Power optimal single-axis articulating strategies

Power optimal single axis articulating PV array motion for Space Station Freedom is investigated. The motivation is to eliminate one of the articular joints to reduce Station costs. Optimal (maximum power) Beta tracking is addressed for local vertical local horizontal (LVLH) and non-LVLH attitudes. Effects of intra-array shadowing are also presented. Maximum power availability while Beta tracking is compared to full sun tracking and optimal alpha tracking. The results are quantified in orbital and yearly minimum, maximum, and average values of power availability

SOYUZ escape trajectory analysis from Space Station Freedom

It has been proposed to utilize the Russian built SOYUZ as an assured crew return vehicle (ACRV) for Space Station Freedom. Three departure directions (nadir, zenith, minus velocity) are evaluated to determine escape path clearances. In addition, the effects of the following parameters were also evaluated: delta-V magnitude, configuration dependent ballistic coefficients, atmospheric density, Freedom attitude control, and canted docking adaptors. The primary factor influencing the escape trajectory was station contingency attitude rate. The nadir and zenith departures were preferable to minus velocity. The impact of atmospheric density and relative ballistic coefficients was minimal

Modelamento netrosférico aumentado para a determinação de campos de vapor d’água atmosféricos com base em sinais de alta resolução gnss

Signals of global navigation satellite systems (GNSS) are delayed by propagatingthrough the Earth’s electrically neutral atmosphere. This delay term plays animportant role in GNSS positioning and has been taken into account in highprecisiongeodetic applications. The neutrospheric delay can be subdivided into adry and a complementary wet component. The wet component amounts to typicallyless than 10% of the total neutrospheric delay and can be used to determine highresolutionatmospheric water vapour fields based on extended neutrosphericmodelling. The approach outlined in the present paper combines empiricalneutrospheric a priori model, site-specific neutrosphere parameters and residuals ofGNSS phase observations. Using so-called single-layer models, the derivedatmospheric water vapour fields are two-dimensionally reconstructed andvisualised. Applying this extended neutrospheric model to generate water vapourfields within a regional GNSS network, the results indicate that both the temporaland the spatial resolution of the determined water vapour fields are improved incomparison to the conventional neutrospheric modelling.Os sinais oriundos dos sistemas de navegação globais por satélite (GNSS) sofremum atraso durante sua propagação através da camada eletricamente neutra daatmosfera terrestre. Este atraso tem um papel fundamental no posicionamentoGNSS e tem sido levado em conta nas aplicações geodésicas de alta precisão. Oatraso neutrosférico pode ser subdividido em uma componente seca e umacomponente complementar úmida. A quantidade correspondente a componenteúmida é tipicamente inferior a 10% do atraso total, e pode ser utilizada nadeterminação de campos de vapor d’água atmosférico de alta resolução baseados nomodelo aumentado da neutrosfera. A abordagem apresentada neste trabalhocombina um modelo a priori empirico, parâmetros neutrosféricos específicos daestação e resíduos das observações de fase GNSS. Utilizando os chamados modelosde camada única, os campos de vapor d’água atmosférico derivados sãoreconstruídos e visualizados, ambos em duas dimensões. Utilizando este modeloneutrosférico aumentado na geração de campos de vapor d’água dentro de uma rederegional GNSS, os resultados indicam uma melhora tanto na resolução temporalquanto na espacial dos campos de vapor d’água determinados, quando comparadoscom a modelagem neutrosférica convencional

IMPACT OF VARIOUS FACTORS ON THE QUALITY OF SITE-SPECIFIC NEUTROSPHERIC PARAMETERS WITHIN GNSS DATA PROCESSING: A CASE STUDY

Os atrasos na propagação dos sinais dos sistemas de navegação globais por satélite (GNSS), causados pela atmosfera neutra, são importantes fatores que limitam a acurácia de aplicações geodésicas precisas. Uma abordagem comum para tratar o atraso neutrosférico é estimar os chamados parâmetros neutrosféricos específicos da estação (SSNP – site-specific neutrospheric parameters) no processamento de dados GNSS, os quais são, então, combinados com valores de um modelo predito calculados principalmente utilizando dados meteorológicos. Portanto, a qualidade do atraso neutrosférico determinado depende não somente dos efeitos que atuam nos sinais GNSS, mas também da estratégia utilizada no processamento dos dados. Neste trabalho, as influências dos fatores que afetam a modelagem neutrosférica como: o comprimento da linha de base, multicaminho, ponderação do peso das observações, resolução das ambigüidades e o modelo de predição neutrosférica, são analisados e quantificados baseando-se nos desvios-padrão dos SSNP estimados. Além disso, um modelo melhorado para a ponderação dos pesos das observações, baseado nas medidas de potência da razão sinal-ruído, é brevemente descrito. Os resultados apresentados nos testes indicam que a aplicação deste avançado modelo de ponderação dos pesos no processamento de dados GNSS, incluindo observações com baixa elevação, pode melhorar os desvios-padrão dos SSNP estimados em torno de 25% comparado com o modelo padrão de ponderação dos pesos dependente de elevação.Propagation delays of the signals of global navigation satellite systems (GNSS) caused by the neutral atmosphere are an important accuracy-limiting factor for precise geodetic applications. A common approach to handle the neutrospheric delay is to estimate so-called site-specific neutrospheric parameters (SSNP) within GNSS data processing which are then combined with the predicted model values calculated primarily based on meteorological data. Therefore, the quality of the determined neutrospheric delay depends not only on the factors impacting the GNSS signals but also on data processing strategies. In this paper, the influence of the factors impacting neutrospheric modelling such as baseline length, multipath, observation weighting, ambiguity resolution, and neutrospheric prediction models are analysed and quantified based on the standard deviations of the estimated SSNP. Additionally, an improved observation weighting scheme based on signal-to-noise power ratio measurements is briefly described. Test results indicate that applying this advanced weight model within GNSS data processing, including observations at low elevation, the standard deviation of the estimated SSNP can be improved by nearly 25% compared with the standard elevation-dependent weighting model

Ultrashort Q-switched pulses from a passively mode-locked distributed Bragg reflector semiconductor laser

A compact semiconductor mode-locked laser (MLL) is presented that demonstrates strong passive Q-switched mode-locking over a wide range of drive conditions. The Q-switched frequency is tunable between 1 and 4 GHz for mode-locked pulses widths around 3.5 ps. The maximum ratio of peak to average power of the pulse-train is >120, greatly exceeding that of similarly sized passively MLLs

Spacecraft attitude control momentum requirements analysis

The relationship between attitude and angular momentum control requirements is derived for a fixed attitude, Earth orbiting spacecraft with large area articulating appendages. Environmental effects such as gravity gradient, solar radiation pressure, and aerodynamic forces arising from a dynamic, rotating atmosphere are examined. It is shown that, in general, each environmental effect contributes to both cyclic and secular momentum requirements both within and perpendicular to the orbit plane. The gyroscopic contribution to the angular momentum control requirements resulting from a rotating, Earth oriented spacecraft is also discussed. Special conditions are described where one or more components of the angular momentum can be made to vanish, or become purely cyclical. Computer generated plots for a candidate space station configuration are presented to supplement the analytically derived results

Investigation of various excitation and detection schemes of stored ions in a Penning trap

Mit einem breitbandigem Fourier-Transformation Ionen-Zyklotron-Resonanz (FT-IZR) Massenspektrometer kann die Masse von Atomen und Molekülen in einem Bereich von einer bis hin zu einigen tausend atomaren Masseneinheiten bestimmt werden. Die Masse kann innerhalb einer kurzen Zeitdauer von ungefähr einer Sekunde mit einer Präzision von ca. 1ppm gemessen werden. Weiterhin können auch Ionensorten mit einer geringen Häufigkeit ab einigen tausend Ionen detektiert werden. In dieser Arbeit wird der Aufbau und die Charakterisierung eines FT-IZR Massenspektrometers präsentiert, welches am Max-Planck-Insitut für Kernphysik in Heidelberg installiert ist. Das Massenspektrometer ist gezielt konstruiert um grundlegende Untersuchungen zu Detektions- und Anregungsschemata durchzuführen. Dazu wurde ein neues FT-ICR Detektionssystem erfolgreich aufgebaut. Es werden Untersuchungen zur Wechselwirkung von Ein- und Zwei-Puls Quadrupol-Anregungsfeldern mit Lithium-Ionen präsentiert. Da für den Nachweis viele Ionen notwendig sind, spielen Coulombwechselwirkungen zwischen den gespeicherten Ionen eine bedeutende Rolle. Die beobachteten Phänomene, wie Abschirmung von Anregungsfeldern und Ion-Ion-Wechselwirkung, werden diskutiert. Um diese Effekte qualitativ zu verstehen, wurden Vielteilchensimulationen durchgeführt. Weiterhin wurde die Genauigkeit und Präzision des Massenspektrometers aus Frequenzverhältnismessungen bestimmt