2,299 research outputs found
Guidance and Control Algorithms for Space Rendezvous and Docking Maneuvers
No full textThe Rendezvous and Docking (RVD) mission is one of the most complex and interesting
space missions. Proximity operations and docking require extremely delicate and precise
translational and rotational maneuvering. During the final approach of the proximity
operations phase, the relative spacecraft states (position, velocity, attitude and angular rates)
must be precisely controlled in order to obtain the required docking interface conditions. As
a consequence, precise relative position, velocity and attitude state estimations are required.
The on-board Guidance, Navigation, and Control (GNC) system can automatically perform
various Rendezvous functions including translational and rotational control, targeting and
relative navigation, but the final approach requires more attention and precision. Thus, the
scope of this work is studying an automated RVD maneuver, implementing guidance and
control algorithms to fulfill the RVD mission, without considering the docking of the two
spacecraft. This paper describes definition and design of Guidance and Control (G&C)
algorithms for space Rendezvous in order to take a moving vehicle, from some known or
unknown state in terms of position and velocity, near or in contact with another one that is
moving with defined parameters. The typical algorithms related to RVD are presented and
the more promising are used for the simulator, combining them in unusual compounds. The
paper is organized as follows. Section II describes the simulator mission profile and the
mathematical model used in the simulator itself to reproduce the translation and rotation of
the spacecraft. In Section III, the main architecture of the simulator is represented, in order
to explain not only the Simulink model but also the functional concept itself. Whereas in
Section IV, the attention is focused on the G&C algorithms implemented in this work. Finally,
the results of several simulations are reported and compared between them in order to define
the best G&C strategy between the proposed ones, that turns out to be the combination of a
Proportional Navigation (PN) algorithm for the guidance and a Linear-Quadratic-Regulator
(LQR) for the attitude control
Tube-based Robust MPC Processor-In-the-Loop Validation for Fixed-Wing UAVs
No full textReal systems, as Unmanned Aerial Vehicles (UAVs),
are usually subject to environmental disturbances, which could
compromise the mission accomplishment. For this reason, the
main idea proposed in this research is the design of a robust
controller, as autopilot control system candidate for a fixedwing
UAV. In detail, the inner loop of the autopilot system
is designed with a tube-based robust model predictive control
(TRMPC) scheme, able to handle additive noise. Moreover, the
navigation outer loop is regulated by a proportional-integralderivative
controller. The proposed TRMPC is composed of two
parts: (i) a linear nominal dynamics, evaluated online with an
optimization problem, and (ii) a linear error dynamics, which
includes a feedback gain matrix, evaluated offline. The key
aspects of the proposed methodology are: (i) offline evaluation
of the feedback gain matrix, and (ii) robustness to random,
bounded disturbances. Moreover, a path-following algorithm is
designated for the guidance task, which provides the reference
heading angle as input to the control algorithm. Software-in-theloop
and processor-in-the-loop simulations have been performed
to validate the proposed approach. The obtained performance
have been evaluated in terms of tracking capabilities and
computational load, assessing the real-time implementability
compliance with the XMOS development board, selected as
continuation of previous works
A Robust MPC-based autopilot for mini UAVs
No full textUnmanned Aerial Vehicles (UAVs) are systems
subject to external disturbances and parametric uncertainties.
A robust Model Predictive Control (MPC) is proposed as
autopilot controller candidate, due to its ability to handle both
parametric uncertainties and additive noise. The navigation
outer loop (heading variation) is regulated via PID control. The
key features of the proposed technique are: (i) the control gain
matrix is evaluated offline to guarantee the real-time feasibility
of the MPC, (ii) the controller is robust to parametric model
uncertainties (i.e. mass and inertia variations) and to random
bounded noise (i.e. gust). The design scheme of a customized
autopilot is illustrated and different aircraft configurations (in
terms of mass, inertia and airspeed variations) are analyzed
to validate the presented approach, both for the linear and
nonlinear case. Moreover, the performance of the controller
system are compared with an L1 adaptive controller
A Comprehensive Modeling Framework for Integrated Mission Analysis and Design of a Reusable Electric Space Tug
No full text"Earth is a small town with many neighborhoods in a very big universe." The quote of the American Astronaut Ronald John Garan Jr. perfectly summarizes the universal and enduring mankind's interest in exploring the unknown, discovering new worlds, pushing the boundaries of scientific and technical limits further and beyond. More than a half century ago, during a speech delivered at Rice University in Houston, President John F. Kennedy claimed the Moon as the new frontier for the human space exploration. The outstanding achievements of the Apollo mission pushed the research in space across the second part of the last century with new goals, as the permanent presence of the human in space. The evolutionary space program built up around that promise was, to say the least, challenging and involved the development of several revolutionary elements. Due to the significant economic effort required by the Apollo mission, only two elements were realized: the Space Shuttle on one side and the Skylab space station on the other. While the Shuttle remained operative until 2011, Skylab was short-lived and disposed after about six years. Only by joining forces with other international partners, NASA was able to realize a long lasting permanent outpost orbiting around Earth, i.e. the International Space Station (ISS). But again, due to the considerable efforts dedicated to build up the ISS and to keep the Space Shuttle operative, the space race suffered a second setback. Until 2007, when the international community drew up a new visionary program. Moon exploration stepped again into the spotlight to extend and sustain human activities beyond Low Earth Orbit (LEO) towards Mars. The new era of space exploration has begun with the intent of expanding the frontiers of knowledge, capability, and opportunities in space. One of the first milestones is represented by the settlement of the so-called Lunar Orbital Platform-Gateway (LOP-G) by the mid 2020's. The Gateway will serve as a manned outpost in the lunar vicinity to support activities on and around the Moon while also servicing as technological and operational testbed to open the frontier for human exploration of Mars, thanks to the exploitation of key technologies, such as high-power electric propulsion. To sustain the LOP-G and its future visiting crews, the Orion spacecraft is currently under development. However, the usability of the Gateway could be extended if new transportation systems would be available to support the station transferring additional supplies and equipment. In compliance with the current plans to efficiently reduce the number of development and validation economic efforts by designing and exploiting same elements for multiple missions, a reusable, high-power electric space tug, i.e. the Lunar Space Tug (LST), is proposed in this Thesis to support the replenishment of the LOP-G. This innovative transportation system should be flexible enough to be adopted in different phases of the Gateway lifetime and for evolving needs. The LST should be in charge of recovering cargo modules released in Earth proximity and transfer them up to the Gateway performing a low-thrust transfer, before return to its operational orbit, ready for the next delivery mission, envisioning a closed-loop mission profile. A tailored multi-input/multi-output design tool has been developed to obtain the preliminary and detailed design, at component level, of the LST spacecraft for several propulsion subsystem architectures. The impact of adopting this technology on the platform design is investigated with respect to several thruster working points and case studies, each one characterized by different refurbishment needs. Then, the optimal LST configuration able to support the Gateway crew for different resupply needs is selected, performing a trade-off analysis among the design solutions that comply with all mission and system constraints previously defined in order to minimize the spacecraft mass, propellant consumption and overall mission cost. From an operational viewpoint, the LST should significantly rely on the Automated Rendezvous and Docking (ARVD) technology, which has been identified as crucial for the transition of space missions from geocentric architectures to self-sustainable, autonomy and independent. At this end, new Guidance Navigation and Control (GNC) algorithms shall be investigated to allow ARVD maneuvers to become reliable routine. In particular, the control problem encapsulates safety restrictions and performance specification that shall be properly addressed verifying the effectiveness and real-time implementability of innovative control strategies. Thus, a 6 Degrees-of-Freedom (DoF) orbital simulator has been developed to simulate the rotational and translational dynamics of the LST and its target vehicles in both Earth orbit and Lunar proximity. Moreover, to reproduce a realistic simulation environment, uncertainty and disturbance affecting the spacecraft dynamics during the maneuver have been modeled and included in the simulator. For attitude and orbital control, three different Model Predictive Control (MPC) algorithms have been implemented and their performance evaluated in the presence of disturbance and parametric uncertainty. In particular, a sampling-based stochastic MPC algorithm is proposed and the typical binding computational effort required by these type of stochastic algorithms, especially when running on low-performing hardware, has been overcome shifting the intensive computations to the offline phase, thus greatly reducing the online computational cost. To complete the algorithms verification process, all three MPC strategies have been experimentally validated exploiting spacecraft mock-up and running the algorithms on the on-board micro-controller, demonstrating their effectiveness and real-time computational applicability
A Comprehensive Analysis of Guidance and Control Algorithms for Orbital Rendezvous Maneuvers
No full textThe purpose of the present paper is to study an autonomous spacecraft rendezvous and docking (RVD) maneuver, in which the Chaser vehicle has to safely and efficiently approach the Target along a controlled trajectory. A 6-degrees-of-freedom (DOF) orbital simulator, which reproduces the dynamics of the spacecraft during the final approach phase of a Low Earth Orbit maneuver, is considered, including the external environment and specific sys- tem features, such as uncertainties affecting the actuators. The main idea is to suitably design guidance and control algorithms for a final cone-approach maneuver, that enforces strict requirements in terms of relative position and attitude of the vehicles. The original- ity of the proposed approach is the novel combination of guidance and control algorithms translated into a numerical algorithm to be implemented on board after validation. Ex- tensive simulations are performed to prove the performance of the combined guidance and control algorithms. These results are presented and widely discusse
Single-state weighted particle filter with application to Earth Observation missions
No full textTo push the boundaries of autonomy in space, the spacecraft must rely on its own sensors to achieve positioning and environmental perception. In this context, the key problem of autonomous navigation is the nonlinear state estimation of the spacecraft in a dynamic 3D environment. In this paper, we propose a new approach based on a single-state sub-partitioning of the state vector and a partial updating of the vector of weights according to the specific information provided by each sensor. In this way, we avoid to lose information in the resampling phase thanks to a parallelization approach. The proposed method has been applied to an Earth observation mission and the efficacy of the proposed approach is demonstrated with a numerical example using a high-fidelity orbital simulator
DESIGN AND COST ANALYSIS OF HIGH-POWER SOLAR ELECTRIC PROPULSION PLATFORMS
No full textNowadays, space agencies are trying to select cost-effective solutions, to minimize space missions cost without affecting the performance. It means that cost analysis needs to cope with mission and feasibility analysis since the early design phases. The paper focuses on the preliminary design of high-power SEP platforms for space exploration and transportation, highlighting how the cost can represent one of the critical parameters to evaluate the feasibility and effectiveness of the solutions proposed. Particular attention is dedicated to the effects of specific design choices, mainly for the SEP subsystem, on the platforms design and cost. Main results are presented and discussed, and main conclusions are drawn
Learning model predictive control for quadrotors minimum-time flight in autonomous racing scenarios
No full textIn this paper, we design a Learning Model Predictive Control (LMPC) algorithm for quadrotors autonomous racing. The proposed algorithm allows to define a highly customizable 3D race track, in which multiple types of obstacles can be inserted. The controller is then able to autonomously find the best trajectory minimizing the quadrotor lap time, by learning from data coming from previous flights within the track, ensuring also the avoidance of all the obstacles therein. We also present novel relaxation approaches for the LMPC optimization problem, that allow to reduce it from a mixed-integer nonlinear program to a quadratic program. The LMPC algorithm is tested via several software-in-the-loop simulations, showing that the algorithm has learned to fly the quadrotor aggressively and dexterously, managing to both find the minimum-time trajectory and avoid the obstacles inside the track
Robust Model Predictive Control for Automated Rendezvous Maneuvers in Near-Earth and Moon Proximity
No full textAutomated rendezvous and docking has been identified by the space community as one of
the cornerstone technologies to enable and support the new era of space exploration towards
the deep space. The strict safety requirements and the limited actuation capabilities require
high-reliable controllability during the close-range rendezvous, i.e., closing and final approach
phases. The presence of persistent environmental disturbances that affect the spacecraft trajectory
and attitude can compromise the mission success. This work presents a tube-based robust
model predictive control approach for a dual-environment spacecraft rendezvous problem in
highly elliptic orbits. During the entire mission, the spacecraft is called to perform several
rendezvous maneuvers in highly elliptic orbits, i.e., a Geostationary Transfer Orbit and a Near
Rectilinear Halo Orbit. The same robust control is exploited in all rendezvous operations and
the robustness of the controller is demonstrated under the presence of persistent internal and
external disturbances. Moreover, the tube-based robust model predictive control performance
have been compared with those of a classic linear-quadratic model predictive control, highlighting
the effectiveness of the robust approach in the presence of disturbance, both in Earth
and Moon proximity
Missions, Architectures and Technologies for a Lunar Space Tug in Support of Cislunar Infrastructures
No full textCuriosity and discovery are vital elements for the future of human space exploration. Starting from past and present experiences in human and robotic exploration, the global community is working on preparing humans to push themselves beyond known boundaries, i.e. the Low Earth Orbit environment, to reach, explore and, eventually, colonize the Mars surface. This goal requires capability evolution and technology investments. The pathway to Mars includes multiple destinations. The Moon and its vicinity seem to represent the most promising intermediate step to fill the technology gap. The Lunar Space Tug represents one of the possible key elements to sustain the growth and the operability of the future Space Station orbiting in Cislunar space, thanks to its reusability and the adoption of electric propulsion. It can transfer unmanned modules from Low Earth Orbit up to the Cislunar Space Station and back, to provide the required replenishment. Among all Lunar Space Tug mission phases, autonomous rendezvous and mating maneuvers represent one of the most critical one from the point of view of the technology involved in the Lunar Space Tug design. The strong environmental impact must be considered to define the optimal rendezvous approach, especially when the maneuver must be performed in different environments as in this case, i.e. Near Earth Orbit and Cislunar. For the rendezvous maneuver, it is crucial to estimate environmental disturbances that can jeopardize the system as well as the maneuver success. To be compliant with the strict safety requirements that characterize this maneuver, a robust control can guarantee the constraints satisfaction, even when persistent disturbances are acting on the system. In this paper, a Linear-Quadratic Model Predictive Control has been adopted to control the Lunar Space Tug during the last phase of the rendezvous maneuver, showing the robustness behavior of this approach in the presence of reduced persistent disturbances and the compliance of the controller with the real-time application. Once the Lunar Space Tug design is defined through a multi-purpose systems engineering tool, the 6 degrees-of- freedom Lunar Space Tug simulator is used to analyze in deep the rendezvous maneuver. The optimal maneuver design is obtained according to the Attitude and Orbit Control Subsystem architecture and the Thrust Management Function adopted for the determination of the proper control actuators selection and command duration, to realize the control action required. Main results on the Lunar Space Tug design and related performance during proximity operations in both Near Earth Orbit and Cislunar environments are discussed and main conclusions are drawn
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