线切割放电加工助航空客户飞得更高

过去20年里线切割的切割速度几乎增加了5倍,粗加工的直线切割速度可达600mm2/min;对大多数复杂型腔的加工速度较慢,但也可达到约350mm2/min。通过优化粗加工和精加工的策略,变质层几乎为零,同时没有材料或微观结构的变化,放电脉冲的控制特别是脉冲的持续时间和频率是达到最小损伤的关键因素。     

Instrumentation for gamma-ray astronomy

There are three distinct energy ranges within the broad spectrum of gamma-ray astronomy, low energy (which in turn is subdivided), high energy, and very high and ultra-high energy. Each has its own unique type of instrumentation. Only in the very high-energy range do the telescopes bear any resemblence to optical telescopes; the rest appear more like instrumentation for high-energy physics. The low- and high-energy ranges are now primarly dependent on spaceflight, although some balloon altitude research is still being accomplished. Satellites planned to be launched in the next two years will carry telescopes with considerably more capability than those previously flown in space. In the very high and ultra-high energy realm, large ground based systems are used to detect the secondary radiation from interactions of the gamma radiation with the air. In all cases, software and data analysis are becoming increasingly important aspects of the subject as the data become ever greater and more complex. Beyond the telescopes to be flown in space or installed on the ground soon, instrumentation, taking advantage of new detector techniques which have come into being or older ones which now seem capable of being adapted to space, are being developed for the more distant future.     

The MESSENGER Gamma-Ray and Neutron Spectrometer

A Gamma-Ray and Neutron Spectrometer (GRNS) instrument has been developed as part of the science payload for NASA’s Discovery Program mission to the planet Mercury. Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) launched successfully in 2004 and will journey more than six years before entering Mercury orbit to begin a one-year investigation. The GRNS instrument forms part of the geochemistry investigation and will yield maps of the elemental composition of the planet surface. Major elements include H, O, Na, Mg, Si, Ca, Ti, Fe, K, and Th. The Gamma-Ray Spectrometer (GRS) portion detects gamma-ray emissions in the 0.1- to 10-MeV energy range and achieves an energy resolution of 3.5 keV full-width at half-maximum for ⁶⁰Co (1332 keV). It is the first interplanetary use of a mechanically cooled Ge detector. Special construction techniques provide the necessary thermal isolation to maintain the sensor’s encapsulated detector at cryogenic temperatures (90 K) despite the intense thermal environment. Given the mission constraints, the GRS sensor is necessarily body-mounted to the spacecraft, but the outer housing is equipped with an anticoincidence shield to reduce the background from charged particles. The Neutron Spectrometer (NS) sensor consists of a sandwich of three scintillation detectors working in concert to measure the flux of ejected neutrons in three energy ranges from thermal to ∼7 MeV. The NS is particularly sensitive to H content and will help resolve the composition of Mercury’s polar deposits. This paper provides an overview of the Gamma-Ray and Neutron Spectrometer and describes its science and measurement objectives, the design and operation of the instrument, the ground calibration effort, and a look at some early in-flight data.     

Is high resolution possible aboard minisatellites?

To achieve the size reductions needed to lower the costs of space imaging, every part of a satellite (telescope, detector, digitization, image compression, memory, telemetry, and of course satellite platform) has to be improved. With regard to the instrument, new dimensioning rules, new optical designs, and new detection systems allow significant gains. Better balance between detector and optics modulation transfer function (MTF) performances can be achieved. Though the involved solutions raise the question of signal level, the latter can be solved with the use of TDI (Time Delay and Integration) detection. The instrumental choices, the optical system under investigation and how the above techniques are allowed for in the next generation SPOT satellites development studies led by CNES will be presented in this paper, showing how they can achieve the goal of weight reductions.     

An icy mineralogy package (IMP) for in-situ studies of Titan’s surface

We describe the scientific case for and preliminary design of an instrument whose primary goal is to determine the chemistry (element abundance) and mineralogy (compound identity and abundance) of Titan’s surface using a combination of energy dispersive X-ray fluorescence spectroscopy (EDXRF) and X-ray diffraction (XRD). XRD is capable of identifying any crystalline substance present on Titan’s surface at relative abundances greater than ∼1 wt%, allowing unambiguous identification of, for example, structure I and II clathrates (even in the presence of ice), and various organic solids, which may include C₂H₂, C₂H₄, C₄H₂, HCN, CH₃CN, HC₃N, and C₄N₂). The XRF component of the instrument will obtain elemental abundances for 16 < Z < 60 with minimum detection limits better than 10 ppm (including detection of atmospheric noble gas isotopes), and may achieve detection limits of 0.01–1% for lighter elements down to Z = 6 (carbon). The instrument is well suited to integration with other analytical tools as part of a light-weight surface chemistry and mineralogy package. Although considerably less sensitive to elemental abundance than GC–MS (10⁻² vs. 10⁻⁸) it is likely to be significantly lighter (<0.5 kg vs. 10 kg).     

A microbial oasis in the hypersaline Atacama subsurface discovered by a life detector chip: implications for the search for life on Mars

The Atacama Desert has long been considered a good Mars analogue for testing instrumentation for planetary exploration, but very few data (if any) have been reported about the geomicrobiology of its salt-rich subsurface. We performed a Mars analogue drilling campaign next to the Salar Grande (Atacama, Chile) in July 2009, and several cores and powder samples from up to 5?m deep were analyzed in situ with LDChip300 (a Life Detector Chip containing 300 antibodies). Here, we show the discovery of a hypersaline subsurface microbial habitat associated with halite-, nitrate-, and perchlorate-containing salts at 2?m deep. LDChip300 detected bacteria, archaea, and other biological material (DNA, exopolysaccharides, some peptides) from the analysis of less than 0.5?g of ground core sample. The results were supported by oligonucleotide microarray hybridization in the field and finally confirmed by molecular phylogenetic analysis and direct visualization of microbial cells bound to halite crystals in the laboratory. Geochemical analyses revealed a habitat with abundant hygroscopic salts like halite (up to 260?g kg(-1)) and perchlorate (41.13?μg g(-1) maximum), which allow deliquescence events at low relative humidity. Thin liquid water films would permit microbes to proliferate by using detected organic acids like acetate (19.14?μg g(-1)) or formate (76.06?μg g(-1)) as electron donors, and sulfate (15875?μg g(-1)), nitrate (13490?μg g(-1)), or perchlorate as acceptors. Our results correlate with the discovery of similar hygroscopic salts and possible deliquescence processes on Mars, and open new search strategies for subsurface martian biota. The performance demonstrated by our LDChip300 validates this technology for planetary exploration, particularly for the search for life on Mars.     

Spiders: water-driven erosive structures in the southern hemisphere of Mars

Recent data from space missions reveal that there are ongoing climatic changes and erosive processes that continuously modify surface features of Mars. We have investigated the seasonal dynamics of a number of morphological features located at Inca City, a representative area at high southern latitude that has undergone seasonal processes. By integrating visual information from the Mars Orbiter Camera on board the Mars Global Surveyor and climatic cycles from a Mars' General Circulation Model, and considering the recently reported evidence for the presence of water-ice and aqueous precipitates on Mars, we propose that a number of the erosive features identified in Inca City, among them spiders, result from the seasonal melting of aqueous salty solutions.     

Astronaut photography and the intelligence community: Who saw what?

Despite NASA's astronaut photography benefiting a wide range of civilian interests, it occasionally conflicted directly with the critical national security requirement to protect the National Reconnaissance Program from public disclosure or compromise. The Intelligence Community consequently imposed a number of restrictions, from reviewing the photography before public release to limiting the capabilities of NASA's image-forming sensors. At the same time, beginning in the Mercury program the Intelligence Community acquired and analyzed some of the photography as a possible source of intelligence data that otherwise was not being collected.