1,721,064 research outputs found
Quaternion versus rotation matrix feedback for tigrisat attitude stabilization
No full textThe purpose of this paper is to compare the performances between quaternion and attitude rate feedback, and rotation matrix and attitude rate feedback used to stabilize the nominal attitude of Tigrisat nanosatellite. From a mathematical point of view an important difference between the two control laws is that only quaternion feedback can exhibit an undesired behavior known as the unwinding phenomenon. Monte Carlo campaigns show that the two control laws perform comparably in terms of speed of convergence. Moreover, they show that rotation matrix feedback requires less energy
Reduced-attitude stabilization for spacecraft boresight pointing using magnetorquers
No full textThis paper presents a method for achieving a desired boresight pointing of an instrument on a spacecraft using only magnetorquers as torque actuators. The desired pointing direction is inertially fixed. The proposed method is of proportional-derivate type and stabilizes the boresight pointing. Numerical simulations illustrate the effectiveness of the method and show that convergence to the desired pointing direction occurs faster than employing a three-axis stabilization approach
A new guidance and control architecture for accurate orbit injection
Full text linkAccurate orbit injection represents a crucial issue in several mission scenarios, e.g. for spacecraft orbiting the Earth or for payload release from the upper stage of an ascent vehicle. This work considers a new guidance and control architecture based on the combined use of (i) the variable-time-domain neighboring optimal guidance technique (VTD-NOG), and (ii) the constrained proportional-derivative (CPD) algorithm for attitude control. More specifically, VTD-NOG & CPD is applied to two distinct injection maneuvers: (a) Hohmann-like finite-thrust transfer from a low Earth orbit to a geostationary orbit, and (b) orbit injection of the upper stage of a launch vehicle. Nonnominal flight conditions are modeled by assuming errors on the initial position, velocity, attitude, and attitude rate, as well as actuation deviations. Extensive Monte Carlo campaigns prove effectiveness and accuracy of the guidance and control methodology at hand, in the presence of realistic deviations from nominal flight conditions
Variable-time-domain neighboring optimal guidance and attitude control of low-thrust lunar orbit transfers
Full text linkLunar orbit dynamics and transfers at low altitudes are subject to considerable perturbations related to the gravitational harmonics associated with the irregular lunar mass distribution. This research proposes the original combination of two techniques applied to low-thrust lunar orbit transfers, i.e. (i) the variable-time-domain neighboring optimal guidance (VTD-NOG), and (ii) a proportional-derivative attitude control algorithm based on rotation matrices (PD-RM). VTD-NOG belongs to the class of feedback implicit guidance approaches, aimed at maintaining the spacecraft sufficiently close to the reference trajectory. This is an optimal path that satisfies the second-order sufficient conditions for optimality. A fundamental original feature of VTD-NOG is the use of a normalized time scale, with the favorable consequence that the gain matrices remain finite for the entire time of flight. VTD-NOG identifies the trajectory corrections by assuming the thrust direction as the control input. Because the thrust direction is fixed with respect to the spacecraft, VTD-NOG generates the desired orientation pursued by the attitude control system. A proportional-derivative approach using rotation matrices (PD-RM) is employed in order to drive the actual spacecraft orientation toward the desired one. Reaction wheels are considered as the actuators that perform attitude control. Extensive Monte Carlo simulations are performed, in the presence of nonnominal flight conditions related to (i) lunar gravitational harmonics, (ii) gravitational pull of the Earth and the Sun as third bodies, (iii) unpredictable propulsive fluctuations, and (iv) errors on initial attitude. The numerical results unequivocally demonstrate that the joint use of VTD-NOG and PD-RM control represents an accurate and effective methodology for guidance and control of low-thrust lunar orbit transfers
Minimum-Time Spacecraft Attitude Motion Planning Using Objective Alternation in Derivative-Free Optimization
Full text linkThis work presents an approach to spacecraft attitude motion planning which guarantees rest-to-rest maneuvers while satisfying pointing constraints. Attitude is represented on the group of three dimensional rotations. The angular velocity is expressed as weighted sum of some basis functions, and the weights are obtained by solving a constrained minimization problem in which the objective is the maneuvering time. However, the analytic expressions of objective and constraints of this minimization problem are not available. To solve the problem despite this obstacle, we propose to use a derivative-free approach based on sequential penalty. Moreover, to avoid local minima traps during the search, we propose to alternate phases in which two different objective functions are pursued. The control torque derived from the spacecraft inverse dynamics is continuously differentiable and vanishes at its endpoints. Results on practical cases taken from the literature demonstrate advantages over existing approaches
Neighboring optimal guidance and attitude control of low-thrust earth orbit transfers
Full text linkRecently, low-thrust propulsion is gaining strong interest from the research community and has already found application in some mission scenarios. This paper proposes an integrated guidance and control methodology, termed variable-time-domain neighboring optimal guidance and proportional derivative-rotation matrix (VTD-NOG and PD-RM), and applies it to orbit transfers from a low Earth orbit (LEO) to a geostationary orbit (GEO), using low thrust. The VTD-NOG is a closed-loop guidance approach based on minimization of the second differential of the objective functional along the perturbed path, and it avoids the singularities that occur using alternate neighboring optimal guidance algorithms. VTD-NOG finds the trajectory corrections considering the thrust direction as the control input. A proportional-derivative scheme based on rotation matrices (PD-RM) is used in order to drive the actual thrust direction toward the desired one determined by VTD-NOG. Reaction wheels are tailored to actuate attitude control. In the numerical simulations, thrust magnitude oscillations, displaced initial conditions, and gravitational perturbations are modeled. Extensive Monte Carlo campaigns show that orbit insertion at GEO occurs with excellent accuracy, thus proving that VTD-NOG and PD-RM represents an effective architecture for guidance and control of low-thrust Earth orbit transfers
Neighboring optimal guidance and constrained attitude control applied to three-dimensional lunar ascent and orbit injection
Full text linkFuture human or robotic missions to the Moon will require efficient ascent path and accurate orbit injection maneuvers, because the dynamical conditions at injection affect the subsequent phases of spaceflight. This research is focused on the original combination of two techniques applied to lunar ascent modules, i.e. (i) the recently-introduced variable-time-domain neighboring optimal guidance (VTD-NOG), and (ii) a constrained proportional-derivative (CPD) attitude control algorithm. VTD-NOG belongs to the class of implicit guidance approaches, aimed at finding the corrective control actions capable of maintaining the spacecraft sufficiently close to the reference trajectory. CPD pursues the desired attitude using thrust vector control and side jet system, while constraining the rates of both the thrust deflection angle and the roll control torque. After determining the optimal two-dimensional ascent path, which represents the reference trajectory, VTD-NOG & CPD is applied in the presence of nonnominal flight conditions, namely those due to navigation and actuation errors, incorrect initial position, unpredictable oscillations of the propulsive thrust, and imperfect modeling of the spacecraft mass distribution and variation. These stochastic deviations are simulated in the context of extensive Monte Carlo campaigns, and yield three-dimensional perturbed trajectories. The numerical results obtained in this work unequivocally demonstrate that VTD-NOG & CPD represents an accurate and effective methodology for guidance and control of lunar ascent path and orbit injection
Spacecraft attitude motion planning using gradient-based optimization
No full textThe purpose of the present work is to perform spacecraft attitude motion planning so that a rest-to-rest rotation is achieved while satisfying pointing constraints. Atti- tude is represented on the group of three dimensional rotations SO(3). The motion planning is executed in two steps. In the first step, path-planning is performed by searching for a time behavior for the angular rates through the formulation of an optimal control problem solved with a gradient-based algorithm. In the second step, the actual input torque is simply determined by the use of inverse attitude dynamics. A numerical example is included to show the effectiveness of the method. From a practical point of view, the control torque resulting from the proposed approach is continuously differentiable and vanishes at its endpoints
Lunar descent and landing via two-phase explicit guidance and pulse-modulated reduced-attitude control
Full text linkThis work considers the three-dimensional descent path of a space vehicle, from periselenium of its operational orbit to the lunar surface. The trajectory is split in two arcs: (1) descent path, up to an altitude of 50 m, and (2) terminal approach and soft touchdown. For phase 1, a new, three-dimensional locally-flat near-optimal guidance is introduced that is based on the local projection of the position and velocity variables. A minimum-time problem is defined using the locally flat coordinates of position and velocity. This leads to identifying closed-form functions of time for the two thrust angles, which identify the commanded thrust direction. During terminal approach (phase 2), correct vertical alignment, modest velocity, and negligible angular rate at touchdown are pursued. With this intent, a predictive bang-off-bang guidance algorithm is proposed that is capable of guaranteeing the desired final conditions. In both phases, the attitude control system has the objective of aligning the actual thrust direction with the commanded one, provided by the guidance algorithm. The resulting reduced-attitude control problem is addressed through the use of a new quaternion-based nonlinear control algorithm, which is proven to enjoyquasi-global stability properties. The attitude actuation system is composed of 12 monopropellant thrusters, ignited using pulse width modulation. Monte Carlo simulations are run, assuming significant displacements from the nominal initial conditions and including several harmonics of the selenopotential. The numerical results unequivocally prove that the guidance and control architecture proposed in this study is effective to achieve lunar descent and safe touchdown in nonnominal flight conditions
A reduction paradigm for output regulation
No full textThe goal of this paper is to provide a reduction paradigm for the design of output regulators which can be of interest for nonlinear as well as linear uncertain systems. The main motivation of the work is to provide a systematic design tool to deal with non-minimum-phase uncertain systems for which conventional high-gain stabilization paradigms are not effective. The contribution of the work is two-fold. First this work extends the nonlinear framework proposed in Marconi et al. (Systems & Control Letters 53 2004) to the case in which the so-called 'immersion into a linear system' does not hold. Furthermore, in the case the uncertain controlled dynamics are linear, we show how the proposed framework leads to a number of systematic design tools of interest in the case of non-minimum-phase linear systems affected by severe uncertainties
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