Power Management, Attitude Determination and Control Systems of Small Satellites

Satellites have always been considered to be extremely expensive and risky business, which not only requires extensive knowledge and expertise in this field but also huge budget. Primarily, this concept was based on initial development and launching cost. Secondly, it was also impossible to repair and substitute parts (this was true up to 1993: the first Hubble Space Telescope servicing mission), which makes design more tough because it requires advanced fault tolerance solutions and extreme reliability. But with the passage of time many space actors entered in this market. Low cost design techniques played an important role in the aerospace market growth in the past years, but they can still play a major part in future developments. At present, several private companies are also providing launch services which further lower the accumulative cost. Many universities and SMEs (Small Medium Enterprises) worldwide are also trying to reduce satellite costs. The Department of Electronics and Telecommunication (DET) at Politecnico di Torino has been working on NanoSatellites since 2002 and developed their first NanoSatellite called PiCPoT, which was intended to be launched together with other university satellites by a DNEPR LV rocket in July 2006. Unfortunately a problem in the first stage of the carrier led to the destruction of all satellites. After that DET started work on a comprehensive NanoSatellite project called AraMiS (Italian acronym for Modular Architecture of Satellites). The main idea of the AraMiS is modularity at mechanical, electronic and testing levels using Commercial-Off-The-Shelf (COTS) components. These modules can be assembled together to get the targeted mission, which allows an effective cost sharing between multiple missions. AraMiS satellites have mass up to 5kg with different shapes and dimensions. AraMiS-C1 is a CubeSat Standard satellite developed on the AraMiS approach. Four sides of the AraMiS-C1 are equipped with identical tiles called 1B8_CubePMT that mount solar panels on the exterior and a combined power management, attitude control and computing subsystem on the interior. The other two sides are devoted to the telecommunication tiles called 1B9_CubeTCT which carry a commercial deployable UHF antenna (one side) and a patch type SHF antenna (the other side).
Thesis discusses in detail the design, implementation and testing of the 1B8_CubePMT module. It is developed on the design approach of AraMiS architecture with dimension 98×82.5×1.6 mm3. 1B8_CubePMT module contains electric power supply (EPS) and attitude determination & control subsystems (ADCS) of AraMiS-C1 satellite. The integration of such a large number of systems in a small area was not a trivial job. Several techniques were employed for reduction of size, weight and power consumption of the different subsystems while still achieving best performances. COTS components were selected for the EPS subsystems, on the basis of power loss analysis and minimum dimensions which helped in efficiency enhancement and also miniaturization of the subsystems. ADCS subsystems components were also selected on the basis of minimum dimensions and lower power consumptions while still achieving targeted performances. The most interesting feature of the 1B8_CubePMT module is the design and integration of a reconfigurable magnetorquer coil within four internal layers occupying no excess space. Coils in each layer are treated separately and can be attached/detached through straps. Changing the arrangement of these straps make the magnetorquer reconfigurable. Different housekeeping sensors have been employed at various points of the 1B8_CubePMT module.
Thesis also discusses thermal modeling of CubeSat, AraMiS-C1 satellite and 1B8_CubePMT module. Thermal resistance and temperature differences between different sides of the satellites
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and individual tiles have been found. At the end, preliminary thermal and spin analysis of NanoSatellites have been presented.
Chapter 1 gives an introduction to the problem and proposed solutions which will be discussed in this thesis. Chapter 2 presents an introduction to AraMiS project and AraMiS-C1 satellite. Chapter 3 discusses different satellite design flow configurations and their comparison.
Chapter 4 discusses 1B8_CubePMT module which is a CubeSat standard power management tile, developed on the AraMiS concept, for AraMiS-C1 satellite. It has EPS and ADCS subsystems which are the most essential elements of any aerospace mission.
Chapter 5 deals with the design and development of the EPS system of AraMiS-C1 satellite. This chapter discusses how to reduce the size, weight and power consumption of the EPS subsystems while achieving better efficiency and fulfilling satellite power requirements. The selection of COTS components on the basis of power loss analysis and minimum dimensions is discussed in detail. Housekeeping sensors such as current, voltage and temperature sensors which are employed at different points of the 1B8_CubePMT module to cope with anomalies, have been discussed in detail in this chapter. At the end of the chapter, the designed EPS is evaluated on the basis of AraMiS-C1 power budget.
Chapter 6 discusses design and implementation of attitude determination sensors (ADS) of the AraMiS-C1 satellite. 1B8_CubePMT has three types of attitude determination sensors: sun sensor, magnetometer and gyroscope. This chapter discusses in detail the design and operation of these sensors. Chapter 7 discusses the attitude control (ADC) system of AraMiS-C1 satellite. The design and implementation of a reconfigurable magnetorquer coil which is embedded inside the 1B8_CubePMT module, is discussed in detail. The designed magnetorquer has been evaluated on different parameters and compared with the magnetic actuator already available in the market. In chapter 8 testing procedure and results of 1B8_CubePMT subsystems are discussed in detail.
Chapter 9 presents thermal modelling of NanoSatellites. Detailed and simplified thermal models of CubeSat panel have been discussed. Thermal resistances measured through both models are compared. Generic thermal model of a CubeSat is presented. Utilizing the proposed models, thermal resistance of 1B8_CubePMT and AraMiS-C1 are measured. In order to verify the theoretical results, the thermal resistance of the AraMiS-C1 is measured through an experimental setup.
Chapter 10 discusses preliminary thermal and spin analysis of NanoSatellites in space environment. All the heat sources and their effects on the satellite have been discussed. A thermal balance equation has been established and satellite temperature for different structures and various conditions has been found. At the end a satellite spin analysis on the basis of different absorption coefficient related with colors, has been discussed.