The Grain Impact Analyser and Dust Accumulator (GIADA) Experiment for the Rosetta Mission: Design, Performances and First Results

The Grain Impact Analyser and Dust Accumulator (GIADA) onboard the ROSETTA mission to comet 67P/Churyumov–Gerasimenko is devoted to study the cometary dust environment. Thanks to the rendezvous configuration of the mission, GIADA will be plunged in the dust environment of the coma and will be able to explore dust flux evolution and grain dynamic properties with position and time. This will represent a unique opportunity to perform measurements on key parameters that no ground-based observation or fly-by mission is able to obtain and that no tail or coma model elaborated so far has been able to properly simulate. The coma and nucleus properties shall be, then, clarified with consequent improvement of models describing inner and outer coma evolution, but also of models about nucleus emission during different phases of its evolution. GIADA shall be capable to measure mass/size of single particles larger than about 15 μm together with momentum in the range 6.5 × 10⁻¹⁰ ÷ 4.0 × 10⁻⁴ kg m s⁻¹ for velocities up to about 300 m s⁻¹. For micron/submicron particles the cumulative mass shall be detected with sensitivity 10⁻¹⁰ g. These performances are suitable to provide a statistically relevant set of data about dust physical and dynamic properties in the dust environment expected for the target comet 67P/Churyumov–Gerasimenko. Pre-flight measurements and post-launch checkouts demonstrate that GIADA is behaving as expected according to the design specifications. The International GIADA Consortium (I, E, UK, F, D, USA).     

The Genesis Solar Wind Concentrator Target: Mass Fractionation Characterised by Neon Isotopes

The concentrator on Genesis provided samples of increased fluences of solar wind ions for precise determination of the oxygen isotopic composition. The concentration process caused mass fractionation as a function of the radial target position. This fractionation was measured using Ne released by UV laser ablation and compared with modelled Ne data, obtained from ion-trajectory simulations. Measured data show that the concentrator performed as expected and indicate a radially symmetric concentration process. Measured concentration factors are up to ∼30 at the target centre. The total range of isotopic fractionation along the target radius is 3.8%/amu, with monotonically decreasing ²⁰Ne/²²Ne towards the centre, which differs from model predictions. We discuss potential reasons and propose future attempts to overcome these disagreements.     

MESSENGER Mission Overview

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched on August 3, 2004, is nearing the halfway point on its voyage to become the first probe to orbit the planet Mercury. The mission, spacecraft, and payload are designed to answer six fundamental questions regarding the innermost planet: (1) What planetary formational processes led to Mercury’s high ratio of metal to silicate? (2) What is the geological history of Mercury? (3) What are the nature and origin of Mercury’s magnetic field? (4) What are the structure and state of Mercury’s core? (5) What are the radar-reflective materials at Mercury’s poles? (6) What are the important volatile species and their sources and sinks near Mercury? The mission has focused to date on commissioning the spacecraft and science payload as well as planning for flyby and orbital operations. The second Venus flyby (June 2007) will complete final rehearsals for the Mercury flyby operations in January and October 2008 and September 2009. Those flybys will provide opportunities to image the hemisphere of the planet not seen by Mariner 10, obtain high-resolution spectral observations with which to map surface mineralogy and assay the exosphere, and carry out an exploration of the magnetic field and energetic particle distribution in the near-Mercury environment. The orbital phase, beginning on March 18, 2011, is a one-year-long, near-polar-orbital observational campaign that will address all mission goals. The orbital phase will complete global imaging, yield detailed surface compositional and topographic data over the northern hemisphere, determine the geometry of Mercury’s internal magnetic field and magnetosphere, ascertain the radius and physical state of Mercury’s outer core, assess the nature of Mercury’s polar deposits, and inventory exospheric neutrals and magnetospheric charged particle species over a range of dynamic conditions. Answering the questions that have guided the MESSENGER mission will expand our understanding of the formation and evolution of the terrestrial planets as a family.     

Solar and Solar-Wind Composition Results from the Genesis Mission

The Genesis mission returned samples of solar wind to Earth in September 2004 for ground-based analyses of solar-wind composition, particularly for isotope ratios. Substrates, consisting mostly of high-purity semiconductor materials, were exposed to the solar wind at L1 from December 2001 to April 2004. In addition to a bulk sample of the solar wind, separate samples of coronal hole (CH), interstream (IS), and coronal mass ejection material were obtained. Although many substrates were broken upon landing due to the failure to deploy the parachute, a number of results have been obtained, and most of the primary science objectives will likely be met. These objectives include He, Ne, Ar, Kr, and Xe isotope ratios in the bulk solar wind and in different solar-wind regimes, and ¹⁵N/¹⁴N and ¹⁸O/¹⁷O/¹⁶O to high precision. The greatest successes to date have been with the noble gases. Light noble gases from bulk solar wind and separate solar-wind regime samples have now been analyzed. Helium results show clear evidence of isotopic fractionation between CH and IS samples, consistent with simplistic Coulomb drag theory predictions of fractionation between the photosphere and different solar-wind regimes, though fractionation by wave heating is also a possible explanation. Neon results from closed system stepped etching of bulk metallic glass have revealed the nature of isotopic fractionation as a function of depth, which in lunar samples have for years deceptively suggested the presence of an additional, energetic component in solar wind trapped in lunar grains and meteorites. Isotope ratios of the heavy noble gases, nitrogen, and oxygen are in the process of being measured.     

Missions to Mercury

Mercury is a very difficult planet to observe from the Earth, and space missions that target Mercury are essential for a comprehensive understanding of the planet. At the same time, it is also difficult to orbit because it is deep inside the Sun’s gravitational well. Only one mission has visited Mercury; that was Mariner 10 in the 1970s. This paper provides a brief history of Mariner 10 and the numerous imaginative but unsuccessful mission proposals since the 1970s for another Mercury mission. In the late 1990s, two missions—MESSENGER and BepiColombo—received the go-ahead; MESSENGER is on its way to its first encounter with Mercury in January 2008. The history, scientific objectives, mission designs, and payloads of both these missions are described in detail.     

Coronal Observations of CMEs

CMEs have been observed for over 30 years with a wide variety of instruments. It is now possible to derive detailed and quantitative information on CME morphology, velocity, acceleration and mass. Flares associated with CMEs are observed in X-rays, and several different radio signatures are also seen. Optical and UV spectra of CMEs both on the disk and at the limb provide velocities along the line of sight and diagnostics for temperature, density and composition. From the vast quantity of data we attempt to synthesize the current state of knowledge of the properties of CMEs, along with some specific observed characteristics that illuminate the physical processes occurring during CME eruption. These include the common three-part structures of CMEs, which is generally attributed to compressed material at the leading edge, a low-density magnetic bubble and dense prominence gas. Signatures of shock waves are seen, but the location of these shocks relative to the other structures and the occurrence rate at the heights where Solar Energetic Particles are produced remains controversial. The relationships among CMEs, Moreton waves, EIT waves, and EUV dimming are also cloudy. The close connection between CMEs and flares suggests that magnetic reconnection plays an important role in CME eruption and evolution. We discuss the evidence for reconnection in current sheets from white-light, X-ray, radio and UV observations. Finally, we summarize the requirements for future instrumentation that might answer the outstanding questions and the opportunities that new space-based and ground-based observatories will provide in the future.     

难加工材料闭式整体构件精密电火花加工技术研究

闭式整体构件因其结构复杂、叶间流道空间弯扭程度大,使得加工可达性极差,且材料一般为难加工的高强度合金,整体制造难度很大。针对这一制造难题,研究了闭式整体构件电火花加工的若干关键技术,如叶间流道加工区域划分、成形电极及其加工运动轨迹设计、工艺基准统一和电参数选择与优化、数控电火花加工过程仿真分析等。在此基础上针对典型闭式整体构件进行了试制加工。试验结果表明,基于所研究的关键技术能够采用数控电火花加工技术精密、可靠地实现闭式整体构件的整体制造。     

基于马尔科夫链模型的脉动装配线运行状态预测

分析了影响脉动生产线运行的因素和状态预测的必要性,提出了基于马尔科夫链模型的状态预测方法。基于马尔科夫链预测理论,对脉动生产线运行状态划分,确定状态转移矩阵,建立马尔科夫预测模型,并对模型准确性进行验证。     

复合材料加筋壁板制造成本的快速估算模型

为了能够在设计阶段早期对复合材料加筋壁板制造成本进行快速估算,提出了一种以结构设计重量为主要驱动因素的制造成本估算模型。该模型的关键是考虑了诸如材料成本比重系数、制造工艺系数、蒙皮形状系数、筋条形状系数、材料利用率系数等合理取值。以某验证试验的试验件制造成本估算为例,估算成本与实际制造成本的偏差为10.8%,说明了采用该方法对复合材料加筋壁板制造成本进行快速估算的结果是可以为设计人员提供决策依据的。     

OSIRIS-REx: Sample Return from Asteroid (101955) Bennu

In May of 2011, NASA selected the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) asteroid sample return mission as the third mission in the New Frontiers program. The other two New Frontiers missions are New Horizons, which explored Pluto during a flyby in July 2015 and is on its way for a flyby of Kuiper Belt object 2014 MU69 on January 1, 2019, and Juno, an orbiting mission that is studying the origin, evolution, and internal structure of Jupiter. The spacecraft departed for near-Earth asteroid (101955) Bennu aboard an United Launch Alliance Atlas V 411 evolved expendable launch vehicle at 7:05 p.m. EDT on September 8, 2016, on a seven-year journey to return samples from Bennu. The spacecraft is on an outbound-cruise trajectory that will result in a rendezvous with Bennu in November 2018. The science instruments on the spacecraft will survey Bennu to measure its physical, geological, and chemical properties, and the team will use these data to select a site on the surface to collect at least 60 g of asteroid regolith. The team will also analyze the remote-sensing data to perform a detailed study of the sample site for context, assess Bennu’s resource potential, refine estimates of its impact probability with Earth, and provide ground-truth data for the extensive astronomical data set collected on this asteroid. The spacecraft will leave Bennu in 2021 and return the sample to the Utah Test and Training Range (UTTR) on September 24, 2023.