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Articles 31 - 60 of 96
Full-Text Articles in Astrodynamics
Investigating Analytical And Numerical Methods To Predict Satellite Orbits Using Two-Line Element Sets, Adam T. Rich
Investigating Analytical And Numerical Methods To Predict Satellite Orbits Using Two-Line Element Sets, Adam T. Rich
Theses and Dissertations
As Low Earth Orbit (LEO) contains an ever-increasing number of objects, the prediction of future object positions must be precise in order to avoid collisions. Object positions are distributed in two-line element (TLE) sets and are generated using the analytical propagator known as Simplified General Perturbations 4 (SGP4). However, a numerical integrator called Special Perturbations (SP) provides an alternative approach to TLE generation and propagation. In this thesis, TLE accuracy was determined with both models, and the length of time that a single element set can provide valid information was also established. With two-line element sets as data, comparisons were …
Formation Flight Of Earth Satellites On Low-Eccentricity Kam Tori, Christopher T. Craft
Formation Flight Of Earth Satellites On Low-Eccentricity Kam Tori, Christopher T. Craft
Theses and Dissertations
The problem of Earth satellite constellation and formation flight is investigated in the context of Kolmogorov-Arnold-Moser (KAM) theory. KAM tori are constructed utilizing Wiesel’s Low-Eccentricity Earth Satellite Theory, allowing numerical representation of the perturbed tori describing Earth orbits acted upon by geopotential perturbations as sets of Fourier series. A maneuvering strategy using the local linearization of the KAM tangent space is developed and applied, demonstrating the ability to maneuver onto and within desired torus surfaces. Constellation and formation design and maintenance on KAM tori are discussed, along with stability and maneuver error concerns. It is shown that placement of satellites …
Orbital Resonances In The Vinti Solution, Laura M. Duffy
Orbital Resonances In The Vinti Solution, Laura M. Duffy
Theses and Dissertations
The Vinti Solution offers a more accurate model than the two-body problem as an orbital propagator. Unfortunately, the Vinti solution contains small divisors near orbital resonances in the perturbative terms of the Hamiltonian, which lead to inaccurate orbital predictions. One approach to avoid the small divisors is to apply transformation theory. The methodology of this research is to identify the perturbative terms of the Vinti Solution, perform a coordinate transformation, and derive the new equations of motion for the Vinti system near orbital resonances. The analysis in this research focuses on the 2:1 resonance, which includes the Global Positioning System. …
Space Object Self-Tracker On-Board Orbit Determination Analysis, Stacie M. Flamos
Space Object Self-Tracker On-Board Orbit Determination Analysis, Stacie M. Flamos
Theses and Dissertations
Due to the United States' growing dependence on space based assets and the in- creasing number of resident space objects (RSO), improvement of Space Situational Awareness (SSA) capabilities is more necessary than ever. As a way to aid in this need, the Air Force Institute of Technology (AFIT) is developing the Space Object Self-Tracker (SOS) as a proof-of-concept experimental satellite for RSO precision tracking and collision avoidance system in Low Earth Orbit (LEO). Specifically, SOS will use Global Positioning System (GPS) position estimates for on-board orbit de- termination. Currently, SOS will use the Simplified General Perturbations-4 (SGP4) algorithm as its …
Short Duration Missions To Earth Crossing Asteroids, James B. Millar Iii
Short Duration Missions To Earth Crossing Asteroids, James B. Millar Iii
Theses and Dissertations
My investigation of the Near Earth Object (NEO) catalog has led to identification of numerous short duration, under 40 days, mission opportunities in the future for three different mission types: uncrewed fly-by, uncrewed arrival, and crewed arrival. 2-body propagation techniques were used to model the orbits of various asteroid candidates and the Earth to determine when a close approach would occur. Once the dates were calculated, distance between the bodies was computed to estimate the ∆V to complete the mission. From the mission ∆V values, a possible mission duration was also computed. The values were analyzed to determine the best …
Leveraging External Sensor Data For Enhanced Space Situational Awareness, Charlie T. Bellows
Leveraging External Sensor Data For Enhanced Space Situational Awareness, Charlie T. Bellows
Theses and Dissertations
Reliable Space Situational Awareness (SSA) is a recognized requirement in the current congested, contested, and competitive environment of space operations. A shortage of available sensors and reliable data sources are some current limiting factors for maintaining SSA. Unfortunately, cost constraints prohibit drastically increasing the sensor inventory. Alternative methods are sought to enhance current SSA, including utilizing non-traditional data sources (external sensors) to perform basic SSA catalog maintenance functions. Astronomical data, for example, routinely collects serendipitous satellite streaks in the course of observing deep space; but tactics, techniques, and procedures designed to glean useful information from those collects have yet to …
Orbit Estimation Of Non-Cooperative Maneuvering Spacecraft, Gary M. Goff
Orbit Estimation Of Non-Cooperative Maneuvering Spacecraft, Gary M. Goff
Theses and Dissertations
Due to the ever increasing congestion of the space environment, there is an increased demand for real-time situation awareness of all objects in space. An unknown spacecraft maneuver changes the predicted orbit, complicates tracking, and degrades estimate accuracies. Traditional orbit estimation routines are implemented, tested, and compared to a multiple model format that adaptively handles unknown maneuvers. Multiple Model Adaptive Estimation is implemented in an original way to track a non-cooperative satellite by covariance inflation and filtering-through a maneuver. Parameters for successful instantaneous maneuver reconstruction are analyzed. Variable State Dimension estimation of a continuously maneuvering spacecraft is investigated. A requirements …
Design And Analysis Of An Attitude Determination And Control Subsystem (Adcs) For Afit's 6u Standard Bus, Erin R. Dannemeyer
Design And Analysis Of An Attitude Determination And Control Subsystem (Adcs) For Afit's 6u Standard Bus, Erin R. Dannemeyer
Theses and Dissertations
The design and testing of AFIT's 6U Attitude Determination and Control Subsystem (ADCS) are explored to establish 3-axis attitude control. The development of AFIT's 6U CubeSat standard bus is an on-going research effort designed to create in-house CubeSat bus components and software. The 6U chassis measures approximately 11 x 24 x 37 cu cm and can have a mass up to 12 kg. The larger bus size (as compared to the more common 3U CubeSat) allows for increased power capabilities and potential to host multiple or larger payloads. Individual ADCS hardware components were either commercially purchased or built in-house and …
Trajectory Optimization For Spacecraft Collision Avoidance, James W. Sales Jr.
Trajectory Optimization For Spacecraft Collision Avoidance, James W. Sales Jr.
Theses and Dissertations
The last several decades have resulted in an unfortunate byproduct of space exploration and development: orbital debris. Satellites in Low Earth Orbit have been required to make an ever increasing number of course corrections in order to avoid collisions. Despite efforts to the contrary, collisions continue to occur, each time creating additional debris and increasing the requirement for the remaining satellites to maneuver. Every required maneuver decreases a satellite's service life. The purpose of this study is to develop a minimum thrust profile to maneuver an orbiting satellite out of its projected error ellipse before a collision occurs. For comparison, …
Trajectory Control And Optimization For Responsive Spacecraft, Costantinos Zagaris
Trajectory Control And Optimization For Responsive Spacecraft, Costantinos Zagaris
Theses and Dissertations
The concept of responsive space has been gaining interest, and growing to include systems that can be re-tasked to complete multiple missions within their lifetime. The purpose of this study is to develop an algorithm that produces a maneuver trajectory that will cause a spacecraft to arrive at a particular location within its orbit earlier than expected. The time difference, delta t, is used as a metric to quantify the effects of the maneuver. Two separate algorithms are developed. The first algorithm is an optimal control method and is developed through Optimal Control Theory. The second algorithm is a feedback …
Applications Of Aerodynamic Forces For Spacecraft Orbit Maneuverability In Operationally Responsive Space And Space Reconstitution Needs, Matthew N. Goodson
Applications Of Aerodynamic Forces For Spacecraft Orbit Maneuverability In Operationally Responsive Space And Space Reconstitution Needs, Matthew N. Goodson
Theses and Dissertations
Each year multiple satellites are launched to provide end users key pieces of information. This information ranges from remote sensing data for military or civilian purposes (e.g., weather forecasting, troop movements, agricultural production, etc.) to large bandwidth telecommunications sensors. No matter the type of information needed, society is demanding more. Because of this continual rise in information needs, the current model of launching one satellite for one mission is not sustainable. To satisfy the information needs of nations across the globe, a means for satellites to transition from one mission type to another must be developed. One means of transitioning …
Design Analysis Of A Sapce Based Chromotomographic Hyperspectral Imaging Experiment, Todd A. Book
Design Analysis Of A Sapce Based Chromotomographic Hyperspectral Imaging Experiment, Todd A. Book
Theses and Dissertations
This research develops the design of several components and/or systems for an experimental space-based chromotomographic hyperspectral imager that is being built by the Air Force Institute of Technology. The design work includes three separate topics. The first topic was the development of a structure utilizing finite element analysis and eigenanalysis for the ground-based version of the chromotomographic experiment (CTEx). The ground-based experiment was performed as a risk mitigation measure for the space-based experiment. The second topic includes a design review of a contractor's proposed off-axis Mersenne telescope for the space-based chromotomographic hyperspectral imager. The work included the creation of preliminary …
Attitude Control Of A Satellite Simulator Using Reaction Wheels And A Pid Controller, Ryan E. Snider
Attitude Control Of A Satellite Simulator Using Reaction Wheels And A Pid Controller, Ryan E. Snider
Theses and Dissertations
Attitude requirements of a satellite are determined by its mission: telecommunications, optical imagery, and meteorology to name a few. A satellite's ability to orient its mission critical hardware (solar arrays, attitude sensors, etc.), as well as its mission specific payload, is incumbent upon the performance of the satellite's attitude control system (ACS). For a highly accurate ACS and for moderately fast maneuverability, reaction wheels are preferred because they allow continuous and smooth control while inducing the smallest possible disturbance torques. The objective of this research is to design, build, test, and evaluate the performance of a reaction wheel ACS on-board …
Prototype Development And Dynamic Characterization Of Deployable Cubesat Booms, Grant M. Thomas
Prototype Development And Dynamic Characterization Of Deployable Cubesat Booms, Grant M. Thomas
Theses and Dissertations
The current barrier to CubeSat proliferation is their lack of utility depth. These small satellites are exceptionally well suited for specific space missions such as space weather observation and other scientific data gathering exploits; however, they are not suited for every mission. The 10cm-cube form factor that gives the CubeSat its unique advantage is also its greatest hindrance. A potential bridge over this gap is the successful integration of deployable booms onto the CubeSat structure. With this research, the Air Force Institute of Technology (AFIT) explored the parameters of deployable tapespring booms using the triangular retractable and collapsible (TRAC) cross- …
Preliminary Electrical Designs For Ctex And Afit Satellite Ground Station, Arthur L. Morse
Preliminary Electrical Designs For Ctex And Afit Satellite Ground Station, Arthur L. Morse
Theses and Dissertations
This thesis outlines the design of the electrical components for the space-based ChromoTomography Experiment (CTEx). CTEx is the next step in the development of high-speed chromotomography at the Air Force Institute of Technology. The electrical design of the system is challenging due to the large amount of data that is acquired by the imager and the limited resources that is inherent with space-based systems. Additional complication to the design is the need to know the angle of a spinning prism that is in the field of view very precisely for each image. Without this precise measurement any scene that is …
Accurate Dynamic Response Predictions Of Pnpsat I, Michael D. Trottier
Accurate Dynamic Response Predictions Of Pnpsat I, Michael D. Trottier
Theses and Dissertations
Researchers at the Air Force Institute of Technology (AFIT) and the Operationally Responsive Space (ORS) Office have conducted extensive vibration testing and structural modeling on the first ORS Plug-and-Play Satellite (PnPSAT I). The intent of this research effort is to evaluate the premise that current post-integration spacecraft environmental test requirements can be reduced or modified using accurately tuned finite element (FE) models. As part of this research, modal testing was conducted on the PnPSAT I structural panels at AFIT. The modal testing was part of a much larger series of experimental trials on various configurations of PnPSAT I at the …
Relative Orbit Elements For Satellites In Elliptical Orbits, Kirk W. Johnson
Relative Orbit Elements For Satellites In Elliptical Orbits, Kirk W. Johnson
Theses and Dissertations
The purpose of this research was to describe the unperturbed relative motion of Earth satellites in elliptical orbits using a simple dynamics model whose parameters allow significant geometrical insight and operational efficacy. The goal was to retain the advantages of the Relative Orbit Elements (ROE) realization of the Hill-Clohessy-Wiltshire (HCW) equations, a linearized dynamics model for circular reference orbits. Specifically, this thesis analyzed the geometry of satellite rendezvous and proximity operations using the ROE parameters to characterize the model’s utility. Next, through a comprehensive literature review, this thesis sought possible approaches for developing a similarly useful parameterization for chief orbits …
Mission Analysis And Design For Space Based Inter-Satellite Laser Power Beaming, Nicholas M. Keller
Mission Analysis And Design For Space Based Inter-Satellite Laser Power Beaming, Nicholas M. Keller
Theses and Dissertations
This research effort develops an interdisciplinary design tool to optimize an orbit for the purpose of wirelessly beaming power from the International Space Stations (ISS) Japanese Experimental Module Exposed Facility (JEM/EF) to a target satellite. For the purpose of this initiative, the target satellite will be referred to as FalconSAT6, a reference to the proposed follow-on satellite to the U.S. Air Force Academy’s (USAFA) FalconSAT5 program. The USAFA FalconSAT program provides cadets an opportunity to design, analyze, build, test and operate small satellites to conduct Department of Defense (DoD) space missions. The tool developed for this research is designed to …
Mission Analysis For Multiple Rendezvous Of Near-Earth Asteroids Using Earth Gravity Assist, Uriah J. Tobey
Mission Analysis For Multiple Rendezvous Of Near-Earth Asteroids Using Earth Gravity Assist, Uriah J. Tobey
Theses and Dissertations
The Jet Propulsion Laboratory (JPL) catalog of near-Earth objects (NEOs) such as asteroids and comets contains over 6600 asteroids and 150 comets as of February of 2010. This includes over 1000 potentially hazardous asteroids, or objects with orbits that pass close enough to Earth to pose a potential impact threat. The asteroid community believes there are a significant number of objects still undiscovered, which makes finding, tracking, and calculating missions to study these objects an active area of research. This study was based on finding orbit solutions using Earth gravity assist to visit one near-Earth object (NEO) a year for …
Formation Flight Of Earth Satellites On Kam Tori, Christopher T. Craft
Formation Flight Of Earth Satellites On Kam Tori, Christopher T. Craft
Theses and Dissertations
Kolmogorov, Arnold and Moser (KAM) theory provides that orbits of satellites whose dynamics are representable by an integrable Hamiltonian plus a small, real perturbation lie on tori in phase space and remain on the KAM tori for all time, unless acted upon by a non-conservative force. A refined technique for constructing KAM tori for Earth-orbiting satellites is developed and implemented using numerically integrated orbital data for hypothetical satellites and involving methods of Fourier analysis and spectral decomposition. Definition of satellite formations on the KAM tori is performed and analyses conducted to investigate both constellations with large separations and clusters with …
Satellite Reentry Control Via Surface Area Amplification, Salvador Alemán
Satellite Reentry Control Via Surface Area Amplification, Salvador Alemán
Theses and Dissertations
This project endeavors to find whether it is feasible to use an increase in surface area as a way of increasing the drag on an orbiting object, thus decreasing its orbital lifetime. The surface area increase can be achieved by an apparatus that deploys a balloon. The balloon will act as a parachute that will decrease the potential energy of the object through atmospheric drag. This is most effective by objects that reach the Low Earth altitudes of less than 500 kilometers, where an object is encountering a firmer atmospheric density. The project is carried out through propagating three different …
Application Of Kam Theorem To Earth Orbiting Satellites, Bryan D. Little
Application Of Kam Theorem To Earth Orbiting Satellites, Bryan D. Little
Theses and Dissertations
An orbit that lies on a Kolmogorov, Arnold, and Moser (KAM) Torus will remain on that torus until and unless it experiences a force that causes it to leave the torus. Earth satellites that are subject only to the Earth's gravity field may lie on such KAM tori. Analyzing on orbit satellite position data should allow for the identification of the fundamental frequencies needed to define the KAM tori for modeling Earth satellite orbits. KAM Tori are created for the Gravity Recovery and Climate Experience (GRACE) and Jason-1 satellites to model their orbital motion. Precise position data for the satellites …
Mission Planning For Close-Proximity Satellites, Barry R. Witt
Mission Planning For Close-Proximity Satellites, Barry R. Witt
Theses and Dissertations
Given an initial orbit and a set of other orbits of interest, the lowest change in velocity "path" between them is of high value. Software was developed to visualize the change in velocity required from a user defined window of burn to a user defined window of intercept. The time between burn and intercept is unrestricted. Multiple intercepts require searching an n! solution space, research then is focused on ways to pick optimal choices without fully calculating out the cost of doing all possible combinations. Some code was translated from BASIC and the rest was newly developed in MATLAB. The …
Minimizing Secular J2 Perturbation Effects On Satellite Formations, Jonathan W. Wright
Minimizing Secular J2 Perturbation Effects On Satellite Formations, Jonathan W. Wright
Theses and Dissertations
The purpose of this thesis is to examine the secular effects of the J2 oblateness perturbation on close proximity satellites. The main objective is to analyze the deputy’s position and velocity with respect to the chief and adjust the initial conditions of the deputy in an attempt to minimize the secular effects of J2 perturbations. Previous work has provided a method of obtaining a closed form solution for J2 invariance with co-planar orbits. Therefore, this work will primarily consider deputy orbits that experience motion outside of the chief’s orbital plane. Upon determining the required initial conditions, the …
Modeling Gps Satellite Orbits Using Kam Tori, Rachel M. Derbis
Modeling Gps Satellite Orbits Using Kam Tori, Rachel M. Derbis
Theses and Dissertations
Global Positioning System (GPS) satellite orbits are modeled using Kolmogorov, Arnold, Moser (KAM) tori. Precise Global Positioning System satellite locations are analyzed using Fourier transforms to identify the three basis frequencies in an Earth Centered, Earth Fixed (ECEF) rotating reference frame. The three fundamental frequencies are 1) the anomalistic frequency, 2) a combination of earth’s rotational frequency and the nodal regression rate, and 3) the apsidial regression rate. A KAM tori model fit to the satellite data could be used to predict future satellite locations. This model would allow rapid determination with fewer computational requirements than the typical method of …
Crew Exploration Vehicle (Cev) Skip Entry Trajectory, Emre Kaya
Crew Exploration Vehicle (Cev) Skip Entry Trajectory, Emre Kaya
Theses and Dissertations
This research effort develops a program using MATLAB® to solve the equations of motion for the atmospheric reentry of the Crew Exploration Vehicle (CEV) which is assumed to be in the phase of a lunar return trajectory that could be initiated any time during the mission. The essential reason for this research is to find a solution for the problem of an unplanned lunar return in addition to the normal procedures. Unlike Apollo type missions, the CEV would still be able to land on any preplanned available landing sites without any additional delay. In Apollo type missions, the return phase …
Initial Determination Of Low Earth Orbits Using Commercial Telescopes, Matthew M. Schmunk
Initial Determination Of Low Earth Orbits Using Commercial Telescopes, Matthew M. Schmunk
Theses and Dissertations
Within the last decade, many new technologies have significantly changed the face of private astronomy. Developments such as inexpensive but high-quality sensors, rapid personal computing, and easy networking inspire a reexamination of an old problem: how practical is it to develop initial orbit estimates for Low Earth Orbiting (LEO) satellites using optical tracking? This paper documents the design and implementation of a commercial telescope system used to answer precisely that question. This analysis deter- mined there are some challenging barriers to successful single-site orbit determination, but it is possible given the right conditions. Considering the low cost and small sup- …
Satellite Attitude Control Using Atmopheric Drag, David B. Guettler
Satellite Attitude Control Using Atmopheric Drag, David B. Guettler
Theses and Dissertations
Attitude control is a requirement for most satellites. Many schemes have been devised over the years including control moment gyros, reaction wheels, spin stabilization and gravity gradient stabilization. For low Earth orbits, the Earth's atmosphere can have an affect on a satellite's orbit and attitude. This research effort examines the feasibility of using the atmosphere to actively control a spacecraft's attitude using drag panels. Using the atmosphere to control spacecraft attitude has been researched in the past however very little research has been done using an active feedback control system to maintain spacecraft attitude. A linear computer model was created …
Spacecraft Proximity Operations Used To Estimate The Dynamical & Physical Properties Of A Resident Space Object, Abraham F. Brunner
Spacecraft Proximity Operations Used To Estimate The Dynamical & Physical Properties Of A Resident Space Object, Abraham F. Brunner
Theses and Dissertations
When conducting a space proximity operation, developing high-fidelity estimates of the dynamical and physical properties of a Resident Space Object (RSO) based on post-rendezvous observational data acquired, is imperative for the understanding of the RSO itself and the operating environment. This research investigates the estimation of relative motion dynamics, rotational dynamics, and the feasibility of estimating the moments of inertia of a RSO. Using the Hill-Clohessy-Wiltshire equations, rigid-body dynamics, and estimation theory, a nonlinear least squares estimation algorithm is implemented in the processing of range data from tracked observation points on the RSO body. Through simulation, it was determined that …
Optimal Orbital Coverage Of Theater Operations And Targets, Kimberly A. Sugrue
Optimal Orbital Coverage Of Theater Operations And Targets, Kimberly A. Sugrue
Theses and Dissertations
The use of satellites as a tactical asset to support theater operations is a desired capability for future space operations. Unlike traditional satellite systems designed to provide coverage over the entire globe or large regions, tactical satellites would provide coverage over a small region which can be modeled as a single ground point defined by a latitude and longitude. In order to provide sufficient utility as a theater asset, a satellite should be placed in an orbit that provides a maximum amount of coverage of the target ground point. This study examined the optimization of orbit parameters to maximize the …