Thermal/structural design verification strategies for large space structures

Requirements for space structures of increasing size, complexity, and precision have engendered a search for thermal design verification methods that do not impose unreasonable costs, that fit within the capabilities of existing facilities, and that still adequately reduce technical risk. This requires a combination of analytical and testing methods. This requires two approaches. The first is to limit thermal testing to sub-elements of the total system only in a compact configuration (i.e., not fully deployed). The second approach is to use a simplified environment to correlate analytical models with test results. These models can then be used to predict flight performance. In practice, a combination of these approaches is needed to verify the thermal/structural design of future very large space systems

Low Cost Detection of Lasers

A low-cost method of detecting lasers based on detecting coherence properties of received light is presented. The method uses an unbalanced Mach–Zehnder interferometer with a modulating piezo-mounted mirror in one arm to discriminate against incoherent background light and identify the presence of laser radiation at the nW level against much brighter backgrounds. The wavelength of the coherent input can be determined by comparing the intensities of the modulation frequency harmonics

A Proposed Method for a Photon-counting Laser Coherence Detection System to Complement Optical SETI

The detection of laser radiation originating from space is a positive indicator of Extra Terrestrial Intelligence (ETI).Thus far, the optical search for ETI (OSETI) has looked for enhanced brightness in the form of either narrow-band spectral emission or time correlated photons from laser pulses. In this paper, it is proposed to look for coherence properties of incoming light in a manner that can distinguish against atomic emission lines. The use of photonsensitive detectors and a modulating asymmetric interferometer has been modeled. The results suggest that the sensitivity of detection for continuous laser sources would be better than current spectroscopic approaches, with detection thresholds of <1 photon s−1 m−2 against a background with a spectral bandwidth of 0.1 nm over an observation time of 750 s

Multiple beam steering using dynamic zone plates on a micromirror array

Three dimensional laser beam steering of focal position has been demonstrated using a single optical device – a DMD micro-mirror array. Laser beam focus position is controlled using dynamically adjustable zone plates. These zone plates take the form of elliptical Fresnel zone plates or other variations such as binary Gabor zone plates. Active beam pointing and control can be realised without the need for a pair of galvanometer mirrors and a focusing lens. Focussing efficiencies into an off-axis diffraction order of a few percent are typically seen and continuity between neighbouring orders increase the effective field of regard. Writing multiple zone plate patterns to the DMD enables multiple focussed spots to be generated and controlled independently

Non-mechanical beam steering: ways and means

One of the very useful aspects of a laser is its well-defined beam, delivering high intensity to a defined location. Directing that beam and specifying the location is generally done with adjustable mirrors. Directing the beam in time varying manner most often requires galvanometer scanning mirrors which translate in one dimension. These mirrors, though now a mature technology, are in general speed limited due to their inertia and can be heavy, power hungry and expensive. There are then benefits to be gained from non-mechanical means of beam steering particularly in terms of speed and weight. This paper gives an overview of methods employed to implement beam steering and then concentrates on methods that do not rely on independent phase control. The use of a micromirror array for 3-dimensional beam control will be presented with the pros and cons that this entails

Photonic processing for wideband cancellation and spectral discrimination of RF signals

Photonic signal processing is used to implement common mode signal cancellation across a very wide bandwidth utilising phase modulation of radio frequency (RF) signals onto a narrow linewidth laser carrier. RF spectra were observed using narrow-band, tunable optical filtering using a scanning Fabry Perot etalon. Thus functions conventionally performed using digital signal processing techniques in the electronic domain have been replaced by analog techniques in the photonic domain. This technique was able to observe simultaneous cancellation of signals across a bandwidth of 1400 MHz, limited only by the free spectral range of the etalon

\u3cem\u3eThe Meaning of the Moment\u3c/em\u3e: A Collection of Short Stories.

This thesis consists of three short stories in very different genres but tied together by a intensely personal look at the lives of its protagonists culminating in epiphanies. One of these epiphanies is intended solely for the reader, but in two cases, the reader and character gains the insight. “The Tears of Angels” looks at the effect one person in a moment, even a stranger, can have on the protagonist’s life. “Climbing Heaven and Gazing on Earth” focuses on the haunting power of history and the need we as humans can feel to share a story, to make sense of it, no matter how personal. In “To Set It Right,” I take history in a different direction, giving it a voice and a power to reach from the past. In all of the stories, the epiphanies serve to point towards meaning and enlightenment in different way

Citizenship education in England 2001-2010 : young people's practices and prospects for the future : the eighth and final report from the Citizenship Education Longitudinal Study (CELS)

On the one hand, there has been a marked and steady increase in young people’s civic and political participation and indications that these young people will continue to participate as adult citizens. In contrast, there has been a hardening of attitudes toward equality and society, a weakening of attachment to communities and fluctuating levels of engagement, efficacy and trust in the political arena. The factors that shape young people’s citizenship outcomes include age and life-stage, background factors, prior citizenship outcomes, as well as levels of ‘received’ citizenship education