Force sensitivity of plant gravisensing.

Rotation at 4, 10, 50 and 100 rpm on a horizontal clinostat and in microgravity exerts limited effects on the morphogenesis of lettuce and cress root statocytes and statoliths if compared with the vertical control or 1 g spaceflight reference centrifuge. However, the average distance of statoliths from the distal wall increases. The pattern of plastid location of microgravity-grown and that of clino-rotated samples has been determined at 10, 50, and 100 rpm. Experiments on the centrifuge-clinostat and spaceflight centrifuge (acceleration forces of 0.005 to 1 g) revealed that the average statolith location depends on the amplitude of acropetally or basipetally directed mass acceleration. Decreasing the acropetally directed force from 1 g to 0.4 g dislocates statoliths towards the cell center possibly mediated by the elastic forces of the cytoskeleton. In statocytes formed on the clinostat or in microgravity, the majority of statoliths are located at the center of the cell. To force the statoliths from the center of the statocyte towards one of its poles, a threshold mass acceleration of 0.01 g is required. Statocytes with centrally-located statoliths are considerably more effective in transducing a gravistimulus than those with distally-located plastids. The latent time of the graviresponse is shorter and the response itself is enhanced in roots grown on the clinostat compared to vertically grown samples. The early phases of graviperception are independent of root growth conditions since presentation time and g-threshold are similar for roots grown stationary and those on a clinostat. We propose a sequence of events in gravitropic stimulation that considers not only the lateral displacement of statoliths, as predicted by the starch-statolith hypothesis, but also its longitudinal motion, together with differential gravisensitivity of mechanotransducing structures along the lower-most longitudinal cell wall.     

SIGMA observations of two new hard X-ray and soft gamma-ray transients: GX 354-0 and Nova Persei

We report the first detection of two soft gamma ray transients GX 354-0 and Nova Persei (GRO J0422+32) by the coded-mask telescope SIGMA. Only preliminary results are presented with regard to Nova Persei while special emphasis is given to the data on GX 354-0 which has been monitored during the 1992 February–April survey of the Galactic Center. GX 354-0 underwent two flares of about two week duration and its average spectrum is well described by a thermal Bremsstrahlung model or a broken power law whereas the Nova Persei spectrum seems to be similar to the one observed for GRS 1124-684 in Musca.     

Observations of stars with the Hopkins Ultraviolet Telescope

The Hopkins Ultraviolet Telescope (HUT) was flown aboard the space shuttle Columbia as part of the Astro-1 mission during December 1990. During the nine-day flight, HUT carried out 3 Å resolution spectrophotometry of a wide variety of astronomical objects, including a number of stellar targets, in the 912–1860 Å range of the far ultraviolet. A few nearby stars were observed in the 415–912 Å range of the extreme ultraviolet as well. For nearly all of these targets, the spectra obtained by HUT are the first ever obtained in the spectroscopically rich region between Lyman (1216 Å) and the Lyman limit (912 Å). Here, we present highlights of the results obtained by HUT in a variety of areas of stellar astronomy.     

Periodic components in Cyg X-3

Hard X-ray observations of Cyg X-3 in the energy range 20–100 keV were made with a Balloon-borne telescope using two large area proportional counters. The source was seen with a total significance of 20.

A 121 s periodicity was seen during Fourier analysis of the data. The phenomenon can be interpreted as due to transient pulsation since no other peak was seen in our data. Quasi-periodic oscillation in the range 0.06–20 mHz have been observed from Cyg X-3 at lower energies. Interestingly, most of the reported periods are multiple of the present measurements. The observed pulsation at high energies indicate the occasional unstable behaviour of the inner parts of the accretion disk connected with the basic rotation period of the compact object.

The 4.8^h modulation, characteristic of the orbital period of the binary system was seen in the data, with a broad maximum between the phase 0.3 to 0.7.     

An Optimally Integrated Track Recovery System for Aerial Bathymetry

An airborne system has been developed for charting shallow coastal and inland waters. The primary components of this system are an aerial survey camera, a profiling laser radar, an analytical stereo plotter, and a multisensor track recovery system (TRS). The TRS comprises a gimbaled inertial navigation system and a number of auxiliary sensors which acquire redundant position and attitude information. The sensor data are combined postmission using a U-D factorized Kalman filter and modified Bryson-Frazier smoother to compute accurate estimates of the orientation parameters of the survey camera at the times of film exposure. These parameters are used to position each overlapping pair of photographs on the analytical plotter to form a stereo image and corresonding analytical stereomodel from which water depth measurements are made. Flight trial results demonstrate that the TRS can achieve radial position and attitude accuracies which exceed 1 m and 2 arcmin root mean square (rms), respectively, and that this level of performance is sufficient to enable water depth measurements to be made to an accuracy of better than 0.65 m (rms).     

Space Station atmospheric monitoring systems.

A technology assessment study on atmospheric monitoring systems was performed by Battelle Columbus Division for the National Aeronautics and Space Administration's John F. Kennedy Space Center under Contract No. NAS 10-11033. In this assessment, the objective was to identify, analyze, and recommend systems to sample and measure Space Station atmospheric contaminants and identify where additional research and technology advancements were required. To achieve this objective, it was necessary to define atmospheric monitoring requirements and to assess the state of the art and advanced technology and systems for technical and operational compatibility with monitoring goals. Three technical tasks were defined to support these needs: Definition of Monitoring Requirements, Assessment of Sampling and Analytical Technology, and Technology Screening and Recommendations. Based on the analysis, the principal candidates recommended for development at the Space Station's initial operational capability were: (1) long-path Fourier transform infrared for rapid detection of high-risk contamination incidences, and (2) gas chromatography/mass spectrometry utilizing mass selective detection (or ion-trap) technologies for detailed monitoring of extended crew exposure to low level (ppbv) contamination. The development of a gas chromatography/mass spectrometry/matrix isolation-Fourier transform infrared system was recommended as part of the long range program of upgrading Space Station trace-contaminant monitoring needs.     

Design for testability for future digital avionics systems

The authors describe an integrated testing approach called the Maintenance and Diagnostic System (MADS), which was developed for digital avionics systems using VHSIC and semicustom devices. Mission/operational requirements dictate high availability with capability to detect 98% of all faults and isolate 90% of these faults to a line replacement module (LRM) or 95% of the faults to two LRMs. MADS achieves these goals by defining a module maintenance node (MMN) chip set for each LRM in the system and the design for testability concepts for hardware. The MMN aids parallel, high-speed testing of LRMs, isolating the fault(s) to a module/chip level while incurring less than 10% overhead. It uses the concepts of scan set design, pseudorandom test vector generation, output response compression, and separate scan set loops to test the SSI-MSI logic on the LRM. It also stores interim test results and run-time fault information to isolate the hard-to-reproduce failures and performs verification of interchip and intermodule wiring     

Computational Precision Requirements for Optimal Weights in Adaptive Processing

The required accuracy for computing the estimated optimum weights of an adaptive processor has been analyzed by investigating the effects of errors in computing the inverse matrix. It is shown that the required precision depends upon the matrix. An equation for the general case is derived. Several special cases are considered in detail. It is shown that the case of a single interference source requires the highest precision. The least stressing case is identifi'ed and compared to the worst case. The requirements for a "typical" case are also considered. A comparison of the requirements for the covariance matrix estimation technique and for adaptive weight implementation using gradient descent techniques is given. It is shown that there is a dichotomy in that cases that do not stress one technique tend to stress the other.     

The Circular Synthetic Radar

A new type of synthetic radar, the circular synthetic radar, uses a simple interferometer whose elements are mounted at the ends of a horizontal boom rotating about a vertical mast. Pulses are radiated alternately ?in-phase? and in ?phase-quadrature.? The returning echoes are also detected incoherently, both ?in-phase? and in ?phase-quadrature.? The four distinct outputs are fed into an on-line computer which, after a Fourier analysis, synthesizes a mapping function of the azimuthal distribution of targets.     

Activity Planning for the Space Station

This paper presents an overview of the identification and selection process of experiments and payloads for manned space flight missions, emphasizing the scope and magnitude of the problem of doing activity planning and the need for a methodology to assure timely flight and appropriate spacecraft design. Conclusions and results derived from the past several years are presented together with an analysis of the current procedure for defining activity for the space station.