Global pictures of the ozone field,from high altitudes,from DE-I

Using the imaging instrumentation aboard the Dynamics Explorer spacecraft (DE-I), total column ozone densities are obtained in the sunlit hemisphere by measuring the intensities of backscattered solar ultraviolet radiation with multiple filters and multiple photometers. The high apogee altitude (23,000 km) of the eccentric polar orbit allows high resolution global-scale images of the terrestrial ozone field to be obtained within 12 minutes. Previous ozone-monitoring spacecraft have required much longer time periods for comparable spatial coverage because of their lower altitudes (<1200 km). The much higher altitude of DE-I also provides hours of continuous imaging of features compared to minutes or seconds with previous spacecraft. Near perigee, high resolution images can be gained with pixel size as small as 3 km to view mesoscale atmospheric variations. Utilizing these data, the effects of planetary-scale, synoptic-scale, and mesoscale dynamical processes, which control the distribution of ozone near the tropopause, can be studied. Preliminary results show short-term (less than one day) variations in the synoptic ozone field and these variations appear to be in accord with meteorological data. Spatial variations in the ozone field are found to be highly negatively correlated with tropopause altitude.     

A reappraisal of the habitability of planets around M dwarf stars

Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are extremely long-lived, and because they are much smaller in mass than the Sun (between 0.5 and 0.08 M(Sun)), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50th of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 M(Earth) orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute.     

Orbital corrections by a single-input impulsive control applied along the geomagnetic field

This paper examines the possibility of regular orbital corrections for a satellite controlled by an impulsive force applied along the induction vector of the local geomagnetic field. The main purpose of the correcting considered in the paper is to eliminate the drift in secular variation of the relative orbital parameters over the orbital period. The obtained results are applied to the formation flying problem. The developed method is tested using numerical simulation.     

拟合激光陀螺数学模型的方法研究…

在分析激光陀螺的数学模型和三欠样条函数拟合原理的基础上,针对俄罗斯某型低精度激光陀螺实际输入－输出特性曲线的数据,应用三次样条合方法进行分析处理,推导出了适用于非线性工作范围误差补偿且实际陀螺特性的数学模型。本文所提方法可用于工作区线性化较差,工作精度低的激光陀螺的精度补偿。