1,721,077 research outputs found
Integrated Magnetic Management of Stored Angular Momentum in Autonomous Attitude Control Systems
Full text linkAutonomous spacecraft operations are at the front end of modern research interests, because they enable space missions that would not be viable only with ground control. The possibility to exploit onboard autonomy to deal with platform management and nominal housekeeping is thus beneficial to realize complex space missions, which could then rely on ground support only for the mission-critical phases. One routine operation that most spacecraft must perform is stored angular momentum management to maintain fully usable momentum exchange actuators. The execution of this activity may be scheduled, commanded from the ground, or automatically triggered when certain thresholds are reached. However, autonomous angular momentum management may interfere with other primary spacecraft operations if executed with a dedicated and separate system mode. This paper presents the magnetic management of stored angular momentum, integrated with the main attitude control system. The system design and implementation are intended for autonomous spacecraft, and it can be operated without significant ground support. The paper describes the system architecture and the attitude control laws integrated with the magnetic angular momentum management. Specifically, the capability of the autonomous system to keep the internal angular momentum far from the saturation and far from the zero-crossing levels is highlighted. The performance of an example attitude control system with four reaction wheels and three magnetic torquers is presented and discussed, with the simulation results at model-in-the-loop (MIL) level
Assembly and operations for a cislunar orbit space station
No full textChallenging space exploration missions are envisaged in the next future, involving a cooperation of humans and robots to accomplish ambitious goals beyond Low-Earth orbit. During the ideation of these forthcoming space programmes, international scientific community is focusing its attention on the sustainability of the entire long-term program, carefully sizing the intermediate steps and meticulously identifying new technologies needed to carry out the proposed activities. In particular, a gradual construction of a space station in cislunar environment is seen as a key element of the entire project and it opens an interesting field of multidisciplinary studies from a space system engineering perspective. The paper is founded on recent works focused on analysing the dynamics and controllability of large and flexible space structures in non-Keplerian orbits. The developed coupled orbit-attitude semi-analytical models, based on a Three-Body Problem modelling approach, are here first exploited to assess innovative and sustainable strategies to assemble the space station in the vicinity of the Moon. In fact, this future large space infrastructure will be credibly set up in-orbit by means of many rendezvous and docking automated activities, which should be carefully and progressively designed to reduce complexity, costs, and ensure reliability and repeatability. Therefore, the paper discusses the emerged potential assembly strategies with respect to selected criteria (e.g. inertia properties to minimize control action, attitude stabilisation techniques and rendezvous trajectories to simplify infrastructure construction). Then, possible rendezvous operations are presented for the proposed assembly baselines. The minimization of active control actions is foreseen: the full space of solutions is studied to highlight possible stable conditions that may be exploited to host and operate the cislunar station with minimum control effort. Analyses are presented according to the non-Keplerian orbits classes evaluated as the most suitable for a large infrastructure location: Halo, NRO and DRO. Rendezvous and docking in non-Keplerian environment have never been tested in real applications and the literature is somehow missing an extensive research on this topic, especially when orbit and attitude dynamics are considered together. Finally, particular operations for the space station in spin stabilised dynamics are examined as artificial gravity generator, which may be very favourable for prolonged astronaut permanence in space
Asteroids Coupled Dynamics Analysis by Means of Accurate Mass Distribution and Perturbations Modeling
Full text linkOne of the most important aspects when dealing with a Potentially Hazardous Object (PHO) is the accurate determination of its dynamical state. In particular, the determi-nation of orbital and rotational perturbations is important to propagate accurately the heliocentric orbital path of an asteroid or a comet, and to be more precise in the im-pact risk determination and related uncertainty containment. The paper discusses the analysis and study of the motion of an irregularly-shaped celestial body, with par-ticular attention to its complex three-dimensional rotational dynamics: the rotation state, nutation and precession motions are considered while modelling. All perturba-tions, relevant to the case of study, are included in the dynamical model, from the classical to the more complex, such as the Solar Radiation Pressure (SRP), the third body gravitational effect (presence of the Sun), the YORP effect and the internal dis-sipation of energy. In addition, particular attention has been paid to accurately model the shape of the asteroid: simple spherical models demonstrated to possess low ac-curacy when the asteroid or the comet is not spherically shaped. Irregular shapes represent, indeed, one of the most important aspects to compute the disturbances affecting the dynamics of these objects. The study has been performed by consider-ing different characteristic shapes for typical irregular bodies: from the quasi-spherical, to the dog-bone and the elongated shapes. The perturbations due to ex-ternal sources are modelled numerically. The sources of disturbances are then ranked and different criteria to propagate rotational motion have been derived de-pending on the shape of the observed asteroid. Even if the simulation results have been verified on selected asteroids dynamics, the presented methods and approach apply to the dynamical propagation of any kind of asteroid or comet
Characterisation of 6DOF natural and controlled relative dynamics in cislunar space
Full text linkAt the 50th anniversary of Apollo 11, the Moon is back to the scene of scientific and commercial space exploration interests. During the next decade, the establishment of a Gateway in cislunar non-Keplerian orbits will open the space frontiers to sustainable manned and robotic missions on and around the Moon. Such infrastructure will require several logistic operations for its assembly and maintenance, which lean on rendezvous and docking capabilities. Even if few missions have flown on non-Keplerian orbits, Rendezvous and Docking (RV&D) operations have not been performed but in Low Earth Orbit (LEO). Investigations about 6 Degrees Of Freedom (DOF) relative dynamics in non-Keplerian environment are now mandatory to highlight criticalities in the design of the cislunar gateway and to translate RV&D protocols, consolidated in LEO for the International Space Station (ISS), to the new non-Keplerian environment. In this direction, the paper analyses the 6DOF natural orbit-attitude dynamics within the Circular Restricted Three-Body Problem (CR3BP) framework. A novel perspective of the dynamical structures, constituting 6DOF manifolds, allows to better characterise the natural relative dynamics in proximity of non-Keplerian orbits. The importance of orbit-attitude manifolds exploitation is underlined for designing reliable and efficient rendezvous trajectories, enhanced by natural cislunar dynamics. Then, an ephemeris cislunar dynamical model is exploited to address guidance laws for proximity operations. The control capability is included in the dynamics of a chaser vehicle, which is employed to solve the 6DOF guidance problem in proximity of a target spacecraft. The results obtained with the controlled dynamics are compared to those available thanks to natural motion, discussing the energetic and time costs to complete the manoeuvres. A control parametrisation to solve the optimal energy rendezvous problem is proposed. Finally, a feasible operational rendezvous scenario is discussed about the identified favourable locations along the non-Keplerian orbit to perform complex proximity operations. Significant relations between RV&D time and non-Keplerian orbit’s period are discussed as well
Floquet modes and stability analysis of periodic orbit-attitude solutions along Earth–Moon halo orbits
Full text linkFuture space programmes pose some interesting research problems in the field of non-Keplerian dynamics, being the Moon and the cislunar space central in the proposed roadmap for the future space exploration. In these regards, the deployment of a cislunar space station on a non-Keplerian orbit in the lunar vicinity is a fundamental milestone to be achieved. The paper investigates the natural orbit-attitude dynamics and the attitude stabilisation of coupled motions for extended bodies in the Earth-Moon system. The discussion is carried out analysing the phase space of natural dynamics, constituted by both the orbital and the rotational periodic motions of a spacecraft in cislunar orbits. Floquet theory is applied to periodic orbit-attitude solutions in lunar proximity, to characterise their attitude stability properties and their attitude manifolds, which are discussed and analysed focusing on their dynamical features applicable to cislunar environment. Attitude stabilisation methods are proposed and developed, with particular attention to spin-stabilised solutions. Periodic orbit-attitude dynamics are studied to highlight possible favourable conditions that may be exploited to host a cislunar space station with a simplified control action. The focus of the analysis is dedicated to halo orbits and near-rectilinear halo orbit in the circular restricted three-body problem Earth-Moon system
Coupled Dynamics Analysis Around Asteroids by Means of Accurate Shape and Perturbations Modeling
No full textThe paper discusses the analysis and the study of the motion around irregular celestial bodies, with particular attention to the representation of their gravitational influence and the characterization of their complex non-principal axis rotational dynamics. The study has been performed considering different characteristic shapes for typical NEO asteroids: from the simple, almost spherical, to more complex shapes, such as the dog-bone and the elongated ones. The gravitational attraction of these irregular objects has been modeled, through accurate shape discretization, with a constant density polyhedron or an ensemble of point masses. All perturbations, relevant to the case of study, are included in the model, such as the Solar Radiation Pressure (SRP) and the third body gravitational effect (presence of the Sun)
Fully magnetic attitude control subsystem for picosat platforms
Full text linkIn this paper, the design of a fully magnetic attitude control subsystem for a picosat platform is discussed. The developed control law is based on a simple and reliable architecture, which can be easily implemented on small spacecrafts for de-tumbling and three-axis stabilization purposes. The subsystem design follows a practical engineering approach, exploiting global optimization methods, which lead to an integral actuation compliant with typical pointing accuracy requirements for picosat missions. Performance of the proposed attitude control subsystem is demonstrated by numerical simulations
Preliminary Results on the Dynamics of Large and Flexible Space Structures in Halo Orbits
Full text linkThe global exploration roadmap suggests, among other ambitious future space programmes, a possible manned outpost in lunar vicinity, to support surface operations and further astronaut training for longer and deeper space missions and transfers. In particular, a Lagrangian point orbit location - in the Earth-Moon system - is suggested for a manned cis-lunar infrastructure; proposal which opens an interesting field of study from the astrodynamics perspective. Literature offers a wide set of scientific research done on orbital dynamics under the Three-Body Problem modelling approach, while less of it includes the attitude dynamics modelling as well. However, whenever a large space structure (ISS-like) is considered, not only the coupled orbit-attitude dynamics should be modelled to run more accurate analyses, but the structural flexibility should be included too. The paper, starting from the well-known Circular Restricted Three-Body Problem formulation, presents some preliminary results obtained by adding a coupled orbit-attitude dynamical model and the effects due to the large structure flexibility. In addition, the most relevant perturbing phenomena, such as the Solar Radiation Pressure and the fourth-body (Sun) gravity, are included in the model as well. A multi-body approach has been preferred to represent possible configurations of the large cis-lunar infrastructure: interconnected simple structural elements - such as beams, rods or lumped masses linked by springs and dampers - build up the space segment. To better investigate the relevance of the flexibility effects, the lumped parameters approach is compared with a distributed parameters semi-analytical technique. A sensitivity analysis of system dynamics, with respect to different configurations and mechanical properties of the extended structure, is also presented, in order to highlight drivers for the lunar outpost design and station-keeping manoeuvres minimisation. Furthermore, a case study for a large and flexible space structure on Halo orbits around one of the Earth-Moon collinear Lagrangian points, L1 or L2, is discussed to point out some relevant outcomes for the potential implementation of such a mission
Fault Tolerant Attitude and Orbit Determination System for Small Satellite Platforms
Full text linkSmall satellite platforms are experiencing increasing interest from the space community, because of the reduced cost and the performance available with current technologies. In particular, the hardware composing the attitude and orbit control system (AOCS) has reached a strong maturity level, and the dimensions of the components allow redundant sets of sensors and actuators. Thus, the software shall be capable of managing these redundancies with a fault tolerant structure. This paper presents an attitude and orbit determination system (AODS) architecture, with embedded failure detection and isolation functions, and autonomous redundant component management and reconfiguration for basic failure recovery. The system design and implementation has been sized for small satellite platforms, characterized by limited computing capacities, and reduced autonomy level. The discussion describes the system architecture, with particular emphasis on the failure detection and isolation blocks at the component level. The set of functions managing failure detection at system level is also described in the paper. The proposed system is capable of reconfiguring and autonomously recalibrating after various failures had occurred. Attention is also dedicated to the achieved performance, satisfying stringent requirements for a small satellite platform. In these regards, the simulation results used to verify the performance of the proposed system at the model-in-the-loop (MIL) level are also reported
A Spacecraft Attitude Determination and Control Algorithm for Solar Arrays Pointing Leveraging Sun Angle and Angular Rates Measurements
Full text linkThe capability to orient the solar arrays of a spacecraft toward the Sun is an ultimate asset for any attitude determination and control subsystem (ADCS). This ability should be maintained in any operative circumstance, either nominal or off-nominal, to avoid the loss of the entire space-borne system. The safe mode implementation should guarantee a positive power generation from the solar arrays, regardless of the health status of the satellite platform. This paper presents a solar array pointing algorithm, to be executed on-board, with a minimal set of sensors and actuators. In fact, the sensors are limited to the solar arrays, exploiting the current/voltage sensing capacity of the electrical power subsystem to measure the Sun angle with respect to the arrays normal, and to the angular rates sensors. The actuators are required to provide a torque only along two axes and, thus, a reduced actuation capacity is still manageable by the proposed algorithm. The paper describes the algorithm, both in the Sun direction determination and in the Sun pointing control capacity. The achieved performance is outlined, considering either an ideal system or a realistic one, being the latter affected by sensors and actuators limitations. The actuation by means of momentum exchange devices or magnetic torquers is discussed, with the purpose to prove the wide applicability range of the presented algorithm, which is capable to guarantee solar array orientation with a minimal hardware set
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