Study of the ground - to -Very Low Earth Orbit (VLEO) satellite communication link

The aim of this study is to analyse the problem of the reduced windows communication between Very Low Earth Orbit (VLEO) satellites and Ground Stations. The objective is to parametrize all elements involved in the data transmission between a satellite and its grounds stations, and to compare the results with the qbapp app. Furthermore, a practical case will be analysed. It will have to be decided between trying to problem or designing a space mission and analysing its data transmission

Savings on Transmit Power through Designed Horizon Plane for LEO Satellite Ground Stations

Low Earth Orbit (LEO) satellites are used for public networking and for scientific purposes. Established satellite ground stations can communicate with LEO satellites only when the satellite is in their visibility region, since LEO satellites move too fast relative to a ground station on the Earth. Each ground station is characterized by its own ideal horizon plane. Because of natural barriers that plane is modified to the designed one, defined by minimal elevation, in order to avoid natural obstacles. Designed horizon plane implementation implies also the power saving from the satellite to be transmitted. The major loss in communication between the LEO satellite and the ground station is the free space loss. Free space loss varies since the distance from the ground station to the satellite varies over time. Free space loss is usually compensated through variable satellite transmit power toward the downlink. In order to obtain the constant downlink margin at the receiver, all over the time, for analytical and simulation purposes, the altitudes from 600km to 1200km are considered. For each altitude it is calculated the power saving by designed horizon plane implementation compared the ideal horizon plane, for different altitudes

Study of attenuation and loss of messages in radiofrequency communication links between Cubesats and Earth

This project aims to study the quality of communication using nanosatellites in LEO orbits. The objective is to study the signal attenuation by radio frequency (RF) antennas between a nanosatellite and a ground station, or another nanosatellite. For this purpose, a MATLAB simulator is developed that allows the modeling of satellite orbits by using TLEs, orbital elements or Walker constellations. As for the communication parameters, different transmission frequencies and atmospheric propagation models can be used. As for the antennas, two different types are used: parabolic reflectors for ground stations and patch antennas for satellites. The quality of a communication link is determined by two different methods: using the received power or the signal-to-noise ratio in reception. In the case of received power, this should be higher than the sensitivity of the transceiver under study, while signal-to-noise takes into account different digital modulations that determine the probability of message loss. Thanks to this simulator, it is possible to obtain results that determine the visibility times between satellites and/or ground stations, and to determine if the communication for a given link meets the minimum communication requirements, as well as to calculate the transmission power necessary to meet these requirements. It also performs a 3D representation in which the orbits of the satellites as well as the ground stations can be observed

Study and simulation of communication links in a LEO satellite constellation based on Link Budget calculations

Currently, about 40% of the world’s population has limited or no access to high-speed Internet. Especially in rural, hard-to-reach areas, there is a challenge in terms of infrastructure to guarantee a quality connection.The need for global coverage has led telecommunications service providers to explore new alternatives to traditional communication. This search has led to the development of a multitude of projects related to satellite constellations in LEO orbits, where a more economical business model has been found, capable of providing global coverage and high-speed connection. The growing interest in LEO communications has motivated this project. The objective of this thesis is to study communication links in a LEO constellation through link budget calculations. Both inter-satellite links and ground-satellite links will be evaluated in order to study the characteristics of each one. For this purpose, an orbit simulator has been used, where the necessary calculations have been introduced to evaluate the links according to parameters such as received power and SNR, among others. The results of this project are expected to determine the viability of communications in a constellation and the effect of the link budget parameters on the communications performance

Cubesat constellation in LEO for air navigation monitoring

This project’s aim is to design a Matlab simulator capable of representing satellite constellations in Low Earth Orbits with the mission of monitoring air navigation trajectories. The objective is to create a tool capable of visually simulate the distribution of satellites in space along with the communication links between satellites, ground stations and aircraft. The aerospace industry is one of the most technologically and economically powerful in the world. This sector has evolved and grown exponentially in recent years thanks to the many applications it offers. In addition, the arrival of the New Space initiative has brought a new paradigm to the aerospace market, which has promoted the use of cubesats in LEO for telecommunication purposes. Furthermore, air transportation is one of the means of mobility that moves more passengers worldwide. Therefore, it is crucial to have the necessary elements to ensure constant and global coverage of air traffic, with the aim of improving the efficiency and safety of aircraft tracking. For the construction of the constellations, an analysis of the Walker pattern has been carried out. This methodology distributes the satellites symmetrically around a celestial body, providing global coverage. In addition, the effect of the different orbital parameters on the operation of the constellation has been studied. Finally, the structure of the ground segment required for the optimal performance of the mission has also been defined. The simulator designed in this thesis allows the user to create customized satellite configurations and visually represent the connections between the different objects in the defined scenario. The obtained result is able to perform a 3D representation of the orbits of the satellites, the ground stations network and the aircraft’s flight trajectory. Moreover, visibility intervals and communication links between satellites and antennas, and between satellites and aircraft are calculated. In addition, the simulator illustrates the efficiency of the constellation defined by the user taking into account the visibility with the aircraft through the entire flight route

Innovative observing strategy and orbit determination for Low Earth Orbit Space Debris

We present the results of a large scale simulation, reproducing the behavior of a data center for the build-up and maintenance of a complete catalog of space debris in the upper part of the low Earth orbits region (LEO). The purpose is to determine the performances of a network of advanced optical sensors, through the use of the newest orbit determination algorithms developed by the Department of Mathematics of Pisa (DM). Such a network has been proposed to ESA in the Space Situational Awareness (SSA) framework by Carlo Gavazzi Space SpA (CGS), Istituto Nazionale di Astrofisica (INAF), DM, and Istituto di Scienza e Tecnologie dell'Informazione (ISTI-CNR). The conclusion is that it is possible to use a network of optical sensors to build up a catalog containing more than 98% of the objects with perigee height between 1100 and 2000 km, which would be observable by a reference radar system selected as comparison. It is also possible to maintain such a catalog within the accuracy requirements motivated by collision avoidance, and to detect catastrophic fragmentation events. However, such results depend upon specific assumptions on the sensor and on the software technologies

Technologies and methods employed to design a university-class microsatellite, according to ESA Standards

The objective of this thesis is the study of the applicability of ESA (European Space Agency) standards to university-class microsatellites missions. At the same time the university microsatellite design technologies used to manufacture EduSAT spacecraft have been investigated in depth and ESA standards have been applied during the EduSAT mission phases. Afterwards a micro satellite optical payload for in-orbit space environment monitoring has been designed, exploiting useful instruments provided by ESA ECSS (European Cooperation for Space Standardization) standards

LEO Download Capacity Analysis for a Network of Adaptive Array Ground Stations

To lower costs and reduce latency, a network of adaptive array ground stations, distributed across the United States, is considered for the downlink of a polar-orbiting low earth orbiting (LEO) satellite. Assuming the X-band 105 Mbps transmitter of NASA s Earth Observing 1 (EO-1) satellite with a simple line-of-sight propagation model, the average daily download capacity in bits for a network of adaptive array ground stations is compared to that of a single 11 m dish in Poker Flats, Alaska. Each adaptive array ground station is assumed to have multiple steerable antennas, either mechanically steered dishes or phased arrays that are mechanically steered in azimuth and electronically steered in elevation. Phased array technologies that are being developed for this application are the space-fed lens (SFL) and the reflectarray. Optimization of the different boresight directions of the phased arrays within a ground station is shown to significantly increase capacity; for example, this optimization quadruples the capacity for a ground station with eight SFLs. Several networks comprising only two to three ground stations are shown to meet or exceed the capacity of the big dish, Cutting the data rate by half, which saves modem costs and increases the coverage area of each ground station, is shown to increase the average daily capacity of the network for some configurations

Savings on Transmit Power through Designed Horizon Plane for LEO Satellite Ground Stations

Low Earth Orbit (LEO) satellites are used for public networking and for scientific purposes. Established satellite ground stations can communicate with LEO satellites only when the satellite is in their visibility region, since LEO satellites move too fast relative to a ground station on the Earth. Each ground station is characterized by its own ideal horizon plane. Because of natural barriers that plane is modified to the designed one, defined by minimal elevation, in order to avoid natural obstacles. Designed horizon plane implementation implies also the power saving from the satellite to be transmitted. The major loss in communication between the LEO satellite and the ground station is the free space loss. Free space loss varies since the distance from the ground station to the satellite varies over time. Free space loss is usually compensated through variable satellite transmit power toward the downlink. In order to obtain the constant downlink margin at the receiver, all over the time, for analytical and simulation purposes, the altitudes from 600km to 1200km are considered. For each altitude it is calculated the power saving by designed horizon plane implementation compared the ideal horizon plane, for different altitudes