Vaios Lappas

Attitude control for small satellites using control moment gyros

Abstract In this paper a new Attitude Control System is proposed, based on Control Moment Gyroscopes (CMG). These actuators can provide unique torque, angular momentum and slew rate capabilities to small satellites without any increase in power, mass or volume. This will help small satellites become more agile. Agility considerably increases the operational envelope and efficiency of spacecraft and substantially increases the return of earth and science mission data. In the proceeding sections the fundamental features of CMGs are presented. A low cost, miniature SGCMG designed for an enhanced microsatellite is analysed. Sizing of a proposed SGCMG indicates the advantages of using CMGs. The SGCMG is able to produce a torque of 9.82 mNm and this is confirmed through experiments performed on an air-bearing table. A comparison between the SGCMG and a RW demonstrates the mass and power savings that can be gained by using CMGs.

Design and testing of a control moment gyroscope cluster for small satellites

Experimental results on the performance of a control moment gyroscope cluster are presented. The goal is to design and evaluate a control moment gyroscope cluster for three-axis control for agile small satellites. The experimental data are compared with simulation (theoretical) results and both are used to verify the principles, advantages, and performance specifications of a control moment gyroscope cluster for a small satellite, in a practical way. Control moment gyroscope systems are considered in the literature to be more efficient devices, from an electrical power point of view, than current actuators such as reaction/momentum wheels. Experimental measurements are presented and then compared to two reaction wheels of different size. Control moment gyroscopes are shown to have a potential performance advantage over reaction/momentum wheels for spacecraft with agile requirements.

Characterising Wireless Sensor Motes for Space Applications

This paper is concerned with application of standard wireless COTS protocols to space. Suitability of commercially available wireless sensor mote kits for communication inside and between satellites is investigated. Spacecraft applications of motes are being considered and a set of requirements are identified. Selected mote kits are tested under various scenarios complying with spacecraft testing procedures. The paper details the results of the carried out functional, EMC/I, vibration, thermal and radiation tests.

Survey of Technology Developments in Flywheel Attitude Control and Energy Storage Systems

Advances in microprocessors and composite materials in the past decade, along with limitations of chemical batteries for U.S. Air Force mission concepts, have caused a renewed interest in flywheel energy storage systems for space applications. This interest has also been driven in the past by the promise of using flywheel systems for energy storage and as attitude control actuators. The primary issues are power efficiency, mass and size, and long-term stability. Flywheels as one-to-one replacements for spacecraft batteries are competitive for only a few special missions. When flywheels replace components in two major bus subsystems, the potential mass and volume benefits are attractive. This especially benefits future small satellite missions that seek agile slewing with high peak power. The objective of this paper is to describe the progression of the flywheel technology state of the art for combined energy storage and attitude control systems in space applications and the current energy storage and attitude control systems efforts.

Sizing/Optimization of a Small Satellite Energy Storage and Attitude Control System

Abstract : The recent advent of miniature single gimbal control moment gyroscopes has spawned interest in variable speed versions for combined energy storage and attitude control systems on small satellites. Although much has been studied on the theory behind such a system, little has been done In optimally sizing these actuators for small satellite applications. Therefore this paper investigates the fundamental design concepts, optimal sizing, and mission benefits for these actuators. Given a set of small satellite agility and energy storage requirements, an optimal, nonlinear programming method is applied to this problem.

Microsolar sails for Earth magnetotail monitoring

Solar sails have been studied in the past as an alternative means of propulsion for spacecraft. Recent advances in solar sail technology and the miniaturization of technology can drive these systems much smaller (<5 kg mass, <10 msail diameter) than existing sails, while still having a highV and acceleration capability. With these unique capabilities of miniature solar sails, called solar kites, some very unique space science missions can be achieved which are difficult to implement using conventional propulsion techniques. One such unique candidate mission is to study the Earths magnetotail. The paper describes the main design features and technologies of a solar kite mission/ platform and demonstrates that a cluster of solar kites with science payloads can provide multiple, in situ measurements of the dynamic evolution of energetic particle distributions of the rotating geomagnetic tail of Earth. With a unique design, a solar kite proves to be an efficient, affordable, and versatile solution for the mission analyzed with a significant science return.

Redundant Reaction Wheel Torque Distribution Yielding Instantaneous L2 Power-Optimal Spacecraft Attitude Control

The attitude-control problem of a rigid spacecraft containing a redundant set of reaction wheels is investigated. Particularly with small spacecraft the available power is very limited due to the small surface area to radiate excess heat. A power-optimal reaction wheel motor torque distribution strategy is developed that minimizes the instantaneous electrical power requirements. Power regeneration from slowing down the wheels is not considered in this work. The new torque distribution is developed as a modification to the traditional minimum-torque solution. Degenerate conditions in which at least one rotor has zero speed are investigated, as well as particular symmetric wheel speed configurations. The new control is able to reduce the amount of mechanical power and energy required by about 10―20%, while only marginally increasing the average required torque.

Time-Efficient Angular Steering Laws for Rigid Satellite

This paper proposes a new integrative control logic for rapid maneuvering of a rigid satellite using reaction wheels. The proposed control algorithm is of a state feedback nature and is designed to accommodate a variety of conditions, such as the general three-dimensional direction of rotation, initial and/or final angular rates, general alignment of three or four reaction wheels, torque and angular rate limits, and system time response limits. Simulations indicate that the new algorithm allows smooth control, free of chattering. The new controller also uses a tuning capability to compensate for time delays and parasitic dynamics. The tuning capability can be varied in order to enhance performance or robustness. Robustness of the algorithm is proven through a stability analysis and supported by detailed and practical simulations.

Wireless Sensor Motes for Small Satellite Applications

Motes are low-cost COTS (commercial off-the-shelf) microchips, which integrate a processor, onboard sensor, RF communications link, and a power unit. High levels of power efficiency can be achieved with the use of the IEEE 802.15.4 protocol for communication between the motes, allowing long-term periods of operation for motes and reducing the power requirements of a spacecraft. The article examines the feasibility of using sensors for harness reduction between satellite subsystems, and for inter-satellite networking capabilities between satellite swarms

Rapid Rotational Maneuvering of Rigid Satellites with Hybrid Actuators Configuration

A new attitude control method for agile rigid spacecrafts that is based on combining single gimbal control moment gyros together with reaction wheels is presented. The method is expected to suit remote sensing spacecrafts that are required to perform multiple rapid retargeting of their line of sight. The main advantage of single gimbal control moment gyros is rapid rotational maneuvering, but their application for high quality pointing requires a very accurate gimbal mechanism. On the other hand, the reaction wheels may be more easily applied for accurate pointing, but their torque-to-power performance is inferior for maneuvering compared to single gimbal control moment gyros. The paper shows that careful coordination between reaction wheels and single gimbal control moment gyros, together in a hybrid configuration, draws more performance from single gimbal control moment gyros in terms of agility and achieves quality pointing between maneuvers by using only reaction wheels. The high-level control is base...