Antideuteron based dark matter search with GAPS: Current progress and future prospects

The General Antiparticle Spectrometer (GAPS) is a new approach to the indirect detection of dark matter. It relies on searching for primary antideuterons produced in the annihilation of dark matter in the galactic halo. Low energy antideuterons produced through Standard Model processes, such as collisions of cosmic-rays with interstellar baryons, are greatly suppressed compared to primary antideuterons. Thus a low energy antideuteron search provides a clean signature of dark matter. In GAPS antiparticles are slowed down and captured in target atoms. The resultant exotic atom deexcites with the emission of X-rays and annihilation pions, protons and other particles. A tracking geometry allows for the detection of the X-rays and particles, providing a unique signature to identify the mass of the antiparticle. A prototype detector was successfully tested at the KEK accelerator in 2005, and a prototype GAPS balloon flight is scheduled for 2011. This will be followed by a full scale experiment on a long duration balloon from Antarctica in 2014. We discuss the status and future plans for GAPS.     

嫦娥一号卫星紫外月球敏感器

探月工程是我国航天领域的又一项重大工程项目,嫦娥一号卫星是探月工程的第一步。嫦娥一号卫星首次采用了一种全新的光学姿态敏感器——紫外月球敏感器,实现在卫星环月飞行期间的姿态测量任务。紫外月球敏感器是一种以月球为姿态参考源的大视场成像式光学姿态敏感器,本文介绍其工作原理、功能与组成以及在轨飞行试验的相关情况。     

月球软着陆的高精度自主导航与控制方法研究

提出了一种月球软着陆的高精度自主导航和控制方法.根据测距波束视线相对月面的几何关系,确定本体系的月心方向,组合利用测速仪获取的本体系三维速度确定本体系相对轨道系的姿态、速度及高度,并根据确定的参数性质选取适应的制导和控制方法.算法基于直接测量数据确定和控制姿态、高度和速度,不受惯性导航误差的影响,可以有效地提高姿态、速度与高度的确定精度和控制精度.数学仿真表明了算法的有效性.     

一种嵌入式月面巡视器移动系统模拟器设计

提出了一种嵌入式月面巡视器移动系统模拟器设计方案,分析了模拟器的功能性能需求,给出了模拟器整体方案设计及硬件、软件的具体实现,最后通过系统测试对模拟器设计的有效性进行了验证.该移动系统模拟器可实现对移动系统电机及负载的功率级模拟,满足移动控制驱动组件的系统测试需求,并具有良好的通用性和可扩展性.     

一类月面钻进采样机构的鲁棒控制

在月面复杂环境下采样机构模型会发生摄动,并会受到系统扰动影响,采样控制器的鲁棒性对顺利完成采样任务具有重要意义.针对回转与进尺复合式月面自动钻进采样机构建立名义控制模型,分析月面工作过程中的模型摄动、系统扰动下的控制系统模型,利用线性矩阵不等式方法进行状态反馈鲁棒控制律设计.仿真结果表明:在有界模型摄动、有界随机系统扰动情况下,系统具有鲁棒性,并对扰动具有抑制能力.     

The Radio Observatory on the Lunar Surface for Solar studies

The Radio Observatory on the Lunar Surface for Solar studies (ROLSS) is a concept for a near-side low radio frequency imaging interferometric array designed to study particle acceleration at the Sun and in the inner heliosphere. The prime science mission is to image the radio emission generated by Type II and III solar radio burst processes with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Specific questions to be addressed include the following: (1) Isolating the sites of electron acceleration responsible for Type II and III solar radio bursts during coronal mass ejections (CMEs); and (2) Determining if and the mechanism(s) by which multiple, successive CMEs produce unusually efficient particle acceleration and intense radio emission. Secondary science goals include constraining the density of the lunar ionosphere by searching for a low radio frequency cutoff to solar radio emission and constraining the low energy electron population in astrophysical sources. Key design requirements on ROLSS include the operational frequency and angular resolution. The electron densities in the solar corona and inner heliosphere are such that the relevant emission occurs at frequencies below 10 MHz. Second, resolving the potential sites of particle acceleration requires an instrument with an angular resolution of at least 2°, equivalent to a linear array size of approximately 1000 m. Operations would consist of data acquisition during the lunar day, with regular data downlinks. No operations would occur during lunar night.     

月球精确软着陆制导轨迹在轨鲁棒跟踪

为实现在月球表面期望的着陆点进行精确软着陆(PPL),在开环制导规划出的最优标称轨迹基础上,考虑动力下降过程中的干扰和不确定性,对在轨闭环轨迹跟踪制导方法进行研究.针对月球PPL三维球体非线性轨道动力学模型,充分考虑自主制导的鲁棒性、实时性要求,采用动态平面控制技术的思想,解决退步法存在的"计算复杂性膨胀"问题,并证明了闭环系统的稳定性.仿真算例表明,该方法不仅算法简单,过渡过程能够实现快速跟踪,而且能够保证稳态跟踪误差在预先给定的范围之内且可以自由调节.     

应用改进果蝇优化算法的月面巡视器路径规划

文章针对果蝇优化算法易陷入局部最优的问题,对果蝇算法中的味道浓度判定值进行改进,并将其用于月球探测巡视器的动态路径规划。为验证算法的有效性,将改进果蝇优化算法与粒子群优化算法的路径规划寻优特性进行了仿真对比分析,结果表明改进果蝇优化算法具有良好的实时性,并有效解决了算法易陷入局部最优的问题。考虑到月球探测巡视器在沿规划路径进行月面巡视的过程中,有可能遇到未知障碍物的情况,提出了动态环境下月球巡视器遇到未知静态障碍物的避障策略。     

神秘的类星体

1960年,美国天文学家桑德奇用一台5米口径的光学望远镜找到了剑桥射电源第三星表上第48号天体（3C48）的光学对应体。他发现3C48的光谱中,在一个奇怪的位置上有一些又宽又亮的发射线。1963年,美国天文学家马丁·施密特发现在3C273的光谱中具有与3C48类似的现象,通过仔细研究,他发现这些发射线实际上是人们早已熟知的氢的发射线,只不过朝着红光的方向移动了相当长的一段距离,也就是说它们具有非常大的红移。     

一种基于LIDAR的精确月球软着陆目标点选定方法

研究了月球探测器不设悬停阶段的精确软着陆运动中实时目标着陆点的自主选定方法．其过程包括着陆器运动补偿、数字高程图（DEM）的生成、障碍识别和最优安全着陆点搜索4个步骤．采用LIDAR敏感器,由经过运动补偿得到的斜距数据生成DEM,给出一种月面地形坡度和粗糙度的定义,根据安全着陆区的判据进行障碍识别,最后设计中心螺旋式搜索方法对探测器最优安全着陆点进行搜索选定．通过仿真验证了本文方法的有效性和优越性．     

A VLBI search for pulsar wind nebulae in supernovae

We examine recent supernovae which have been observed with very-long-baseline interferometry in order to detect or limit the emission from a possible compact remnant of the explosion. Such a remnant could be a neutron star, generating a pulsar wind nebula, or a black hole with an accretion disk and jets. Four supernovae, and also more than a dozen supernovae or their young remnants in M82, have structure sufficiently resolved to allow useful conclusions as to the strength of the emission from such young neutron stars or black holes. We recently discovered a compact component in the center of SN 1986J’s shell with a spectral luminosity at 15 GHz 200 times that of the Crab Nebula. This is most likely the compact remnant of the explosion, the first and only one found in any modern supernova. For other modern supernovae, the upper limits on the radio spectral luminosities of such young compact remnants range from 180 times that of the Crab Nebula for SN 1979C in M100 in the Virgo cluster to 0.001 times that of the Crab Nebula for SN 1987A in the Large Magellanic Cloud.     

Studies in the search for life on Mars.

The ability of living organisms to survive extraterrestrial conditions has implications for the origins of life in the solar system. We have therefore studied the survival of viruses, bacteria, yeast, and fungi under simulated Martian conditions. The environment on Mars was simulated by low temperature, proton irradiation, ultraviolet irradiation, and simulated Martian atmosphere (CO2 95.46%, N2 2.7%, water vapor 0.03%) in a special cryostat. After exposure to these conditions, tobacco mosaic virus and spores of Bacillus, Aspergillus, Clostridium, and some species of coccus showed significant survival.     

Bio-markers and the search for extinct life on Mars.

Geologic and climatologic studies suggest that conditions on early Mars were similar to early Earth. Because life on Earth is believed to have originated during this early period (3.5 billion years ago), the Martian environment could have also been conducive to the origin of life. To investigate this possibility we must first define the attributes of an early Martian biota. Then, specific geographic locations on Mars must be chosen where life may have occurred (i.e. areas which had long standing water), and within these distinct locations search for key signatures or bio-markers of a possible extinct Martian biota. Some of the key signatures or bio-markers indicative of past biological activity on Earth may be applicable to Mars including: reduced carbon and nitrogen compounds, CO3(2-), SO4(2-), NO3-, NO2- [correction of NO2(2)], Mg, Mn, Fe, and certain other metals, and the isotopic ratios of C, N and S. However, we must also be able to distinguish abiotic from biologic origins for these bio-markers. For example, abiotically fixed N2 would form deposits of NO3- and NO2-, whereas biological processes would have reduced these to ammonium containing compounds, N2O, or N2, which would then be released to the atmosphere. A fully equipped Mars Rover might be able to perform analyses to measure most of these biomarkers while on the Martian surface.     

Coherent matter wave inertial sensors for precision measurements in space

We analyze the advantages of using ultra-cold coherent sources of atoms for matter-wave interferometry in space. We present a proof-of-principle experiment that is based on an analysis of the results previously published in Richard et al. (2003) from which we extract the ratio h/m for ⁸⁷Rb. This measurement shows that a limitation in accuracy arises due to atomic interactions within the Bose–Einstein condensate. Finally we discuss the promising role of coherent-matter-wave sensors, in particular inertial sensors, in future fundamental physics missions in space.     

A hybrid,self-adjusting search algorithm for optimal space trajectory design

The aim of the present paper is to propose a hybrid, self adjusting, search algorithm for space trajectory optimization. By taking advantage of both direct and indirect methods, the present algorithm allows the finding of the optimal solution through the introduction of some new control parameters, whose number is smaller than that of the Lagrange multipliers, and whose range is bounded. Eventually, the optimal solution is determined by means of an iterative self-adjustment of the search domain occurring at “runtime”, without any correction by an external user. This new set of parameters can be found through a reduction process of the degrees of freedom, obtained through the transversality conditions before entering the search loop. Furthermore, such a process shows that Lagrange multipliers are subject to a deep symmetry mirroring the features of the state vector. The algorithm reliability and efficiency is assessed through some test cases, and by reproducing some optimal transfer trajectories: a full three-dimensional, minimum time Mars mission, an optimal transfer to Jupiter, and finally an injection into a circular Moon orbit.     

Hierarchical global search for fuel-optimal impulsive transfers between lunar libration orbits

The attention to the periodic orbit in the Earth-Moon restricted three-body system continues to grow due to its special environment and locations. This research investigates the feasibility of constructing fuel-optimal single and multiple impulse transfers between unstable periodic orbits at L₁ and L₂ points. Invariant manifolds, which could provide the appropriate initial trajectories for optimization, are analyzed deeply to enable previously unknown orbit options and potentially to reduce mission cost. A global search strategy based on comparing the orbital state of the unstable and stable manifolds, incorporated with low-thrust techniques, is performed to seek a suitable matching point for maneuver application. Then the sequential quadratic programming (SQP) is adopted to further optimize the velocity increment and obtain the single/multiple impulse optimal transfers. The associated constraint gradients are derived to achieve higher accuracy and rapidity of the algorithm. To highlight the effectivity of the transfer scheme, three-dimensional low-energy transfers between different types and spatial regions of performing single and multiple impulses are explored. The total Delta-V required varies between a few meters per second and tens of meters per second, and the related flight time is about several weeks, mainly depending on the energy of periodic orbits and the invariant manifold structure. The results obtained in this paper can provide a useful reference for the selection of escape and capture site along the manifolds, maneuver magnitude and transfer time.     

Exobiology and future Mars missions: The search for Mars'' earliest biosphere

The primordial Mars may have possessed a thick carbon dioxide atmosphere, with liquid water common on the surface, similar in many ways to the primordial Earth. During this epoch, billions of years ago, the surface of Mars could have been conducive to the origin of life. It is possible that life evolved on Mars to be later eliminated as the atmospheric pressure dropped. Analysis of the surface of Mars for the traces of this early martian biota could provide many insights into the phenomenon of life and its coupling to planetary evolution.     

考虑地球自转的探月返回反馈线性化跟踪制导律设计

研究考虑地球自转的探月返回跳跃式再入的纵向制导问题.通过对制导动力学进行详细分析,给出了地球自转对制导精度产生影响的原因.在此基础上,针对探月返回跳跃式再入的纵向制导问题,研究了考虑地球自转的反馈线性化跟踪制导律的设计问题.当考虑地球自转时,制导动力学十分复杂,如果直接按照非线性系统反馈线性化控制理论进行制导律设计,所需测量量较多,制导律难以实现.设计了一种简化的反馈线性化跟踪制导律,并分析了设计机理.最后进行了数学仿真,与航天飞机反馈线性化跟踪制导律进行了比较,所设计的制导律在一定不确定下制导精度更高.