GNSS transpolar earth reflectometry exploriNg system (G-TERN): mission concept

The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA's Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a “dynamic mapper”of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (<;10 cm precision), roughness, and polarimetry aspects at 30-km resolution and 3-days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, the G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025-2030 or optimally 2025-2035, covering key stages of the transition toward a nearly ice-free Arctic Ocean in summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation, and finally, it estimates the expected performance.Peer ReviewedPostprint (published version

The Deep Space Network. An instrument for radio navigation of deep space probes

The Deep Space Network (DSN) network configurations used to generate the navigation observables and the basic process of deep space spacecraft navigation, from data generation through flight path determination and correction are described. Special emphasis is placed on the DSN Systems which generate the navigation data: the DSN Tracking and VLBI Systems. In addition, auxiliary navigational support functions are described

The Asolant/Rubin-5 Technology Demonstration Mission - System Description and First Flight Results

This paper addresses the Asolant/Rubin-5 flight experiment conducted onboard the upper stage of a Cosmos rocket in late 2005. The main objective of the project was to flight-qualify a newly developed combined solar cell/antenna device, the so-called Advanced SOLar ANTenna (ASOLANT) technology. In order to assess both, the reception as well as emission of R/F signals, two different devices were involved in the mission. One was linked to a space-borne Phoenix-S GPS receiver to examine the receiving performance. A second device was designed to send out S-Band beacon signals generated by the SAFIR-S amateur radio transmitter to evaluate the radiation characteristics. Moreover, both ASOLANT devices supplied the electrical power for the onboard systems. Telecommand and telemetry functionalities were provided by an ORBCOMM communicator making use of the ORBCOMM satellite network to relay data between space and ground. This unit, furthermore, served as onboard computer. The experiment was launched along with eight multinational payload satellites. It was designed to remain attached to the rockets upper stage after burnout. Due to a separation failure of one of the copassengers, the primary mission objectives could not be fully met. Nevertheless, a sufficient number of data was retrieved to confirm the good overall performance of the ASOLANT devices. Roughly ten month after the launch, still most system components are operational and experiment data are transmitted to ground. Following a description of the main flight system components and the overall ystem architecture, the paper summarizes the hitherto obtained experiment results

System using leo satellites for centimeter-level navigation

Disclosed herein is a system for rapidly resolving position with centimeter-level accuracy for a mobile or stationary receiver [4]. This is achieved by estimating a set of parameters that are related to the integer cycle ambiguities which arise in tracking the carrier phase of satellite downlinks [5,6]. In the preferred embodiment, the technique involves a navigation receiver [4] simultaneously tracking transmissions [6] from Low Earth Orbit Satellites (LEOS) [2] together with transmissions [5] from GPS navigation satellites [1]. The rapid change in the line-of-sight vectors from the receiver [4] to the LEO signal sources [2], due to the orbital motion of the LEOS, enables the resolution with integrity of the integer cycle ambiguities of the GPS signals [5] as well as parameters related to the integer cycle ambiguity on the LEOS signals [6]. These parameters, once identified, enable real-time centimeter-level positioning of the receiver [4]. In order to achieve high-precision position estimates without the use of specialized electronics such as atomic clocks, the technique accounts for instabilities in the crystal oscillators driving the satellite transmitters, as well as those in the reference [3] and user [4] receivers. In addition, the algorithm accommodates as well as to LEOS that receive signals from ground-based transmitters, then re-transmit frequency-converted signals to the ground

Performance Assessment of Navigation Using Carrier Doppler Measurements from Multiple LEO Constellations

The goal of this work is to characterize a novel navigation method which uses carrier Doppler shift measurements from LEO satellites. An ever-growing reliance on the GNSS has coincided with an increase in ways it can be degraded or denied, whether naturally occurring or man-made. These potentially disastrous threats to traditional navigation and timing have necessitated new technologies to augment GNSS in the case of an outage. LEO constellations, whose size and higher signal power make them potentially useful for navigation, are one technology that has been explored. The navigation algorithms detailed in this research use Doppler measurements from 8 or more LEO satellites to simultaneously solve for position, clock offset, velocity, and clock offset rate. Through simulation, a user-satellite geometry analysis is conducted for a number of emerging LEO constellations, as well as navigation simulations with the same constellations. Results are presented which show promise from both a satellite geometry perspective and PVT solution convergence perspective

Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View

Small satellite systems enable whole new class of missions for navigation, communications, remote sensing and scientific research for both civilian and military purposes. As individual spacecraft are limited by the size, mass and power constraints, mass-produced small satellites in large constellations or clusters could be useful in many science missions such as gravity mapping, tracking of forest fires, finding water resources, etc. Constellation of satellites provide improved spatial and temporal resolution of the target. Small satellite constellations contribute innovative applications by replacing a single asset with several very capable spacecraft which opens the door to new applications. With increasing levels of autonomy, there will be a need for remote communication networks to enable communication between spacecraft. These space based networks will need to configure and maintain dynamic routes, manage intermediate nodes, and reconfigure themselves to achieve mission objectives. Hence, inter-satellite communication is a key aspect when satellites fly in formation. In this paper, we present the various researches being conducted in the small satellite community for implementing inter-satellite communications based on the Open System Interconnection (OSI) model. This paper also reviews the various design parameters applicable to the first three layers of the OSI model, i.e., physical, data link and network layer. Based on the survey, we also present a comprehensive list of design parameters useful for achieving inter-satellite communications for multiple small satellite missions. Specific topics include proposed solutions for some of the challenges faced by small satellite systems, enabling operations using a network of small satellites, and some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications Surveys and Tutorial

Satellitenorbit und -ephemeridenbestimmung mit Hilfe von Intersatellitenverbindungen

Global navigation satellite systems like GPS, GLONASS or the future systems like Galileo require precise orbit and clock estimates in order to provide high positioning performance. Within the frame of this Ph. D. thesis, the theory of orbit determination and orbit computation is reviewed and a new approach for precise orbit and ephemeris determination using inter-satellite links is developed. To investigate the achievable accuracy, models of the various perturbing forces acting on a satellite have been elaborated and coded in a complex software package, allowing system level performance analysis as well as detailed evaluation of orbit prediction and orbit estimation algorithms. Several satellite constellations have been simulated, involving nearly all classes of orbit altitude and the results are compared. The purpose of orbit determination in a satellite navigation system is the derivation of ephemeris parameters which can be broadcast to the user community (or the other satellites) and allow easy computation of the satellites position at the desired epoch. The broadcast ephemeris model of both today existing satellite navigation systems, GPS and GLONASS are investigated, as well as two new models developed within this thesis, which are derivates of the GLONASS model. Furthermore, the topic of autonomous onboard processing is addressed. A conceptual design for an onboard orbit estimator is proposed and investigated with respect to the computational load. The algorithms have been implemented. The main benefits of ISL onboard processing, especially with respect to the great potential to ephemeris and clock state monitoring are investigated using complex simulations of failure scenarios. By simulating several types of non-integrity cases, it is showed that one single fault detection mechanism is likely to be insufficient. Within the algorithm design of the onboard processor, a reasonable combination of fault detection mechanisms is presented, covering different fault cases.Globale Navigationssysteme wie GPS, GLONASS oder zukünftige Systeme wie Galileo erfordern die hochpräzise Bestimmung der Orbital- und Uhrenparameter, um hohe Navigationsgenauigkeit bieten zu können. Im Rahmen dieser Dissertation wurde die Theorie der Orbitprädiktion und der Orbitbestimmung erörtert und ein neuer Ansatz für die präzisen Orbitbestimmung mit Hilfe von Intersatelliten-Messungen entwickelt. Um die erreichbare Genauigkeit und Präzision der Orbitbestimmung zu untersuchen, wurden mathematische Modelle der zahlreiche Orbitstörungen erarbeitet und in einem komplexen Software-Paket implemetiert. Dieses bietet die Möglichkeit für Systemstudien von Satellitennavigations-Systemen beliebiger Orbitklassen, sowie zur detaillierten Untersuchung spezieller Fragestellungen der Orbitprädiktion und -bestimmung. Eine Reihe von Simulationen mit existierenden sowie fiktiven Satelliten-Navigations-Systemen wurden durchgeführt, deren Ergebnisse in dieser Arbeit präsentiert werden. Die präzise Orbitbestimmung in einem SatNav-System ist kein Selbstzweck, sondern dient lediglich der Bestimmung der Ephemeridenparameter, die - vom Satellite gesendet - es dem Nutzer-Empfänger erlauben, mit Hilfe einfacher Berechnungen die Position des Satelliten zu ermitteln. Die Ephemeridenformate beider existierender SatNav-Systeme - GPS und GLONASS - wurden untersucht und mit zwei weiteren Formaten verglichen, die im Rahmen dieser Arbeit entwickelt wurden. Desweiteren wurde das Thema der bordautonomen Verarbeitung von Messungen behandelt. Ein konzeptuelles Design für einen Onboard-Prozessor wurde vorgeschlagen und die Algorithmen implementiert. Dabei erfolgte eine Abschätzung der benötigten Prozessorleistung. Einer der Hauptvorteile der bordautonomen Verarbeitung von Intersatellitenmessungen, die Möglichkeit zur Überwachung der Integrität der Ephemeriden und Uhrenparameter, wurde in komplexen Simulationen untersucht. Durch die Simulation verschiedener Fehlerfälle wurde gezeigt, das kein Detektionsmechanismus allein, wohl aber eine sinnvolle Kombination solcher Mechanismen, zur bordautonomen Integritätsüberwachung geeignet sind. Die Ergebissen werden hier präsentiert

Radio Frequency Emitter Geolocation Using Cubesats

The ability to locate an RF transmitter is a topic of growing interest for civilian and military users alike. Geolocation can provide critical information for the intelligence community, search and rescue operators, and the warfighter. The technology required for geolocation has steadily improved over the past several decades, allowing better performance at longer baseline distances between transmitter and receiver. The expansion of geolocation missions from aircraft to spacecraft has necessitated research into how emerging geolocation methods perform as baseline distances are increased beyond what was previously considered. The CubeSat architecture is a relatively new satellite form which could enable small-scale, low-cost solutions to USAF geolocation needs. This research proposes to use CubeSats as a vehicle to perform geolocation missions in the space domain. The CubeSat form factor considered is a 6-unit architecture that allows for 6000 cm3 of space for hardware. There are a number of methods which have been developed for geolocation applications. This research compares four methods with various sensor configurations and signal properties. The four methods\u27 performance are assessed by simulating and modeling the environment, signals, and geolocation algorithms using MATLAB. The simulations created and run in this research show that the angle of arrival method outperforms the instantaneous received frequency method, especially at higher SNR values. These two methods are possible for single and dual satellite architectures. When three or more satellites are available, the direct position determination method outperforms the three other considered methods