Reconfigurable Control for the Formation Flying of Multiple Spacecraft
Several results on the reconfigurable control architecture for the formation flying of multiple spacecraft are presented.
formation↗
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Constellation Templates: An Approach to Autonomous Formation Flying
Multiple spacecraft flying in formation is a new paradigm that is key to the success of several future NASA missions.
formation flying interferometry spacecraft constel↗
A Robust Control Approach for the Formation Flying of Multiple Spacecraft
We present a disturbance rejection mechanism for the formation flying of multiple spacecraft based on a robust control approach in terms of an H(sub infinity) control problem. The corresponding H(sub infinity) control problem is then solved numerically using linear matrix inequalities.
Mesbahi, M.↗
Reconfigurable Control for the Formation Flying of Multiple Spacecraft
Several results on the reconfigurable control architecture for the formation flying of multiple spacecraft are presented. In this direction, simple control laws are combined with logic-based switching to propose a hybrid control architecture for leader reassignment, leader-following capturing, and dealing with control saturations.
Mesbahi, Mehran↗
Precision Formation Delta-V Requirements for Distributed Platforms in Earth Orbit
Distributed spacecraft flying in formation can overcome the resolution limitations of monolithic, Earth-sensing systems. However, formation spacecraft must now expend fuel to counteract disturbances and the gravity gradients between spacecraft. We consider three different formation architectures and determine the (Delta)(nu) required to maintain relative positions at accuracies from 0.1 to 10 m (1(sigma)). The three architectures considered are: (i) Leader/Follower, in which individual spacecraft controllers track with respect to a passive, leader spacecraft, (ii) Center of Formation, in which individual spacecraft controllers track with respect to the geometric center of the formation, and (iii) Iterated Virtual Structure, in which a formation template is fit each timestep and individual spacecraft controllers track with respect to the fitted template.
formation flying↗
An Integrated Vision-Based System for Spacecraft Attitude and Topology Determination for Formation Flight Missions
With the space industry's increasing focus upon multi-spacecraft formation flight missions, the ability to precisely determine system topology and the orientation of member spacecraft relative to both inertial space and each other is becoming a critical design requirement. Topology determination in satellite systems has traditionally made use of GPS or ground uplink position data for low Earth orbits, or, alternatively, inter-satellite ranging between all formation pairs. While these techniques work, they are not ideal for extension to interplanetary missions or to large fleets of decentralized, mixed-function spacecraft. The Vision-Based Attitude and Formation Determination System (VBAFDS) represents a novel solution to both the navigation and topology determination problems with an integrated approach that combines a miniature star tracker with a suite of robust processing algorithms. By combining a single range measurement with vision data to resolve complete system topology, the VBAFDS design represents a simple, resource-efficient solution that is not constrained to certain Earth orbits or formation geometries. In this paper, analysis and design of the VBAFDS integrated guidance, navigation and control (GN&C) technology will be discussed, including hardware requirements, algorithm development, and simulation results in the context of potential mission applications.
Rogers, Aaron↗
Spacecraft Autonomous Navigation for Formation Flying Earth Orbiters Using GPS
This paper extends earlier analysis for autonomous orbit determination and control of Earth orbiting spacecraft. The earlier analysis was limited to a single spacecraft with a ground track repeat requirement. This work shows that a similar technique is applicable for two spacecraft flying in formation. Tracking and orbit determination functions are performed using the Global Positioning System (GPS).
spacecraft↗
Investigation of Space Interferometer Control Using Imaging Sensor Output Feedback
Numerous space interferometry missions are planned for the next decade to verify different enabling technologies towards very-long-baseline interferometry to achieve high-resolution imaging and high-precision measurements. These objectives will require coordinated formations of spacecraft separately carrying optical elements comprising the interferometer. High-precision sensing and control of the spacecraft and the interferometer-component payloads are necessary to deliver sub-wavelength accuracy to achieve the scientific objectives. For these missions, the primary scientific product of interferometer measurements may be the only source of data available at the precision required to maintain the spacecraft and interferometer-component formation. A concept is studied for detecting the interferometer's optical configuration errors based on information extracted from the interferometer sensor output. It enables precision control of the optical components, and, in cases of space interferometers requiring formation flight of spacecraft that comprise the elements of a distributed instrument, it enables the control of the formation flying vehicles because independent navigation or ranging sensors cannot deliver the high-precision metrology over the entire required geometry. Since the concept can act on the quality of the interferometer output directly, it can detect errors outside the capability of traditional metrology instruments, and provide the means needed to augment the traditional instrumentation to enable enhanced performance. Specific analyses performed in this study include the application of signal-processing and image-processing techniques to solve the problems of interferometer aperture baseline control, interferometer pointing, and orientation of multiple interferometer aperture pairs.
Cheng, Victore H. L.↗
Investigation of Space Interferometer Control Using Imaging Sensor Output Feedback
Numerous space interferometry missions are planned for the next decade to verify different enabling technologies towards very-long-baseline interferometry to achieve high-resolution imaging and high-precision measurements. These objectives will require coordinated formations of spacecraft separately carrying optical elements comprising the interferometer. High-precision sensing and control of the spacecraft and the interferometer-component payloads are necessary to deliver sub-wavelength accuracy to achieve the scientific objectives. For these missions, the primary scientific product of interferometer measurements may be the only source of data available at the precision required to maintain the spacecraft and interferometer-component formation. A concept is studied for detecting the interferometer's optical configuration errors based on information extracted from the interferometer sensor output. It enables precision control of the optical components, and, in cases of space interferometers requiring formation flight of spacecraft that comprise the elements of a distributed instrument, it enables the control of the formation-flying vehicles because independent navigation or ranging sensors cannot deliver the high-precision metrology over the entire required geometry. Since the concept can act on the quality of the interferometer output directly, it can detect errors outside the capability of traditional metrology instruments, and provide the means needed to augment the traditional instrumentation to enable enhanced performance. Specific analyses performed in this study include the application of signal-processing and image-processing techniques to solve the problems of interferometer aperture baseline control, interferometer pointing, and orientation of multiple interferometer aperture pairs.
Leitner, Jesse A.↗
A Convex Guidance Algorithm for Formation Reconfiguration
In this paper, a reconfiguration guidance algorithm for formation flying spacecraft is presented. The formation reconfiguration guidance problem is first formulated as a continuous-time minimum-fuel or minimum-energy optimal control problem with collision avoidance and control constraints. The optimal control problem is then discretized to obtain a finite dimensional parameter optimization problem. In this formulation, the collision avoidance constraints are imposed via separating planes between each pair of spacecraft. A heuristic is introduced to choose these separating planes that leads to the convexification of the collision avoidance constraints. Additionally, convex constraints are imposed to guarantee that no collisions occur between discrete time samples. The resulting finite dimensional optimization problem is a second order cone program, for which standard algorithms can compute the global optimum with deterministic convergence and a prescribed level of accuracy. Consequently, the formation reconfiguration algorithm can be implemented onboard a spacecraft for real-time operations.
formation reconfiguration↗
Formation Flying Control of Multiple Spacecraft
The problem of coordination and control of multiple spacecraft (MS) moving in formation is considered. Here, each MS is modeled by a rigid body with fixed center of mass. First, various schemes for generating the desired formation patterns are discussed, Then, explicit control laws for formation-keeping and relative attitude alignment based on nearest neighbor-tracking are derived. The necessary data which must be communicated between the MS to achieve effective control are examined. The time-domain behavior of the feedback-controlled MS formation for typical low-Earth orbits is studied both analytically and via computer simulation. The paper concludes with a discussion of the implementation of the derived control laws, and the integration of the MS formation coordination and control system with a proposed inter-spacecraft communication/computing network.
Hadaegh, F. Y.↗
Considerations on formation flying separations for earth observing satellite missions
We assume that scientific requirements (or other mission requirements) call for simultaneous observations from sensors located on different formation-flying spacecraft, and assess how well various kinds of formations of two and three spacecraft can meet these simultaneity requirements. We simulate two types of formation, one where the slave spacecraft moves with respect to the reference spacecraft, and the other where the two spacecraft are kept at a constant time separation. For each type of formation we consider two attitudes: a perfect local vertical local horizontal (LVLH) and an attitude which represents the maximum allowable mission tolerance offset from the mission requirements for attitude determination. We simulate formations of multiple spacecraft and determine how well they can perform simultaneous observations. For each spacecraft we compute the instantaneous ground projection of the center of the imager's fieId of view and plot the movement of the instantaneous ground projection of one spacecraft in the formation relative to the other. The size and shape of this effective ground target parametrize the size and shape of the actual ground target as well as the size and shape of the imager's field of view and the percentage of overlap required.
Folta, David↗
Formation-Initialization Algorithm for N Spacecraft
A paper presents an algorithm to initialize a formation of N distributed spacecraft in deep space.
Ploen, Scott↗
Overview of ultra-precise time transfer formation flying, and spacecraft-spacecraft tracking systems
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formation flying GPS↗
Formation Flying of Tethered and Nontethered Spacecraft
A paper discusses the effect of the dynamic interaction taking place within a formation composed of a rigid and a deformable vehicle, and presents the concept of two or more tethered spacecraft flying in formation with one or more separated free-flying spacecraft. Although progress toward formation flight of nontethered spacecraft has already been achieved, the document cites potential advantages of tethering, including less consumption of fuel to maintain formation, very high dynamic stability of a rotating tethered formation, and intrinsically passive gravity-gradient stabilization. The document presents a theoretical analysis of the dynamics of a system comprising one free-flying spacecraft and two tethered spacecraft in orbit, as a prototype of more complex systems. The spacecraft are modeled as rigid bodies and the tether as a mass-less spring with structural viscous damping. Included in the analysis is a study of the feasibility of a centralized control system for maintaining a required formation in low Earth orbit. A numerical simulation of a retargeting maneuver is reported to show that even if the additional internal dynamics of the system caused by flexibility is considered, high pointing precision can be achieved if a fictitious rigid frame is used to track the tethered system, and it should be possible to position the spacecraft with centimeter accuracy and to orient the formation within arc seconds of the desired direction also in the presence of low Earth orbit environmental perturbations. The results of the study demonstrate that the concept is feasible in Earth orbit and point the way to further study of these hybrid tethered and free-flying systems for related applications in orbit around other Solar System bodies.
Quadrelli, Marco B.↗
Magnetospheric Multi Scale (MMS) Patching Story for DARPA AMP Collaboration
NASA’s Magnetospheric Multiscale (MMS) spacecraft are part of a robotic space mission that studies the Earth's magnetosphere. Launched in March 2015, MMS consists of four identical spacecraft that fly in a tetrahedral formation. The spacecraft gather information about the microphysics of magnetic reconnection including turbulence and energetic particle acceleration —processes common in many astrophysical plasmas.
Gilberto Alves Vicente↗
Formation Flying Control of Multiple Spacecraft: Graph Theoretic Properties and Switching Schemes
We present several results on the leader-following (LF) paradigm in the formation flying of multiple spacecraft in free space.
Formation↗
Very High Resolution Solar X-ray Imaging Using Diffractive Optics
This paper describes the development of X-ray diffractive optics for imaging solar flares with better than 0.1 arcsec angular resolution. X-ray images with this resolution of the greater than or equal to 10 MK plasma in solar active regions and solar flares would allow the cross-sectional area of magnetic loops to be resolved and the coronal flare energy release region itself to be probed. The objective of this work is to obtain X-ray images in the iron-line complex at 6.7 keV observed during solar flares with an angular resolution as fine as 0.1 arcsec - over an order of magnitude finer than is now possible. This line emission is from highly ionized iron atoms, primarily Fe xxv, in the hottest flare plasma at temperatures in excess of approximately equal to 10 MK. It provides information on the flare morphology, the iron abundance, and the distribution of the hot plasma. Studying how this plasma is heated to such high temperatures in such short times during solar flares is of critical importance in understanding these powerful transient events, one of the major objectives of solar physics.We describe the design, fabrication, and testing of phase zone plate X-ray lenses with focal lengths of approximately equal to 100 m at these energies that would be capable of achieving these objectives. We show how such lenses could be included on a two-spacecraft formation-flying mission with the lenses on the spacecraft closest to the Sun and an X-ray imaging array on the second spacecraft in the focal plane approximately equal to 100 m away. High resolution X-ray images could be obtained when the two spacecraft are aligned with the region of interest on the Sun. Requirements and constraints for the control of the two spacecraft are discussed together with the overall feasibility of such a formation-flying mission.
Dennis, B. R.↗