Radiation exposure predictions for short-duration stay Mars missions

The human radiation environment for several short-duration stay manned Mars missions is predicted using the Mission Radiation Calculation (MIRACAL) program, which was developed at NASA Langley Research Center. This program provides dose estimates for galactic cosmic rays (GCR) and large and ordinary solar proton flare events for various amounts of effective spacecraft shielding (both operational and storm shelter thicknesses) and a given time history of the spacecraft's heliocentric position. The results of this study show that most of the missions can survive the most recent large flares (if they were to occur at the missions' perihelion) if a 25 g/cm2 storm shelter is assumed. The dose predictions show that missions during solar minima (when solar flare activity is the lowest) are not necessarily the minimum dose cases, due to increased GCR contribution during this time period. The direct transfer mission studied has slightly lower doses than the outbound Venus swingby mission [on the order of 10-20 centi-Sieverts (cSv) lower], with the greatest dose differences for the assumed worst case scenario (when the large flares occur at perihelion). The GCR dose for a mission can be reduced by having the crew spend some fraction of its day nominally in the storm shelter (other than during flare events).     

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.     

多电技术趋势下APU的发展

飞机的舵面、飞控、起落架、仪表等系统由飞机二次能源驱动。目前随着电子电力技术的进步，一些操纵部件由气动、液压系统改为电力操控系统，使飞机技术的发展趋于多电化。多电APU的出现顺应了未来飞机的发展趋势，集成组合动力装置（IPU）是APU发展的一种形式。     

高陡度内表面精密车削的刀具稳定性研究

通过分析高陡度内表面精密车削刀杆振颤的原因、动态特性及其对加工表面质量的影响，建立动力学模型，分析稳定性条件；通过优化设计，将刀杆刚度提高2.52倍；在此基础上，以口径为124mm、长径比为1.16的典型MgF₂高陡度头罩为对象开展精密车削实验，测试结果表明加工表面粗糙度稳定达到R_a3.1nm，满足红外光学头罩的使用要求，验证了理论分析的正确性。