Autonomous spacecraft attitude control using magnetic torquing only

Magnetic torquing of spacecraft has been an important mechanism for attitude control since the earliest satellites were launched. Typically a magnetic control system has been used for precession/nutation damping for gravity-gradient stabilized satellites, momentum dumping for systems equipped with reaction wheels, or momentum-axis pointing for spinning and momentum-biased spacecraft. Although within the small satellite community there has always been interest in expensive, light-weight, and low-power attitude control systems, completely magnetic control systems have not been used for autonomous three-axis stabilized spacecraft due to the large computational requirements involved. As increasingly more powerful microprocessors have become available, this has become less of an impediment. These facts have motivated consideration of the all-magnetic attitude control system presented here. The problem of controlling spacecraft attitude using only magnetic torquing is cast into the form of the Linear Quadratic Regulator (LQR), resulting in a linear feedback control law. Since the geomagnetic field along a satellite trajectory is not constant, the system equations are time varying. As a result, the optimal feedback gains are time-varying. Orbit geometry is exploited to treat feedback gains as a function of position rather than time, making feasible the onboard solution of the optimal control problem. In simulations performed to date, the control laws have shown themselves to be fairly robust and a good candidate for an onboard attitude control system

Design study for LANDSAT-D attitude control system

The gimballed Ku-band antenna system for communication with TDRS was studied. By means of an error analysis it was demonstrated that the antenna cannot be open loop pointed to TDRS by an onboard programmer, but that an autotrack system was required. After some tradeoffs, a two-axis, azimuth-elevation type gimbal configuration was recommended for the antenna. It is shown that gimbal lock only occurs when LANDSAT-D is over water where a temporary loss of the communication link to TDRS is of no consequence. A preliminary gimbal control system design is also presented. A digital computer program was written that computes antenna gimbal angle profiles, assesses percent antenna beam interference with the solar array, and determines whether the spacecraft is over land or water, a lighted earth or a dark earth, and whether the spacecraft is in eclipse

Evaluation of a semi-active gravity gradient system. Volume II - Appendices

Evaluation of semi-active gravity gradient system - appendixe

A Brief Survey of Attitude Control Systems for Small Satellites using Momentum Concepts

High-accuracy pointing capabilities are desired for many three-axis stabilized small satellites. Momentum-based attitude control system actuators, initially developed for larger satellites, are being utilized by small satellites to meet these pointing requirements. This paper provides an overview of momentum devices available for small satellite applications and three-axis attitude control system (ACS) configurations using these devices. Factors affecting the selection and sizing of ACS components are also addressed. Included are suggestions for potential ACS improvements and cost-saving measures that will make momentum devices more accessible to the small satellite community

Magsat attitude dynamics and control: Some observations and explanations

Before its reentry 7 months after launch, Magsat transmitted an abundance of valuable data for mapping the Earth's magnetic field. As an added benefit, a wealth of attitude data for study by spacecraft dynamicists was also collected. Because of its unique configuration, Magsat presented new control problems. With its aerodynamic trim boom, attitude control was given an added dimension. Minimization of attitude drift, which could be mapped in relative detail, became the goal. Momentum control, which was accomplished by pitching the spacecraft in order to balance aerodynamic and gravity gradient torques, was seldom difficult to achieve. Several interesting phenomena observed as part of this activity included occasional momentum wheel instability and a rough correlation between solar flux and the pitch angle required to maintain acceptable momentum. An overview is presented of the attitude behavior of Magsat and some of the control problems encountered. Plausible explanations for some of this behavior are offered. Some of the control philosophy used during the mission is examined and aerodynamic trimming operations are summarized

Design study for LANDSAT D attitude control system

A design and performance evaluation is presented for the LANDSAT D attitude control system (ACS). Control and configuration of the gimballed Ku-band antenna system for communication with the tracking and data relay satellite (TDRS). Control of the solar array drive considered part of the ACS is also addressed

Orbiting Geophysical Observatory Attitude Control Subsystem design survey

Development history and design modifications for attitude control subsystem of OG

Spacecraft attitude control for a solar electric geosynchronous transfer mission

A study of the Attitude Control System (ACS) is made for a solar electric propulsion geosynchronous transfer mission. The basic mission considered is spacecraft injection into a low altitude, inclined orbit followed by low thrust orbit changing to achieve geosynchronous orbit. Because of the extended thrusting time, the mission performance is a strong function of the attitude control system. Two attitude control system design options for an example mission evolve from consideration of the spacecraft configuration, the environmental disturbances, and the probable ACS modes of operation. The impact of these design options on other spacecraft subsystems is discussed. The factors which must be considered in determining the ACS actuation and sensing subsystems are discussed. The effects of the actuation and sensing subsystems on the mission performance are also considered

Flexible Booms, Momentum Wheels, and Subtle Gravity-Gradient Instabilities

A gravity-gradient boom and a momentum wheel provides a passive, three-axis attitude control system for a small satellite requiring 10° Earth-oriented pointing In a low Earth orbit. The Polar BEAR satellite Is a small satellite using just such a system that has experienced unexpected attitude instabilities during some of Its full-sun orbit periods. This paper examines the attitude dynamles and disturbances associated with gravlty-gradientlmomentum-wheel systems In an attempt to identify potential destabilizing mechanisms common to the configuration. Polar BEAR is not the only such configuration to experience problems In full sun. and several other examples are briefiy discussed. Although we place particular emphasis on trying to understand Polar BEAR\u27s anomaly, Its performance may be symptomatic of problems with the Dexible-boom/momentum-wheel configuration

The Effects of Momentum Bias on a Gravity Gradient Stabilized Spacecraft with Active Magnetic Control

The improvements achieved by adding a momentum bias wheel to a Gravity Gradient (GG) stabilized spacecraft are evaluated. Mass, power, and computational processing requirements, as well as performance, are compared for three Attitude Determination and Control Subsystem (ADACS) scenarios. Spacecraft which require low mass and power have long Incorporated GG torques as a passive stabilization technique. The spacecraft is oriented in the general direction required by the mission, but the overall attitude and attitude rate errors are not exceptionally tight. In order to improve the spacecraft pointing accuracies the GG stabilized ADACS .can be augmented by an active control technique. Previously, the use of three TORQRODs was evaluated. With one oriented along each of the spacecraft axis. For this analysis, the incorporation of a small momentum bias wheel is shown to significantly improve the magnetic attitude control from a few degrees to a few tenths of a degree by providing additional gyroscopic stiffness. The ADACS impacts of a constant speed wheel vs an active pitch control loop are also compared. Attitude control techniques are one part of the overall ADACS solution. The knowledge of how well the spacecraft attitude can be determined defines the net ADACS performance for a given mission scenario. If an accuracy of few degrees is sufficient a novel approach is to determine the attitude simply from three-axis magnetometer data. The addition of an Earth horizon sensor to provide accurate roll and pitch information can Improve the overall ADACS performance to approximately 0.5 , but at the expense of Increased mass and power requirements