Analysis of bare-tether systems for deorbiting low-earth-orbit satellites

Performances, design criteria, and system mass of bare tethers for satellite deorbiting missions are analyzed. Orbital conditions and tether cross section define a tether length, such that 1) shorter tethers are electron collecting practically in their whole extension and 2) longer tethers collect practically the short-circuit current in a fixed segment length. Long tethers have a higher drag efficiency (defined as the drag force vs the tether mass) and are better adapted to adverse plasma densities. Dragging efficiency and mission-related costs are used to define design criteria for tether geometry. A comparative analysis with electric thrusters shows that bare tethers have much lower costs for low- and midinclination orbits and remain an attractive option up to 70 deg.

Elaboración de cartografía temática de usos de suelo del valle de Tamanart (Marruecos) a partir de imágenes Landsat.

El objetivo del presente Proyecto Fin de Carrera es la elaboración de cartografía base de la zona del Valle de Tamanart y la elaboración de un documento cartográfico que muestre la distribución de minerales en ella. Se pretende poder facilitar el reconocimiento del área arqueológica de estudio desde la perspectiva del análisis físico para correlacionar el material de superficie con la aparición de petroglifos o restos arqueológicos. En la investigación arqueológica de países emergentes es difícil contar con cartografía previa de la zona de interés en la realización de las campañas de campo. Se pretende plantear una metodología general de creación de cartografía básica y cartografía temática de distribución de minerales en superficie mediante técnicas de teledetección utilizando imágenes de satélite que sean gratuitas a través de la red. El proyecto consta de dos partes: 1. Confección de la cartografía base: - Primero: se realiza una breve descripción documentada de los aspectos físicos globales (geomorfológicos, geológicos, hidrológicos…) del área de estudio, a través de los documentos que puedan existir en Internet con acceso libre y con la información aportada por el grupo de investigación. - Segundo: Para poder obtener la base cartográfica se realiza el tratamiento de datos de las escenas de los satélites. Las escenas gratuitas disponibles han sido dos imágenes de la misma zona, una del satélite Landsat7 y otra del satélite Landsat5, descargadas del servidor GLOVIS (USGS Global Visualization Viewer). Confección de la cartografía temática: - Selección de la zona de estudio en las imágenes de teledetección ya tratadas en la primera parte del proyecto. - Clasificación de la imagen para usos de suelo. - Edición de la cartografía temática. El resultado del proyecto son la cartografía base y de coberturas superficiales de distribución de minerales sobre la que se ubican los yacimientos arqueológicos de la zona, yacimientos y paneles que fueron georreferenciados en la campaña de campo 2013. El PFC se realiza en colaboración con el Departamento de Prehistoria de la UNED, responsables de la investigación arqueológica en la zona de estudio.

Análisis de las capacidades de los sistemas Landsat y E01 para la actualización cartográfica. Estudio de un caso práctico.

Junto con el incremento de la resolución espacial, el desarrollo de las técnicas de interpretación multiespectrales e hiperespectrales es otro de los campos de investigación actual en teledetección. Es de suponer que una de las vías naturales de evolución de las plataformas espaciales será sin duda la incorporación de sensores de mayor resolución espectral. A partir de ahí se comenzará a sustituir el tradicional análisis multiespectral,basado en los datos de a lo sumo cinco o seis bandas, por el hiperespectral, que habrá de manejar datos de varios centenares de bandas simultáneamente. Ya existen satélites con sensores hiperespectrales en órbita, como Hyperion, montado sobre el satélite EO-1, el cual estudiamos en este proyecto. La detección de cambios, surge ante la necesidad de actualizar la cartografía de forma periódica. La evaluación de cambios producidos en el terreno se realiza manualmente y requiere de la supervisión por parte de un operador experto. Esto implica una importante inversión en tiempo, con su consecuente coste económico. Las imágenes satélite constituyen una valiosa fuente para estudiar los cambios que se producen en la superficie terrestre. En un ciclo productivo basado en imágenes numéricas, es de esperar que se ahorre una importante cantidad de trabajo introduciendo procedimientos de detección de cambios que se puedan implementar en procesos de carácter automático. Desde hace unas décadas, se están utilizando como fuentes de datos para diversos usos en detección de cambios, los sensores transportados en plataformas aeroespaciales. En resumen, el objetivo de éste proyecto es analizar los métodos de análisis multitemporal aplicados a imágenes de satélite, para lo cual se hará un estudio comparativo de las características de las imágenes proporcionadas por las plataformas Landsat y EO-1.Como resultado de ello, se obtendrá documentación cartográfica.

An universal system to de-orbit satellites at end of life

A 3-year Project financed by the European Commission is aimed at developing a universal system to de-orbit satellites at their end of life, as a fundamental contribution to limit the increase of debris in the Space environment. The operational system involves a conductive tapetether left bare to establish anodic contact with the ambient plasma as a giant Langmuir probe. The Project will size the three disparate dimensions of a tape for a selected de-orbit mission and determine scaling laws to allow system design for a general mission. Starting at the second year, mission selection is carried out while developing numerical codes to implement control laws on tether dynamics in/off the orbital plane; performing numerical simulations and plasma chamber measurements on tether-plasma interaction; and completing design of subsystems: electronejecting plasma contactor, power module, interface elements, deployment mechanism, and tether-tape/end-mass. This will be followed by subsystems manufacturing and by currentcollection, free-fall, and hypervelocity impact tests.

Drought estimation maps by means multidate landsat fused images

The purpose of this paper is to analyze the usefulness of traditional indexes, such as NDVI and NDWI along with a recently proposed index (NDDI) using merged data for multiple dates, with the aim of obtaining drought data to facilitate the analysis for government premises. In this study we have used Landsat 7 ETM+ data for the month of June (2001-2009), which merged to get bands with twice the resolution. The three previous indices were calculated from these new bands, getting in turn drought maps that can enhance the effectiveness of decision making.

Long-term dynamics of fast rotating tethers around planetary satellites

We derive a semi-analytic formulation that enables the study of the long-term dynamics of fast-rotating inert tethers around planetary satellites. These equations take into account the coupling between the translational and rotational motion, which has a non-negligible impact on the dynamics, as the orbital motion of the tether center of mass strongly depends on the tether plane of rotation and its spin rate, and vice-versa. We use these governing equations to explore the effects of this coupling on the dynamics, the lifetime of frozen orbits and the precession of the plane of rotation of the tether.

Magnetic Attitude Control for Satellites in Polar or Sun-Synchronous Orbits

In this work, a new law for magnetic control of satellites in near-polar orbits is presented. This law has been developed for the UMPSat-2 microsatellite, which has been designed and manufactured by Universidad Politécnica de Madrid, Madrid. The control law is a modification of the B-dot strategy that enables the satellite to control the rotation rate. Besides, the satellite?s equilibrium state is characterized by having the rotation axis perpendicular to the orbit?s plane. The control law described in the present work only needs magnetometers and magnetorquers, as sensors and actuators, respectively, to carry out a successful attitude control on the spacecraft. A description of the analysis is included. Performance and applicability of the proposed method have been demonstrated by control dynamics together with Monte Carlo techniques and by implementing the control law in the UPMSat-2 mission simulator. Results show good performance in terms of acquisition and stability of the satellite rotation rate and orientation with respect to its orbit?s plane.

Optimum sizing of bare-tape tethers for de-orbiting satellites at end of mission

De-orbiting satellites at end of mission would prevent generation of new space debris. A proposed de-orbit technology involves a bare conductive tape-tether, which uses neither propellant nor power supply while generating power for on-board use during de-orbiting. The present work shows how to select tape dimensions for a generic mission so as to satisfy requirements of very small tether-to-satellite mass ratio mt/MS and probability Nf of tether cut by small debris, while keeping de-orbit time tf short and product tf ×× tether length low to reduce maneuvers in avoiding collisions with large debris. Design is here discussed for particular missions (initial orbit of 720 km altitude and 63° and 92° inclinations, and 3 disparate MS values, 37.5, 375, and 3750 kg), proving it scalable. At mid-inclination and a mass-ratio of a few percent, de-orbit time takes about 2 weeks and Nf is a small fraction of 1%, with tape dimensions ranging from 1 to 6 cm, 10 to 54 μμm, and 2.8 to 8.6 km. Performance drop from middle to high inclination proved moderate: if allowing for twice as large mt/MS, increases are reduced to a factor of 4 in tf and a slight one in Nf, except for multi-ton satellites, somewhat more requiring because efficient orbital-motion-limited electron collection restricts tape-width values, resulting in tape length (slightly) increasing too.

Characterizing the satellites of massive galaxies up to z ∼ 2: young populations to build the outskirts of nearby massive galaxies

The accretion of minor satellites is currently proposed as the most likely mechanism to explain the significant size evolution of the massive galaxies during the last ∼10 Gyr. In this paper, we investigate the rest-frame colours and the average stellar ages of satellites found around massive galaxies (M_star ∼ 10^11 M_⊙) since z ∼ 2. We find that the satellites have bluer colours than their central galaxies. When exploring the stellar ages of the galaxies, we find that the satellites have similar ages to the massive galaxies that host them at high redshifts, while at lower redshifts they are, on average, ≳1.5 Gyr younger. If our satellite galaxies create the envelope of nearby massive galaxies, our results would be compatible with the idea that the outskirts of those galaxies are slightly younger, metal-poorer and with lower [α/Fe] abundance ratios than their inner regions.

Identification of geostationary satellites using polarization data from unresolved images

In order to protect critical military and commercial space assets, the United States Space Surveillance Network must have the ability to positively identify and characterize all space objects. Unfortunately, positive identification and characterization of space objects is a manual and labor intensive process today since even large telescopes cannot provide resolved images of most space objects. Since resolved images of geosynchronous satellites are not technically feasible with current technology, another method of distinguishing space objects was explored that exploits the polarization signature from unresolved images. The objective of this study was to collect and analyze visible-spectrum polarization data from unresolved images of geosynchronous satellites taken over various solar phase angles. Different collection geometries were used to evaluate the polarization contribution of solar arrays, thermal control materials, antennas, and the satellite bus as the solar phase angle changed. Since materials on space objects age due to the space environment, it was postulated that their polarization signature may change enough to allow discrimination of identical satellites launched at different times. The instrumentation used in this experiment was a United States Air Force Academy (USAFA) Department of Physics system that consists of a 20-inch Ritchey-Chrétien telescope and a dual focal plane optical train fed with a polarizing beam splitter. A rigorous calibration of the system was performed that included corrections for pixel bias, dark current, and response. Additionally, the two channel polarimeter was calibrated by experimentally determining the Mueller matrix for the system and relating image intensity at the two cameras to Stokes parameters S0 and S1. After the system calibration, polarization data was collected during three nights on eight geosynchronous satellites built by various manufacturers and launched several years apart. Three pairs of the eight satellites were identical buses to determine if identical buses could be correctly differentiated. When Stokes parameters were plotted against time and solar phase angle, the data indicates that there were distinguishing features in S0 (total intensity) and S1 (linear polarization) that may lead to positive identification or classification of each satellite.

Procedures for analyzing data obtained from LANDSAT multispectral imagery /

Thesis (M. S.)--University of Illinois at Urbana-Champaign.

Etude sur le système solaire; nouvelle loi des distances des planètes et des satellites,

Mode of access: Internet.