IMAGE mission overview

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission is the first mission in NASA's MIDEX (Mid-size Explorer) program. It is the first satellite mission that is dedicated to imaging the Earth's magnetosphere. IMAGE will utilize the techniques of ultraviolet imaging, neutral atom imaging, and radio plasma imaging to map out global distributions of the electron and proton aurora; the helium ions of the plasmasphere; the ionospheric ion outflow; the medium-energy ions of the near-Earth plasma sheet, ring current, and polar cusp; the high-energy ions of the ring current and trapped radiation belts; and the total plasma density from the ionosphere out to the magnetopause. The imaging perspective is from an elliptical polar orbit with apogee at latitudes from 40° to 90° in the northern hemisphere. For ultraviolet and neutral atom imaging, the time resolution is set by the two-minute spin period of the IMAGE spacecraft, which will be sufficient to track the development of magnetospheric substorms. An important feature of the IMAGE mission is its completely open data set with no proprietary data or intervals. All data, along with software needed for plotting and analysis, will be available within 24 hours of acquisition.     

Dayside Proton Aurora: Comparisons between Global MHD Simulations and IMAGE Observations

The IMAGE mission provides a unique opportunity to evaluate the accuracy of current global models of the solar wind interaction with the Earth's magnetosphere. In particular, images of proton auroras from the Far Ultraviolet Instrument (FUV) onboard the IMAGE spacecraft are well suited to support investigations of the response of the Earth's magnetosphere to interplanetary disturbances. Accordingly, we have modeled two events that occurred on June 8 and July 28, 2000, using plasma and magnetic field parameters measured upstream of the bow shock as input to three-dimensional magnetohydrodynamic (MHD) simulations. This paper begins with a discussion of images of proton auroras from the FUV SI-12 instrument in comparison with the simulation results. The comparison showed a very good agreement between intensifications in the auroral emissions measured by FUV SI-12 and the enhancement of plasma flows into the dayside ionosphere predicted by the global simulations. Subsequently, the IMAGE observations are analyzed in the context of the dayside magnetosphere's topological changes in magnetic field and plasma flows inferred from the simulation results. Finding include that the global dynamics of the auroral proton precipitation patterns observed by IMAGE are consistent with magnetic field reconnection occurring as a continuous process while the IMF changes in direction and the solar wind dynamic pressure varies. The global simulations also indicate that some of the transient patterns observed by IMAGE are consistent with sporadic reconnection processes. Global merging patterns found in the simulations agree with the antiparallel merging model, though locally component merging might broaden the merging region, especially in the region where shocked solar wind discontinuities first reach the magnetopause. Finally, the simulations predict the accretion of plasma near the bow shock in the regions threaded by newly open field lines on which plasma flows into the dayside ionosphere are enhanced. Overall the results of these initial comparisons between global MHD simulation results and IMAGE observations emphasize the interplay between reconnection and dynamic pressure processes at the dayside magnetopause, as well as the intricate connection between the bow shock and the auroral region.     

The IMAGE science and mission operations center

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) will produce forefront science by quantifying the response of the magnetosphere to the time variable solar wind. It will acquire, for the first time, a variety of three-dimensional images of magnetospheric boundaries and plasma distributions extending from the magnetopause to the inner plasmasphere. The images will be produced on time scales needed to answer important questions about the interactions of the solar wind and the magnetosphere. The IMAGE team will provide open access to all IMAGE data. Thus there will be no proprietary rights or periods. All IMAGE data products will be archived and available to the scientific research community. The IMAGE mission will operate with a near 100% duty cycle with all instruments in their baseline operational modes. A Science and Mission Operations Control Center or SMOC has been developed at the NASA Goddard Space Flight Center (GSFC) to be the main data and command processing system for IMAGE. The IMAGE Level-0 data will be processed into Level 0.5 and Level-1 data and browse products within 24 hours after their receipt of raw data in the SMOC. These data products will be transferred to the NSSDC, for long-term archiving, and posted immediately on the world-wide-web for use by the international scientific community and the public.     

Medium energy neutral atom (MENA) imager for the IMAGE mission

The Medium Energy Neutral Atom (MENA) imager was developed in response to the Imaging from the Magnetopause to the Aurora for Global Exploration (IMAGE) requirement to produce images of energetic neutral atoms (ENAs) in the energy range from 1 to 30 keV. These images will be used to infer characteristics of magnetospheric ion distributions. The MENA imager is a slit camera that images incident ENAs in the polar angle (based on a conventional spherical coordinate system defined by the spacecraft spin axis) and utilizes the spacecraft spin to image in azimuth. The speed of incident ENAs is determined by measuring the time-of-flight (TOF) from the entrance aperture to the detector. A carbon foil in the entrance aperture yields secondary electrons, which are imaged using a position-sensitive Start detector segment. This provides both the one-dimensional (1D) position at which the ENA passed through the aperture and a Start time for the TOF system. Impact of the incident ENA on the 1D position-sensitive Stop detector segment provides both a Stop-timing signal and the location that the ENA impacts the detector. The ENA incident polar angle is derived from the measured Stop and Start positions. Species identification (H vs. O) is based on variation in secondary electron yield with mass for a fixed ENA speed. The MENA imager is designed to produce images with 8°×4° angular resolution over a field of view 140°×360°, over an energy range from 1 keV to 30 keV. Thus, the MENA imager is well suited to conduct measurements relevant to the Earth's ring current, plasma sheet, and (at times) magnetosheath and cusp.     

An Overview of Results From rpi on Image

The Radio Plasma Imager (RPI) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft was designed as a long-range magnetospheric radio sounder, relaxation sounder, and a passive plasma wave instrument. The RPI is a highly flexible instrument that can be programmed to perform these types of measurements at times when IMAGE is located in key regions of the magnetosphere. RPI is the first radio sounder ever flown to large radial distances into the magnetosphere. The long-range sounder echoes from RPI allow remote sensing of a variety of plasmas structures and boundaries in the magnetosphere. A profile inversion technique for RPI echo traces has been developed and provides a method for determining the density distribution of the plasma from either direct or field-aligned echoes. This technique has enabled the determination of the evolving density structure of the polar cap and the plasmasphere under a variety of geomagnetic conditions. New results from RPI show that the plasmasphere refills in slightly greater than a day at L values of 2.8 and that ion heating is probably playing a major role in the overall density distribution along the field-line. In addition, RPI's plasma resonance observations at large radial distances over the polar cap provided in situ measurements of the plasma density with an accuracy of a few percent. For the first time in the magnetosphere, RPI has also observed the plasma D resonances. RPI's long antennas and its very low noise receivers provide excellent observations in the passive receive-only mode when the instrument measures the thermal plasma noise as well as natural emissions such as the continuum radiation and auroral kilometric radiation (AKR). Recent passive measurements from RPI have been compared extensively with images from the Extreme Ultraviolet (EUV) imager on IMAGE resulting in a number of new discoveries. For instance, these combined observations show that kilometric continuum can be generated at the plasmapause from sources in or very near the magnetic equator, within a bite-out region of the plasmasphere. The process by which plasmaspheric bite-out structures are produced is not completely understood at this time. Finally, RPI has been used to successfully test the feasibility of magnetospheric tomography. During perigee passages of the Wind spacecraft, RPI radio transmissions at one and two frequencies have been observed by the Waves instrument. The received electric field vector was observed to rotate with time due to the changing density of plasma, and thus Faraday rotation was measured. Many future multi-spacecraft missions propose to use Faraday rotation to obtain global density pictures of the magnetosphere.     

THE CLUSTER MISSION: ESA'S SPACEFLEET TO THE MAGNETOSPHERE

During the first half of 1996, the European Space Agency (ESA) will launch a unique flotilla of spacecraft to study the interaction between the solar wind and the Earth's magnetosphere in unprecedented detail. The Cluster mission was first proposed to the Agency in late 1982 and was selected, together with SOHO, as the Solar Terrestrial Science Programme (STSP), the first cornerstone of ESA's Horizon 2000 Programme. It is a complex four-spacecraft mission designed to carry out three-dimensional measurements of the magnetosphere, covering both large- and small-scale phenomena in the sunward and tail regions. The mission is a first for ESA in a number of ways: – the first time that four identical spacecraft have been launched on a single launch vehicle, – the first time that ESA has built spacecraft in true series production and operated them as a single group, – the first time that European scientific institutes have produced a series of up to five instruments with full intercalibration, and – the first launch of the Agency's new heavy launch vehicle Ariane-5. The article gives an overview of this unique mission and the requirements that governed the spacecraft design. It then describes in detail the resulting design and how the particular engineering challenges posed by the series production of four identical spacecraft and sets of scientific instruments were met by the combined efforts of the ESA Project Team, Industry and the experiment teams.     

The New Horizons Spacecraft

The New Horizons spacecraft was launched on 19 January 2006. The spacecraft was designed to provide a platform for seven instruments designated by the science team to collect and return data from Pluto in 2015. The design meets the requirements established by the National Aeronautics and Space Administration (NASA) Announcement of Opportunity AO-OSS-01. The design drew on heritage from previous missions developed at The Johns Hopkins University Applied Physics Laboratory (APL) and other missions such as Ulysses. The trajectory design imposed constraints on mass and structural strength to meet the high launch acceleration consistent with meeting the AO requirement of returning data prior to the year 2020. The spacecraft subsystems were designed to meet tight resource allocations (mass and power) yet provide the necessary control and data handling finesse to support data collection and return when the one-way light time during the Pluto fly-by is 4.5 hours. Missions to the outer regions of the solar system (where the solar irradiance is 1/1000 of the level near the Earth) require a radioisotope thermoelectric generator (RTG) to supply electrical power. One RTG was available for use by New Horizons. To accommodate this constraint, the spacecraft electronics were designed to operate on approximately 200 W. The travel time to Pluto put additional demands on system reliability. Only after a flight time of approximately 10 years would the desired data be collected and returned to Earth. This represents the longest flight duration prior to the return of primary science data for any mission by NASA. The spacecraft system architecture provides sufficient redundancy to meet this requirement with a probability of mission success of greater than 0.85. The spacecraft is now on its way to Pluto, with an arrival date of 14 July 2015. Initial in-flight tests have verified that the spacecraft will meet the design requirements.     

航天器自动化测试语言研究

航天器测试语言是支撑航天器自动化测试的形式体系及航天器测试过程标准,在当前多航天器批产网络化测试的新需求下,测试语言标准体系研究对于提高航天器测试自动化水平和保障测试过程安全具有重要意义。通过对现有典型航天器测试语言的全面分析和比较,总结出基本特征,并结合当前先进的网络计算技术,提出了我国航天器测试语言发展的目标和方向,同时针对国内航天器测试语言研究设计工作的不足,给出一种航天器测试语言CATOL(China Aerospace Test and Operation Language)。该研究对提高我国航天器测试业务规范水平和测试人员的工作效率、促进航天器测试自动化研究的发展将起到一定的推动作用。     

Far ultraviolet imaging from the IMAGE spacecraft. 2. Wideband FUV imaging

The Far Ultraviolet Wideband Imaging Camera (WIC) complements the magnetospheric images taken by the IMAGE satellite instruments with simultaneous global maps of the terrestrial aurora. Thus, a primary requirement of WIC is to image the total intensity of the aurora in wavelength regions most representative of the auroral source and least contaminated by dayglow, have sufficient field of view to cover the entire polar region from spacecraft apogee and have resolution that is sufficient to resolve auroras on a scale of 1 to 2 latitude degrees. The instrument is sensitive in the spectral region from 140–190 nm. The WIC is mounted on the rotating IMAGE spacecraft viewing radially outward and has a field of view of 17° in the direction parallel to the spacecraft spin axis. Its field of view is 30° in the direction perpendicular to the spin axis, although only a 17°×17° image of the Earth is recorded. The optics was an all-reflective, inverted Cassegrain Burch camera using concentric optics with a small convex primary and a large concave secondary mirror. The mirrors were coated by a special multi-layer coating, which has low reflectivity in the visible and near UV region. The detector consists of a MCP-intensified CCD. The MCP is curved to accommodate the focal surface of the concentric optics. The phosphor of the image intensifier is deposited on a concave fiberoptic window, which is then coupled to the CCD with a fiberoptic taper. The camera head operates in a fast frame transfer mode with the CCD being read approximately 30 full frames (512×256 pixel) per second with an exposure time of 0.033 s. The image motion due to the satellite spin is minimal during such a short exposure. Each image is electronically distortion corrected using the look up table scheme. An offset is added to each memory address that is proportional to the image shift due to satellite rotation, and the charge signal is digitally summed in memory. On orbit, approximately 300 frames will be added to produce one WIC image in memory. The advantage of the electronic motion compensation and distortion correction is that it is extremely flexible, permitting several kinds of corrections including motions parallel and perpendicular to the predicted axis of rotation. The instrument was calibrated by applying ultraviolet light through a vacuum monochromator and measuring the absolute responsivity of the instrument. To obtain the data for the distortion look up table, the camera was turned through various angles and the input angles corresponding to a pixel matrix were recorded. It was found that the spectral response peaked at 150 nm and fell off in either direction. The equivalent aperture of the camera, including mirror reflectivities and effective photocathode quantum efficiency, is about 0.04 cm². Thus, a 100 Rayleigh aurora is expected to produce 23 equivalent counts per pixel per 10 s exposure at the peak of instrument response.     

THE CLUSTER DATA PROCESSING SYSTEM: A DISTRIBUTED SYSTEM IN SUPPORT OF A CHALLENGING SCIENTIFIC MISSION

The Cluster mission is aimed at the study of small-scale structures that are believed to be fundamental in determining the behaviour of key interactive processes of cosmic plasma. The mission will be controlled from the European Space Operations Centre (ESOC). ESOC is also in charge of the commanding of the scientific payloads on-board the four Cluster spacecraft after negotiation with the Cluster Principal Investigators (PIs) and of collecting and distributing the mission's scientific results to the Cluster community. This paper describes the process of translating the scientific requirements of the Cluster mission into a data-processing system supporting the mission via the definition of an appropriate operational scenario. In particular, the process of negotiation between the PIs and ESOC to command the spacecraft is mediated by the Joint Science Operations Centre (JSOC) and finalised by the Cluster Mission Planning System (CMPS) while the return of the data to the Cluster community is actuated by the Cluster Data Disposition System (CDDS). The Cluster Mission Control System (CMCS) provides the interface between these two systems and the spacecraft. These elements constitute the Cluster Data-Processing System (CDPS).     

基于模型的载人航天器研制方法研究与实践

载人航天器具有系统规模大、技术难度高、单件小批量、无法通过多次飞行持续完善设计、可靠性要求高等特点。当前载人航天器研制中仍存在着参数化和模型化程度不高、基于模型的系统综合仿真验证不足、研制各环节缺乏数字化集成等问题，传统基于文本的系统工程方法已无法满足研制需求，亟需采用基于模型的系统工程方法。本文针对载人航天器的研制现状和应用需求，提出了面向载人航天器全生命周期的模型体系，定义了需求模型、功能模型、产品模型、工程模型、制造模型、实做模型等六类模型，提出了基于模型的研制流程，包含系统设计闭环验证、产品设计闭环验证、实做产品闭环验证3个验证环节，并深入探索了各研制环节中不同模型间的传递与关联关系。以某型号载人航天器为应用基础，系统地验证了提出的方法。     

Space Interferometry Mission spacecraft pointing error budgets

Preliminary error budgets for the pointing knowledge, control, and stability of the Space Interferometry Mission (SIM) spacecraft are constructed using the specifications of commercial off-the-shelf attitude determination sensors, attitude control actuators, and other spacecraft capabilities that have been demonstrated in past missions. Results obtained indicate that we can meet all the presently known spacecraft pointing requirements. A large number of derived requirements are generated from this study. Examples are specifications on attitude determination sensors, attitude control actuators, minimum settling time after a rest-to-rest spacecraft slew. Preliminary error budgets constructed in this study must be updated to reflect the changing spacecraft design and requirements     

The image/poetry education and public outreach program

Education and public outreach are viewed by NASA as significant undertakings for all of its space missions. The IMAGE satellite is one of the first missions to explicitly include `E&PO in its original proposal to NASA in 1996. We will discuss what IMAGE has accomplished in this area to date, and what new activities it will conduct following a successful launch.     

ACTIVE SPACECRAFT POTENTIAL CONTROL

Charging of the outer surface or of the entire structure of a spacecraft in orbit can have a severe impact on the scientific output of the instruments. Typical floating potentials for magnetospheric satellites (from +1 to several tens of volts in sunlight) make it practically impossible to measure the cold (several eV) component of the ambient plasma. Effects of spacecraft charging are reduced by an entirely conductive surface of the spacecraft and by active charge neutralisation, which in the case of Cluster only deals with a positive potential. The Cluster spacecraft are instrumented with ion emitters of the liquid-metal ion-source type, which will produce indium ions at 5 to 8 keV energy. The operating principle is field evaporation of indium in the apex field of a needle. The advantages are low power consumption, compactness and high mass efficiency. The ion current will be adjusted in a feedback loop with instruments measuring the spacecraft potential (EFW and PEACE). A stand-alone mode is also foreseen as a back-up. The design and principles of the operation of the active spacecraft potential control instrument (ASPOC) are presented in detail. Flight experience with a similar instrument on the Geotail spacecraft is outlined.     

Modeling of Thermal Perturbations Using Raytracing Method with Preliminary Results for a Test Case Model of the Pioneer 10/11 Radioisotopic Thermal Generators

Electromagnetic radiation emitted from a source carries momentum. Thus, the dissipation of waste thermal energy can produce disturbance forces on spacecraft surfaces if the energy is not dissipated in a symmetric pattern. This force can be computed for a plate element as the quotient of the radiated power in normal direction and the speed of light. Depending on mission and spacecraft design the resulting surface forces have to be included into the disturbance budget. At ZARM an elaborated method for the exact modeling of the disturbances caused by heat radiation was developed which can be used for any satellite mission with high requirements on perturbation knowledge (e.g. LISA, LISA pathfinder, MICROSCOPE). The method which will be presented in this paper is based on raytracing and finite element (FE) thermal analysis. As a demonstration of the potential of the method, preliminary results acquired with a test case model of the Pioneer 10/11 Radioisotopic Thermal Generators (RTGs) will be shown.     

CLUSTER MISSION OPERATIONS

The Cluster ground segment design and mission operations concept have been defined according to the basic mission requirements, namely, to allow the transfer of the four spacecraft from the initial geostationary transfer orbit achieved at separation from the launcher into the final highly elliptical polar orbits, such that in the areas of scientific interest along their orbits, the four spacecraft will form a tetrahedral configuration with pre-defined separation distances, to be changed every six months during the mission. The Cluster mission operations will be carried out by ESA from its European Space Operations Centre; the task of merging the Principal Investigators' requests into coordinated, regular scientific mission planning inputs to ESOC will be undertaken by the Joint Science Operations Centre. The mission products will be distributed to the scientific community regularly in form of CD-ROMs. Principal Investigators will also have access to quick-look science, housekeeping telemetry and auxiliary data via an electronic network.     

The design features of the GGS wind and polar spacecraft

The Global Geospace Science (GGS) WIND and POLAR spacecraft employ unique configuration and design features driven by the requirements of the science instruments which they host. The WIND and POLAR spacecraft are cylindrically shaped spinners (WIND 20 rpm, POLAR 10 rpm) approximately 2.4 m in diameter and 1.8 m high. Each spacecraft has a pair of lanyard booms, which hold magnetometers, four radial wire antennas and two spin-axis antennas. While satisfying different mission requirements, both share a common basic design. The WIND laboratory contains 8 instruments, designed to optimize measurements of waves, fields and particle distributions. The POLAR laboratory contains 12 instruments, with a similar design emphasis on waves, fields and particle measurements, as well as on auroral imaging. The main difference between the two spacecraft is a despun platform on POLAR which provides a stable environment for the auroral imager instruments. Both laboratories are designed to be launched on Delta II model 7925 launch vehicle and have total masses of approximately 1150 g (WIND) and 1240 kg (POLAR).