| 1. |
- Felicetti, Leonard, et al.
(författare)
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A comparison among classical and SDRE techniques in formation flying orbital control
- 2013
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Ingår i: 2013 IEEE Aerospace Conference. - Piscataway, NJ : IEEE Communications Society. - 9781467318112
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Konferensbidrag (refereegranskat)abstract
- A key point in formation flying mission design is represented by the accuracy and the cost of maintaining the requested orbital configuration. In fact, the relative geometry among spacecraft should be kept within tight limits in order to accomplish payload missions. At the same time, this effort requires to accommodate onboard the relevant amount of propellant, which should be correctly evaluated. The quest for optimal control strategy faces the non linear nature of the orbital dynamics, furthermore affected by perturbations that can be only modeled and therefore not perfectly known. As a result, traditional optimal strategies as the Linear Quadratic Controller (LQR), which design can be achieved under the hypothesis of simplified (as an example linearized) dynamics, not always meet the objective. Innovative approaches, like the State Dependent Riccati Equation (SDRE) technique, allow to better take into account, at an increasing level of approximations, the real dynamics. The paper presents extensive results of the simulations carried out for two different problems in formation flying control: the maintaining of a desired relative geometry and the acquisition of a requested configuration. A relevant point, also with respect to currently available literature, is the fact that the considered reference orbits have an eccentricity different from zero
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| 2. |
- Felicetti, Leonard, et al.
(författare)
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A multi-spacecraft formation approach to space debris surveillance
- 2016
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Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765 .- 1879-2030. ; 127, s. 491-504
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a new mission concept devoted to the identification and tracking of space debris through observations made by multiple spacecraft. Specifically, a formation of spacecraft has been designed taking into account the characteristics and requirements of the utilized optical sensors as well as the constraints imposed by sun illumination and visibility conditions. The debris observations are then shared among the team of spacecraft, and processed onboard of a “hosting leader” to estimate the debris motion by means of Kalman filtering techniques. The primary contribution of this paper resides on the application of a distributed coordination architecture, which provides an autonomous and robust ability to dynamically form spacecraft teams once the target has been detected, and to dynamically build a processing network for the orbit determination of space debris. The team performance, in terms of accuracy, readiness and number of the detected objects, is discussed through numerical simulations.
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| 3. |
- Felicetti, Leonard, et al.
(författare)
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Adaptive thrust vector control during on-orbit servicing
- 2014
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Ingår i: AIAA SPACE 2014 Conference and Exposition. - : American Institute of Aeronautics and Astronautics, AIAA. - 9781624102578
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Konferensbidrag (refereegranskat)abstract
- On-orbit servicing missions often include a final propulsive phase where a spacecraft pushes the other one towards a different orbit. Specifically this is the case of the debris grasping mission where the chaser, after capturing the target by means of robotic arms, has to perform a de-orbit operation. The large thrust involved needs a perfect alignment with respect to the center of mass or the system composed by chaser and target, in order to avoid attitude changes. Such accurate alignment is quite difficult to achieve especially when the characteristics of the target are not perfectly known. A procedure is proposed in this paper, allowing a complete estimation of the center of mass position and of the moments of inertia of the system, starting from the data obtained by the gyros mounted on board of the spacecraft. The output is used to design a maneuver for correcting the target and chaser relative position by moving the robotic arms. Numerical simulations show the proficiency and the applicability of the estimation algorithm and of re-alignment maneuver to a selected mission scenario.
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| 4. |
- Felicetti, Leonard, et al.
(författare)
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Analytical and numerical investigations on spacecraft formation control by using electrostatic forces
- 2016
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Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765 .- 1879-2030. ; 123, s. 455-469
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Tidskriftsartikel (refereegranskat)abstract
- The paper investigates some analytical and numerical aspects of the formation control exploited by means of inter-spacecraft electrostatic actions. The analysis is based on the evaluation and check of the stability issues by using a sequence of purposely defined Lyapunov functions. The same Lyapunov approach can also define a specific under-actuate control strategy for controlling selected “virtual links” of the formation. Two different selection criteria for these links are then discussed, showing the implications on the control chain. An optimal charge distribution strategy, which assigns univocally the charges to all the spacecraft starting from the charge products computed by the control, is also presented and discussed. Numerical simulations prove the suitability of the proposed approach to a formation of 4 satellites.
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| 5. |
- Felicetti, Leonard, 1982-, et al.
(författare)
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Attitude and Orbital Dynamics of a Variable-Geometry, Spinning Solar Sail in Earth Orbit
- 2017
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Konferensbidrag (refereegranskat)abstract
- At the ISSS 2013, a novel concept of variable-geometry solar sail was introduced: deployed in the shape of a three-dimensional quasi-rhombic pyramid (QRP), the sail exploited its shape and shift between center of mass and center of pressure to naturally achieve heliostability (stable sun-pointing) throughout the mission. In addition, mechanisms allowed to vary the flare angle of the four booms in opposite pairs, thus allowing to control the area exposed to the sun without the need of slew maneuvers. Using these adjustments in favorable orbital positions, it is possible to build a regular pattern of acceleration to achieve orbit raising or lowering without the need of propulsion system or attitude control. Subsequent more detailed investigations revealed that eclipses, even if lasting only a fraction of the orbit, have a substantial (and negative) impact on the heliostability effect: and even a small residual angular velocity, or disturbance torque, are enough to cause the spacecraft to tumble. In this work, we present a novel and improved concept which allows the sail to preserve its attitude not only with eclipses, but also in presence of disturbance torques such as the gravity gradient. The solution we propose is to add a moderate spin to the solar sail, combined with ring dampers. The gyroscopic stiffness due to the spin guarantees stability during the transient periods of the eclipses, while the heliostability effect, combined with the dampers, cancels any residual unwanted oscillation during the parts of the orbit exposed to the sun, and at the same time guarantees continuous sun-pointing as the apparent direction of the sun rotates throughout the year. Both theoretical and numerical analyses are performed. First, stability bounds on the sail design are calculated, obtaining conditions on the flare angles of the sail, in the different orbital regimes, to test the robustness of the concept. Then, a numerical analysis is performed to validate the study in a simulated scenario where all perturbations are considered, over extended amount of time. The concept targets equatorial orbits above approximately 5,000 km. Results show that an increase of 2,200 km per year for a small device at GEO can be achieved with a CubeSat-sized sail.
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| 6. |
- Felicetti, Leonard, et al.
(författare)
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Attitude Coordination of Multiple Spacecraft for Space Debris Surveillance
- 2017
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Ingår i: Advances in Space Research. - : Elsevier. - 0273-1177 .- 1879-1948. ; 59:5, s. 1270-1288
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses the attitude coordination of a formation of multiple spacecraft for space debris surveillance. Off-the-shelf optical sensors and reaction wheels, with limited field of view and control torque, respectively, are considered to be used onboard the spacecraft for performing the required attitude maneuvers to detect and track space debris. The sequence of attitude commands are planned by a proposed algorithm, which allows for a dynamic team formation, as well as performing suitable maneuvers to eventually point towards the same debris. A control scheme based on the nonlinear state dependent Riccati equation is designed and applied to the space debris surveillance mission scenario, and its performance is compared with those of the classic linear quadratic regulator and quaternion feedback proportional derivative controllers. The viability and performance of the coordination algorithm and the controllers are validated through numerical simulations.
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| 7. |
- Felicetti, Leonard, et al.
(författare)
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Attitude coordination strategies in satellite constellations and formation flying
- 2015
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Ingår i: 2015 IEEE Aerospace Conference. - Piscataway, NJ : IEEE Communications Society. - 9781479953790
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Konferensbidrag (refereegranskat)abstract
- The coordination of the attitude among different spacecraft belonging to a multiple platform system (formation or constellation) is a basic requirement in several missions, mainly the ones involving sensors like radars or optical interferometers. It is also an open topic in research, above all as it matches the characteristics of the current trend towards interoperability and federated systems. Different approaches are possible to define and chase such a coordinated attitude. The classic control strategy is the socalled leader-follower architecture, where all spacecraft depend on ("follow") the behavior of a single master. Alternatively, the behavioral approach involves a continuous re-selection of the desired target configuration which is computed on the basis of the behavior of all the platforms. A third possibility is to define a "virtual" architecture, especially suitable with respect to the mission requirements, which is not dependent on the current kinematic state of the platforms. The paper proposes a unified treatment of these concepts by using some fundamental definitions of the consensus dynamics and cooperative control. The convergence to the targeted configuration is addressed both analytically, by using Lyapunov stability criteria, and numerically, by means of numerical simulations. The attitude requirements and constraints are highlighted and a solution for the control algorithm - involving continuous actuators on each platform - is developed. A comparative analysis of different optimal control strategies, the Linear Quadratic Regulation (LQR) and the State Dependent Riccati Equation (SDRE) - suitably modified to address the needs of coordination - is presented. The results show the general value of the proposed approach with respect to either linear or nonlinear models of the dynamics.
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| 8. |
- Felicetti, Leonard, 1982-, et al.
(författare)
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Attitude Stability and Altitude Control of a Variable-Geometry Earth-Orbiting Solar Sail
- 2016
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Ingår i: Journal of Guidance Control and Dynamics. - 0731-5090 .- 1533-3884. ; 39:9, s. 2112-2126
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Tidskriftsartikel (refereegranskat)abstract
- A variable-geometry solar sail for on-orbit altitude control is investigated. It is shown that, by adjusting the effective area of the sail at favorable times, it is possible to influence the length of the semimajor axis over an extended period of time. This solution can be implemented by adopting a spinning quasi-rhombic pyramidal solar sail that provides the heliostability needed to maintain a passive sun-pointing attitude and the freedom to modify the shape of the sail at any time. In particular, this paper investigates the variable-geometry concept through both theoretical and numerical analyses. Stability bounds on the sail design are calculated by means of a first-order analysis, producing conditions on the opening angles of the sail, while gravity gradient torques and solar eclipses are introduced to test the robustness of the concept. The concept targets equatorial orbits above approximately 5000km. Numerical results characterize the expected performance, leading to (for example) an increase of 2200km/yr for a small device at geostationary Earth orbit.
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| 9. |
- Felicetti, Leonard, et al.
(författare)
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Coordinated attitude control for enhanced shape stability of a space web
- 2011
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Ingår i: 62nd International Astronautical Congress 2011 : (IAC 2011). - Paris : International Astronautical Federation. - 9781618398055 ; , s. 8127-8134
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Konferensbidrag (refereegranskat)abstract
- Large, reconfigurable and light orbiting structures are necessary to accomplish a number of tasks, such as the ones related to astronomy and fundamental physics missions, where very large telescope or other sensor arrays are needed. Given the technical limits imposed to the mass at launch, a mostly studied solution can be found in the formation of many satellites controlled in such a way that they can be considered as a virtual structure. This is possible only if synchronized and very accurate control is accomplished. The present paper focuses on the alternative solution represented by the space webs, intended as a set of small corner satellites connected by tethers: along the ropes of the web small robotic systems can move like spiders to position and re-locate, at will, pieces of hardware devoted to specific missions. In this sense, this work is the natural prosecution of previous studies of the same authors, where the advantages, drawbacks and possible solutions have been analyzed. In fact, the presence of rigid links would add the advantage of a simpler control strategy to the typical benefits of formation flying. Unfortunately, there is no stable configuration for an orbiting two dimensional web made by light, flexible tethers, since it cannot support compression forces caused by the gravity gradient. However, if the net is initially rotating (at a sufficiently high velocity) in the orbital plane, the centrifugal force counteracting the gravity gradient compression leads to a stable motion. Residual shape deformations are still present: in order to increase the desired shape stability of the web, it is possible to introduce a coordinated attitude control of the corner satellites, as an example by means of reaction wheels. This paper shows some preliminary results on the dynamics of tethers which are subjected to a torque at their tip. The analysis requires to add to previous models the attitude of the corner spacecraft as well as of the section the tethers are divided in. At this step, tethers are modeled as axial springs with no compression resistance. The paper, based on a performing code specifically written, reports the results for a number of simulations in order to provide helpful insight in this unusual dynamics
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| 10. |
- Felicetti, Leonard, et al.
(författare)
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Coordinated attitude control for multiple heterogeneous satellites missions
- 2012
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Ingår i: AIAA/AAS Astrodynamics Specialist Conference 2012. - Reston, VA : American Institute of Aeronautics and Astronautics, AIAA. - 9781624101823
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Konferensbidrag (refereegranskat)abstract
- The paper investigates cooperative control strategies for spacecraft formations, also in case platforms are not homogeneous but differs in attitude control actuators. Specifically, either a common inertial or a time-varying pointing are considered as requirements for a formation of spacecraft, controlled either entirely by reaction wheels or partly by wheels and partly by thrusters. Two control strategies, namely the classical leader-follower or a more cooperative one, also labelled as behavioural based, where the kinematic state of each spacecraft is known to the others and enters in their command loop, are applied. In order to actually compute the actions, two controllers are considered: a classical proportionalderivative (PD) and an optimal one using the variable gain state dependent Riccati equation (SDRE). Numerical simulations to validate the approach are presented and, within this implementation, SDRE approach shows to succeed even in cases when PD fails
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