Deuterium Observations in the Galaxy

An accurate measurement of the primordial value of D/H would provide one of the best tests of nucleosynthesis models for the early Universe and the baryon density. Such evaluations have been traditionally made using present estimations of the deuterium abundance in the interstellar medium, extrapolated backwards in time with the use of galactic evolution models. Direct estimations of the primordial deuterium abundance have been carried out only recently in QSOs absorbers at high redshift.We will summarize galactic observations of deuterium and suggest that, perhaps, a single D/H value for the interstellar medium is not representative. These evaluations mainly came from observations completed in the far UV with first the Copernicus satellite over the Lyman lines series followed then by H and D Lyman-alpha lines observations with both the IUE and the GHRS on the Hubble Space Telescope. We discuss different known systematics and show that the situation is not yet clear. It is not possible today to claim that we know "the" D/H value in the interstellar medium, if any.Overall and in the context of additional D observations made in the solar system, we conclude that the actual evolution of deuterium from Big-Bang nucleosynthesis to now is not yet understood. More observations, recently made with IMAPS (the Interstellar Medium Absorption Profile Spectrograph) and hopefully to be made with FUSE (the Far Ultraviolet Spectroscopic Explorer to be launched in the fall of 1998), at higher spectral resolution or in many different galactic sites are certainly needed to help us reach a better global view of the evolution of that key element, and thus better constrain any evaluation of its primordial abundance.     

A technique for enhanced slant range resolution for SAR systems inknowledge-based environment

Synthetic Aperture Radar (SAR) is an airborne (or spaceborne) radar mapping technique for generating high resolution maps of surface target areas including terrain. High resolution is achieved by coherently combining the returns from a number of radar transmissions. The resolution of the images is determined by the parameters of the emissions, with more data giving greater resolution. A requirement of the Microwave Radar Division's SAR radar is to provide classification of targets. This paper presents a technique for enhancing slant range resolution in SAR images by dithering the carrier centre frequency of the transmitted signal. The procedure controls the radar waveforms so they will optimally perform the classification function, rather than provide an image of best quality. It is shown that a Knowledge-Based engineering approach to determining the waveform of the radar gives considerably improved performance as a classifier of targets (of large radar cross-section), even though the corresponding image is degraded     

Ulysses' race to the pole: Symposium Summary

This paper reproduces the Symposium Summary presentation at the 28th ESLAB Symposium on The High Latitude Heliosphere. The summary is not comprehensive but with considerable latitude covers the highlights of the conference. Featured are the observations of the high-speed wind from the growing southern polar coronal hole, new measurements of the interstellar gas and pickup ions, new measurements of cosmic ray modulation at high latitude, and our growing awareness of the three-dimensional heliosphere.     

An Overview of the Instrument Suite for the Deep Impact Mission

A suite of three optical instruments has been developed to observe Comet 9P/Tempel 1, the impact of a dedicated impactor spacecraft, and the resulting crater formation for the Deep Impact mission. The high-resolution instrument (HRI) consists of an f/35 telescope with 10.5 m focal length, and a combined filtered CCD camera and IR spectrometer. The medium-resolution instrument (MRI) consists of an f/17.5 telescope with a 2.1 m focal length feeding a filtered CCD camera. The HRI and MRI are mounted on an instrument platform on the flyby spacecraft, along with the spacecraft star trackers and inertial reference unit. The third instrument is a simple unfiltered CCD camera with the same telescope as MRI, mounted within the impactor spacecraft. All three instruments use a Fairchild split-frame-transfer CCD with 1,024× 1,024 active pixels. The IR spectrometer is a two-prism (CaF₂ and ZnSe) imaging spectrometer imaged on a Rockwell HAWAII-1R HgCdTe MWIR array. The CCDs and IR FPA are read out and digitized to 14 bits by a set of dedicated instrument electronics, one set per instrument. Each electronics box is controlled by a radiation-hard TSC695F microprocessor. Software running on the microprocessor executes imaging commands from a sequence engine on the spacecraft. Commands and telemetry are transmitted via a MIL-STD-1553 interface, while image data are transmitted to the spacecraft via a low-voltage differential signaling (LVDS) interface standard. The instruments are used as the science instruments and are used for the optical navigation of both spacecraft. This paper presents an overview of the instrument suite designs, functionality, calibration and operational considerations.     

Analysis of a redshifted plasma flow over a sunspot

The ultraviolet spectrum of a redshifted plasma flow appearing over a sunspot observed during the first flight of the High Resolution Telescope Spectrograph (HRTS I) is analysed, and interpreted as a radiatively cooling plasma. For most of the lines emitted from this plasma, the assumption of ionization equilibrium during the cooling is good. However for He II (and other ions with a single electron outside of closed shells), this is not the case. Integrating differential equations for the various ionization fractions of helium and the temperature allows an approximate determination of the abundance of helium relative to other elements whose lines appear in the spectrum of the plasma flow.     

The Swift Ultra-Violet/Optical Telescope

The Ultra-Violet/Optical Telescope (UVOT) is one of three instruments flying aboard the Swift Gamma-ray Observatory. It is designed to capture the early (∼1 min) UV and optical photons from the afterglow of gamma-ray bursts in the 170–600 nm band as well as long term observations of these afterglows. This is accomplished through the use of UV and optical broadband filters and grisms. The UVOT has a modified Ritchey–Chrétien design with micro-channel plate intensified charged-coupled device detectors that record the arrival time of individual photons and provide sub-arcsecond positioning of sources. We discuss some of the science to be pursued by the UVOT and the overall design of the instrument.     

Biosignatures from Earth-like planets around M dwarfs

Coupled one-dimensional photochemical-climate calculations have been performed for hypothetical Earth-like planets around M dwarfs. Visible/near-infrared and thermal-infrared synthetic spectra of these planets were generated to determine which biosignature gases might be observed by a future, space-based telescope. Our star sample included two observed active M dwarfs-AD Leo and GJ 643-and three quiescent model stars. The spectral distribution of these stars in the ultraviolet generates a different photochemistry on these planets. As a result, the biogenic gases CH4, N2O, and CH3Cl have substantially longer lifetimes and higher mixing ratios than on Earth, making them potentially observable by space-based telescopes. On the active M-star planets, an ozone layer similar to Earth's was developed that resulted in a spectroscopic signature comparable to the terrestrial one. The simultaneous detection of O2 (or O3) and a reduced gas in a planet's atmosphere has been suggested as strong evidence for life. Planets circling M stars may be good locations to search for such evidence.     

柯马中国亮相航展——本刊总编辑刘柱对话柯马北美航空运营总监约翰·纳克斯先生

刘柱:首先,请您简单介绍一下柯马公司.目前,柯马在航空领域的业务范围主要包括哪些内容? 约翰·纳克斯:柯马(COMAU)是一家隶属于FIAT(菲亚特)集团的全球化企业.     

关注飞机数字化柔性装配技术新进展——第一届飞机数字化柔性装配技术研讨会隆重召开

2009年8月14日,由总装备部先进制造技术专业组、中航工业科技委和北京航空航天大学联合主办,北京航空制造工程研究所承办的第一届飞机数字化柔性装配技术研讨会在北京航空制造工程研究所召开.