active Control Experiment

An in-depth analysis is presented of the closed-loop results and insights from the on-orbit control experiments of the Middeck Active Control Experiment (MACE). MACE was e own in the Shuttle middeck on STS-67 in March 1995 to investigate issues associated with a change in operational environment from ground to space for a payload pointing spacecraft that cannot be tested ina realisticground simulation. Theseresults show 1)equivalent performance can be obtained using enite element-based and measurement-based control design models; 2) the beneets available from testing the structure on the ground prior to eight, even if these tests are in a different cone gurationthanthatusedonorbit;and3)theperformancelimitationsassociatedwithvariouscontroltopologies. Theseclosed-loop results provide insight intohow future on-orbit closed-loop experiments could beimproved, and they also help build conedence in the on-orbit capabilities of future multipayload spacecraft.

Parametric uncertainty model for control design and analysis

An approach is presented that develops an accurate model of parametric uncertainty suitable for structural control design and analysis. This approach requires a number of different data sets to capture the dynamics of the system and its variability. Using an identification technique, the modal parameters of the finite element model are estimated. The parameter estimates are combined into a parametric uncertainty model in the form of mean errors and bounds on the modal parameters, which can then be used for robust control design and analysis. The development and utilization of this uncertainty model is demonstrated using the middeck active control experiment, a shuttle middeck experiment that flew on STS-67 in March 1995.

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.

Classically Rationalized Low-Order, Robust Structural Controllers

An experimental and analytical comparison of classically rationalized and optimal control design techniques is conducted. Classically rationalized compensators blend the loop assignments, complex topological design, and robustness of optimal controllers and the lower order, robustness, and practical insight of classical controllers. The single-input/single-output disturbance rejection problem for controlled structures is divided into four distinct topologies, and optimal controllers aredesignedand interpreted classically.Theobservationsarethen summarized into a set of design rules forthedesign oflow-order robustcontrollers. Classically rationalized and robust compensators are experimentally implemented on the Middeck Active Control Experiment, a Shuttle e ight experiment

Flight results from the Middeck Active Control Experiment (MACE)

Flight results from the Middeck Active Control Experiment (MACE)

Experimental Verification of Vibration Reduction in Flexible Spacecraft Using Input Shaping

The performance of many spacecraft can be improved by using closed-loop control and command-shaping techniques. However, because little information exists about the operation of controlled structures in zero gravity, it is dife cult for designers to anticipate and place cone dence in the on-orbit performance of their ground-based control designs. To address this issue, the middeck active control experiment was conducted aboard the Space Shuttle Endeavor in March of 1995. The results of the command shaping experiments implemented during the mission are presented, and guidelines forusing command shaping to suppress unwanted vibration in e exible space structures are proposed. HE combination of stringent performance specie cations and lightly damped structural modes makes the effective operation of many space systems vulnerable to vibration. To attack this problem, closed-loop control and open-loop command-shaping techniques are often enlisted. However, with only ground-based testing available prior to on-orbit implementation, uncertainty about zerogravity(0-g) behavior can hamper the success of these 0- g control designs. The Massachusetts Institute of Technology (MIT) middeck activecontrolexperiment (MACE)isaSpaceShuttlee ightexperiment designed to expose critical issues associated with the design of controllers and shaped commands for 0 g. As part of this experiment, data were collected from a e exible structure on-orbit, and results illustrated that both the control and command-shaping strategies employed on the test article could effectively reduce problematic vibration. Additionally, as a result of careful ground-based modeling efforts, predictions of 0- g behavior were accurate enough to achieve high-performance control and command shaping without on-orbit redesign. After introducing the MIT MACE project and the MACEcommand-shaping efforts, this paper presents the results from a specie c subset of the mission experiments: the MACE input shaping tests. Based on these results, key points are summarized and conclusions are drawn.

Vibration Reduction Using Multi-Hump Input Shapers

Input shaping is a method for reducing residual vibrations in computer-controlled machines. Vibration is eliminated by convolving an input shaper, which is a sequence of impulses, with a desired system command to produce a shaped input. The shaped input then becomes the command to the system. Requiring the vibration reduction to be robust to modeling errors and system nonlinearities is critical to the success of the shaping process on any real system, Input shapers can be made very insensitive to parameter uncertainty; however, increasing robustness usually increases system delays. A design process is presented that generates input shapers with insensitivity-to-time-delay ratios that are much larger than traditionally designed input shapers. The advantages of the new shapers are demonstrated with computer simulations and their performance is verified with experimental results from the MIT Middeck Active Control Experiment, which was performed on board the Space Shuttle Endeavor.

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.

MACE: Anatomy of a Modern Control Experiment

The Middeck Active Control Experiment (MACE) was designed as a Space Shuttle flight experiment to be used 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 which is at the forefront of flexible structural control. MACE was flown on STS-67 in March 1995, and this paper introduces a session devoted to the results of the mission.

Overview of Closed Loop Results for MACE

This paper presents closed loop results and insight from the on-orbit experiments of the Middeck Active Control Experiment (MACE). MACE was flown in the shuttle middeck on STS-67 in March 1995 to investigate issues associated with a change in operational environment from ground to space based operations of a payload pointing spacecraft that cannot be tested in a realistic ground simulation. These results show that equivalent performance can be obtained using finite element based and measurement based control, the benefits available from testing a structure on the ground, even in a different configuration to that used on-orbit, and the limitations associated with various control topologies. These MACE results provide much insight into how future on-orbit closed loop experiments can be improved.

On-Orbit Modeling and Identification for MACE

The Middeck Active Control Experiment (MACE) is a space shuttle flight experiment which flew on STS-67 in March, 1995. The objective of the experiment was to explore advanced control techniques to achieve high precision pointing and vibration control of future spacecraft. Modeling and identification methodologies are presented whose end results are models useful for modern control design techniques. These methodologies are validated using on-orbit experimental data from two configurations of the MACE test article, with limitations discussed based on flight experience. Nonlinearities, which were not anticipated before flight, are investigated by exciting the structure with different excitation amplitudes.

Vibration Reduction in Flexible Space Structures Using Input Shaping on MACE: Mission Results

The performance of many spacecraft can be improved by using closed-loop control and command-shaping techniques. However, since little information exists about the operation of controlled structures in zerogravity, it is difficult for designers to anticipate and place confidence in the on-orbit performance of their ground based control designs. To address this issue, the Middeck Active Control Experiment (MACE) was conducted aboard the Space Shuttle Endeavor in March of 1995. This paper presents the results of the command shaping experiments implemented during the mission and proposes guidelines for using command shaping to suppress unwanted vibration in flexible space structures.

Identification and Parameter Estimation for Control Design

An approach is proposed which unifies finite element and measurement modeling of flexible systems for the purpose of creating an accurate uncert ainty model suitable for control design. The Discrete Extended Kalman Filter is used to estimate modal parameters and a measurement modd. Using a number of measurement models that capture the actual dynamics of the structure, a "mean" model is created with bounds on critical parameters of the system which can thpn be used with a robust control technique. The process is demonstrated using the Middeck Active Control Experiment, a shuttle middeck experiment which flew on STS-67 in March 1995.

Control Analysis for MACE: Methods and Limitations

Analysis of a control system design prior to implementation is critical for determining expected stability and performance of the true system. For the Middeck Active Control Experiment (MACE), a Shuttle Middeck experiment which flew on STS-67 in March 1995, two distinct analysis procedures are followed. One utilizes open loop data which is only available during the flight. The other involves development and use of an uncertainty model and a mixed-μ analysis to test for stability over the full range of uncertainty. Using the extensive on-orbit data accumulated during the 14-day Shuttle mission, the effectiveness of both procedures is assessed

Frequency Domain Structural System Identification by Observability Range Space Extraction

This paper presents the Frequency Domain Observability Range Space Extraction (FORSE) identification algorithm. FORSE is a singular value decomposition based identification algorithm which constructs a state space model directly from frequency domain data. The concept of system identification by observability range space extraction was developed by generalizing the Q-Markov Covariance Equivalent Realization and Eigensystem Realization Algorithm. The numerical properties of FORSE are well behaved when applied to multi-variable and high dimensional structural systems. It can achieve high modeling accuracy by properly overparameterizing the system. The effectiveness of this algorithm for structural system identification is demonstrated using the MIT Middeck Active Control Experiment (MACE). MACE is an active structural control experiment to be conducted in the Space Shuttle middeck. Results of ground experiments using this algorithm will be discussed.

Optimal Popov controller analysis and synthesis for systems with real parameter uncertainties

Robust performance analysis plays an important role in the design of controllers for uncertain multivariable systems. Recent research has investigated the use of absolute stability criteria to develop less conservative analysis tests for systems with linear and nonlinear real parameter uncertainties. This note extends previous work on optimal /spl Hscr/2 performance analysis using the Popov criterion by presenting a numerical homotopy algorithm that can be used to analyze systems with less restrictive assumptions on the structure of the uncertainty block. The technique is used to compare relative robustness capabilities of the various control algorithms that have been designed for the Middeck active control experiment (MACE). The analysis is combined with the previously presented Popov controller synthesis to yield compensators that guarantee robust performance for systems with real parameter uncertainty.

Time Domain State Space Identification of Structural Systems

An integrated time domain state space identification technique for structural systems is presented. This technique integrates the Observability Range Space Extraction identification algorithm, Balanced Realization model reduction algorithm, and Least Square model updating algorithm to generate low order and highly accurate state space models for structural systems based upon time domain data. The algorithms are integrated in such a manner that the Observability Range Space Extraction identification algorithm is used to generate an initial overparameterized state space model and then the Balanced Realization model reduction and Least Square model updating algorithms are used to iteratively reduce and update the model to achieve minimum prediction errors in time domain. We shall present the Observability Range Space Extraction identification algorithm and the Least Square model updating algorithm and discuss the integrated identification technique. The MIT Middeck Active Control Experiment (MACE) is used as an application example. MACE is an active structure control experiment to be conducted in the Space Shuttle middeck. Results of ground experiments using this technique will be discussed.

Development of on-orbit predictions for the middeck active control experiment

The paper presents the modeling and control design issues associated with a change in the operating environment for the Middeck Active Control Experiment (MACE): a Shuttle program scheduled to fly on STS-67, March 1995. MACE was designed to investigate the extent to which the on-orbit behavior of flexible spacecraft can be predicted and controlled using analysis and ground testing. In this paper, a refined analytic model is used to predict the on-orbit dynamics, and several techniques for estimating the on-orbit errors are discussed. Current closed-loop results using error models based on prior ground experiments predict a 35 dB performance improvement.