Degradation of cyanobacterial biosignatures by ionizing radiation

Primitive photosynthetic microorganisms, either dormant or dead, may remain today on the martian surface, akin to terrestrial cyanobacteria surviving endolithically in martian analog sites on Earth such as the Antarctic Dry Valleys and the Atacama Desert. Potential markers of martian photoautotrophs include the red edge of chlorophyll reflectance spectra or fluorescence emission from systems of light-harvesting pigments. Such biosignatures, however, would be modified and degraded by long-term exposure to ionizing radiation from the unshielded cosmic ray flux onto the martian surface. In this initial study into this issue, three analytical techniques--absorbance, reflectance, and fluorescence spectroscopy--were employed to determine the progression of the radiolytic destruction of cyanobacteria. The pattern of signal loss for chlorophyll reflection and fluorescence from several biomolecules is characterized and quantified after increasing exposures to ionizing gamma radiation. This allows estimation of the degradation rates of cyanobacterial biosignatures on the martian surface and the identification of promising detectable fluorescent break-down products.     

Predictive guidance algorithms for maximal downrange maneuvrability with application to low-lift re-entry

The paper concerns the general problem of a bounded final state control of non-linear dynamic systems with reference to near-optimal predictive guidance for low lift-to-drag ratio re-entry vehicles. More specifically, it addresses deriving guidance strategies capable to provide a maximal downrange maneuvrability for a maximal remaining flight time. Such robust, “guaranteed”, or assured, guidance keeps the remaining range-to-go to be coincident with the center of instant attainability domain. The paper discusses the existing guaranteed guidance strategy, and presents more general approach that provides an on-board planning of the entry trajectory, thus giving future state and control profiles. As a consequence the proposed guidance law is able to satisfy not only specified terminal conditions but also typical inequality constraints such as the maximal load factor and heat load. Computer simulations show that the algorithm can generate the feasible trajectories with equal downrange margins, using simple two-parametric families of control functions.     

Hands-on education system using water rocket

Trial of hands-on education of rocket technology for university students using water rocket, which consists of structural study, propulsion system study, aerodynamic study, stability study, and flight trajectory study, has been performed. Integrating each subject into a group of tasks, a hands-on education system of aerospace technology will become feasible. Advantage of the system is that students can verify the theory by hands-on practice. Development of recovery mechanism for water rocket will be a good subject of hands-on innovative design. Although the system has been developed mostly for university students, it can easily be converted to hands-on education system for school children and high school students.     

Setting priorities in US space science

Two new long-range US space science strategy studies are notable not only for what the new reports say and do for their respective discipline areas but also for what they demonstrate in terms of shared conclusions and in terms of the feasibility of forging consensus on community priorities. Both studies engaged a broad segment of the research community to survey their respective fields, recommend top priority scientific goals and directions for the next decade, provide recommendations for programmatic directions and explicit priorities for government investment in research facilities, and address issues of advanced technology, infrastructure, interagency coordination, education, and international cooperation. The two studies demonstrate that cross-program priorities can be established when a community sees the effort as being beneficial to the long-term health of the field.     

Mechanisms of gamma-ray generation by neutron stars

Some astrophysical mechanisms responsible for gamma-ray bursts on or near neutron stars are briefly reviewed.     

VLBI observations to the APOD satellite

The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10?cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1?s integration time of the correlator output is on the level of 0.1?ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype.     

Patterns of carbon monoxide in the middle atmosphere and effects of solar variability

We determine the spatial-time patterns of zonally averaged carbon monoxide (CO) in the middle atmosphere by applying Principle Component Analysis to the CO data obtained from the Microwave Limb Sounder (MLS) measurements on the Aura satellite in 2004–2012. The first two principal components characterize more than 90% of the CO variability. Both principal components are localized in the low thermosphere near the mesopause. The first principal component is asymmetric relative to the poles. It has opposite signs in the Northern and Southern Hemisphere at mid to high latitudes and strongly oscillates with an annual periodicity. The second principal component has the same sign in both hemispheres and oscillates mainly with a semi-annual frequency. Both principal components are modulated by the 11-year solar cycle and display short-term variations. To test possible correlations of these variations with the short term solar ultraviolet (UV) variability we use the simultaneous measurements of the UV solar radiance from the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) on the Solar Radiation and Climate Experiment (SORCE) satellite to investigate the correlation between CO in the middle atmosphere and solar UV in 2004–2012. Using a wavelet coherence technique a weak, intermittent 27-day signal is detected in high-frequency parts of the CO principal components.     

俄月球-全球等探测任务中的无线电科学试验

俄罗斯航天局正在规划和推进新的月球探测计划,包括月球-资源和月球-全球探测任务,它们搭载了3个无线电科学载荷:2个无线电信标机分别安装在2个着陆器上,1个Ka波段接收机安装在月球-全球轨道器上。信标机发射频率为8.4GHz和32GHz。8.4GHz的微波信号将被发回地球,利用地面VLBI监测网对信号进行测量,其结果可用于精密的天体力学观测及导航,还能用于月球天平动研究;32GHz信号将用于定轨和月球重力场研究。Ka波段信号天线轴指向着陆区天顶方向,信号由轨道器接收。本文基于对Ka波段信号多普勒频移的精确测量,通过研究着陆区附近重力场的微小变化(约3~5mGal精度),探讨月球重力场的不均匀性,其测量数据的空间分辨率约为20km。     

Spherule beds 3.47-3.24 billion years old in the Barberton Greenstone Belt,South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution

Four layers, S1-S4, containing sand-sized spherical particles formed as a result of large meteorite impacts, occur in 3.47-3.24 Ga rocks of the Barberton Greenstone Belt, South Africa. Ir levels in S3 and S4 locally equal or exceed chondritic values but in other sections are at or only slightly above background. Most spherules are inferred to have formed by condensation of impact-produced rock vapor clouds, although some may represent ballistically ejected liquid droplets. Extreme Ir abundances and heterogeneity may reflect element fractionation during spherule formation, hydraulic fractionation during deposition, and/or diagenetic and metasomatic processes. Deposition of S1, S2, and S3 was widely influenced by waves and/or currents interpreted to represent impact-generated tsunamis, and S1 and S2 show multiple graded layers indicating the passage of two or more wave trains. These tsunamis may have promoted mixing within a globally stratified ocean, enriching surface waters in nutrients for biological communities. S2 and S3 mark the transition from the 300-million-year-long Onverwacht stage of predominantly basaltic and komatiitic volcanism to the late orogenic stage of greenstone belt evolution, suggesting that regional and possibly global tectonic reorganization resulted from these large impacts. These beds provide the oldest known direct record of terrestrial impacts and an opportunity to explore their influence on early life, crust, ocean, and atmosphere. The apparent presence of impact clusters at 3.26-3.24 Ga and approximately 2.65-2.5 Ga suggests either spikes in impact rates during the Archean or that the entire Archean was characterized by terrestrial impact rates above those currently estimated from the lunar cratering record.     

大功率离子推力器和流动控制单元验证现状 及其2000小时寿命试验

为了发展基于电推进的大功率空间运输系统,需要开发和验证功率达数十千瓦的电推进系统,深空任务电推进系统优化的比冲要求高达10⁵s。凯尔迪什研究中心（KeRC）正在开发这样的电推进部件。本文概述了 35kW离子推力器 IT-500及其流动单元FCU-500的验证现状。作为其验证的一部分,完成了IT-500 和 FCU-500的2000h寿命试验。其中,离子推力器大部分验证条件是：输入功率17.8kW,使用了40kg氙,2018h寿命试验。本文介绍了磁场和离子光学以及石墨格栅开发现状。