Onboard Communication Systems for Low Cost Small Satellites

The development of a large number of Nano and Pico-satellite missions, with spacecrafts of mass lower than 10 kg and 1 kg respectively, started in the beginning of this century due to the availability of low-cost piggyback launch opportunities. Such small satellites are usually built using commercially available electronic components that are not qualified for the space environment. This approach reduces the total cost of the satellite missions but at the expense of design effort which is needed not to compromise the reliability of the designed spacecrafts. One of the foremost design efforts in this regard is the design re-use method which extends the cost reduction to the system level, and helps in simplifying the development cycle for a space mission. The on-board communication subsystem consist of critical set of elements common to every mission, and therefore is not exempt from such a design philosophy. The on-board networks, on-board transceivers, and the protocols are all critical elements for a spacecraft mission and, at the same time, some of the most specialized and complex ones. Innovative data communication systems are therefore desirable for the future space missions. The size of the satellites keeps reducing as the time progresses, therefore the harness mass and complexity inside the satellite becomes a prime challenge. An innovative approach to smart harness is therefore necessary which reduces the wiring harness for intra-satellite communication. This thesis copes with several problems related to spacecraft subsystem development, integration and testing and proposes some solutions that can help in both keeping system development and production cost low while still achieving good performances. Chapter 1 starts with the design goals of the work and introduction to the Modular Architecture of Small Satellites (AraMiS) project. The biggest design goals of space systems of current era are the cost, time and complexity issues. Modularity and cost-sharing between multiple missions will appear as optimal solutions for reducing development costs, while the use of commercial components (COTS) will be presented as a way to simplify procurement and further lower system cost In Chapter 2, the smart harness approach is proposed which reduces the traditional harness complexities inside the small spacecrafts. The chapter focuses on the design of small spacecrafts which are completely modular and flexible. Modularity at mechanical, electrical and testing level will be discussed in this chapter. Chapter 3 addresses the complete life cycle of a subsystem module i.e. from conception to the final design and testing. The module life cycle uses a variety of Unified Modelling Language (UML) diagrams to fulfill different design stages. Chapter 4 proposes different types of spacecraft configurations based on smart harness approaches including physical module based, satellite on demand and reusable design configurations.A design trade-off is also performed for these configurations. Chapter 6 proposes the design technique of physical module based spacecraft configuration which is based on physical plug and play connectors and logical slots for the subsystem modules. A honeycomb based tile is discussed in this chapter which is used for larger and more demanding spacecraft structures. In Chapter 7, the requirement of data communication across different subsystems of the spacecrafts are described. The use cases have been discussed and the implementation rules have been defined in this Chapter. Chapters 8,9 and 10 focus on module design for intra-satellite communication purposes. The modules have been designed for wired as well as wireless data communication. The wired solution is based on on-board data bus module for inter-tile data communication. Wireless solutions included both optical and radio frequency based solutions. The optical module has been designed for optical free space as well as glass fiber based communication purposes. The comparison between theoretical and practical results has been made. The radio frequency based module is based on commercial module and simpliciTI protocol stack. In Chapter 11, the functional testing of modules, tiles and whole satellites is discussed. The testing scheme of functional test board is also highlighted in this chapter.