The Coulomb propulsion system has no exhaust plume impingement problem with neighboring spacecraft and does not contaminate their sensors because it requires essentially no propellant. It is suitable to close formation control on the order of dozens of meters. The Coulomb forces are internal forces of the formation and they influence all charged spacecraft at the same time. Highly nonlinear and strongly coupled equations of motion of Coulomb formation makes creating a Coulomb control method a challenging task. Instead of positioning all spacecraft, this study investigates having a sensor craft be sequentially controlled using dedicated drone craft. At least three drone craft are required to control a general sensor craft position in the inertial space. However, the singularity of a drone plane occurs when a sensor craft moves across the drone plane. A bang-bang control method with a singularity check can avoid this problem but may lose formation control as the relative distances grow bounded. A bang-coast-bang control method utilizing a reference trajectory profile and drone rest control is introduced to increase the control effectiveness. The spacecraft are assumed to be floating freely in inertial space, an approximation of environments found while underway to other solar system bodies. Numerical simulation results show the feasibility of sensor craft control using Coulomb forces. / Master of Science

Spacecraft formations offer more powerful and robust space system architectures than single spacecraft systems. Investigations into the dynamics and control of spacecraft formations are vital for the development and design of future successful space missions. The problem of controlling the attitude of a formation of spacecraft is investigated. The spacecraft formation is modelled as a distributed system, where the individual spacecraft's attitude control systems are the local control agents. A decentralized attitude controller utilizing behavior-based control is developed. The global stability of the controller is proven using Lyaponuv stability theory. Convergence of the attitude controller is proven through the use of an invariance argument. The attitude controller's stability and convergence characteristics are investigated further through numeric simulation of the attitude dynamics of the spacecraft formation. / Master of Science

Recently there is an increase in interest in the Moon as a destination for space missions. This increased interest is in the composition and geography of the Moon as well as using the Moon to travel beyond the Earth to other planets in the solar system. This thesis explores the mechanics behind a lunar mission and the costs and benefits of different approaches. To constrain this problem, the launch criteria are those of Wallops Flight Facility (WFF), which has expressed interest in launching small spacecraft to the Moon for exploration and study of the lunar surface. The flight from the Earth to the Moon and subsequent lunar orbits, referred to hereafter as the mission, is broken up into three different phases: first the launch and parking orbit around the Earth, second the transfer orbit, and finally the lunar capture and orbit. A launch from WFF constrains the direction of the launch and the possible initial parking orbits. Recently WFF has been offered the use of a Taurus XL launch vehicle whose specifications will be used for all other limitations of the launch and initial parking orbit. The orbit investigated in this part of the mission is a simple circular orbit with limited disturbances. These disturbances are only a major factor for long duration orbits and don't affect the parking orbit significantly. The transfer orbit from the Earth to the Moon is the most complex and interesting part of the mission. To fully describe the dynamics of the Earth-Moon system a three-body model is used. The model is a restricted three-body problem keeping the Earth and Moon orbiting circularly around the system barycenter. This model allows the spacecraft to experience the influence of the Earth and Moon during the entire transfer orbit, making the simulation more closely related to what will actually happen rather than what a patched conic solution would give. This trajectory is examined using Newtonian, Lagrangian, and Hamiltonian mechanics along with using a rotating and non-rotating frame of reference for the equations of motion. The objective of the transfer orbit is to reduce the time and fuel cost of the mission as well as allow for various insertion angles to the Moon. The final phase of the mission is the lunar orbit and the analysis also uses a simple two body model similar to the parking orbit. The analysis investigates how the orbits around the Moon evolve and decay and explores more than just circular orbits, but orbits with different eccentricities. The non-uniform lunar gravity field is investigated to accurately model the lunar orbit. These factors give a proper simulation of what happens to the craft for the duration of the lunar orbit. Tracking the changes in the orbit gives a description of where it will be and how much of the lunar surface it can observe without any active changes to the orbit. The analysis allows for either pursuing a long duration sustained orbit or a more interesting orbit that covers more of the lunar surface. These three phases are numerically simulated using MATLAB, which is a focus of this thesis. In all parts of the mission the simulations are refined and optimized to reduce the time of the simulation. Also this refinement gives a more accurate portrayal of what would really happen in orbit. This reduction in time is necessary to allow for many different orbits and scenarios to be investigated without using an unreasonable amount of time. / Master of Science

As the use of small satellites for advanced space missions continues to grow, the importance of low mass and cost three-axis attitude stabilization systems increases as well, with these systems requiring high accuracy attitude knowledge. Star trackers provide the most accurate attitude knowledge of any type of attitude sensor, but the high cost, size, and weight of commercial star trackers can be prohibitive to small satellite missions. Many simple star trackers have been developed using commercial off-the-shelf camera sensors and processing hardware, but the challenge remains in testing and characterizing these devices. A common solution is night sky tests, in which the star tracker is held up to the night sky to image the star field and perform attitude determination. Commercial star trackers, on the other hand, are regularly tested with manufacturer provided star field images that attach directly to the sensor. These methods, however, severely limit the sky conditions that can be used in testing. Night sky tests depend on weather and can only image regions of the sky the user has access to, while lab-based testing uses the few provided still images. This thesis presents a hardware-in-the-loop star tracker test bed developed for comprehensive ground-based testing of both in-house and commercial star trackers. The system consists of a small screen to display a star field, a simple in-house camera star tracker, and a microprocessor. This test bed allows any star field image to be simulated. The system is set up for use on a stationary tabletop, but its small size lends itself for use with a spacecraft dynamics platform, which can facilitate testing of control algorithms using real star tracker output.

A spacecraft formation possesses several benefits over a single-satellite mission. However, launching a fleet of satellites is a high-cost, high-risk venture. One way to mitigate much of this risk is to demonstrate hardware and algorithm performance in groundbased testbeds. It is typically difficult to experimentally replicate satellite dynamics in an Earth-bound laboratory because of the influences of gravity and friction. An air bearing provides a very low-torque environment for experimentation, thereby recapturing the freedom of the space environment as effectively as possible. Depending upon con- figuration, air-bearing systems provide some combination of translational and rotational freedom; the three degrees of rotational freedom provided by a spherical air bearing are ideal for investigation of spacecraft attitude dynamics and control problems. An interest in experimental demonstration of formation flying led directly to the development of the Distributed Spacecraft Attitude Control System Simulator (DSACSS). The DSACSS is a unique facility, as it uses two air-bearing platforms working in concert. Thus DSACSS provides a pair of "spacecraft" three degrees of attitude freedom each. Through use of the DSACSS we are able to replicate the relative attitude dynamics between nodes of a formation such as might be required for co-observation of a terrestrial target. Many dissertations present a new mathematical technique or prove a new theory. This dissertation presents the design and development of a new experimental system. Although the DSACSS is not yet fully operational, a great deal of work has gone into its development thus far. This work has ranged from configuration design to nonlinear analysis to structural and electrical manufacturing. In this dissertation we focus on the development of the attitude determination subsystem. This work includes development of the equations of motion and analysis of the sensor suite dynamics. We develop nonlinear filtering techniques for data fusion and attitude estimation, and extend this problem to include estimation of the mass properties of the system. We include recommendations for system modifications and improvements. / Ph. D.

Spacecraft fulfill a myriad of critical functions on orbit, from defense and intelligence to science, navigation, and telecommunication. Spacecraft can also cost several hundred millions of dollars to design and launch, and given that physical access for maintenance remains difficult if not impossible to date, designing high reliability and survivability into these systems is an engineering and financial imperative. While reliability is recognized as an essential attribute for spacecraft, little analysis has been done pertaining to actual field reliability of spacecraft and their subsystems. This thesis consists of two parts. The first part fills the gap in the current understanding of spacecraft failure behavior on orbit through extensive statistical analysis and modeling of anomaly and failure data of Earth-orbiting spacecraft. The second part builds on these results to develop a novel theoretical basis (interdependent multi-layer network approach) and algorithmic tools for the analysis of survivability of spacecraft and space-based networks. Space-based networks (SBNs) allow the sharing of on-orbit resources, such as data storage, processing, and downlink. Results indicate and quantify the incremental survivability improvement of the SBN over the traditional monolith architecture. A trade-space analysis is then conducted using non-descriptive networkable subsystems/technologies to explore survivability characteristics of space-based networks and help guide design choices.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / In 1998, AlliedSignal Technical Services (ATSC) installed three fully autonomous 13-meter satellite tracking systems for the Integrated Program Office of the National Oceanic and Atmospheric Administration (NOAA) at the Command and Data Acquisition Station near Fairbanks, Alaska. These systems track and command NOAA Polar Orbiting Weather Satellites and Defense Meteorological Satellites. Each tracking system operates for extended periods of time with little intervention other than periodic scheduling contacts. Schedule execution initiates equipment configuration, including establishing the RF communications link to the satellite. Station autonomy is achieved through use of a robust scheduler that permits remote users and the System Administrator to request pass activities for any of the supported missions. Spacecraft in the mission set are scheduled for normal operations according to the priority they have been assigned. Once the scheduler resolves conflicts, it builds a human-readable control script that executes all required support activities. Pass adds or deletes generate new schedule scripts and can be performed in seconds. The systems can be configured to support CCSDS and TDM telemetry processing, but the units installed at Fairbanks required only telemetry and command through-put capabilities. Received telemetry data is buffered on disk-storage for immediate, post-pass playback, and also on tape for long-term archiving purposes. The system can autonomously support up to 20 spacecraft with 5 different configuration setups each. L-Band, S-Band and X-Band frequencies are supported.

A three-rotational degree of freedom attitude control system has been developed for the NASA Jet Propulsion Laboratory’s INSPIRE Project by the Texas Spacecraft Laboratory at The University of Texas at Austin. Using 3D plastic printing manufacturing techniques, a cold gas thruster system was created in order to detumble and maintain the attitude of two 3U CubeSats traveling through interplanetary space. A total of four thruster units were produced, including two engineering designs and two flight units. The units feature embedded sensors and millisecond level thrust control while using an inert, commercially-available refrigerant as a propellant. The thrust, minimum impulse bit, and specific impulse performance of the cold gas units was characterized using a ballistic pendulum test stand within a microtorr vacuum chamber. A heating element was used to change the temperature conditions of the propellant and determine the relationship between temperature and performance. The flight units were delivered in January of 2014 and the INSPIRE satellites are expected to launch in the upcoming year. / text

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / When hundreds of millions of dollars are invested in building, launching, and command/control of modern military space systems, the developers and operators need assurance that when their system achieves orbit, it will be able to "talk" with the ground network, exchanging commands, telemetry and ranging signals. Furthermore, prior to launch they need proof of compatibility with the ground data systems, showing that operational ground-based crypto keys, database parameters, and processing software are in-fact compatible with the spacecraft. This paper describes Air Force Materiel Command (AFMC), Space & Missile Center (SMC) Detachment 2's four classes of deployable test assets, emphasizing deployable's contribution to successful on-orbit performance. With not only the huge dollar investment, but even more important, the ability to execute a vital test or operational mission riding on compatibility, and launch vehicle and on-orbit test and evaluation operations the watchwords are "Don't leave the pad without it."

A visualization of the NASA Deep Space Network activity. Implemented in an interactive 3D environment. A thesis work by students from the Media technology and engineering program at Linköping University.