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Constellation Reconfiguration: Tools and AnalysisDavis, Jeremy John 2010 August 1900 (has links)
Constellation reconfi guration consists of transforming an initial constellation
of satellites into some final constellation of satellites to maintain system optimality.
Constellations with phased deployment, changing mission requirements, or satellite
failures would all benefi t from reconfi guration capability. The constellation reconfiguration problem can be broken into two broad sub-problems: constellation design
and constellation transfer. Both are complicated and combinatorial in nature and
require new, more efficient methods. Having reviewed existing constellation design
frameworks, a new framework, the Elliptical Flower Constellations (EFCs), has been
developed that offers improved performance over traditional methods. To assist in
rapidly analyzing constellation designs, a new method for orbit propagation based
on a sequential solution of Kepler's equation is presented. The constellation transfer
problem requires an optimal assignment of satellites in the initial orbit to slots in
the final orbit based on optimal orbit transfers between them. A new method for
approximately solving the optimal two-impulse orbit transfer with fixed end-points,
the so-called minimum Delta v Lambert's problem, is developed that requires the solution
of a 4th order polynomial, as opposed to the 6th or higher order polynomials or
iterative techniques of existing methods. The recently developed Learning Approach
to sampling optimization is applied to the particular problem of general orbit transfer between two generic orbits, with several enhancements specifi c to this problem that
improve its performance. The constellation transfer problem is then posed as a Linear
Assignment Problem and solved using the auction algorithm once the orbit transfers
have been computed. Constellations designed for global navigation satellite systems
and for global communications demonstrate signifi cant improvements through the use
of the EFC framework over existing methods. An end-to-end example of constellation
recon figuration for a constellation with changing regional coverage requirements
shows the effectiveness of the constellation transfer methods.
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Orbit design and estimation for surveillance missions using genetic algorithmsAbdelkhalik, Osama Mohamed Omar 12 April 2006 (has links)
The problem of observing a given set of Earth target sites within an assigned time
frame is examined. Attention is given mainly to visiting these sites as sub-satellite
nadir points. Solutions to this problem in the literature require thrusters to continuously
maneuver the satellite from one site to another. A natural solution is proposed.
A natural solution is a gravitational orbit that enables the spacecraft to satisfy the
mission requirements without maneuvering. Optimization of a penalty function is
performed to find natural solutions for satellite orbit configurations. This penalty
function depends on the mission objectives. Two mission objectives are considered:
maximum observation time and maximum resolution. The penalty function poses
multi minima and a genetic algorithm technique is used to solve this problem. In
the case that there is no one orbit satisfying the mission requirements, a multi-orbit
solution is proposed. In a multi-orbit solution, the set of target sites is split into
two groups. Then the developed algorithm is used to search for a natural solution
for each group. The satellite has to be maneuvered between the two solution orbits.
Genetic algorithms are used to find the optimal orbit transfer between the two orbits
using impulsive thrusters. A new formulation for solving the orbit maneuver problem
using genetic algorithms is developed. The developed formulation searches for a mini mum fuel consumption maneuver and guarantees that the satellite will be transferred
exactly to the final orbit even if the solution is non-optimal. The results obtained
demonstrate the feasibility of finding natural solutions for many case studies.
The problem of the design of suitable satellite constellation for Earth observing
applications is addressed. Two cases are considered. The first is the remote sensing
missions for a particular region with high frequency and small swath width. The second
is the interferometry radar Earth observation missions. In satellite constellations
orbit's design, a new set of compatible orbits, called the "Two-way orbits",whose
ground track path is a closed-loop trajectory that intersects itself, in some points,
with tangent intersections is introduced. Conditions are derived on the orbital elements
such that these Two-way Orbits exist and satellites flying in these orbits pass
the tangent intersection points at the same time. Finally, the recently proposed concept
of observing a space object from onboard a spacecraft using a star tracker is
considered. The measurements of the star tracker provide directions to the target in
space and do not provide range measurements. Estimation for the orbit of the target
space object using the measurements of the star tracker is developed. An observability
analysis is performed to derive conditions on the observability of the system states.
The Gaussian Least Squares Differential Correction Technique is implemented. The
results obtained demonstrate the feasibility of using the measurements of the star
tracker to get a good estimate for the target orbit within a period of measurements
ranging from about 20 percent to 50 percent of the orbital period depending on the
two orbits.
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The Spatial 2:1 Resonant Orbits in Multibody Models: Analysis and ApplicationsAndrew Joseph Binder (18848701) 24 June 2024 (has links)
<p dir="ltr">Within the aerospace community in recent years, there has been a marked increase in interest in cislunar space. To this end, the study of the dynamics of this regime has flourished in both quantity and quality in recent years, spearheaded by the use of simplified dynamical models to gain insight into the dynamics and to generate viable mission concepts. The most popular and simple of these models, the Circular Restricted Three-Body Problem, has been thoroughly explored to meet these goals (even well-prior to the recent spike in interest). Much work has been done investigating periodic orbits within these models, and similarly has been performed on non-periodic transfers into periodic orbits. Studied less is the superposition of these two concepts, or using periodic orbits as a way to transit, for example, cislunar space. In this thesis, the development of periodic orbits amenable to transiting is accomplished. Beginning from periodic orbit families already present in the literature, this research finds a novel and useful family of periodic orbits, here dubbed the spatial 2:1-resonant orbit family. Within this newly-discovered family, multitudes of qualitative behaviors interesting to the astrodynamics community are found. Many family members seem accommadating to a diverse set of mission profiles, from purely-unstable family members best suited to use as transfers, to marginally stable ones best suited to longer-term use. This family as a whole is analyzed and catalogued with thorough descriptions of behavior, both quantitative and qualitative. While the Circular Restricted Three-Body Problem serves as an excellent starting point for analysis, trajectories found there must be generalized to higher-fidelity modeling. In this spirit, this thesis also focuses on demonstrating such generalization and putting it into practice using the more sophisticated Elliptic-Restricted Three-Body Problem. Documentation of the numerical tools necessary and helpful in accomplishing this generalization is included in this work. Prototypically, the truly 2:1 sidereally-resonant unstable member of the 2:1 family is transitioned into the elliptic problem, as is a nearly-stable L2 Halo orbit family member. This new trajectory is paired with a more classically-present example to show the validity of the methodology. To aid this analysis, symmetries present within the elliptic model are also explored and explained. With this analysis completed, this orbit family is demonstrated to be both interesting and useful, when considered under even more realistic modelling. Further work to mature this novel family of orbits is merited, both for use as the fundamental building block for transfers and for use for more-permanent habitation. More broadly, this work aims to achieve a further proliferation of the merger between transfer and orbit, concepts which seem distinct at first, but deserve more gradual consideration as different flavors of the same idea.</p>
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