Hubble Space Telescope Reduced-Gyro Control Law Design, Implementation, and On-Orbit Performance

Following gyro failures in April 2001 and April 2003, HST Pointing Control System engineers designed reduced-gyro control laws to extend the spacecraft science mission. The Two-Gyro Science (TGS) and One-Gyro Science (OGS) control laws were designed and implemented using magnetometers, star trackers, and Fine Guidance Sensors in succession to control vehicle rate about the missing gyro axes. Both TGS and OGS have demonstrated on-orbit pointing stability of 7 milli-arcseconds or less, which depends upon the guide star magnitude used by the Fine Guidance Sensor. This paper describes the design, implementation, and on-orbit performance of the TGS and OGS control law fine-pointing modes using Fixed Head Star Trackers and Fine Guidance Sensors, after successfully achieving coarse-pointing control using magnetometers

Deorbiting Algorithms Development for CubeSats using Propulsion and Sails

CubeSats are becoming increasingly popular within the scientific and commercial community, as they provide relatively cheap and quick access to space. However, as their launching rates increase rapidly, the concern that they may have a negative impact in the space debris problem also increases. This calls for the development of novel deorbiting technologies for CubeSats. In a response to this need, this thesis presents two new attitude controllers and deorbiting algorithms, which enable ionic thrusters, as well as drag sails, in order to accelerate CubeSat orbital disposal. These algorithms are designed with nanosatellites capabilities in mind, requiring minimum attitude determination and control. Their efficacy is demonstrated through numerical models in all cases. In the first approach, a geomagnetic field tracker controller is presented. This controller aligns the thrusting carrying axis of the satellite with the local magnetic field vector. The only sensors and actuators required are magnetometers and magnetorquers respectively. A suitable deorbiting algorithm is also presented, which is activated once the CubeSat is tracking the geomagnetic vector. This algorithm determines the portions of the orbit in which thrust must be applied, and it only requires a model of Earth's magnetic field. This approach is simulated with ionic thrusters, obtaining deorbiting rates between 0.35 km/day and 50 km/day, depending on the type of engine used. Proof of stability is provided through Floquet theory, while robustness analysis is executed through Monte Carlo simulations. This approach has advantages such as minimum sensing and actuating requirements, and it doesn't require movable parts nor deployables, minimizing the probability of failures in orbit. In the second approach, a gyroless spin-stabilization controller is proposed. This algorithm fixes the thrusting carrying axis of the CubeSat in the inertial frame. Just as the first approach, this controller only requires magnetometers and magnetorquers. Once the satellite is stabilized, an orbit sampling algorithm is introduced. This algorithm is able to determine the portions of the orbit where to apply thrust, using only Global Positioning System inputs. This approach is simulated with electrospray thrusters, achieving deorbiting rates in the order of 45 km/day. Stability analysis is provided through Lyapunov theory, while Monte Carlo simulations are used to prove the robustness of the algorithm. The attitude stabilization phases of both approaches are very flexible, in that they can work with a variety of thrusters, as well as non propulsive technologies. Dragsails are often proposed as means for deorbiting CubeSats, however, there is a gap in the literature when it comes to their stabilization in orbit. Therefore, the efficacy of these stabilization approaches when used in conjunction with drag sails is analysed. In the case of the geomagnetic field tracking algorithm, deorbiting rates in the order of 19 km/day are attained. In the case of the gyroless spin-stabilization algorithm, deorbiting times of up to 12.5 km/day are achieved. These algorithms provide convenient means for CubeSat deorbiting, contributing to space debris mitigation efforts. They require minimum hardware and software capabilities, and because of this the probability of failures is low, and they provide excellent deorbiting rates

Augmented stellar sensor for a small spacecraft

Thesis (MEng)--Stellenbosch University, 2019.ENGLISH ABSTRACT: With the maturity of the CubeSat industry and advancements in commercial off-the-shelf components, CubeSat-based projects have become an attractive option for advanced outer space missions. This increase in mission complexity has given rise to the necessity of a new generation of accurate attitude determination subsystems. The purpose of this work, therefore, entailed the design and development of an augmented stellar sensor. The focus was not only on the development of a suitable high-performance, lowpower hardware platform, but also on the identification, implementation, and development of suitable software techniques as well as the simulation, integration and testing of the augmented platform. This developed sensor delivers accurate attitude and rate estimates, whilst conforming to the small satellite power and size requirements. The augmented system uses inertial rate sensor data, with error compensation performed by use of matched vector measurements obtained from a star sensor. Measurements are combined in an Extended Kalman filter, providing both high rate attitude propagation and bias drift compensation. The designed system features a robust tracking mode as well as a stellar gyro algorithm to deliver accurate, low-frequency rate estimates independent of host dynamics. To prove overall system functionality, the sensor has undergone verification during simulated conditions, testing in an in-house developed star emulation environment, as well as testing under night sky conditions. During these tests, it was exposed to conditions typically experienced by satellites throughout their mission lifetimes. These conditions range from low-rate tumbling, to fine pointing. Initial testing shows that the system offers a robust response regardless of satellite rate and orientation whilst simultaneously adhering to CubeSat standards. IMU bias compensation worked successfully, and estimated results show that the average 3σ stellar gyro rate accuracies were in the order of 0.01 °/s whilst the cross-axis 3σ orientation accuracy was close to 0.01° during low rates.AFRIKAANSE OPSOMMING: Met die volwassewording van die CubeSat-industrie en vooruitgang van kommersieël beskikbare elektroniese komponente, het die CubeSat-platform ’n aantreklike keuse geword vir ruimtevaartsendings. Hierdie belangstelling in die CubeSat-platform het tot ’n vermeerdering van sendingskompleksiteit gelei wat die behoefte vir ’n nuwe generasie akkurate oriëntasiebeheer-substelsels geskep het. Gevolglik was die doel van hierdie werk die ontwerp en ontwikkeling van ’n uitgebreide stersensor. Die fokus was egter nie net om ’n gepaste hardewarestelsel te ontwerp nie, maar ook om geskikte sagtewaretegnieke en algoritmes te identifiseer, te ontwikkel, en toe te pas. Die ontwikkelde stelsel lewer akkurate oriëntasie- en hoeksnelheidafskattings, terwyl dit geskik vir gebruik in ’n nanosatelliet is. Hierdie uitgebreide stelsel gebruik inersiële sensormetings waarop foutkorrigering, soos afgeskat deur middel van vektorinligting vanaf ’n sterkamera, toegepas is. Die sensormetings word gekombineer in ’n uitgebreide Kalman filter, wat beide hoë-frekwensie oriëntasie-afskattings kan verskaf, sowel as om die inersiële sensor foutkorrigering te beheer. Die ontwerpte stelsel bevat verder ’n robuuste stervolgmodus om die mikroverwerker se berekeninge te verminder, sowel as ’n hoeksnelheid-afskattingsalgoritme om baie akkurate lae-frekwensie afskattings te bied. Die laasgenoemde algoritme kan onafhanklik van ’n dinamiese model funksioneer. Om die oorhoofse stelsel se werking te bevestig, is die sensor tydens gesimuleerde, geëmuleerde, en praktiese omstandighede getoets. Gedurende hierdie toetse is die stelsel blootgestel aan tipiese gebruikstoestande soos lae-snelheid tuimel en fyn oriëntasiebeheer. Aanvanklike toetse wys dat die stelsel goed werk ongeag die hoeksnelheidstoestande waaraan dit blootgestel word. Inersiële sensor hoeksnelheidsmetings kon suksesvol gekorrigeer word. Afgeskatte resultate toon daarop dat ’n stervektor se hoeksnelheid oor die kruisas akkuraat tot 0.01 °/s, op die 3σ-vlak, afgeskat kon word. Resultate aangaande oriëntasie-akkuraatheid was in die orde van 0.01°, 3σ, oor die kruisas tydens ’n lae hoeksnelheid

Quaternionic Attitude Estimation with Inertial Measuring Unit for Robotic and Human Body Motion Tracking using Sequential Monte Carlo Methods with Hyper-Dimensional Spherical Distributions

This dissertation examined the inertial tracking technology for robotics and human tracking applications. This is a multi-discipline research that builds on the embedded system engineering, Bayesian estimation theory, software engineering, directional statistics, and biomedical engineering. A discussion of the orientation tracking representations and fundamentals of attitude estimation are presented briefly to outline the some of the issues in each approach. In addition, a discussion regarding to inertial tracking sensors gives an insight to the basic science and limitations in each of the sensing components. An initial experiment was conducted with existing inertial tracker to study the feasibility of using this technology in human motion tracking. Several areas of improvement were made based on the results and analyses from the experiment. As the performance of the system relies on multiple factors from different disciplines, the only viable solution is to optimize the performance in each area. Hence, a top-down approach was used in developing this system. The implementations of the new generation of hardware system design and firmware structure are presented in this dissertation. The calibration of the system, which is one of the most important factors to minimize the estimation error to the system, is also discussed in details. A practical approach using sequential Monte Carlo method with hyper-dimensional statistical geometry is taken to develop the algorithm for recursive estimation with quaternions. An analysis conducted from a simulation study provides insights to the capability of the new algorithms. An extensive testing and experiments was conducted with robotic manipulator and free hand human motion to demonstrate the improvements with the new generation of inertial tracker and the accuracy and stability of the algorithm. In addition, the tracking unit is used to demonstrate the potential in multiple biomedical applications including kinematics tracking and diagnosis instrumentation. The inertial tracking technologies presented in this dissertation is aimed to use specifically for human motion tracking. The goal is to integrate this technology into the next generation of medical diagnostic system

Flight Mechanics/Estimation Theory Symposium 1995

This conference publication includes 41 papers and abstracts presented at the Flight Mechanics/ Estimation Theory Symposium on May 16-18, 1995. Sponsored by the Flight Dynamics Division of Goddard Space Flight Center, this symposium featured technical papers on a wide range of issues related to orbit-attitude prediction, determination, and control; attitude sensor calibration; attitude determination error analysis; attitude dynamics; and orbit decay and maneuver strategy. Government, industry, and the academic community participated in the preparation and presentation of these papers

Aeronautical Engineering: A special bibliography with indexes, supplement 89, November 1977

This bibliography lists 538 reports, articles, and other documents introduced into the NASA scientific and technical information system in October 1977

Magnetometer-only attitude determination with application to the M-SAT mission

The topic of this thesis focuses on attitude determination for small satellites. The method described uses only a magnetometer to resolve the three-axis attitude of the satellite. The primary challenge is that magnetometers only instantaneously resolve two axes of a satellite\u27s attitude. Typically, magnetometers are used in conjunction with other sensors to resolve all three axes. However, by using a filter over an adequately long orbit arc, the magnetometer data can yield all the information necessary. The magnetic field data are filtered to obtain the magnetic field derivative vector, which are combined with the magnetic field vector to fully resolve the attitude. Once the magnetic field vector and its derivative are calculated, the filtered measurement and derivative are used as pseudo-measurements for a second filter that estimates the attitude quaternion and the angular rates. This estimate must meet the system requirements that are typically required of the attitude determination and control subsystem for the mission under consideration. In this thesis research, the Missouri University of Science and Technology\u27s M-SAT mission was used as a case study to demonstrate the methods developed. Finally, the method is tested using varying initial conditions and orbit parameters. The inclination in particular is cautiously observed. The method in which the magnetic field derivative is determined suffers a loss in accuracy for lower inclinations, suggesting that a parametric study with respect to orbit inclination is prudent. Accordingly, such a parametric study was conducted and is presented as part of this thesis --Abstract, page iii

AAS/GSFC 13th International Symposium on Space Flight Dynamics

This conference proceedings preprint includes papers and abstracts presented at the 13th International Symposium on Space Flight Dynamics. Cosponsored by American Astronautical Society and the Guidance, Navigation and Control Center of the Goddard Space Flight Center, this symposium featured technical papers on a wide range of issues related to orbit-attitude prediction, determination, and control; attitude sensor calibration; attitude dynamics; and mission design

Design and implementation of a mobile sensor system for human posture tracking

De reconstructie van menselijke houding en het traceren van bewegingen kan in vele toepassingen worden gebruikt. Van animatie waar de bewegingen van acteurs kunnen gekoppeld worden aan een digitaal personage, tot revalidatie waar artsen na biomechanische analyse snel accurate diagnoses kunnen stellen. De snelle evolutie in de ontwikkeling van microsensoren en de opkomst van draadloze sensornetwerken hebben ertoe geleid dat draadloze nodes met verschillende sensoren hiervoor kunnen worden gebruikt. Door de informatie van deze sensoren te combineren is het immers mogelijk om absolute oriëntatie te berekenen. Eens deze informatie van elk lichaamsdeel bekend is, kan de volledige houding gereconstrueerd worden. In dit onderzoek werd een inertieel traceringssysteem ontwikkeld waarbij, in tegenstelling tot commerciële oplossingen, geen gyroscopen werden gebruikt. De sensor nodes worden enkel voorzien van accelerometers en magnetometers. Computer software implementeert het traceringssalgoritme en visualiseert de gereconstrueerde menselijke houding. Ingebedde software bepaalt dan weer de werking van de nodes en implementeert een draadloos protocol op maat dat toelaat om de informatie van verschillende nodes te ontvangen. De werking van het volledige systeem werd gevalideerd aan de hand van experimenten waarbij de houding van een persoon werd gevolgd.Human posture reconstruction and motion tracking is of interest for many different applications. From animation where captured motion sequences from actors can be mapped to a digital character in order to obtain a realistic visualization, to revalidation, where biomechanical analysis enables physicians to determine which exercises should be executed for a better and faster recovery. The combination of the increasingly fast evolution in the development of micromachined and the rise of wireless sensor networks as a distributed solution has allowed inertial sensors to become a fast emerging technology for orientation tracking. Sensor nodes equipped with accelerometers, magnetometers and gyroscopes supply three dimensional readings that can be used to determine driftfree absolute orientation. By approximating the human body by a set of rigid structures interconnected by joints, posture reconstruction is made possible when each of the individual bodyparts is equipped with a sensor node. In this work, an inertial tracking system was developed where, contrast to commercial applications, no gyroscopes were included. The sensor nodes were only equipped with accelerometers and magnetometers. Computer software implements the tracking algorithm and visualizes the reconstructed human posture. Embedded software determines the functionality of the nodes and implements a fully custom wireless protocol that allows to receive information from several nodes. The functionality of the entire system was validated by conducting full body tracking experiments