Public support for Mars missions: The importance of informing the next generation

This paper explores and compares the perceptions of the risks associated with Mars Sample Return (MSR) among schoolchildren and adults. Comparable surveys were constructed and administered to two sample groups; science students aged 11–15 and adults with an interest in science aged 18 and over. Contingency table analyses were used to quantify any differences in perception between the two groups. Schoolchildren were less likely to consider Mars exploration to be quite or very useful (44.7% vs. 68.9%; p=0.005) and recorded significantly higher levels of risk perception regarding both a MSR mission and also towards other societal risks. These results have important implications for policy-makers, as they can inform education programs now that will enhance the viability and public support for future missions.     

Changes in gravitational force induce alterations in gene expression that can be monitored in the live, developing zebrafish heart.

Little is known about the effect of microgravity on gene expression, particularly in vivo during embryonic development. Using transgenic zebrafish that express the gfp gene under the influence of a beta-actin promoter, we examined the affect of simulated-microgravity on GFP expression in the heart. Zebrafish embryos, at the 18-20 somite-stage, were exposed to simulated-microgravity for 24 hours. The intensity of GFP fluorescence associated with the heart was then determined using fluorescence microscopy. Our measurements indicated that simulated-microgravity induced a 23.9% increase in GFP-associated fluorescence in the heart. In contrast, the caudal notochord showed a 17.5% increase and the embryo as a whole showed only an 8.5% increase in GFP-associated fluorescence. This suggests that there are specific effects on the heart causing the more dramatic increase. These studies indicate that microgravity can influence gene expression and demonstrate the usefulness of this in vivo model of 'reporter-gene' expression for studying the effects of microgravity.     

Aircraft flight parameter estimation using acoustical Lloyd'smirror effect

A model is developed for the acoustical Lloyd's mirror effect observed in the output time-frequency distribution of a microphone located near the ground during the transit of a jet aircraft. The feasibility of using this effect for flight parameter estimation is assessed by a simple Cramer-Rao lower bound analysis. The nonlinear least-squares method and the generalized Hough transform method are formulated for flight parameter estimation. The performances of both methods are evaluated and compared using real acoustic data     

Flight path estimation using frequency measurements from a wideaperture acoustic array

A narrowband technique based on the acoustical Doppler effect is proposed for estimating the trajectory of a turbo-prop aircraft in level flight with constant velocity as it transits over a ground-based passive acoustic sensor array. The basic principle is to measure the temporal variation of the instantaneous frequency (IF) of the acoustic signal received by each sensor and then to minimize the sum of the squared deviations of the IF estimates from their predicted values over a sufficiently long period of time for all sensors. The technique provides estimates of the propeller blade rate and the five source motion parameters that describe the aircraft trajectory. The six dimensional minimization problem is reduced to a five dimensional maximization problem, which is solved numerically using the quasi-Newton method. A simple method is described that provides the initial parameter estimates required for the numerical maximization. The effectiveness of the motion parameter estimation technique is verified using real acoustic data recorded from a wide aperture microphone array during various transits of a turbo-prop aircraft     

The Modelling of Background Noise in Astronomical Gamma Ray Telescopes

Gamma ray photons interact with matter through a wide variety of complex physical mechanisms, which can be readily imitated by other particle processes. Unfortunately since γ-ray telescopes are obliged to function in a hostile radiation environment above the earth's atmosphere the net result is low signal to noise observations and a corresponding loss in sensitivity. Consequently, understanding the generation of the systematic background noise is crucial if the full performance of a γ-ray instrument is to be realised. In the past it was not possible to reliably estimate the background levels in a fully quantitative manner; semi-empirical methods were employed. Although the basic underlying sources of the background noise were reasonably well understood, and the spectral intensities of the associated particles were reasonably well known, it was not possible to associate resultant noise components with the input source of that noise with any real degree of accuracy. The advent of sophisticated and accurate computer programmes capable of dependably representing the requisite particle physics processes and interactions coupled with the advances made in the context of high power/low cost computers has revolutionised the situation. The so-called ‘mass modelling’ technique is a truly physics-based approach, which takes the input particle spectra of the local radiation environment together with a computer representation of the mechanical structure and chemical composition of the instrumentation and associated spacecraft to trace the trajectories and interactions of all the incident particles throughout the system. All energy deposits from the various interactions and likewise those from the prompt and delayed secondary products are also accurately recorded. Subsequent energy discriminators and time coincidences can be applied to the event arrays with additional software to simulate on-board electronics systems. Internal spectral counting rates may be readily derived and analysed in terms of a wide variety of desired purposes. The impact of an accurate physics-based mass modelling technique has been to expand application of the procedure to effectively all the main aspects of a space γ-ray astronomy mission: instrument design; internal counting rates and spectral sensitivity estimates; optimisation of the design of the on-board processing electronics; operational planning and mission optimisation; estimation of radiation damage and its limitation; calibration planning and interpretation; the production of accurate instrumental response matrices; data analysis software; normalisation of astronomical results across instrument and instrumental degradation boundaries; and data archiving. This revised version was published online in June 2006 with corrections to the Cover Date.     

Broadband passive acoustic technique for target motion parameterestimation

A nonlinear least-squares method is formulated to estimate the motion parameters of a target whose broadband acoustic energy emissions are received by a ground-based array of sensors. This passive technique is applied to real acoustic sensor data recorded during the passage of a variety of ground vehicles past a planar cross array and its effectiveness verified by comparing the results with the actual values of the target motion parameters. The technique cam also be applied to airborne targets     

Cosmic dust analog simulation in a microgravity environment: the STARDUST program.

We have undertaken a project called STARDUST which is a collaboration with Italian and American investigators. The goals of this program are to study the condensation and coagulation of refractory materials from the vapor and to study the properties of the resulting grains as analogs to cosmic dust particles. To reduce thermal convective currents and to develop valuable experience in designing an experiment for the Gas-Grain Simulation Facility aboard Space Station Freedom we have built and flown a new chamber to study these processes under periods of microgravity available on NASA's KC-135 Research Aircraft. Preliminary results from flights with magnesium and zinc are discussed.     

Aircraft flight parameter estimation using acoustic multipath delays

The signal emitted by an airborne acoustic source arrives at a stationary sensor located above a flat ground via a direct path and a ground-reflected path. The difference in the times of arrival of the direct path and ground-reflected path signal components, referred to as the multipath delay, provides an instantaneous estimate of the elevation angle of the source. A model is developed to predict the variation with time of the multipath delay for a jet aircraft or other broadband acoustic source in level flight with constant velocity over a hard ground. Based on this model, two methods are formulated to estimate the speed and altitude of the aircraft Both methods require the estimation of the multipath delay as a function of time. The methods differ only in the way the multipath delay is estimated; the first method uses the autocorrelation function, and the second uses the cepstrum, of the sensor output over a short time interval. The performances of both methods are evaluated and compared using real acoustic data. The second method provides the most precise aircraft speed and altitude estimates as compared with the first and two other existing methods.     

A comparison of radiation shielding effectiveness of materials for highly elliptical orbits

The Canadian Space Agency (CSA) has proposed a Polar Communications and Weather (PCW) satellite mission, in conjunction with other partners. The PCW will provide essential communications and meteorological services to the Canadian Arctic, as well as space weather observations of in situ ionizing radiation along the orbit. The CSA has identified three potential Highly Elliptical Orbits (HEOs) for a PCW satellite constellation, Molniya, Modified Tundra and Triple Apogee (TAP), each having specific merits, which would directly benefit the performance/longevity of a PCW spacecraft. Radiation shielding effectiveness of various materials was studied for the three PCW orbit options to determine the feasibility of employing materials other than conventional aluminium to achieve a specified spacecraft shielding level with weight savings over aluminium. It was found that, depending on the orbit-specific radiation environment characteristics, the benefits of using polyethylene based materials is significant enough (e.g., 22% in Molniya for PE at 50 krad TID) to merit further investigation.     

Automatic detection and tracking of a small surface watercraft in shallow water using a high-frequency active sonar

A high-frequency (HF) active sonar can be used to detect and track a small fast surface watercraft in shallow water based on the evolution of the watercraft wake observed in the sonar image sequence. An automatic detection and tracking (ADT) algorithm is described for this novel application. For each ping, the measurement of the target's polar position consists of 2 steps. First, the target bearing is estimated by finding the direction of arrival of the cavitation noise emitted by the watercraft. Then range measurements are extracted from the range profile (constant-angle cut of the sonar image) at the estimated target bearing. Range normalization and clutter map processing are used to reduce the number of false measurements. Estimates of the target's Cartesian position and velocity are updated at the sonar pulse repetition rate using the Kalman filter with debiased consistent converted measurements and nearest neighbour data association. The proposed algorithm is demonstrated using real data.