UVSTAR, a spectrographic telescope for the shuttle Hitchhiker-M bridge

UVSTAR is an EUV spectral imager intended as a facility instrument devoted to solar system astronomy and to astronomy. It covers the wavelength range of 500 to 1250 Å, with sufficient spectral resolution to separate atomic emission lines and to form spectrally resolved images of extended plasma sources. Targets include the Io plasma torus at Jupiter, hot stars, planetary nebulae and extragalactic sources. UVSTAR will make useful measurements of emissions from the Earth's atmosphere as well. UVSTAR consists of a pair of telescopes and concave-grating spectrographs that cover the overlapping spectral ranges of 500–900 Å and 850–1250 Å. The telescopes use two 30 cm diameter off-axis paraboloids having a focal length of 1.4 m. An image of the target is formed at the entrance slits of two concave grating spectrographs. The gratings provide dispersion and re-image the slits at the detectors, intensified CCDs. The readout format of the detectors can be chosen by computer, and three slit widths are selectable to adapt the instrument to specific tasks. The spectrograph package has internal gimbals which allow rotation of ±3° about each of two axes. Dedicated finding and tracking telescopes will acquire and track the target after rough pointing is achieved by orienting the Orbiter. Responsibilities for the implementation and utilization of UVSTAR are shared by groups the U.S. and Italy. UVSTAR is scheduled for flight in early 1994.     

Mapping lunar surface chemistry: New prospects with the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS)

Surface chemistry of airless bodies in the solar system can be derived from remote X-ray spectral measurements from an orbiting spacecraft. X-rays from planetary surfaces are excited primarily by solar X-rays. Several experiments in the past have used this technique of X-ray fluorescence for deriving abundances of the major rock forming elements. The Chandrayaan-2 orbiter carries an X-ray fluorescence experiment named CLASS that is designed based on results from its predecessor C1XS flown on Chandrayaan-1. We discuss the new aspects of lunar science that can be potentially achieved with CLASS.     

Integration and calibration of a multi slit spectropolarimeter

Multi-slit spectropolarimeter is a next-generation spectropolarimeter to obtain vector magnetic field information at high spatial, spectral, and temporal resolution for studying the magnetic structures on the Sun. Once developed, it can be used as ground based instrument at solar observatories, also as a space payload for various solar missions. A high spectral resolution is invariably an important parameter for accurate vector magnetic field measurements and faster cadence is required for the study of dynamical evolution of structures (e.g., solar flares, sunspots etc.) on the Sun and hence better understanding on the physics behind their evolution.     

Very low frequency interferometry for the Chang’E-2 project

Very low frequency interferometry among two astronomical experiments has been proposed and accepted for further study for the second phase of China’s lunar exploration programme (the Chang’E Programme), which is envisaged to operate a lander and a rover on the surface of the moon. This experiment is an interferometer experiment in the very low frequency (VLF, f < 15 MHz) regime of radio frequencies with at least degree-level angular resolution. The goals include observing solar storm activities, Coronal Mass Ejections, Auroral Kilometric Radiation, and planetary radiation in the solar system, studying the origin of Cosmic Rays, spectral properties of pulsars, surveying ionized hydrogen in the Galaxy, and exploring coherent radio emissions.     

Arctic — Antarctic night airglow comparisons

Airglow observations from Eureka, Canada (80° N) and South Pole (90° S) observatories have been made through the winters during the past 1/2 solar cycle. Seasonal and solar activity changes are evident. The intensities also show temporal variations due to wave activity, with periods from 6 hours to 15 days, particularly in the Arctic OI and Na emissions. Comparisons are made of the OH intensities measured at Eureka and South Pole during their respective winters.     

Scientific requirements for future spatially resolved white-light and broad-band high-cadence observations of the Sun

Several important issues are open in the field of solar variability and they wait their solution which up to now was attempted using critical ground-based instrumentations. However, accurate photometric data are attainable only from space. New observational material should be collected with high enough spatial and spectral resolution, covering the whole visible range of the electromagnetic spectrum as well infrared and ultraviolet to reconstruct the total solar irradiance: (1) the absolute contributions of different small-scale structural entities of the solar atmosphere from the white light flares and from micro-flares are still poorly known; (2) we do not know the absolute contributions of different structural elements of the solar atmosphere to the long-term and to the cyclic variations of the solar irradiance, including features of the polar regions of the Sun; (3) the variations of the chromospheric magnetic network are still poorly evaluated; (4) only scarce information is available about the spectral variations of different small-scale features in the high photosphere. Variability of the Sun in white light can be studied with higher spectral, spatial and time resolution using space-born telescopes, which are more appropriate for this purpose than ground based observatories because of better seeing conditions, no interference of the terrestrial atmosphere and a more precise calibration procedure. Scientific requirements for such observations and the possible experimental tools proposed for their solution. Suggested solar studies have broader astrophysical importance.     

The pinhole/occulter facility

The Pinhole/Occulter Facility concept uses a remote occulting mask to provide high resolution observations of the solar corona and of astronomical X-ray sources. With coded-aperture and Fourier-transform techniques, the Pinhole/Occulter makes images at a resolution of 0.2 arc sec for 2 - 120 keV X-rays, using a 50-m boom erected from the payload bay of the Space Shuttle or mounted on a free-flying platform. The remote occulter also creates a large shadow area for solar coronal observations; the Pinhole/Occulter concept includes separate optical and ultraviolet telescopes with 50-cm apertures. These large telescopes will provide a new order of resolution and sensitivity for diagnostic observations of faint structures in the solar corona. The Pinhole/Occulter is a powerful and versatile tool for general-purpose X-ray astronomy, with excellent performance in a broad spectral band complementary to that accessible with AXAF. The large collecting area of 1.5 m² results in a 5σ detection threshold of about 0.02 μJy for the 2 - 10 keV band, or about 10^?5 ph(cm²sec keV)^?1 at 20 keV.     

Comparison of solar soft X-ray irradiance from broadband photometers to a high spectral resolution rocket observation

The solar soft X-ray (XUV; 1–30 nm) radiation is highly variable on all time scales and strongly affects the ionosphere and upper atmosphere of Earth, Mars, as well as the atmospheres and surfaces of other planets and moons in the solar system; consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. While there have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially its variability during flares, has been hampered by the lack of high spectral resolution measurements in this wavelength range. The conversion of the XUV photometer signal into irradiance requires the use of a solar spectral model, but there has not been direct validation of these spectral models for the XUV range. For example, the irradiance algorithm for the XUV Photometer System (XPS) measurements uses multiple CHIANTI spectral models, but validation has been limited to other solar broadband measurements or with comparisons of the atmospheric response to solar variations. A new rocket observation of the solar XUV irradiance with 0.1 nm resolution above 6 nm was obtained on 14 April 2008, and these new results provide a first direct validation of the spectral models used in the XPS data processing. The rocket observation indicates very large differences for the spectral model for many individual emission features, but the differences are significantly smaller at lower resolution, as expected since the spectral models are scaled to match the broadband measurements. While this rocket measurement can help improve a spectral model for quiet Sun conditions, many additional measurements over a wide range of solar activity are needed to fully address the spectral model variations. Such measurements are planned with a similar instrument included on NASA’s Solar Dynamics Observatory (SDO), whose launch is expected in 2009.     

Attitude control actuator scaling laws for orbiting solar reflectors

The rapid evolution of in-orbit manufacturing will enable the fabrication of low-cost, large-scale space structures. In particular, the use of 3D printing technologies will remove traditional payload constraints associated with launch vehicles, due to fairing size and launch loads, thus allowing the construction of larger and lighter structures, such as orbiting solar reflectors. These structures will require efficient attitude control systems, able to provide the necessary torque for maneuvers and to counteract perturbations, such as gravity gradient and solar radiation pressure. In this paper, a top-level overview of actuator performances for orbiting solar reflectors is provided, and scaling laws associated with the required actuator mass and input power are developed. For each class of actuator, upper bounds on the maximum size of the structure which can be effectively controlled are presented. The results can also be extended to other classes of large planar Earth-pointing structures such as solar power satellites, solar sails, or large antennae.     

Thermospheric neutral density response to solar forcing

Recent measurements by the Solar EUV (Extreme Ultra Violet) Experiment (SEE) aboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics satellite (TIMED) provide solar EUV spectral irradiance with adequate spectral and temporal resolution, and thus the opportunity to use solar measurements directly in upper atmospheric general circulation models. Thermospheric neutral density is simulated with the NCAR Thermosphere–Ionosphere–Electrodynamic General Circulation Model (TIEGCM) using TIMED/SEE measurements and using the EUVAC solar proxy model. Neutral density is also calculated using the NRLMSISE-00 empirical model. These modeled densities are then compared to density measurements derived from satellite drag data. It is found that using measured solar irradiance in the general circulation model can improve density calculations compared to using the solar proxy model. It is also found that the general circulation model can improve upon the empirical model in simulating geomagnetic storm effects and the solar cycle variation of neutral density.     

Active stars and systems

The most notable manifestations of stellar activity are reviewed with particular emphasis on the merging picture of solar-type activity in physical conditions different from those in the Sun. Evidence for starspots, plages and high-level coronal emissions is presented from observations covering a wide range of spectral bands: from X-ray to radio wavelengths. The main physical parameters of the active areas in the active stars, when compared with solar values, indicate that the basic requirement for activity phenomena to develop is the presence of observationally elusive localized magnetic fields on and above the stellar surface. The importance of coordinated programs involving simultaneous observations from the ground and from space - aiming at empirical and theoretical modeling of activity phenomena - is stressed.     

宇宙黑暗时代探路者——鸿蒙计划

低频射电探测任务构想——鸿蒙计划旨在利用多颗卫星绕月编队形成超长波天文观测阵列,在月球背面开展空间低频射电天文探测。其科学目标是高精度测量全天射电频谱,揭示宇宙黑暗时代与黎明的演化历史;实现首次高分辨率超长波巡天,打开最后一个电磁窗口;观测太阳和行星超长波活动,揭示空间环境相互作用规律。该任务将获得超长波频段全天空图像,获取超长波波段天文射电源的强度、频谱、分布等信息。这些科学数据对于探索宇宙黑暗时代和黎明时代、研究银河系星际介质、宇宙线起源与传播、河外射电星系、类星体和星系团的演化、太阳活动与行星磁场等,具有重要的科学价值。     

1997年1月空间天气事件的三维MHD模拟

以1997年1月空气天气事件期间的观测为依据，在构造了比较接近真实的背景太阳风基础上，进一步利用三维时变的MHD模式，模拟了CME（日冕物质抛射）激发的扰动在行星际空间的传播过程，对地球空间环境的影响及行星际磁场南向分量Bz在1AU的时间经历。模拟结果与WIND卫星的测量进行了比较。结果表明，模拟与观测得到的扰动得到地球的时间、地球空间环境各量的变化及Bz的时间经历基本一致。     

太阳电池电路深空探测服役环境与关键技术分析

针对月球、火星、木星等不同的深空探测任务,本文通过在轨服役环境分析,说明了火星探测火星表面光谱计算方法、火星光谱太阳电池设计思路、火星表面除尘技术路线及木星探测低温低光强技术风险。结合工程技术经验,给出了特殊任务应用条件下单片太阳电池推算整板输出功率的计算方法,解决了我国尚无特殊条件的瞬态大太阳模拟器作为整板输出功率测试地面模拟光源的工程难题,为相关科研人员提供参考。     

Infrared astronomy on the Hubble Space Telescope

The Hubble Space Telescope offers enormous advantages to infrared astronomy in certain situations. The advantages of being above the atmosphere include an increase in spatial resolution, a much wider range of wavelengths available, and lower background radiation. Compared to proposed cooled telescopes, HST offers higher spatial resolution and increased collecting area. HST is particularly well suited to observations at wavelengths less than ～5 μm, where the diffraction limit is less than the seeing limit from the ground and thermal emission does not seriously compromise the sensitivity of the detectors. HST is also favorable for observations requiring high spectral resolution at all wavelengths not accessible from the ground.     

Comets in other planetary systems?

Comets in our solar system appear to have provided a bridge between the cold, volatile-rich outer solar system, and the warm, but volatile-poor inner solar system. Excluding tidal and possible extinct radionuclide heating sources, only in the inner solar system are temperatures high enough for liquid water, and therefore life as we know it, to exist for times comparable to the age of the solar system. Comets may have been crucial for providing biogenic volatiles and perhaps organic molecules to this warm environment. It is therefore interesting from an exobiological point of view to ask if comets exist in other planetary systems. Most attempts to detect comets around other stars or in interstellar space have failed. However, there is growing spectroscopic evidence for comet-like bodies orbiting the star Beta Pictoris.     

多谱段全日面极紫外成像仪

在极紫外波段对太阳进行成像观测是研究太阳活动、日冕中等离子体物理特性的重要手段.传统极紫外成像仪或光谱仪无法同时实现高光谱分辨率和大视场的太阳成像.本文设计了一种新型太阳极紫外多谱段成像系统,采用无狭缝光栅分光方式实现了高光谱分辨率和空间分辨率的全日面成像,成像视场可达47',光谱分辨率每像素2×10-3 nm,空间分辨率每像素1.4',全日面时间分辨率优于60s.通过分析谱线的全日面成像图和系统响应,表明成像仪能大范围的观测太阳活动形态演化,为太阳物理研究和空间天气预报提供更完整的观测数据.      

Imaging systems using modulation and coded aperture masks

The advent of improved γ-ray telescopes which incorporate high angular resolution imaging properties and adequate sensitivity will advance this branch of astronomy from the discovery phase to the exploratory phase. As in other fields, such as radio and X-ray astronomy, which have recently undergone this change, it will prove a fascinating era. The recent development of position sensitive γ-ray detection planes operated in conjunction with a suitable coded aperture mask have made γ-ray telescopes feasible which are capable of generating γ-ray images of the sky with a precision of 1 arc minute over the photon energy range 0.1 to 10 MeV. With a sensitivity of at least 1–10 milliCrab and scintillation standard spectral resolution not only can a large number of discrete γ-ray objects be identified and studied in detail but nuclear γ-ray line images of extended objects such as the Galactic Plane, Cloud Complexes, and supernovae remnants may be generated by this class of astronomical instrument.     

Numerical modeling of inhomogeneous orographic wave influence on planetary waves in the middle atmosphere

Parameterization of dynamical and thermal effects of stationary orographic gravity waves (OGWs) generated by the Earth’s surface topography is incorporated into a numerical model of general circulation of the middle and upper atmosphere. Responses of atmospheric general circulation and characteristics of planetary waves at altitudes from the troposphere up to the thermosphere to the effects of OGWs propagating from the earth surface are studied. Changes in atmospheric circulation and amplitudes of planetary waves due to variations of OGW generation and propagation in different seasons are considered. It is shown that during solstices the main OGW dynamical and heat effects occur in the middle atmosphere of winter hemispheres, where changes in planetary wave amplitudes due to OGWs may reach up to 50%. During equinoxes OGW effects are distributed more homogeneously between northern and southern hemispheres.     

A roadmap towards a space-based radio telescope for ultra-low frequency radio astronomy

The past two decades have witnessed a renewed interest in low frequency radio astronomy, with a particular focus on frequencies above 30 MHz e.g., LOFAR (LOw Frequency ARray) in the Netherlands and its European extension ILT, the International LOFAR Telescope. However, at frequencies below 30 MHz, Earth-based observations are limited due to a combination of severe ionospheric distortions, almost full reflection of radio waves below 10 MHz, solar eruptions and the radio frequency interference (RFI) of human-made signals. Moreover, there are interesting scientific processes which naturally occur at these low frequencies. A space or Lunar-based ultra-low-frequency (also referred to as ultra-long-wavelength, ULW) radio array would suffer significantly less from these limitations and hence would open up the last, virtually unexplored frequency domain in the electromagnetic spectrum.A roadmap has been initiated by astronomers and researchers in the Netherlands to explore the opportunity of building a swarm of satellites to observe at the frequency band below 30 MHz. This roadmap dubbed Orbiting Low Frequency Antennas for Radio Astronomy (OLFAR), a space-based ultra-low frequency radio telescope that will explore the Universe’s so-called dark ages, map the interstellar medium, and study planetary and solar bursts in the solar system and search them in other planetary systems. Such a radio astronomy system will comprise of a swarm of hundreds to thousands of satellites, working together as a single aperture synthesis instrument deployed sufficiently far away from Earth to avoid terrestrial RFI. The OLFAR telescope is a novel and complex system, requiring yet to be proven engineering solutions. Therefore, a number of key technologies are still required to be developed and proven. The first step in this roadmap is the NCLE (Netherlands China Low Frequency Explorer) experiment, which was launched in May 2018 on the Chinese Chang’e 4 mission. The NCLE payload consists of a three monopole antenna system for low frequency observations, from which the first data stream is expected in the second half of 2019, which will provide important feedback for future science and technology opportunities.In this paper, the roadmap towards OLFAR, a brief overview of the science opportunities, and the technological and programmatic challenges of the mission are presented.