Torey Davis

Vibration isolation and suppression system for precision payloads in space

This paper describes the design and performance testing of a vibration isolation and suppression system (VISS) which can be used to isolate a precision payload from spacecraft borne disturbances. VISS utilizes six hybrid isolation struts in a hexapod configuration. Central to the concept is a novel hybrid actuation concept which provides both passive isolation and active damping. The passive isolation is provided using a flight proven D-strut design. The passive design is supplemented by a voice coil based active system. The active system is used to enhance the performance of the passive isolation system at lower frequencies, and provide the capability to steer the payload.

Optical payload isolation using the Miniature Vibration Isolation System (MVIS-II)

Precision satellite payloads commonly require isolation from bus disturbance sources, such as reaction wheels, thrusters, stepper motors, cryo-coolers, solar array drives, thermal popping, and other moving devices. Since nearly every satellite essentially has a unique construction, custom isolation systems are usually designed to attenuate a wide bandwidth of disturbance frequencies. The disadvantage of these custom solutions is that they are not easily reusable or transferable and are generally not robust to changes in payload geometry and mass properties during the development. The MVIS-II isolation system is designed to provide vibration disturbance attenuation over a wide bandwidth, as well as being able to adapt to changes in payload mass properties and geometry, through active control of a smart material. MVIS-II is a collaborative effort between the Air Force Research Laboratory (AFRL) Space Vehicle Directorate and Honeywell Defense and Space to validate miniature hybrid (passive/active) vibration isolation of sensitive optical payloads. The original flight experiment was intended to isolate a non-critical representative payload mass for demonstration purposes; however, the MVIS-II has been adapted to support the primary optical payload onboard the Tactical Satellite 2 (TacSat-2). Throughout the program MVIS-II has been able to adapt to changes in the payload geometry and mass properties with modification limited to support structures only. The MVIS-II system consists of a hexapod of hybrid struts, where each strut includes a patented passive 3-parameter DStrut n series with a novel hydraulically amplified piezoelectric actuator with integral load cell. Additionally, Honeywells Flexible I/O controller electronics and software are used for command and control of the hardware. The passive D-Strut element provides a 40 dB/decade passive roll-off to attenuate mid-to-high frequency disturbances, while the active piezoelectric actuator is used for enhanced low frequency isolation. MVIS-II struts are 90% smaller in size and have 91% less mass than previous struts including Honeywells Vibration Isolation, Suppression, and Steering (VISS). The MVIS-II system is currently integrated in the TacSat-2, which has successfully launched from Wallops Flight Facility on Wallops Island, Virginia in December 2006. MVIS-II was launched under direction of the DoD Space Test Program. This paper will discuss the adaptive design of the MVIS-II isolation system including simulation, testing, and integration. Active and passive strut test results will be presented that demonstrate the wide bandwidth attenuation of vibration disturbances. Simulation results of expected on-orbit performance will also be discussed.

Hybrid active/passive actuator for spacecraft vibration isolation and suppression

A high-performance active/passive actuator has been developed for a multi-axis isolation and positioning system. This system will be used for pointing and vibration isolation of an optical spacecraft payload. The complementary active and passive elements are designed to provide passive broadband isolation,with active low- frequency isolation and steering. The active element is a linear, voice coil motor, based on Lorentzs force equation, and designed specifically for this application. The passive element consists of a tuned, three-parameter passive isolator. The governing relationships and methodology used in the active/passive actuator design are discussed along with integration issues. Actuator test data are presented and compared to expected performance demonstrating the actuators predictability.

Miniature vibration isolation system for space applications

In recent years, there has been a significant interest in, and move towards using highly sensitive, precision payloads on space vehicles. In order to perform tasks such as communicating at extremely high data rates between satellites using laser cross-links, or searching for new planets in distant solar systems using sparse aperture optical elements, a satellite bus and its payload must remain relatively motionless. The ability to hold a precision payload steady is complicated by disturbances from reaction wheels, control moment gyroscopes, solar array drives, stepper motors, and other devices. Because every satellite is essentially unique in its construction, isolating or damping unwanted vibrations usually requires a robust system over a wide bandwidth. The disadvantage of these systems is that they typically are not retrofittable and not tunable to changes in payload size or inertias. Previous work, funded by AFRL, DARPA, BMDO and others, developed technology building blocks that provide new methods to control vibrations of spacecraft. The technology of smart materials enables an unprecedented level of integration of sensors, actuators, and structures; this integration provides the opportunity for new structural designs that can adaptively influence their surrounding environment. To date, several demonstrations have been conducted to mature these technologies. Making use of recent advances in smart materials, microelectronics, Micro-Electro Mechanical Systems (MEMS) sensors, and Multi-Functional Structures (MFS), the Air Force Research Laboratory along with its partner DARPA, have initiated an aggressive program to develop a Miniature Vibration Isolation System (MVIS) (patent pending) for space applications. The MVIS program is a systems-level demonstration of the application of advanced smart materials and structures technology that will enable programmable and retrofittable vibration control of spacecraft precision payloads. The current effort has been awarded to Honeywell Space Systems Operation. AFRL is providing in-house research and testing in support of the program as well. The MVIS program will culminate in a flight demonstration that shows the benefits of applying smart materials for vibration isolation in space and precision payload control.

Performance of a launch and on-orbit isolator

A recently qualified Honeywell vibration isolation system does two things well. It supports and protects its payload during launch environments, and subsequently provides micro-inch level jitter reduction on-orbit. An elliptical hexapod provides six-degree-of-freedom support and isolation. The fluid-damped D-Strut isolation system maintains its payload optical alignment after vibration and thermal exposure. Vibration tests at one micro-inch input and at one- tenth of an inch input show almost identical damping and isolation responses. The 70-lb test payload was made from wood with an aluminum backbone. The payload provided accurate mounting geometries for the six isolator struts, and precision locations for ten accelerometers and an optical cube. Shock testing, launch-level random vibration, and launch sine vibration were imposed. The system was also subjected to thermal cycling. Functional transmissibility tests were performed before, midway, and after launch environments, at 0.25-g and 2.5-g sine input levels. Honeywells Matlab Isolator Design Tool predicted transmissibility between 6 degrees-of-freedom inputs and the six rigid body outputs. Another analysis code took these 36 transmissibilities and used optical element transfer functions to calculate an overall jitter number. Finally, 18 measured transmissibility curves from functional tests were fed through the optical jitter code.

Passive and active launch vibration studies in the LVIS program

A U.S. Air Force-sponsored team consisting of Boeing (formerly McDonnell Douglas), Honeywell Satellite Systems, and CSA Engineering has developed technology to reduce the vibration felt by an isolated payload during launch. Spacecraft designers indicate that a launch vibration isolation system (LVIS) could provide significant cost benefits in payload design, testing, launch, and lifetime. This paper contains developments occurring since those reported previously. Simulations, which included models of a 6,500 pound spacecraft, an isolating payload attach fitting (PAF) to replace an existing PAF, and the Boeing Delta II launch vehicle, were used to generate PAF performance requirements for the desired levels of attenuation. Hardware was designed to meet the requirements. The isolating PAF concept replaces portions of a conventional metallic fitting with hydraulic- pneumatic struts featuring a unique hydraulic cross-link feature that stiffens under rotation to meet rocking restrictions. The pneumatics provide low-stiffness longitudinal support. Two demonstration isolating PAF struts were designed, fabricated and tested to determine their stiffness and damping characteristics and to verify the performance of the hydraulic crosslink concept. Measurements matched analytical predictions closely. An active closed-loop control system was simulated to assess its potential isolation performance. A factor of 100 performance increase over the passive case was achieved with minor weight addition and minimal power consumption.

Heavy load vibration isolation system for airborne payloads

A high-performance vibration isolation system has been developed to isolate large-sensitive payloads from aircraft disturbances. The isolation system senses and adjusts for low frequency aircraft maneuvers and changes in the aircrafts flight angle of attack. Additionally, the isolation system passively filters higher frequency disturbances from aircraft to payload. Six pneumatic struts configured as a hexapod or Stewart Platform make up the primary portion of the isolation system and accomplish vibration isolation and payload support. Each isolator strut is a unique Patented design that takes advantage of gas (the ultimate smart material), because it has a capacity for large energy storage and it possesses a near linear viscosity over a broad temperature range. Any gas that exhibits a somewhat perfect-gas characteristic can be used inside the strut with similar performance results. For our application, gaseous nitrogen (GN2) was used. The pneumatic strut has shown an ideal isolator roll-off quality that is tunable for a variety of payloads and linear over a large dynamic range. Tunability stems from a dual chamber design that allows air-spring-rate changes while maintaining constant support of the load. The strut performance trait combined with the deterministic nature of the hexapod affords predictability and controllability. The system design enables a soft floating support of large payloads with accurate knowledge of their orientation with respect to the aircraft. Another distinctive feature of the isolation system design is a servo-controlled leveling system that senses a set point from an integrally mounted LVDT and fills or exhausts gas, as necessary, maintaining strut position during the rigors of flight. A combination of Commercial Off The Shelf (COTS) and control cards with custom plumbing provides the leveling function. All tolled, the isolation system has functioned flawlessly in service, and has raised the bar for vibration isolator performance. In this paper the isolation system design will be detailed, and its performance measurements will be presented.

Passive damper exhibiting the ideal dashpot characteristic: F=CV

One of the most difficult tasks in the structural control industry is providing linear, predictable, passive damping over a wide frequency range. This challenge has been worked around successfully in the past, but rarely has it been performed ideally. The subject matter of this paper takes a radical step toward attaining the goal of linear damping performance, while adding very low static stiffness to the system being damped.