Satellite Navigation for the Age of Autonomy

Global Navigation Satellite Systems (GNSS) brought navigation to the masses. Coupled with smartphones, the blue dot in the palm of our hands has forever changed the way we interact with the world. Looking forward, cyber-physical systems such as self-driving cars and aerial mobility are pushing the limits of what localization technologies including GNSS can provide. This autonomous revolution requires a solution that supports safety-critical operation, centimeter positioning, and cyber-security for millions of users. To meet these demands, we propose a navigation service from Low Earth Orbiting (LEO) satellites which deliver precision in-part through faster motion, higher power signals for added robustness to interference, constellation autonomous integrity monitoring for integrity, and encryption / authentication for resistance to spoofing attacks. This paradigm is enabled by the 'New Space' movement, where highly capable satellites and components are now built on assembly lines and launch costs have decreased by more than tenfold. Such a ubiquitous positioning service enables a consistent and secure standard where trustworthy information can be validated and shared, extending the electronic horizon from sensor line of sight to an entire city. This enables the situational awareness needed for true safe operation to support autonomy at scale.Comment: 11 pages, 8 figures, 2020 IEEE/ION Position, Location and Navigation Symposium (PLANS

Multi-Criteria Ground Segment Dimensioning for Non-Geostationary Satellite Constellations

Non-Geostationary Orbit (NGSO) satellite constellations are becoming increasingly popular as an alternative to terrestrial networks to deliver ubiquitous broadband services. With satellites travelling at high speeds in low altitudes, a more complex ground segment composed of multiple ground stations is required. Determining the appropriate number and geographical location of such ground stations is a challenging problem. In this paper, we propose a ground segment dimensioning technique that takes into account multiple factors such as rain attenuation, elevation angle, visibility, and geographical constraints as well as user traffic demands. In particular, we propose a methodology to merge all constraints into a single map-grid, which is later used to determine both the number and the location of the ground stations. We present a detailed analysis for a particular constellation combining multiple criteria whose results can serve as benchmarks for future optimization algorithms

A Low, Cost Portable Ground Station to Track and Communicate with Satellites in VHF Band

In this thesis, we present the architecture and implementation of a low-cost, small, mobile and easily deployable ground station to track and receive signals from satellites that operate on the VHF-band (144 MHz to 147 MHz). The ground station uses a handheld 5-dB gain Yagi-Uda antenna, a low noise amplifier with 23 dB gain and a software defined radio (FUNcube Dongle) to receive the signals. The analog front end’s software-defined nature gives it the flexibility to target satellites with diverse power, modulation and error-correcting schemes. Software for satellite tracking, signal decoding and processing is freely-available. The low cost of the ground station makes its affordable for classroom and laboratory activities in a research or educational institution that involve satellite signal processing in wireless communication courses. The small size and portability of the proposed ground station means it can be adopted in locations with limited access to fixed outdoor antennas, whether because of financial, regulatory or other restrictions. Examples of ground station-tracked and received signals include satellites such as FUNcube (AO-73), International Space Station (ISS) and NOAA satellites. Specifically, the National Oceanographic and Atmospheric Administration (NOAA) series of satellites (NOAA 15, 18, 19) were tracked. The signals received were processed to recover images of the earth using various software. This thesis also presents the details of decoding the image using MATLAB

Low Earth orbit microsatellite constellation utilizing satellite Hellas Sat 5 as a relay

Με δεδομένο ότι βρισκόμαστε σε μια εποχή ορόσημο για την ανάπτυξη στον διαστημικό τομέα, το σύνολο σχεδόν όλων των ανεπτυγμένων χωρών έχει συνειδητοποιήσει ότι η επένδυση στο σύνολο των διαστημικών τεχνολογιών αποτελεί μονόδρομο ανάπτυξης και ευημερίας. Τα δαπανούμενα ποσά είναι απολύτως ενδεικτικά της φρενίτιδας που επικρατεί στη λεγόμενη κούρσα του διαστήματος. Η εισαγωγή πλέον και του ιδιωτικού τομέα στη κούρσα αυτή έχει επιτρέψει την προώθηση του ανταγωνισμού κάτι το οποίο με τη σειρά του έχει ελαττώσει εντυπωσιακά το κόστος χρήσης και αξιοποίησης του διαστημικού τομέα. Αυτό το νέο διαστημικό οικοσύστημα που έχει αναπτυχθεί παγκοσμίως τις τελευταίες δεκαετίες, έχει επιτρέψει τη πρόσβαση στις διαστημικές τεχνολογίες από το σύνολο σχεδόν των χωρών του πλανήτη, τη στιγμή που κατά τις προηγούμενες δεκαετίες, οι μοναδικές χώρες που είχαν τη δυνατότητα να επενδύσουν στον τομέα ήταν οι ΗΠΑ και οι Ρωσία. Δορυφορική παρατήρηση της γης, πλοήγηση, αποτροπή φυσικών καταστροφών, εξερεύνηση του διαστήματος, επιστημονική ανάλυση της επιφάνειας του εδάφους, εκμετάλλευση φυσικών πόρων αλλά και πολιτικές και στρατιωτικές τηλεπικοινωνίες, είναι μόνο μερικές από τις νέες τεχνολογίες που έχει να προσφέρει ο διαστημικός τομέας. Κάθε ένας από αυτούς τους τομείς μπορεί δυνητικά να αποτελέσει πυλώνα ανάπτυξης αν αξιοποιηθεί σωστά και πλέον όλες οι χώρες έχουν συνειδητοποιήσει πως η επένδυση σε κάποιον ή και σε όλους αυτούς τους τομείς μπορούν να επιφέρουν πολλαπλά οφέλη. Ένα χαρακτηριστικό παράδειγμα του νέου διαστημικού οικοσυστήματος που έχει διαμορφωθεί κατά τις τελευταίες δεκαετίες και που δείχνει το πόσο πολύ επενδύουν πλέον οι χώρες στον διαστημικό τομέα, είναι ο υπερδιπλασιαμός των ενεργών δορυφορικών συστημάτων κατά τη πενταετία 2015 – 2020, ιδιαίτερα των τηλεπικοινωνιακών. Αξίζει να σημειωθεί πως τον Δεκέμβριο του 2015, σύμφωνα με τα στοιχεία της UCS, ο αριθμός των ενεργών δορυφόρων του έτους ανήλθε σε 1.381, αριθμός ο οποίος κατά τον ίδιο μήνα του έτους 2020 είχε φτάσει τους 3.372. Έχοντας πει όλα τα παραπάνω, η παρούσα διπλωματική εργασία στοχεύει στην παρουσίαση μιας ολοκληρωμένης ανάλυσης όλων των απαιτούμενων βημάτων που πρέπει να εξετάσει ένας μηχανικός / σχεδιαστής συστημάτων προκειμένου να κατασκευάσει και να αναπτύξει μια πλήρως λειτουργική και αξιόπιστη δορυφορική ζεύξη επικοινωνίας. Η μεθοδολογία περιλαμβάνει μια πλήρη περιγραφή των βασικών νόμων του διαστημικού περιβάλλοντος καθώς και μια εκτενή ανάλυση της τροχιακής μηχανικής και των παραμέτρων. Η ιδέα ήταν να παρουσιαστεί πώς η θεωρία μπορεί να εφαρμοστεί σε μια πραγματική δορυφορική προσομοίωση καθώς και πώς επηρεάζεται από αυτήν. Το τελευταίο βήμα ήταν ο σχεδιασμός και η κατασκευή ενός πραγματικού συστήματος δορυφορικής επικοινωνίας σε ένα εξειδικευμένο λογισμικό και η παρουσίαση των αποτελεσμάτων. Το κύριο συμπέρασμα της παραπάνω υλοποίησης είναι το γεγονός ότι μέσω της χρήσης ενός αστερισμού δορυφόρων χαμηλής Γήινης τροχιάς σε συνδυασμό με έναν γεωστατικό δορυφόρο που χρησιμοποιείται αναμεταδότης, είναι δυνατό να επιτευχθεί μια ανθεκτική και αξιόπιστη επικοινωνιακή ζεύξη με εξαιρετικά υψηλούς ρυθμούς μετάδοσης δεδομένων και σχεδόν παγκόσμια κάλυψη.Given that we are in a landmark era of the space sector development , most countries have realized that an investment in space technologies is the only way for development and prosperity. The invested budgets are absolutely indicative of the so-called space race. The introduction of the private sector in this race has allowed the promotion of competition, which in turn has dramatically reduced the cost of using and exploiting the space sector. This new space ecosystem that has been developed worldwide in recent decades, has allowed access to space technologies from almost all countries on the planet, while in previous decades, the only countries that had the opportunity to invest in the sector were USA and Russia. Satellite earth observation, navigation, prevention of natural disasters, space exploration, scientific analysis of the earth's surface, exploitation of natural resources, but also civil and military telecommunications, are just some of the new technologies that the space sector has to offer. Each of these sectors can potentially be a pillar of development if exploited properly and almost all of the modern countries have realized that investing in one or all of these sectors can offer multiple benefits. A typical example of the new space ecosystem that has been formed during the last decades and that shows how much money countries are now investing in the space sector, is the dramatic increase of the active satellite systems during the years 2015 – 2020, especially the telecommunication ones. It is worth mentioning that in December 2015, according to UCS data, the number of active satellites was 1.381, a number which during the same month in 2020 reached the astonishing number of 3.372. The rapid development of the space sector combined with the cost reducing methods that private sectors have introduced, is showing that the imminent future seems to be very promising. Having said all of the above, this thesis aims at presenting a comprehensive analysis of all the required steps that a system engineer / designer must consider in order to build and deploy a fully functional and reliable satellite communication link. The methodology entails a fully description of the basic laws of the space environment as well as an extensive analysis of the orbital mechanics and parameters. The idea was to demonstrate how the theory can be utilized in an actual satellite project simulation as well as how it is affected by it. The last step was to design and build an actual satellite communication system on a specialized software and present the results. The main conclusion of the above implementation is the fact that through the use of a low Earth orbit satellite constellation combined with a geostationary satellite used as a relay, it’s possible to achieve a resilient and reliable communication link with exceptional high data rates and an almost worldwide coverage

James Webb Space Telescope - L2 Communications for Science Data Processing

JWST is the first NASA mission at the second Lagrange point (L2) to identify the need for data rates higher than 10 megabits per second (Mbps). JWST will produce approximately 235 Gigabits of science data every day that will be downlinked to the Deep Space Network (DSN). To get the data rates desired required moving away from X-band frequencies to Ka-band frequencies. To accomplish this transition, the DSN is upgrading its infrastructure. This new range of frequencies are becoming the new standard for high data rate science missions at L2. With the new frequency range, the issues of alternatives antenna deployment, off nominal scenarios, NASA implementation of the Ka-band 26 GHz, and navigation requirements will be discussed in this paper. JWST is also using Consultative Committee for Space Data Systems (CCSDS) standard process for reliable file transfer using CCSDS File Delivery Protocol (CFDP). For JWST the use of the CFDP protocol provides level zero processing at the DSN site. This paper will address NASA implementations of Ground Stations in support of Ka-band 26 GHz and lesson learned from implementing a file base (CFDP) protocol operational system