Jack H. Jacobs

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.

A SPIDER TECHNOLOGY OVERVIEW

Increased satellite requirements in terms of maneuverability, imaging resolution, and imaging bandwidth continue to drive the technological development of large, ultra-light, flexible structures. However, due to the immense size of some of these proposed structures (25 m in diameter or even larger), the question remains as to whether or not the satellite could maintain the required surface accuracy and tolerance for useful image processing. Current research into gossamer satellites and structures is progressing from passive systems to actively controlled systems. The controllability of a gossamer membrane or surface depends on the development of two primary technologies: material science and distributed active control systems. As material science continues to advance toward areal densities on the order of 0.1 kg/m 2

Configurable spacecraft control architectures for on-orbit servicing and upgrading of long life orbital platforms

Large orbital platforms provide unique and essential space-based capabilities for science, intelligence, and defense missions potentially supporting very large aperture imagers, antenna farms, SARs, radiometers and other systems. In order to provide maximum return on the investment required, it is essential to have a significant autonomous on-orbit servicing, upgrade and repair capability such that the platform can operate successfully for decades and have new capabilities added to it. The dependence on human upgrades on-orbit must diminish as we go farther in space to minimize the risk to life. In order for such autonomous operations to be practical, current technologies from robotics, distributed computing, and spacecraft operation need to be integrated and demonstrated. We are exploring the application of collaborative control strategies designed for multi-agent critical systems, as well as network and distributed agent computing to demonstrate some of the basic functionality needed to coordinate tasks autonomously in a dynamic environment.

Miniature vibration isolation system for space applications. Phase II

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. During the Phase I MVIS program, funded by AFRL and DARPA, a hybrid piezoelectric/D-strut isolator was built and tested to prove its viability for retroffitable insertion into sensitive payload attachments. A second phase of the program, which is jointly funded between AFRL and Honeywell, was started in November of 2002 to build a hexapod and the supporting interface electronics and do a flight demonstration of the technology. The MVIS-II 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. This paper describes the simulations, overall test plan and product development status of the overall MVIS-II program as it approaches flight.

Structural control of a flexible satellite bus for improved jitter performance

The increasing demand for global communications and limitations on RF communications bandwidth has driven several constellations to baseline laser cross-links between the satellites within their constellations. The use of laser communications over a long distance dictates the need for accurate pointing and jitter suppression in order to maintain signal continuity. Vibrations upon a satellite bus or orbit come from several sources including: momentum systems, flexible appendages, motors and cryocoolers. Attenuation of these vibrations requires a combination of disturbance reduction, disturbance isolation, payload isolation, input command shaping, appendage damping and passive/active bus structural control. This paper addresses these techniques in a systems approach to satellite structural control. Experimental results from a representative flexible satellite truss structure using a series of integral D-Strut structural dampers is presented. The passive damping system is used to reduce resonant amplification of disturbances on precision optical equipment jitter. The use of different combinations of longitudinal, transverse and diagonal dampers is discussed to achieve specific modal damping. In addition, the design of the integral truss dampers is discussed along with their application to satellite bus construction.

Cold interferometric nulling demonstration in space (CINDIS)

The Cold Interferometric Nulling Demonstration in Space (CINDIS) is a modest-cost technology demonstration mission, in support of interferometer architectures for Terrestrial Planet Finder (TPF). It is designed to provide as complete as possible a demonstration of the key technologies needed for a TPF interferometer at low risk, for a cost less than

Design and fabrication of a full-scale actively controlled satellite appendage simulator unit

300M. CINDIS foregoes scientific objectives at the outset, enabling significant cost savings that allow us to demonstrate important features of a TPF interferometer, such as high-contrast nulling interferometry at 10 μm wavelength, vibration control strategies, instrument pointing and path control, stray light control, and possibly 4-aperture compound nulling. This concept was developed in response to the NASA Extra-Solar Planets Advanced Concepts NRA (NRA-01-OSS-04); this paper presents the results of the first phase of the study.

Hybrid passive and active vibration isolator architecture

Modern satellites require the ability to slew and settle quickly in order to acquire or transmit data efficiently. Solar arrays and communication antennas cause low frequency disturbances to the satellite bus during these maneuvers causing undesirable induced vibration of the payload. The ability to develop and experimentally demonstrate attitude control laws which compensate for these flexible body disturbances is of prime importance to modern day satellite manufacturers. Honeywell has designed and fabricated an actively controlled Appendage Simulator Unit (ASU) which can physically induce the modal characteristics of satellite appendages on to a ground based satellite test bed installed on an air bearing. The ASU consists of two orthogonal fulcrum beams weighting over 800 pounds each utilizing two electrodynamic shakers to induce active torques onto the bus. The ASU is programmed with the state space characteristics of the desired appendage and responds in real time to the bus motion to generate realistic disturbances back onto the satellite. Two LVDTs are used on each fulcrum beam to close the loop and insure the system responds in real time the same way a real solar array would on-orbit. Each axis is independently programmable in order to simulate various orientations or modal contributions from an appendage. The design process for the ASU involved the optimization of sensors, actuators, control authority, weight, power and functionality. The smart structure system design process and experimental results are described in detail.