This paper discusses the development and results of two intelligent structures space-flight experiments, each of which could affect architecture designs of future spacecraft. The first, the advanced controls technology experiment I (ACTEX I), is a variable stiffness tripod structure riding as a secondary payload on a classified spacecraft. It has been operating well past its expected life since becoming operational in 1996. Over 60 on-orbit experiments have been run on the ACTEX I flight experiment. These experiments form the basis for in-space controller design problems and for concluding lifetime/reliability data on the active control components. Transfer functions taken during the life of ACTEX I have shown consistent predictability and stability in structural behavior, including consistency with those measurements taken on the ground prior to a three year storage period and the launch event. ACTEX I can change its modal characteristics by employing its dynamic change mechanism that varies preloads in portions of its structure. Active control experiments have demonstrated maximum vibration reductions of 29 dB and 16 dB in the first two variable modes of the system, while operating over a remarkable on-orbit temperature range of -80 °C to 129 °C. The second experiment, ACTEX II, was successfully designed, ground-tested, and integrated on an experimental Department of Defense satellite prior to its loss during a launch vehicle failure in 1995. ACTEX II also had variable modal behavior by virtue of a two-axis gimbal and added challenges of structural flexibility by being a large deployable appendage. Although the loss of ACTEX II did not provide space environment experience, ground testing resulted in space qualifying the hardware and demonstrated 21 dB, 14 dB, and 8 dB reductions in amplitude of the first three primary structural modes. ACTEX II could use either active and/or passive techniques to affect vibration suppression. Both experiments trailblazed spacecraft bus smart structures by developing over 20 new technologies. As pathfinders, experience was gained in the implications of space system analyses, verification tests, and for ways to leverage this technology to meet new satellite performance requirements.

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This paper describes the design of a computer-controlled planar manipulator and the modeling necessary to derive the dynamic equations of motion. The planar manipulator was built as an experimental research device for work in kine matics, dynamics, controls, design, and sensor development. The device consists of three joints and three links with a gripper and operates in a horizontal plane on air bearings. The planar manipulator was instrumented for position, veloc ity, and torque feedback from each joint and is controlled either manually, using a teach pendant, or directly from a computer. A modularity feature was also designed into the robot to allow for interchanging any electromechanical com ponents and to enable structural substitutions for investiga tions into flexibility and vibrations. The completed robot successfully exceeded performance specifications and design criteria. The next phase of the research focused on the development and evaluation of a computer model designed to simulate the open-loop dynamic behavior of the three-link, three-jointed, high-speed planar manipulator. Describing equations were developed for both the servo actuator and arm dynamics at each joint. Significant terms included were coulomb, viscous, and hysteresis damping; and centripetal, Coriolis, and cou pling inertial effects induced by relative motions of the arm structure. The model used the voltage into the power ampli fiers for each servo drive as the system input, and the joint angular position, velocity, and acceleration as the system output. Results from various inputs including a step-input function, a sinusoidal-input function, and a ramp-input func tion were found to compare closely with experimental data measured from the actual planar manipulator built during the course of the research.