Terre | EPFL Graph Search

La Terre est la troisième planète par ordre d'éloignement au Soleil et la cinquième plus grande du Système solaire aussi bien par la masse que par le diamètre. Par ailleurs, elle est le seul objet céleste connu pour abriter la vie. Elle orbite autour du Soleil en solaires et réalise une rotation sur elle-même relativement au Soleil en un jour sidéral (environ ), soit un peu moins que son jour solaire de du fait de ce déplacement autour du Soleil. L'axe de rotation de la Terre possède une inclinaison de 23°, ce qui cause l'apparition des saisons. D'après la datation radiométrique, la Terre s'est formée il y a d'années. Elle possède un unique satellite naturel, la Lune, qui s'est formée peu après. L'interaction gravitationnelle avec son satellite crée les marées, stabilise son axe de rotation et réduit graduellement sa vitesse de rotation. La vie serait apparue dans les océans il y a au moins d'années, ce qui a affecté l'atmosphère et la surface terrestre par la prolifération d'or

Doppler-based positioning using LEO augmented satellite constellation - Simulations of perspectives

Alice Andreetti

The Global Navigation Satellite System (GNSS) refers to a constellation of satellites emitting signals from space, used to provide Position, Navigation and Timing (PNT) services to the receivers on Earth. Nowadays, the GNSS is exploited in a wide range of applications among which ground mapping, transportation, machine control, timing, surveying, defense, or aerial photogrammetry [1]. However, as we become more dependent on GNSS technology, we also become more vulnerable to its limitations [2]. The GNSS operates with satellites orbiting in Medium Earth Orbits (MEO, approximately 20200 [km] in altitude). On one hand, this great distance allows to have a large footprint of the satellite signal on Earth, but on the other hand, it requires the signal to cross a wide path in the atmosphere before reaching the receiver. This results in a decrease of signal strength, which is not an issue in open-sky condition, but becomes a limitation in deep attenuation environments, with little or no service in urban canyon, in dense cities or indoors [3]. In this contribution, a possible strategy to cope with this issue is proposed and evaluated through a simulation process. It implies the use of Low Earth Orbits (LEO) satellites as a support for the GNSS PNT service. Since nowadays no broadband big LEO constellation broadcasting navigation messages exist, in this project various LEO constellation setups have been simulated and tested. Because LEOs are much closer to Earth (200 to 1500 [km]), they move faster in the sky, passing overhead in minutes instead of hours like MEOs. This gives rise to the possibility to exploit the Doppler effect to accurately locate the user. Therefore, three different PNT algorithms, employing the Kalman filter, are implemented and the evaluation of the localization quality is made at four distinct locations on the globe. The results show that, for most of the cases, compared to the standard GPS pseudorange only PNT, the addition of LEO pseudoranges already improve the localization quality. The performance of the PNT algorithm increases even more with the exploitation of both pseudoranges and pseudorangerates (Doppler) measurements. Nevertheless, the choice of constellation parameters such as satellites altitude, total number of satellites, orbit inclination or the frequency of the emitted signal, has a great impact on the magnitude of the improvement in the localization quality. The factor that has the most significant influence seems to be the signal frequency and for that reason it must be carefully chosen: the higher the better. Moreover, it has been demonstrated that at high elevation cut-off angles (denied environments), the addition of LEO constellation is a valid option and allows us to obtain an accurate position even when the GNSS only can not provide a solution. Finally, the LEO only system seems to be a promising alternative to cope with GNSS jamming or spoofing. However, the optimal LEO parameters providing an accurate solution for all the location on the globe has not yet been identified. In conclusion, the result of this effort is the awareness that, once the optimal parameters for the LEO system have been found, it is a valid option to augment the GNSS, or even as a standalone backup, especially when the Doppler-based positioning is applied. Nevertheless, we are still far from that end and much more research needs to be done.

2020

Biomechanics at the workplace under hypogravity conditions

Tatiana Volkova

The main goal of my research is to establish guidelines for workplace design based on human biomechanics: specifically sitting workplaces and handling areas in 1/6G-1/3G (Moon, Mars) conditions. Such a workplace could be used in long-term space missions in order to maximize worker performance and minimize the risks of musculoskeletal injuries.Research objective is to formalize a baseline workplace design based on best practices limited to the tasks: operating a computer, assembling/maintenance operations.Proposed steps:1) Data collection and methods definitions2) Measurement and simulation of the human fatigue in the variation of sitting postures and handling areas (identification of typical poses, 3D simulation, graph analysis)3) Optimization of the workplace design based on human biomechanics (motion capture, factor analysis, optimization) 4) Simulation of workplace design in different environments (validation methods).Scientific & technological novelty: 1) Measurement of human muscular fatigue as a function of workload in reduced gravity conditions and integration of the results into the design model2) Modeling of the biomechanics of human movements in the workplace in reduced gravity conditions;3) Developing of sitting workplace design in reduced gravity conditions - taking into account human biomechanics.This research addresses problems revealed by workplace design in confined conditions found in Earth or near-Earth facilities in extreme environments including in underwater conditions, remote & non-remote locations and Low Earth Orbit (LEO), habitat simulators. Human-centered design strategies and biomechanics issues for creating an effective workplace design for long-term missions will also be addressed. The recommendations for design, maintenance, and usage of this workplace in different gravity conditions (1G, 1/6G,1/3G) will be provided. The design optimization of such a workplaces design based on human biomechanics will be done with the help of numerical simulations and digital human modeling. Physical experiments will validate these results by means of the suspension system, underwater experiment and possible by parabolic flights. This work may have a significant impact on workplace designs for both Earth and Space projects. Keywords: biomechanics, workplace, posture, extreme environments, human-centered design, Moon/Mars exploration, comfort conditions, task performance, reduced gravity, digital human modeling, motion capture

EPFL2022

Systems engineering and design of a Mars Polar Research Base with a human crew

Anton Ivanov, Claudio Leonardi, Anne-Marlene Rüede, Tatiana Volkova

Mars Polar Ice caps have been known ever since they were first observed by Cassini. Robotic exploration mis- sions, starting with Mariner 9, have confirmed that they are composed of water ice. During later missions, instruments such as Mars Global Surveyor's MOLA have established a detailed topography and have estimated their depth at about 3 km in the thickest part, while detailed internal structure has been investigated by MARSIS from Mars Express and SHARAD from the Mars Reconnaissance Orbiter. This analysis proposes to establish a base near North Polar Layered Deposits to investigate Mars' climate, hydrological processes and to test for possible traces of life. The objectives of the mission are to sustain a crew for nine months on the surface of Mars, near the North Pole, and to bring the crew back to Earth safely. During the surface mission, the crew will drill and analyze Polar Layered Deposits in ice samples. Furthermore, because the North Polar region provides an easy access to water ice, this area has the potential of sustaining a long-term human presence. The Mars Polar Research mission shall therefore prepare for long term missions, spanning over multiple crew generations. Indeed, longer duration missions and larger crews should be facilitated by this first mission. This paper describes a mission design for a Mars Polar Research base using systems engineering approach and scenario testing. The goal of the work is to establish a strategy composed of various technologies that have been selected accordingly. The requirements related to crew composition, human physiology and psychology adaptation, quality of com- munication, challenges and prospects of advancing science, as well as optimum habitat design and its usability, are derived and compiled into mass, volume, data and power consumption. A design for the base and mission scenario is also proposed. Given the identified requirements, possible technologies for life support systems, radiation protection, in-situ propellant production, thermal control, air pressure difference compensation and availability of power are discussed and solutions to focus on are recommended. Furthermore, the requirements for a long-term mission preparation are also identified and solutions to include in a first Mars mission with crew are recommended. In conclusion, approximately 110 metric tons and 160 kW are required to enable a Mars Polar mission with a human crew. A two-phase mission is recommended for enabling the testing of key in-situ resource utilization technologies allowing to minimize mass, while ensuring the security of the crew. The use of optimal payload and fairing, a Mars orbit crane system and deployable structures are recommended. Finally, in pre- paration for a long-term presence of humans on Mars, including in-situ testing of key technologies enabling the production of consumables facilitating autonomy from Earth is suggested. The consumables that have been identified as not being able to be tested before a first crew is sent to Mars are food and energy production. These developments may serve as priorities for current Mars settlement programs.

2019