Advancing Tests of Relativistic Gravity via Laser Ranging to Phobos

Phobos Laser Ranging (PLR) is a concept for a space mission designed to advance tests of relativistic gravity in the solar system. PLR's primary objective is to measure the curvature of space around the Sun, represented by the Eddington parameter $\gamma$, with an accuracy of two parts in $10^7$, thereby improving today's best result by two orders of magnitude. Other mission goals include measurements of the time-rate-of-change of the gravitational constant, $G$ and of the gravitational inverse square law at 1.5 AU distances--with up to two orders-of-magnitude improvement for each. The science parameters will be estimated using laser ranging measurements of the distance between an Earth station and an active laser transponder on Phobos capable of reaching mm-level range resolution. A transponder on Phobos sending 0.25 mJ, 10 ps pulses at 1 kHz, and receiving asynchronous 1 kHz pulses from earth via a 12 cm aperture will permit links that even at maximum range will exceed a photon per second. A total measurement precision of 50 ps demands a few hundred photons to average to 1 mm (3.3 ps) range precision. Existing satellite laser ranging (SLR) facilities--with appropriate augmentation--may be able to participate in PLR. Since Phobos' orbital period is about 8 hours, each observatory is guaranteed visibility of the Phobos instrument every Earth day. Given the current technology readiness level, PLR could be started in 2011 for launch in 2016 for 3 years of science operations. We discuss the PLR's science objectives, instrument, and mission design. We also present the details of science simulations performed to support the mission's primary objectives.Comment: 25 pages, 10 figures, 9 table

Sistemas de comunicação por luz visível aplicados para assistência ao tráfego automóvel

Motivated by the topic of promoting traffic safety applications and information systems, this work aims to bring a study on VLC outdoor application scenarios. The developed topic is part of intelligent transportation systems (ITS) that aim at the delivery of traffic safety and information amongst other safety functions. VLC technology in traffic communication applications gains interest due to some advantages it presents. The use of LEDs in traffic signaling infrastructures and vehicle headlights started to be a growing standard. With the combination of illuminating proprieties and communication in the same device, VLC becomes a very attractive technology for the implementation of outdoor communication systems for traffic information and control. Outdoor VLC channels present variable ambient conditions, with the presence of different optical sources. One major problem in this communication channel is the presence of shot-noise, generated by optical background radiance from different light sources. This dissertation presents two different communication scenarios for traffic information systems, the first being directed at the infrastructure to car (I2C) link and the second one for car to car (C2C) communication. In order to simulate the communication link performance with variable ambient channel conditions, several models for optical propagation, emitter, receiver and noise sources were implemented in MATLAB. Models for different optical sources were also implemented, with field measurements on the illuminance incident on a photo detector and their impact on the noise generated. In the simulation’s performance of the VLC link, several baseband modulation schemes were considered, aiming at the assessment of link performance, based on the traditional digital modulation performance metrics.Motivado em promover o tópico de segurança rodoviária e sistemas de informação, este trabalho providência um estudo dedicado a sistemas de comunicação por luz visível (VLC) para aplicação em cenários de exterior. O tópico desenvolvido faz parte de sistemas de transporte inteligentes (ITS) cujo propósito é a disseminação de sistemas de segurança no tráfego e transferência de informação, para aplicações de segurança. A tecnologia VLC aplicada a sistemas de comunicação de tráfego rodoviário suscita elevado interesse devido a vantagens que esta apresenta. O uso de LED’s em semáforos e faróis de carros começa a ser bastante comum. Com a combinação de diferentes valências, como iluminação e transferência de dados no mesmo dispositivo, a tecnologia VLC torna-se muito atrativa para a implementação em sistema de comunicação exterior dedicados a sistemas de informação e controlo de tráfego. O canal de comunicação VLC exterior apresenta condições variáveis, devido ao fato de existirem condições ambientais diferentes. Um grave problema neste tipo de canal de comunicação é a presença de ruido Shot, que é normalmente gerado devido á radiância causada por diferentes fontes de luz de fundo. Nesta dissertação estão presentes dois tipos de cenários para sistemas de informação de tráfego, em que o primeiro dedica-se á comunicação semáforo-carro (I2C) e o segundo cenário para a comunicação entre carros (C2C). Para simular o desempenho do canal de comunicação com diferentes condições ambientais, foram implementados em MATLAB modelos para a propagação ótica, descrição do emissor, recetor e fontes de ruido. Também foram incluídos modelos para diferentes fontes óticas de radiação, com medições de campo da iluminância incidente num foto recetor e modulado o impacto na geração de ruido. Nas simulações de desempenho da comunicação por luz visível, foram considerados diferentes esquemas de modulação da informação com o intuito de avaliar o desempenho da ligação, a qual foi feita recorrendo a métricas clássicas de desempenho de modulações digitais.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Virtual image out-the-window display system study. Volume 2 - Appendix

Virtual image out-the-window display system imaging techniques and simulation devices - appendices containing background materia

Characterizing Resident Space Object Earthshine Signature Variability

There are three major sources of illumination on objects in the near Earth space environment: Sunshine, Moonshine, and Earthshine. For objects in this environment (satellites, orbital debris, etc.) known as Resident Space Objects (RSOs), the sun and the moon have consistently small illuminating solid angles and can be treated as point sources; this makes their incident illumination easily modeled. The Earth on the other hand has a large illuminating solid angle, is heterogeneous, and is in a constant state of change. The objective of this thesis was to characterize the impact and variability of observed RSO Earthshine on apparent magnitude signatures in the visible optical spectral region. A key component of this research was creating Earth object models incorporating the reflectance properties of the Earth. Two Earth objects were created: a homogeneous diffuse Earth object and a time sensitive heterogeneous Earth object. The homogeneous diffuse Earth object has a reflectance equal to the average global albedo, a standard model used when modeling Earthshine. The time sensitive heterogeneous Earth object was created with two material maps representative of the dynamic reflectance of the surface of the earth, and a shell representative of the atmosphere. NASA’s Moderate-resolution Imaging Spectroradiometer (MODIS) Earth observing satellite product libraries, MCD43C1 global surface BRDF map and MOD06 global fractional cloud map, were utilized to create the material maps, and a hybridized version of the Empirical Line Method (ELM) was used to create the atmosphere. This dynamic Earth object was validated by comparing simulated color imagery of the Earth to that taken by: NASAs Earth Polychromatic Imaging Camera (EPIC) located on the Deep Space Climate Observatory (DSCOVR), and by MODIS located on the Terra satellite. The time sensitive heterogeneous Earth object deviated from MODIS imagery by a spectral radiance root mean square error (RMSE) of ±14.86 [watts/m^2srμm] over a sample of ROIs. Further analysis using EPIC imagery found a total albedo difference of +0.03% and a cross correlation of 0.656. Also compared to EPIC imagery it was found our heterogeneous Earth model produced a reflected Earthshine radiance RMSE of ±28 [watts/m^2srμm] incident on diffuse spherical RSOs, specular spherical RSOs, and diffuse flat plate RSOs with an altitude of 1000km; this resulted in an apparent magnitude error of ±0.28. Furthermore, it was found our heterogeneous Earthmodel produced a reflected Earthshine radiance RMSE of ±68 [watts/m^2srμm] for specular flat plate RSOs with an altitude of 1000km; this resulted in an apparent magnitude error of ±0.68. The Earth objects were used in a workflow with the Digital Imaging and Remote Sensing Image Generation (DIRSIG) tool to explore the impact of a range of characteristic RSO geometries, geographies, orientations, and materials on the signatures from an RSO due to Earthshine. An apparent magnitude was calculated and used to quantify RSO Earthshine signature variability; this is discussed in terms of the RMSE and maximum deviations of visible RSO Earthshine apparent magnitude signatures comparing the homogeneous Earth model to heterogeneous Earth model. The homogeneous diffuse Earth object was shown to approximate visible RSO Earthshine apparent magnitude signatures from spheres with a RMSE in reflected Earthshine apparent magnitude of ±0.4 and a maximum apparent magnitude difference of 1.09 when compared to the heterogeneous Earth model. Similarly for diffuse flat plates, the visible RSO Earthshine apparent magnitude signature RMSE was shown to be ±0.64, with a maximum apparent magnitude difference of 0.82. For specular flat plates, the visible RSO Earthshine apparent magnitude signature RMSE was shown to be ±0.97 with maximum apparent magnitude difference of 2.26. This thesis explored only a portion of the parameter dependencies of Earth shine, but has enabled a preliminary understanding of visible RSO Earthshine signature variability and its geometric dependence. This research has demonstrated the impact of Earth heterogeneity on the observed apparent magnitude signatures of RSOs illuminated by Earthshine and the potential for error that comes with approximating the Earth as a diffuse homogeneous object

Técnicas de detección y caracterización de la materia interplanetaria próxima a la Tierra desde observatorios en tierra

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Astrofísica y Ciencias de la Atmósfera, leída el 05/06/2017Interplanetary matter covers a wide range of mass and size in the Universe, from micrometric dust to multi-kilometre asteroids. This matter plays countless roles in planetary sciences. Dust fills the space in the Solar System, but also in a myriad of exoplanetary systems. Indeed, the interplanetary dust usually outshines the planets in infrared and these hot debris disks have already been observed in several exoplanetary systems. The near-Earth interplanetary matter is also relevant for Earth sciences and space exploration. Extraterrestrial dust plays several roles in the upper atmosphere. Moreover the asteroids are a threat for humankind due to the energy they release in the case of impact against the planet. Asteroids larger than 1 km could produce global devastation and 90% of them are already catalogued. Current efforts are focused on the population larger than 140 m, able to produce an impact of regional proportions. Beyond Earth’s atmosphere, these bodies pose a hazard to spacecraft, especially the small particles that are the most numerous but still carry enough energy to jeopardise their systems. This dissertation undertakes the research of the interplanetary matter near the Earth using two different observational approaches. The first one is based on the detection of the sunlight reflected by the bodies. Individuals bodies can be observed with the use of telescopes, they are the asteroids. For objects close to the Earth the accessible range in size is wider, down to the decametre size and consequently this population are a probe to general population of asteroids in the Solar System. Especially if we consider that recent works suggest that objects larger and smaller than 200 m could be two different populations, being the smaller monolithic bodies while larger ones are more likely rubble piles. And we only have access to the smaller population if they come close enough to the be observable. The detection and characterisation of these nearby population require networks of medium-sized telescopes to survey and track them. We design a robotic system (the TBT telescopes) for the European Space Agency as a prototype for a future network. The first unit is already installed in Spain and we present the results of the commissioning. Additionally we evaluate the expected performance of such an instrument using a simulation with a synthetic population. We consider that the system designed is a powerful instrument for nearby asteroid discovery and tracking. It is based on commercial components, and therefore ready for a scalable implementation in a global network...Bajo el término de materia interplanetaria se engloban objetos en un gran rango de masas y tamaños en el Universo, desde el polvo micrométrico hasta los asteroides de centenares de kilómetros de diámetro. Esta materia toma parte de innumerables procesos en las ciencias planetarias. Además el polvo no sólo está presente en el espacio del Sistema Solar, sino también en una infinidad de sistemas extrasolares. Más aún, el polvo interplanetario es más brillante en el infrarrojo que los propios planetas y ya se han observado muchos de estos discos circunestelares de polvo caliente. La materia interplanetaria en las cercanías de nuestro planeta es también relevante para el estudio de las ciencias de la Tierra y en la exploración espacial. El polvo extraterrestre participa en muchos procesos que tienen lugar en las capas más altas de la atmósfera. Asimismo los asteroides son una amenaza para la humanidad debido a la energía que pueden liberar en caso de impacto contra la Tierra. Se considera que los asteroides mayores de 1 km podrían provocar una catástrofe de proporciones globales y por ello el 90% de ellos ya han sido identificados. Actualmente los esfuerzos se centran en los objetos mayores de 140 m, con consecuencias sólo a nivel regional en caso de colisión. Fuera de la atmósfera terrestre estos cuerpos suponen un peligro para las naves espaciales, especialmente las partículas pequeñas que son las más numerosas y que pese a ello transportan energía suficiente como para comprometer su funcionamiento. Esta tesis estudia la materia interplanetaria desde dos aproximaciones observacionales distintas. Por un lado se observa la luz solar reflejada por estos cuerpos. En este caso encontramos a los asteroides, cuerpos que se pueden observar con telescopios hasta cierto tamaño. Para la población de objetos próximos a la Tierra el rango de tamaños que podemos observar es mayor, hasta tamaños de apenas decenas de metros. Por ello esta población se considera como una muestra relevante a la hora de estudiar la población general de asteroides en el Sistema Solar. Especialmente cuando estudios recientes afirman que puede haber una diferencia estructural entre las poblaciones con diámetro mayor y menor a unos 200 m, donde los pequeños son objetos monolíticos mientras que los grandes son agregados de objetos. Los objetos menores sólo son accesibles a los instrumentos si se aproximan lo suficiente a la Tierra. La detección y caracterización de estos objetos próximos requieren redes de telescopios de tamaño moderado. En este trabajo presentamos el diseño de un sistema robótico (los telescopios TBT) para la Agencia Espacial Europea (ESA), como prototipos de una red futura. El primero de ellos se encuentra ya instalado en España y se incluyen los resultados del comisionado. Por otro lado hemos analizado el rendimiento que se espera de ellos con ayuda de una simulación de las observaciones de una población sintética de objetos. Consideramos que el sistema diseñado es una herramienta potente para el descubrimiento y seguimiento de estos objetos próximos a la Tierra. Es un sistema basado en componentes comerciales y que por tanto se puede replicar para desarrollar una red global...Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEunpu

Roving vehicle motion control Final report

Roving vehicle motion control for unmanned planetary and lunar exploratio

Application of advanced technology to space automation

Automated operations in space provide the key to optimized mission design and data acquisition at minimum cost for the future. The results of this study strongly accentuate this statement and should provide further incentive for immediate development of specific automtion technology as defined herein. Essential automation technology requirements were identified for future programs. The study was undertaken to address the future role of automation in the space program, the potential benefits to be derived, and the technology efforts that should be directed toward obtaining these benefits

Three-D multilateration: A precision geodetic measurement system

A technique of satellite geodesy for determining the relative three dimensional coordinates of ground stations within one centimeter over baselines of 20 to 10,000 kilometers is discussed. The system is referred to as 3-D Multilateration and has applications in earthquake hazard assessment, precision surveying, plate tectonics, and orbital mechanics. The accuracy is obtained by using pulsed lasers to obtain simultaneous slant ranges between several ground stations and a moving retroreflector with known trajectory for aiming the lasers

Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars

The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained