OPTIMIZATION OF INTER-CUBESAT COMMUNICATION LINKS

Cubesat constellations may become the next generation of communication backbone architecture to provide future worldwide communication services. In this thesis, we investigate the feasibility of deploying Cubesat constellations with inter-satellite links (ISL) for the delivery of continuous global communication. Cubesat constellation designs for various mission scenarios are proposed and verified using a simulation toolkit commonly used by space engineers. Link optimization to improve the overall theoretical data rate is also discussed. The results obtained affirm that a Cubesat constellation at an orbital height of 450 km can achieve a data rate of 11.46 kbps and requires the least number of satellites in the constellation. We ascertained that using ISL as the communication backbone in a network architecture, complete with space and globally distributed ground nodes, is achievable. In the near future, there is a high potential for the implementation of ISL with optical communication links, whereby there is assurance of a significantly higher data rate and lower power requirements.Civilian, Singapore Technologies ElectronicsApproved for public release; distribution is unlimited

Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View

Small satellite systems enable whole new class of missions for navigation, communications, remote sensing and scientific research for both civilian and military purposes. As individual spacecraft are limited by the size, mass and power constraints, mass-produced small satellites in large constellations or clusters could be useful in many science missions such as gravity mapping, tracking of forest fires, finding water resources, etc. Constellation of satellites provide improved spatial and temporal resolution of the target. Small satellite constellations contribute innovative applications by replacing a single asset with several very capable spacecraft which opens the door to new applications. With increasing levels of autonomy, there will be a need for remote communication networks to enable communication between spacecraft. These space based networks will need to configure and maintain dynamic routes, manage intermediate nodes, and reconfigure themselves to achieve mission objectives. Hence, inter-satellite communication is a key aspect when satellites fly in formation. In this paper, we present the various researches being conducted in the small satellite community for implementing inter-satellite communications based on the Open System Interconnection (OSI) model. This paper also reviews the various design parameters applicable to the first three layers of the OSI model, i.e., physical, data link and network layer. Based on the survey, we also present a comprehensive list of design parameters useful for achieving inter-satellite communications for multiple small satellite missions. Specific topics include proposed solutions for some of the challenges faced by small satellite systems, enabling operations using a network of small satellites, and some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications Surveys and Tutorial

Distributed computing in space-based wireless sensor networks

This thesis investigates the application of distributed computing in general and wireless sensor networks in particular to space applications. Particularly, the thesis addresses issues related to the design of "space-based wireless sensor networks" that consist of ultra-small satellite nodes flying together in close formations. The design space of space-based wireless sensor networks is explored. Consequently, a methodology for designing space-based wireless sensor networks is proposed that is based on a modular architecture. The hardware modules take the form of 3-D Multi-Chip Modules (MCM). The design of hardware modules is demonstrated by designing a representative on-board computer module. The onboard computer module contains an FPGA which includes a system-on-chip architecture that is based on soft components and provides a degree of flexibility at the later stages of the design of the mission.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

System-of-Systems Tools for the Analysis of Technological Choices in Space Propulsion

Difficulties in space mission architecture design arise from many factors. Performance, cost, and risk constraints become less obvious due to complex interactions between the systems involved in the mission; decisions regarding long-term goals can heavily impact technological choices for short-term parts of the mission, while conversely decisions in the near future will impact the whole flexibility of long-term plans. Furthermore, the space community is broadening its borders, and space agencies from different countries are collaborating with industry and commercial partners towards large-scale endeavors. This paradigm shift is prompting the development of non-traditional approaches to the design of space missions. This paper reports the results of the first year of a continuing collaboration of the authors to develop and demonstrate System-of-System engineering methodologies for the deep analysis of dependencies and synthesis of robust architectures in exploration mission contexts. We present the procedure that we followed to develop and apply our methodology, obstacles found, steps taken to improve the methods based on the needs of experts and decision makers, required data for the analysis, and results produced by our holistic analysis. In particular, we focus on the analysis of technological choices for space propulsion for a generic cislunar mission, including both complex interactions between subsystems in different type of propulsion and availability of different providers. We identify critical systems and sets of systems based on cascading effects of performance degradation, assessment of the robustness of different designs in the operational domain, and simultaneous analysis of schedule dependencies between the constituent systems

Development of an Additively Manufactured Microthruster for Nanosatellite Applications

Next generation small satellites, also known as nanosatellites, have masses significantly lower than traditional satellites. Including the propellant mass, the total mass of a nanosatellite is often in the range of 1 to 4 $kg$. These satellites are being developed for numerous applications related to research, defense, and industry. Since their popularity began in the early 2000\u27s, limitations on the downscaling of propulsion systems has proven to be problematic. Due to this, the vast majority of nanosatellite missions have limited lifespans of 90-120 days in low Earth orbit before they reenter the Earth\u27s atmosphere. Although satellites on this scale have little available space for instrumentation, the development in the fields of microsensors, microelectronics, micromachinery, and microfluidics has increased the capabilities of small satellites tremendously. With limited options for primary propulsion and attitude control, nanosatellites would benefit greatly from the development of an inexpensive and easily implemented propulsion system. This work focuses on the development of an additively manufactured chemical propulsion system suitable for nanosatellite primary propulsion and attitude control. The availability of such a propulsion system would allow for new nanosatellite mission concepts, such as deep space exploration, maneuvering in low gravity environments, and formation flying. Experimental methods were used to develop a dual mode microthruster design which can operate in either low impulse, pseudo-monopropellant mode, or high impulse, bipropellant mode. Through the use of a homogeneous catalysis scheme for gas generation, nontoxic propellants are used to produce varying levels of thrust suitable for application in nanosatellite propulsion. The use of relatively benign propellants results in a system which is safe and inexpensive to manufacture, store, transport, and handle. In addition to these advantages, the majority of the propulsion system, including propellant storage, piping, manifolding, reaction chambers, and nozzles can be 3D printed directly into the nanosatellite chassis, further reducing the overall cost of the system. This work highlights the selection process of propellants, catalysts, and nozzle geometry for the propulsion system. Experiments were performed to determine a viable catalyst solution, validate the gas generation scheme, and validate operation of the system

On Development of 100-Gram-Class Spacecraft for Swarm Applications

A novel space system architecture is proposed, which would enable 100-g-class spacecraft to be flown as swarms (100 s-1000 s) in low Earth orbit. Swarms of Silicon Wafer Integrated Femtosatellites (SWIFT) present a paradigm-shifting approach to distributed spacecraft development, missions, and applications. Potential applications of SWIFT swarms include sparse aperture arrays and distributed sensor networks. New swarm array configurations are introduced and shown to achieve the effective sparse aperture driven from optical performance metrics. A system cost analysis based on this comparison justifies deploying a large number of femtosatellites for sparse aperture applications. Moreover, this paper discusses promising guidance, control, and navigation methods for swarms of femtosatellites equipped with modest sensing and control capabilities

BIRDS-2: Multi-Nation Cubesat Constellation Project for Learning and Capacity Building

The BIRDS project began in October, 2015 with an objective to provide hands on experience to the graduate students on satellite technology. In a BIRDS project, the students define missions, design, build, test, and operate satellite within given time frame of the project. A 1U CubeSat is built per participating country which are then released from International Space Station (ISS) into Low Earth Orbit (LEO) and operated through a ground station network, with one ground station established in each member nation. That being the first is series, the second BIRDS project or so called BIRDS-2 project started in November, 2016 with students from, Philippines, Bhutan, Malaysia and Japan. Lean philosophy is adopted for the development of CubeSats and an overlap of a year is created between successive projects so that the lessons learned and knowledge gained from each project is properly passed on. The BIRDS program targets to improve the development process of a CubeSat while maintaining/improving the reliability and reducing waste. But the true success of the program is indicated by the ability of project members to replicate what they learn from this project, at their home country after graduating

Dtn and non-dtn routing protocols for inter-cubesat communications: A comprehensive survey

CubeSats, which are limited by size and mass, have limited functionality. These miniaturised satellites suffer from a low power budget, short radio range, low transmission speeds, and limited data storage capacity. Regardless of these limitations, CubeSats have been deployed to carry out many research missions, such as gravity mapping and the tracking of forest fires. One method of increasing their functionality and reducing their limitations is to form CubeSat networks, or swarms, where many CubeSats work together to carry out a mission. Nevertheless, the network might have intermittent connectivity and, accordingly, data communication becomes challenging in such a disjointed network where there is no contemporaneous path between source and destination due to satellites’ mobility pattern and given the limitations of range. In this survey, various inter-satellite routing protocols that are Delay Tolerant (DTN) and Non Delay Tolerant (Non-DTN) are considered. DTN routing protocols are considered for the scenarios where the network is disjointed with no contemporaneous path between a source and a destination. We qualitatively compare all of the above routing protocols to highlight the positive and negative points under different network constraints. We conclude that the performance of routing protocols used in aerospace communications is highly dependent on the evolving topology of the network over time. Additionally, the Non-DTN routing protocols will work efficiently if the network is dense enough to establish reliable links between CubeSats. Emphasis is also given to network capacity in terms of how buffer, energy, bandwidth, and contact duration influence the performance of DTN routing protocols, where, for example, flooding-based DTN protocols can provide superior performance in terms of maximizing delivery ratio and minimizing a delivery delay. However, such protocols are not suitable for CubeSat networks, as they harvest the limited resources of these tiny satellites and they are contrasted with forwarding-based DTN routing protocols, which are resource-friendly and produce minimum overheads on the cost of degraded delivery probability. From the literature, we found that quota-based DTN routing protocols can provide the necessary balance between delivery delay and overhead costs in many CubeSat missions

Communication Analysis of QB50 CubeSat Network

In this thesis a communication architecture for QB50 space mission is analyzed. This mission will provide the biggest CubeSat network in orbit. A constellation of 50 CubeSats in a ‘string-of-pearls’ configuration will be launched together in January 2016 by a single rocket, into a circular orbit at 350 km altitude. Due to the atmospheric drag the orbit will decay and progressively lower layers of the atmosphere will be explored. Main goals are exploration of the lower thermosphere with multi-point measurements, re-entry research and in-orbit science and technology demonstration. In this analysis of communication functions the ground segment is analyzed, with a global overview of different architectures, the main elements of a ground station, mission and control centers, and the link between them. This study is realized through the development of a tool which computes the number of stations required to recover a certain amount of data generated by a constellation of satellites. This tool ensures the efficiency of the communication system taking into account various design parameters like data rates, limited elevation angles from ground stations, and the effects on the link quality such as orbit perturbations, space and atmospheric losses and Doppler shifts. Particular attention is devoted to frequencies: two different types of systems (UHF/VHF and S-band) are analyzed. In order to optimize the positioning and number of stations, an iterative method is applied to compute the fraction of time when a station is in view of a CubeSat in function of various parameters such as the latitude of the station, its elevation and the altitude of the satellite. AGI-STK software was used to compute the access between satellites in the constellation and ground stations, simulating system operability

Real-time agent middleware experiments on java-based processors towards distributed satellite systems

Distributed satellite systems are large research topics, spanning many fields such as communications, networking schemes, high performance computing, and distributed operations. DARPA's F6 fractionated spacecraft mission is a prime example, culminating in the launch of technology demonstration satellites for autonomous and rapidly configurable satellite architectures. Recent developments at Surrey Space Centre have included the development of a Java enabled system-on-a-chip solution towards running homogenous agents and middleware software configurations