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Space systems miniaturization has been increasingly popular for the past decades, with over 1600 CubeSats and 300 sub-CubeSat sized spacecraft estimated to have been launched since 1998. This trend towards decreasing size enables the execution of unprecedented missions in terms of quantity, cost and development time, allowing for massively distributed satellite networks, and rapid prototyping of space equipment. Pocket-sized spacecraft can be designed in-house in less than a year and can reach weights of less than 10g, reducing the considerable effort typically associated with orbital flight. However, while Systems Engineering methodologies have been proposed for missions down to CubeSat size, there is still a gap regarding design approaches for picosatellites and smaller spacecraft, which can exploit their potential for iterative and accelerated development. In this paper, we propose a Systems Engineering methodology that abstains from the classic waterfall-like approach in favor of agile practices, focusing on available capabilities, delivery of features and design "sprints". Our method, originating from the software engineering disciplines, allows quick adaptation to imposed constraints, changes to requirements and unexpected events (e.g. chip shortages or delays), by making the design flexible to well-defined modifications. Two femtosatellite missions, currently under development and due to be launched in 2023, are used as case studies for our approach, showing how miniature spacecraft can be designed, developed and qualified from scratch in 6 months or less. We claim that the proposed method can simultaneously increase confidence in the design and decrease turnaround time for extremely small satellites, allowing unprecedented missions to take shape without the overhead traditionally associated with sending cutting-edge hardware to space.

The lower thermosphere (between 100 and 550 km of height) is known with lesser accuracy than desired. The use of spherical satellites to determine the density could result in a substantial improvement of the present situation. The orbits of satellites at these heights are affected by drag and the inhomogeneities of the terrestrial gravitational potential (among other perturbations). This projects has as main goal to analyse how the atmospheric drag affects the orbit of a real satellite, and then, determine the thermospheric density. Hence, it will be necessary to reconstruct the orbit accounting for the perturbations in the most accurate way possible. Regarding the gravitational potential of the Earth, we have employed three approximations: spherical symmetry, a zonal model truncated at sixth order and a tesseral model truncated at tenth order. This last model has revealed as the most accurate. To achieve our goal, we have analysed the telemetry gathered by one of the satellites of the FSSCat mission. Then, we have determined its orbital elements. Afterwards, we have considered two possible methods for orbit reconstruction: Non-Linear Least Squares and Extended Kalman Filter. After this analysis, we have chosen the Non-Linear Least Squares method for the purpose of orbit reconstruction. The orbital elements determined from a physical analysis of the telemetry and the ones resulting from the non-linear least square method coincide with a remarkable accuracy.

The lower thermosphere (between 100 and 250 km) is badly known due to the scarcity of operating satellites in this region. Nevertheless, it is very relevant for the study of Earth-Sun relations, satellite re-entry forecasting, and climate change, among other disciplines. We propose the analysis of a swarm of femtosatellites to directly analyze the thermosphere by means of a MEMS accelerometer onboard each satellite. The goal is to use the deceleration caused by drag to determine the local density, thus drawing a map of the thermosphere on multiple locations. The shape of the satellites will be spherical (with a diameter of 5 or 10 cm), thus simplifying the measurement of drag. The mass distribution will be that of a spherical top (then, no attitude control), or will have the center of mass separated from the geometric center (thus providing aerodynamic stability). Each satellite will also count with a MEMS GNSS receiver that will provide precise location and time-tagging to the measurements. A small onboard computer, mass storage system, radio transmitter, and primary battery will form the bus of the satellite. The goal of this Master Thesis is to develop a self-consistent mission analysis of the mission, with special interest in comparing the properties of the non-stabilized and aerodynamically stabilized satellites. The main objectives must be: Σ Design and analysis of the optimal orbit for these satellites. Of particular interest is the study of the different alternatives for orbital injection and dissemination. Σ Analysis of orbital decay using DRAMA. Evaluation of the risk for third-party satellites posed by a large swarm. Proposals for decreasing this risk. Σ Data gathering strategy. Σ Sources of noise for the accelerometer, both instrumental and environmental. Σ Communication strategy. Determination of the link budget, proposal for ground station typology and location. Σ Energy budget. Analysis of mission’s life limitations due to the endurance of the battery

The aim of this thesis is to determine the characteristics of the noise of an ultralow noise MEMS accelerometer. The study of these characteristics will allow to determine if the accelerometer can be used in the scientific payload aboard a femtosat. And it the case that it is used, it will allow to calibrate the accelerometer to provide a better signal. The method for studying the noise characteristics is the Allan Variance, which allows to identify and determine the most important noise terms that affect accelerometers. An experiment to perform the Allan Variance has been designed and performed. The sensor studied is ultralow noise and for this reason it must be isolated from its surroundings during the experiment, which will corrupt the output signal and not allow to clearly study the noise of the sensor. To achieve this task two isolations systems have been designed and built, one for protecting the sensor from vibrations transmitted through air like currents of air created either naturally or by people moving in the room of the experiment. And another to isolate the sensor from vibrations travelling through ground such as the natural vibrations of the ground or vibrations caused moving objects in contact with the floor or people walking. These isolation systems have been installed in an underground laboratory located on the EETAC campus to ensure that there almost no sources of vibration present during the experiment and that there are no changes in the temperature. The isolation systems have worked properly and the sensor has not been affected by external accelerations. The results obtained are satisfactory, they agree with the information provided by the datasheet and it is considered that the sensor noise properties have been characterized properly. Even though the results are satisfactory, it cannot be yet defined if the sensor will be used for the scientific payload aboard a femtosat.

The open sea is an area in which numerous legal activities occur, such as trade, transportation, and scientific research, but it also is a place that attracts persons with illegal, criminal, and terrorist intentions. Naval nations, often acting in alliance, conduct operations to stop this illegal activity. Maritime interdiction operations (MIO) are the usual type of operation employed, and, because of their nature, they require robust communications and an uninterrupted flow of information. Establishing communications and networks in the open seas via terrestrial means is possible only in certain areas, and it is not feasible around the clock. Therefore, the communications needed for maritime interdiction operations is significantly limited as to speed, accuracy, and efficiency. This thesis examines the feasibility of integrating small satellites into an MIO ad hoc network. Since such integration has never been tested, the thesis proposes a large-scale experiment for further research into the advantages and disadvantages of using small satellites as nodes in an MIO network.