Microprocessor-Controlled Digital Shunt Regulator

A new approach to the design of power systems is presented in which a microprocessor is used as a controller for a digital shunt regulator (DSR). This approach meets the demands of future space and ground missions, i. e., high efficiency, high reliability, low weight, low volume, increased flexibility, and less development time. This approach responds to future demands by permitting realtime modification of system parameters for system optimization. This feature is especially important in the event of an anomaly. As the microprocessor need not be dedicated to the DSR, it can simultaneously be used for battery management and for charge regulator/discharge regulator control. This approach also reduces the component count, simplifies assembly and testing of the unit, results in significant time saving, and increases the reliability.     

Polar format algorithm for bistatic SAR

Matched filtering (MF) of phase history data is a mathematically ideal but computationally expensive approach to bistatic synthetic aperture radar (SAR) image formation. Fast backprojection algorithms (BPAs) for image formation have recently been shown to give improved O(N/sup 2/ log/sub 2/N) performance. An O(N/sup 2/ log/sub 2/N) bistatic polar format algorithm (PFA) based on a bistatic far-field assumption is derived. This algorithm is a generalization of the popular PFA for monostatic SAR image formation and is highly amenable to implementation with existing monostatic image formation processors. Limits on the size of an imaged scene, analogous to those in monostatic systems, are derived for the bistatic PFA.     

The Galileo Probe Atmosphere Structure instrument

The Galileo Probe Atmosphere Structure Instrument will make in-situ measurements of the temperature and pressure profiles of the atmosphere of Jupiter, starting at about 10^-10 bar level, when the Probe enters the upper atmosphere at a velocity of 48 km s^-1, and continuing through its parachute descent to the 16 bar level. The data should make possible a number of inferences relative to atmospheric and cloud physical processes, cloud location and internal state, and dynamics of the atmosphere. For example, atmospheric stability should be defined, from which the convective or stratified nature of the atmosphere at levels surveyed should be determined and characterized, as well as the presence of turbulence and/or gravity waves. Because this is a rare opportunity, sensors have been selected and evaluated with great care, making use of prior experience at Mars and Venus, but with an eye to special problems which could arise in the Jupiter environment. The temperature sensors are similar to those used on Pioneer Venus; pressure sensors are similar to those used in the Atmosphere Structure Experiment during descent of the Viking Landers (and by the Meteorology Experiment after landing on the surface); the accelerometers are a miniaturized version of the Viking accelerometers. The microprocessor controlled experiment electronics serve multiple functions, including the sequencing of experiment operation in three modes and performing some on-board data processing and data compression.     

Moving target imaging algorithm for SAR data

A digital processing algorithm for fine-resolution imaging of synthetic aperture radar (SAR) moving targets is described. The targets may have any translational and rotational motion components relative to the data collection platform. The algorithm requires the presence of up to three prominent points in the image of the target; the signals from these points provide estimates of the unknown target motion parameters. Phase compensation and data formatting based on these estimates eliminate motion-induced phase errors. This algorithm has been implemented on a VAX computer and used to process both simulated and real SAR data of moving targets. Results obtained using the simulated data are presented     

OSIRIS-REx low-velocity particles during outbound cruise

We analyzed high-angular rate streaks first recorded by OSIRIS-REx’s MapCam during a 2017 search for Earth Trojan asteroids. We interpret them as water-ice particles that translated across the imager’s field of view, originating from the spacecraft itself. Their translation velocities approximated 0.1–1?m/s based on reasonable conclusions about their range. Pursuing several lines of investigation to seek a coherent hypothesis, we conclude that the episodic releases of the water ice particles are associated with spacecraft attitudes that resulted in solar illumination of previously shadowed regions. This correlation suggests that the OSIRIS-REx spacecraft itself possesses micro-climatic zones consisting of hot regions and cold traps that may temporarily potentially pass volatiles back and forth before losing most of them.     

Filtering of discontinuous processes arising in marine integratednavigation systems

A refined stochastic model for the errors of the Loran-C radio navigation aid is described, and it is shown how this model can be used to improve the performance of integrated navigation systems. In addition to the usual propagation errors, Loran-C time of arrival measurements are occasionally plagued with sudden intermittent errors of a particular magnitude and caused by receiver cycle selection errors. These result in sudden large jumps in the calculated position solution. The Loran-C error has been modeled as the sum of a diffusion process, representing the normal propagating errors, and a pure jump process of Poisson type, representing the cycle selection errors. A simple integrated navigation system is then described, based on the Loran-C model and the standard dead reckoning (heading and speed) system model. Assuming that the observed process is governed by a linear stochastic difference equation, a recursive linear unbiased minimum variance filter is developed, from which the Loran-C and dead reckoning errors, and hence position and velocity, can be estimated     

Ballistics, navigation, and motion control for a spacecraft during its landing on the surface of Phobos

Basic concepts and algorithms laid as foundations of the scheme of landing on the Martian moon Phobos (developed for the Phobos-Grunt project) are presented. The conditions ensuring the landing are discussed. Algorithms of onboard navigation and control are described. The equations of spacecraft motion with respect to Phobos are considered, as well as their use for correction of the spacecraft motion. The algorithm of estimation of the spacecraft’s state vector using measurements with a laser altimeter and Doppler meter of velocity and distance is presented. A system for modeling the landing with a firmware complex including a prototype of the onboard computer is described.     

Charged-particle mutagenesis II. Mutagenic effects of high energy charged particles in normal human fibroblasts.

The biological effects of high LET charged particles are a subject of great concern with regard to the prediction of radiation risk in space. In this report, mutagenic effects of high LET charged particles are quantitatively measured using primary cultures of human skin fibroblasts, and the spectrum of induced mutations are analyzed. The LET of the charged particles ranged from 25 KeV/micrometer to 975 KeV/micrometer with particle energy (on the cells) between 94-603 MeV/u. The X-chromosome linked hypoxanthine guanine phosphoribosyl transferase (hprt) locus was used as the target gene. Exposure to these high LET charged particles resulted in exponential survival curves; whereas, mutation induction was fitted by a linear model. The Relative Biological Effect (RBE) for cell-killing ranged from 3.73 to 1.25, while that for mutant induction ranged from 5.74 to 0.48. Maximum RBE values were obtained at the LET of 150 keV/micrometer. The inactivation cross-section (alpha i) and the action cross-section for mutant induction (alpha m) ranged from 2.2 to 92.0 micrometer2 and 0.09 to 5.56 x 10(-3) micrometer2, respectively. The maximum values were obtained by 56Fe with an LET of 200 keV/micrometer. The mutagenicity (alpha m/alpha i) ranged from 2.05 to 7.99 x 10(-5) with the maximum value at 150 keV/micrometer. Furthermore, molecular analysis of mutants induced by charged particles indicates that higher LET beams are more likely to cause larger deletions in the hprt locus.     

Gravitaxis and graviperception in Euglena gracilis.

Gravitactic orientation in the flagellate Euglena gracilis is mediated by an active physiological receptor rather than a passive alignment of the cells. During a recent space flight on the American shuttle Columbia the cells were subjected to different accelerations between 0 and 1.5 x g and tracked by computerized real-time image analysis. The dependence of orientation on acceleration followed a sigmoidal curve with a threshold at < or = 0.16 x g and a saturation at about 0.32 x g. No adaptation of the cells to the conditions of weightlessness was observed over the duration of the space mission (12 days). Under terrestrial conditions graviorientation was eliminated when the cells were suspended in a medium the density of which (Ficoll) equaled that of the cell body (1.04 g/ml) and was reversed at higher densities indicating that the whole cytoplasm exerts a pressure on the respective lower membrane. There it probably activates stretch-sensitive calcium specific ion channels since gravitaxis can be affected by gadolinium which is a specific inhibitor of calcium transport in these structures. The sensory transduction chain could involve modulation of the membrane potential since ion channel blockers, ionophores and ATPase inhibitors impair graviperception.     

Detection of chi-square fluctuating targets in arbitrary clutter

In a recent paper, general expressions were derived for the density and cumulative probability functions of the amplitude of a linear matched-filter output given a nonfluctuating target in a clutter-limited environment. These expressions were based on the clutter amplitude density function. The results are extended to calculate the cumulative probability function of the output of a linear matched filter used to detect a chi-square fluctuating target in a clutter-limited environment. The resulting method is applied to a common radar clutter model, and experimental sonar data.