Exobiology research on Space Station Freedom.

The Gas-Grain Simulation Facility (GGSF) is a multidisciplinary experiment laboratory being developed by NASA at Ames Research Center for delivery to Space Station Freedom in 1998. This facility will employ the low-gravity environment of the Space Station to enable aerosol experiments of much longer duration than is possible in any ground-based laboratory. Studies of fractal aggregates that are impossible to sustain on Earth will also be enabled. Three research areas within exobiology that will benefit from the GGSF are described here. An analysis of the needs of this research and of other suggested experiments has produced a list of science requirements which the facility design must accommodate. A GGSF design concept developed in the first stage of flight hardware development to meet these requirements is also described.     

Interacting acceleration compensation algorithm for trackingmaneuvering targets

The two-stage Kalman estimator has been studied for state estimation in the presence of random bias and applied to the tracking of maneuvering targets by treating the target acceleration as a bias vector. Since the target acceleration is considered a bias, the first stage contains a constant velocity motion model and estimates the target position and velocity, while the second stage estimates the target acceleration when a maneuver is detected, the acceleration estimate is used to correct the estimates of the first stage. The interacting acceleration compensation (IAC) algorithm is proposed to overcome the requirement of explicit maneuver detection of the two-stage estimator. The IAC algorithm is viewed as a two-stage estimator having two acceleration models: the zero acceleration of the constant velocity model and a constant acceleration model. The interacting multiple model (IMM) algorithm is used to compute the acceleration estimates that compensate the estimate of the constant velocity filter. Simulation results indicate the tracking performance of the IAC algorithm approaches that of a comparative IMM algorithm while requiring approximately 50% of the computations     

A study of volume versus frequency for soft switching IGBTconverters

Earlier references have described a new soft switched ZVS/ZCS (zero voltage switching, zero current switching) converter for IGBTs that allows operation above 20 kHz. Although frequencies above 20 kHz are now possible for IGBT converters, the optimum frequency for minimum volume may be below 20 kHz because of heat sink requirements. A comparative study considers the reactive component versus heat sink volume tradeoff for two 6 kW converters, one using ZVS/ZCS and the other using a more conventional circuit with hard switching     

Space education policy — a global imperative

The discoveries and knowledge gained from space exploration and technology development are valuable scientific education tools which are not being adequately used in the classroom. Moreover, the increasing application of space technology to everyday life and industry requires a work force educated to be able to work productively in this field and to take advantage of all it has to offer. This article provides a survey of what is presently being done in the field of space education in Europe and the USA. Although encouraging, it is not nearly enough to meet the needs of 21st century society, principally because current efforts lack government or industry support. The author argues that this state of affairs must change, and proposed an international symposium as a first step towards this goal.     

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     

Field-aligned expansion of plasma clouds in the ionosphere

The field-aligned expansion of plasma clouds in the ionosphere was studied with different mathematical models and for a wide range of conditions. In all cases, the expanding plasma cloud acted as an electrostatic snowplow, creating an O⁺ hole in the ionosphere coincident with the cloud and O⁺ bumps on the two sides of the cloud that are aligned with the geomagnetic field.     

Where does human factors fit in R&D organizations?

It is argued that human factors professionals in large R&D organizations should have a centralized human factors group (or department) with a manager sensitive to human factors organizational issues. This arrangement permits these professionals to maximize their contributions to the design, development, and testing of a product or service. Managers of human factors groups and departments can help educated project managers about the value of human factors. Human factors groups, departments, and managers provide benefits to the company by resolving project conflicts concerning user-oriented designs. They help foster a sense of a behavioral sciences community within the R&D organization and aid in recruiting job candidates. They are good for the product or service, the company, and the human factors profession     

Resolution of a 2π ambiguity problem in multiple frequencyspectral estimation

An algorithm is proposed to resolve a fundamental 2π ambiguity problem occurring in multiple frequency spectral estimation. Given M frequencies f_m, and I separate frequency estimators with unambiguous bandwidths F_i, the ambiguity problem can be stated as solving for the fm, given the estimator outputs, α_mi, (1⩽m⩽M;1⩽i⩽I) where f_m=α_mi+K_miF_i and K_mi is some integer. The proposed algorithm exhaustively resolves all possible α_mi groupings into single frequency values using a noise insensitive technique that exchanges system bandwidth for noise protection. The correct multiple frequencies are then defined as the single frequencies that repeat a specified number of times. A complete analysis is included     

Coherent detection in Laplace noise

The discrete-time detection of a time-varying, additive signal in independent Laplace noise is considered. Previous efforts in this area have been restricted to the constant signal, and identically distributed noise case. Theoretical (closed form) expressions for the false alarm and detection probabilities are developed for both the Neyman-Pearson optimal detector and the classical matched filter detector. Comparisons between the two detectors are made which illustrate the effects of signal-to-noise power ratio and sample size for certain false alarm and detection probability constraints. In view of the fact that the optimal Laplace detector is not UMP, we also investigate the effect of signal amplitude mismatch