abstract: CubeSats are a newly emerging, low-cost, rapid development platform for space exploration research. They are small spacecraft with a mass and volume of up to 12 kg and 12,000 cm3, respectively. To date, CubeSats have only been flown in Low Earth Orbit (LEO), though a large number are currently being designed to be dropped off by a mother ship on Earth escape trajectories intended for Lunar and Martian flyby missions. Advancements in propulsion technologies now enable these spacecraft to achieve capture orbits around the moon and Mars, providing a wealth of scientific data at low-cost. However, the mass, volume and launch constraints of CubeSats severely limit viable propulsion options. We present an innovative propulsion solution using energy generated by onboard photovoltaic panels to electrolyze water, thus producing combustible hydrogen and oxygen for low-thrust applications. Water has a high storage density allowing for sufficient fuel within volume constraints. Its high enthalpy of formation provides more fuel that translates into increased ∆V and vastly reduced risk for the launch vehicle. This innovative technology poses significant challenges including the design and operation of electrolyzers at ultra-cold temperatures, the efficient separation of the resultant hydrogen and oxygen gases from liquid water in a microgravity environment, as well as the effective utilization of thrust to produce desired trajectories. Analysis of the gas combustion and flow through the nozzle using both theoretical equations and finite-volume CFD modeling suggests an expected specific impulse of 360 s. Preliminary results from AGI's Satellite Toolkit (STK) indicate that the ΔV produced by the system for an 8kg CubeSat with 6kg of propellant in a LEO orbit (370 km altitude) is sufficient for an earth escape trajectory, lunar capture orbit or even a Mars capture orbit. These results suggest a promising pathway for an in-depth study supported by laboratory experiments to characterize the strengths and weaknesses of the proposed concept. / Dissertation/Thesis / Masters Thesis Aerospace Engineering 2015

abstract: CubeSats offer a compelling pathway towards lowering the cost of interplanetary exploration missions thanks to their low mass and volume. This has been possible due to miniaturization of electronics and sensors and increased efficiency of photovoltaics. Interplanetary communication using radio signals requires large parabolic antennas on the spacecraft and this often exceeds the total volume of CubeSat spacecraft. Mechanical deployable antennas have been proposed that would unfurl to form a large parabolic dish. These antennas much like an umbrella has many mechanical moving parts, are complex and are prone to jamming. An alternative are inflatables, due to their tenfold savings in mass, large surface area and very high packing efficiency of 20:1. The present work describes the process of designing and building inflatable parabolic reflectors for small satellite radio communications in the X band. Tests show these inflatable reflectors to provide significantly higher gain characteristics as compared to conventional antennas. This would lead to much higher data rates from low earth orbits and would provide enabling communication capabilities for small satellites in deeper space. This technology is critical to lowering costs of small satellites while enhancing their capabilities. Principle design challenges with inflatable membranes are maintaining accurate desired shape, reliable deployment mechanism and outer space environment protection. The present work tackles each of the mentioned challenges and provides an understanding towards future work. In the course of our experimentation we have been able to address these challenges using building techniques that evolved out of a matured understanding of the inflation process. Our design is based on low cost chemical sublimates as inflation substances that use a simple mechanism for inflation. To improve the reliability of the inflated shape, we use UV radiation hardened polymer support structures. The novelty of the design lies in its simplicity, low cost and high reliability. The design and development work provides an understanding towards extending these concepts to much larger deployable structures such as solar sails, inflatable truss structures for orbit servicing and large surface area inflatables for deceleration from hypersonic speeds when re-entering the atmosphere. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2015

abstract: There is a growing need for interplanetary travel technology development. There are hence plans to build deep space human habitats, communication relays, and fuel depots. These can be classified as large space structures. To build large structures, it is essential that these are modular in nature. With modularization of structures, it becomes essential that interconnection of modules is developed. Docking systems enable interconnection of modules. The state-of-the-art technology in docking systems is the Power Data Grapple Fixture (PDGF), used on the International Space Station by the Canadarm2 robotic arm to grapple, latch onto and provide power to the object it has grappled. The PDGF is operated by highly skilled astronauts on the ISS and are prone to human errors. Therefore, there is a need for autonomous docking. Another issue with the PDGF is that it costs around 1 to 2 million US dollars to build the 26-inch diameter docking mechanism. Hence, there is a growing need to build a lower cost and scalable, smaller docking systems. Building scalable smaller docking systems will hence enable testing them on small satellites. With the increasing need for small, low cost, autonomous docking systems, this thesis has been proposed. This thesis focuses on modeling and autonomous control of an electromagnetic probe and cone docking mechanism. The electromagnetic docking system is known to be a highly nonlinear system. Hence, this work discusses various control strategies for this docking system using a levitation strategy. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2018

Thesis submitted in fulfillment of the requirements for the degree Master of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology / Small satellites, such as CubeSats are mainly utilized for space and earth imaging missions. Imaging CubeSats are equipped with high resolution cameras for the capturing of digital images, as well as mass storage devices for storing the images. The captured images are transmitted to the ground station and subsequently stored in a database. The main problem with stored images in a large image database, identified by researchers and developers within the last number of years, is the retrieval of precise, clear images and overcoming the semantic gap. The semantic gap relates to the lack of correlation between the semantic categories the user requires and the low level features that a content-based image retrieval system offers. Clear images are needed to be usable for applications such as mapping, disaster monitoring and town planning. The main objective of this thesis is the design and development of an image classification, storage and retrieval system for a CubeSat. This system enables efficient classification, storing and retrieval of images that are received on a daily basis from an in-orbit CubeSat. In order to propose such a system, a specific research methodology was chosen and adopted. This entails extensive literature reviews on image classification techniques and image feature extraction techniques, to extract content embedded within an image, and include studies on image database systems, data mining techniques and image retrieval techniques. The literature study led to a requirement analysis followed by the analyses of software development models in order to design the system. The proposed design entails classifying images using content embedded in the image and also extracting image metadata such as date and time. Specific features extraction techniques are needed to extract required content and metadata. In order to achieve extraction of information embedded in the image, colour feature (colour histogram), shape feature (Mathematical Morphology) and texture feature (GLCM) techniques were used. Other major contributions of this project include a graphical user interface which enables users to search for similar images against those stored in the database. An automatic image extractor algorithm was also designed to classify images according to date and time, and colour, texture and shape features extractor techniques were proposed. These ensured that when a user wishes to query the database, the shape objects, colour quantities and contrast contained in an image are extracted and compared to those stored in the database. Implementation and test results concluded that the designed system is able to categorize images automatically and at the same time provide efficient and accurate results. The features extracted for each image depend on colour, shape and texture methods. Optimal values were also incorporated in order to reduce retrieval times. The mathematical morphological technique was used to compute shape objects using erosion and dilation operators, and the co-occurrence matrix was used to compute the texture feature of the image.

CubeSat projects in various universities around the world have become predominant in the study and research for developing CubeSats. Such projects have broadened the scope for understanding this new area of space research. Different CubeSats have been developed by other universities and institutions for different applications. The process of design, development and deployment of CubeSats involves several stages of theoretical and practical work ranging from understanding the concepts associated with communication subsystems, data handling subsystems to innovations in the field like implementing compatible operating systems in the CubeSat processors and new designs of transceivers and other components. One of the future trend setting research areas in CubeSat projects is the implementation of ROS in CubeSat. Robot Operating System (ROS) is aiming to capture the future of many embedded systems including Robotics. In this thesis, an attempt is made to understand the challenges faced during implementing ROS in CubeSat to provide a foundation for the OBDH subsystem and provide important guidelines for future developers relying on ROS run CubeSats. Since using traditional transceivers and power supply would be expensive, we have tried simulating Arduino to act as transceiver and power supply subsystems. Arduino is an open-source physical computing platform based on a simple microcontroller board, and a development environment for writing software for the board designed to make the process of using electronics in major embedded projects more accessible and inexpensive. Another important focus in this thesis has been to establish communication between CubeSat kit and Arduino. The major motivating factor for this thesis was to experiment with and come up with alternate ways which could prove as important measures in future to develop an effective and useful CubeSat by cutting down on development costs. An extensive literature review is carried out on the concepts of Arduino boards and ROS and its uses in Robotics which served as a base to understand its use in CubeSat. Experiment is conducted to communicate the CubeSat kit with Arduino. The results from the study of ROS and experiments with Arduino have been highly useful in drafting major problems and complications that developers would encounter while implementing ROS in CubeSat. Comprehensive analysis to the results obtained serve as important suggestions and guidelines for future researchers working in this field. / One of the future trend setting research areas in CubeSat projects is the implementation of ROS in CubeSat. Robot Operating System (ROS) is aiming to capture the future of many embedded systems including Robotics. In this thesis, an attempt is made to understand the challenges faced during implementing ROS in CubeSat to provide a foundation for the OBDH subsystem and provide important guidelines for future developers relying on ROS run CubeSats. Since using traditional transceivers and power supply would be expensive, we have tried simulating Arduino to act as transceiver and power supply subsystems. Arduino is an open-source physical computing platform based on a simple microcontroller board, and a development environment for writing software for the board designed to make the process of using electronics in major embedded projects more accessible and inexpensive.

We present a preliminary design for a novel neutron detection system that is compact, lightweight, and low power consuming, utilizing the CubeSat platform making it suitable for space-based applications. This is made possible using the scintillating crystal lithium indium diselenide ((LiInSe2)-Li-6), the first crystal to include Li-6 in the crystalline structure, and a silicon avalanche photodiode (Si-APD). The schematics of this instrument are presented as well as the response of the instrument to initial testing under alpha, gamma and neutron radiation. A principal aim of this work is to demonstrate the feasibility of such a neutron detection system within a CubeSat platform. The entire end-to-end system presented here is 10 cm x 10 cm x 15 cm, weighs 670 grams and requires 5 V direct current at 3 Watts.

This thesis presents a wireless communication system for intra-satellite communication based on Bluetooth Low Energy technology, which can have many benefits regarding the design and operation of satellites. The proposed design based on the nRF53832 chip from Nordic Semiconductor is described, followed by the results of several tests regarding the most important design criteria for its application in small satellites. The tested aspects include the power consumption of the wireless module in different operation modes, which is sufficiently low for the application even in small satellites. Signal strength measurements for various output power settings and obstacles show that reliable communication is possible in a satellite mockup. No packet error was detected, and latencies of less than 30 ms combined with achievable data rates between 200 and 700 kbps should be sufficient for most CubeSat satellites. Additionally, details are given to successfully integrate the chip with existing satellite subsystems. A code library is provided to simplify the communication between the modules, and a concept of a redundant system is established to increase the reliability for critical satellite subsystems. The overall assessment of the technology suggests that the presented system is suitable for in-orbit deployment with the Aalto-3 satellite (currently being developed at Aalto University), which will provide further validation of the technology.

Ingeniero Civil Eléctrico / Las estaciones terrenas son las encargadas de recibir la información enviada por los satélites, para que dicha información sea utilizada por los usuarios que la requieran en tierra. En particular, el uso de nanosatélites por distintas instituciones de investigación y universidades, crea la necesidad de que estas estaciones terrenas sean capaces de mantener un enlace de comunicaciones estable y de un desempeño tolerable para la transmisión de datos utilizados para la ciencia. En el presente trabajo se presenta el diseño e implementación de un esquema de comunicaciones en la banda de 2,4GHz para desarrollar una estación terrena que opere en dicha frecuencia y pueda ser utilizada en un enlace de comunicaciones para nanosatélites. En la primera parte de esta memoria se presenta el marco teórico que permite entender los distintos bloques que componen un esquema de comunicación digital, para luego analizar el uso de enlaces de radio en comunicaciones. Junto con lo anterior, se explican los elementos que componen a los sistemas de comunicación satelital, y se detalla el esquema de comunicación del proyecto Suchai 1, para luego introducir la problemática abordada. Se diseñó e implementó un esquema de comunicaciones en la banda ISM en torno a 2,4 GHz, por medio de la utilización de Radios Definidas por Software, lo cual permitía modificar de manera versátil los parámetros fundamentales de dicho sistema de comunicaciones. Se procedió a adaptar una antena satelital existente a la banda de operación deseada, y así, incluir dicha antena al sistema de comunicaciones implementado en Radios Definidas por Software. De esta forma, se definen por completo los bloques de una estación terrena satelital. Se realizaron pruebas para cuantificar tanto el desempeño del enlace como la adaptación realizada. De esta forma, utilizando como figura de mérito la tasa de error de bits, y aprovechando la versatilidad de las radios definidas por software, se pudo observar el desempeño del sistema de comunicaciones digitales mediante la variación de la razón señal a ruido del sistema. Por otro lado, se realizaron mediciones del parámetro de scattering S11 en la entrada de la antena para asegurar que su operación este dentro de la banda. También se realizaron pruebas para medir el punto de máxima ganancia y el valor de esta última para cuantificar si la adaptación era óptima. Una vez hecho lo anterior, se realizaron pruebas del esquema de comunicaciones incluyendo a la antena adaptada y en un escenario con pérdidas equivalentes a la distancia entre la estación terrena y el satélite en órbita. Finalmente, utilizando modulación FSK en la banda de 2,4 GHz, se logró obtener un enlace de comunicaciones con una tasa de 10 kbps, logrando alcanzar una distancia equivalente superior a 700 km, con lo que se puede concluir que la arquitectura propuesta mediante el uso de radios definidas por software para una estación terrena satelital es factible.

Benefits of developing missions with multiple formation flying spacecraft as an alternative to a traditional monolithic vehicle are becoming apparent. In some cases, these missions can lower cost and increase flexibility among other situational advantages. However, there are various limitations that are imposed by these missions that are centered on the concept of maintaining the necessary formation. One such limitation is that of the propulsion system required for each spacecraft. To mitigate the complexity and mass of the onboard propulsion, the pairing of electromagnetic actuators and differential drag to replace the functionality of a propulsive system is investigated. By using COTS magnetorquer boards to command satellite orientation, a scenario in which two 3U CubeSats are initially deployed from the ISS NanoRacks at an altitude of 400 km. They are then commanded to achieve a relative separation of 1 km and hold the spacing to demonstrate the capability of formation flight. The scenario was simulated through the MATLAB/Simulink platform and the magnitude of the necessary command torques were determined. By comparison to the ISIS magnetorquer board, the necessary command torques seem relatively high than compared to what the actuator is capable of. The ISIS board may supply ~5e-6 Nm of torque while the mission requires as much as 3e-3 Nm at times. However, by extending the settling time of the control law at the expense of absolute orientation control, the control torques necessary to carry out the simulated mission are well within the bounds of the ISIS magnetorquer boards as well as other COTS boards. With this alteration, mission feasibility is determined. It should be noted that further analysis should be conducted regarding concerns with CubeSat detumble to further confirm feasibility.

Interplanetary space exploration has thus far consisted of single, expensive spacecraft missions. Mission costs are particularly high on missions to the outer planets and while invaluable, finite budgets limit our ability to perform extensive and frequent investigations of the planets. Planetary systems such as Jupiter and Saturn provide extremely complex exploration environments with numerous targets of interest. Exploring these targets in addition to the main planet requires multiple fly-bys and long mission timelines. In LEO, CubeSats have changed the exploration paradigm, offering a fast and low cost alternative to traditional space vehicles. This new mission development philosophy has the potential to significantly change the economics of interplanetary exploration and a number of missions are being developed to utilize CubeSat class spacecraft beyond earth orbit (e.g., NEAScout, Lunar Ice Cube, Marco and BioSentinel). This paper takes the CubeSat philosophical approach one step further by investigating the potential for small satellite swarms to provide extensive studies of the Saturn system. To do this, an architecture was developed to best replicate the Cassini Primary Mission science objectives using swarms of CubeSats. Cassini was chosen because of its complexity and it defines a well-understood baseline to compare against. The paper outlines the overall mission architecture developed and provides a feasible initial design for the spacecraft in the architecture. The number of swarms needed, number of CubeSats per swarm, size of the CubeSats, overall science output and estimated mission cost are all presented. Additional science objectives beyond Cassini's capabilities are also proposed. Significant scientific returns can be achieved by the swarm based architecture and the risk tolerance afforded by the utilization of large numbers of low-cost sensor carriers. This study found a potential architecture that could reduce the cost of replicating Cassini by as much as 63%. The results of this investigation are not constrained to Saturn and can be easily translated to other targets such as Uranus, Neptune or the asteroid belt.