This paper presents the stability and control analysis for large angle feedback reorientation maneuvers using reaction jets. The strapdown inertial reference system provides spacecraft attitude changes in terms of quaternions. Reaction jets with pulse-width pulse-frequency modulation provide nearly proportional control torques. The use of quaternions as attitude errors for large angle feedback control is investigated. Closed-loop stability analysis for the three-axis maneuvers is performed using the Liapunov stability theorem. Unique characteristics of the quaternion feedback are discussed for single-axis motion using a phase-plane plot. The practical feasibility of a three-axis large angle feedback maneuver is demonstrated by digital simulations.

Quaternion feedback for spacecraft large angle maneuvers

We introduced some of the basic principles, techniques, and key design issues common to ISPs used in many diverse scientific, military, and commercial applications, and we touched on some of the less intuitive effects that must be dealt with. Many of these effects can influence the initial configuration of the system as well as design details later in the design process. The successful design of an ISP usually requires a multidisciplinary design team. The design of an ISP must often be closely coordinated with that of other major subsystems such as the primary sensor and the optics. The role of the systems engineer in the design process is perhaps the most critical because other members of the team may not be aware of the consequences of many of the effects discussed above. Inertially stabilized platforms (ISPs) are used to stabilize and point a broad array of sensors, cameras, telescopes, and weapon systems.

Inertially stabilized platform technology Concepts and principles

Euler parameters, a form of normalized quaternions, are used to model the hand-orientation errors in resolved-rate and resolved-acceleration control of manipulators. The quaternion formulation simplifies the stability analysis of the orientation error dynamics. Two types of quaternion feedback have been considered. The first type uses only the vector portion of the quaternion error, while the second is based on a Euler rotation representation. The quaternion vector approach leads to a linear feedback control law for which the global asymptotic convergence of the orientation error is readily established. The Euler rotation approach also results in asymptotic error convergence in the large except for a singularity where the hand orientation differs from its desired orientation by a rotation of 180 degrees . >

Closed-loop manipulator control using quaternion feedback

This paper considers the problem of motion synchronization of free-flying robotic spacecraft and serviceable floating objects in space. The synchronization maneuvers are a combination of relative position tracking and attitude reorientation. Control laws are developed that ensure that the relative position vector between a pursuer and target spacecraft is always directed toward the docking port of the target. The tracking-error reference signals are generated based on a novel "virtual target" construction. Also, the attitude reorientation of the pursuer is achieved by constructing a desired attitude from the virtual target, and the control law seeks to nullify the errors between the current and desired attitude parameters. The control law synthesis proceeds along familiar, established procedures motivated by feedback-linearization-based approaches. Disturbance torques due to gravity gradient and other unknown but bounded disturbances are accounted for using an adaptive control formulation. The stability of the control laws are demonstrated via Lyapunov analysis and Matrosov's theorem Numerical simulations are performed to demonstrate the efficacy of this control formulation.

Nonlinear Control of Motion Synchronization for Satellite Proximity Operations

Cassini Spacecraft Attitude Control System Flight Performance

This paper presents a coordinate-free ray-trace analysis of optical beam trains consisting of mirrors, lenses and reference surfaces The analysis leads to optical models that can be directly integrated with standard structure and control models for integrated instrument design, analysis and simulation This capability is required for a coming generation of spaceborn optical instruments which use controlled optical elements supported by flexible structures New results include analytic formulas for optical sensitivities as functions of structural and control geometric parameters An example problem calculates a linear (small-motion) optical model, derives optical gains for small- and large-angle controlled mirrors, and shows the propagation of a wavefront

Optical modeling for dynamics and control analysis

This paper presents a coordinate-free ray-trace analysis of optical beam trains consisting of mirrors, lenses and reference surfaces. The analysis leads to optical models that can be directly integrated with standard structure and control models for integrated instrument design, analysis and simulation. This capability is required for a coming generation of spaceborn optical instruments which use controlled optical elements supported by flexible structures. New results include analytic formulas for optical sensitivities as functions of structural and control geometric parameters. An example problem calculates a linear (small-motion) optical model, derives optical gains for small- and large-angle controlled mirrors, and shows the propagation of a wavefront.

The Cassini planetary mission to Saturn and Titan requires accurate pointing and complex maneuvers of the spacecraft, which is comprised of a Saturn orbiter and Titan probe. An attitude control design is described to achieve the many capabilities of Cassini including thrust vector control, precision pointing and stability control fc)r remote sciences, tracking of a probe released to the Titan atmosphere, and radar mapping of the Titan surface. Additional constraints for control design have been imposed by a high percentage of liquid propellant (60.% at launch) and lowly damped flexible spacecraft appendages. Computer simulation results of attitude determination, pointing and maneuver controls are provided to demonstrate the design capability.

An Attitude Control Design for the Cassini Spacecraft

The sensitivity model of a complex optical system obtained by linear ray tracing is used to compute a control gain matrix by imposing the mathematical condition for minimizing the total wavefront error at the optical system's exit pupil. The most recent deformations or error states of the controlled segments or optical surfaces of the system are then assembled as an error vector, and the error vector is transformed by the control gain matrix to produce the exact control variables which will minimize the total wavefront error at the exit pupil of the optical system. These exact control variables are then applied to the actuators controlling the various optical surfaces in the system, causing the immediate reduction in total wavefront error observed at the exit pupil of the optical system.

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William G. Breckenridge

Papers

Optical modeling for dynamics and control analysis

Optical modeling for dynamics and control analysis

An Attitude Control Design for the Cassini Spacecraft

Feedback controlled optics with wavefront compensation

Self-tuning thruster control for Cassini spacecraft