Space clocks and fundamental tests: The ACES experiment

In this article we give an overview of the applications of ultrastable clocks in space. We focus on the case of the ESA space mission ACES, which is scheduled for flight onboard the international space station in 2013. With a laser cooled cesium clock, PHARAO, a space hydrogen maser, SHM, and a precise time and frequency transfer system, MWL, several precision tests in fundamental physics can be performed such as a measurement of Einstein’s gravitational frequency shift with 2 ppm sensitivity and a search for time variations of the fundamental physical constants at 10^-17/year. We present the advancement of the various mission instruments and present briefly applications in geodesy and Global Navigation Satellite Systems (GNSS).     

Design of the cold atom PHARAO space clock and initial test results

In this paper we describe the cold atom clock PHARAO, designed for microgravity operation. All elements of the PHARAO engineering model have been manufactured and delivered to CNES, the French space agency. We present the clock design, its main characteristics, and initial science operation. PHARAO is one of the main components of the Atomic Clock Ensemble in Space payload that is scheduled to fly on board the International Space Station in 2010. PACS 07.87.+v; 06.30.Ft; 95.55.Sh; 32.80.Pj     

Space tests of relativistic gravity with precision clocks and atom interferometers

Precision clocks and interferometers in space can test relativistic gravity with extremely high sensitivity. Yet, only a single such test has been performed, namely the celebrated flight of a hydrogen maser in a sub-orbital trajectory in 1976 (GP-A mission). This paper suggests some of the obstacles to space flight of precision instruments, and describes how the emergence of new technology might offer a pathway for removing those obstacles. A brief review of emerging technologies is made, and new mission concepts based on them are described. Some of the technologies that can impact more tests of relativistic gravity in space at a more distant future are also described.     

Cold atoms in space and atomic clocks: ACES

In this article, the interest of space environment for cold atoms is outlined. After a brief review of cooling techniques and Bose–Einstein condensation, the case of atomic clocks in microgravity is discussed. The scientific objectives of the European mission ACES are presented. ACES will fly onboard the international space station in 2005–2006.     

TSS core equipment I.—Electrodynamic package and rationale for system electrodynamic analysis

Summary The first Tethered-Satellite System (TSS-1) Electrodynamic mission has been launched aboard the Space Shuttle STS-46 on July 31, 1992, as a joint mission between the United States and Italy. A 500 kg, spherical Satellite (1.6 m diameter), attached to the Orbiter by a thin (0.24 cm), conducting, insulated wire (Tether), has been reeled upwards from the Orbiter payload bay to a distance of 256 m, rather than the expected 20 km, when the Shuttle was at a projected altitude of 300 km. ASI, the Italian Space Agency, had the responsibility for developing the reusable Satellite, while NASA had the responsibility for developing the Deployer system and the Tether, integrating the payload and providing transportation into space. One of the main scientific goals of this first mission is to demonstrate the possibility of energy conversion from mechanical to electrical by using a long Tether orbiting through the Earth's magnetic field. ASI designed and developed an active experiment, referred to as Core Equipment, in order to carry out this demonstration, and to support all the scientific investigations related to the study of the TSS electrodynamic interactions with the Earth's ionosphere. The experiment uses two Electron Generator Assemblies (EGAs), located on the Orbiter, to re-emit into the ionosphere, as an electron beam, the electrons collected on the Satellite from the ionosphere. Other instruments provide current, voltage, and ambient pressure measurements, and allow, via a series of switches, different electrical configurations of the TSS. The Core Equipment was innovative for space experiments in general and Shuttle experiments in particular. In fact, it was the first flight in which the Shuttle has been used as an integral part of the experiment and not only as an observing platform. It was the first mission with an integrated approach to science, will all the instrumentation and their operative modes selected to characterize the electric properties of the TSS.     

Some fundamental physics experiments using atomic clocks and sensors

We present several experiments in fundamental physics that use atomic clocks and sensors together with high performance time/frequency transfer methods. Our account is far from being exhaustive and instead concentrates on a chosen subset of present and future experiments, whilst providing some theoretical background. We only give very brief overviews of the experiments and theories, but provide ample references for the interested reader.     

Review: Experiments in Fundamental Physics Scheduled and in Development for the ISS

This is a review of those experiments in the area of Fundamental Physics that are either approved by ESA and NASA, or are currently under development, which are to be performed in the microgravity environment of the International Space Station. These experiments cover the physics of liquid Helium (SUE, BEST, MISTE, DYNAMX, and EXACT), ultrastable atomic clocks (PHARAO, PARCS, RACE), ultrastable microwave resonators (SUMO), and particle detectors (AMS and EUSO). The scientific goals are to study more precisely the universality properties of liquid Helium under microgravity conditions, to establish better time standards and to test the universality of the gravitational red shift, to make more precise tests of the constancy of the speed of light, and to measure the particle content in space directly without disturbances from the Earth's inner atmosphere.     

In-situ M?ssbauer spectroscopy with MIMOS II

The miniaturized M?ssbauer spectrometer MIMOS II was developed for the exploration of planetary surfaces. Two MIMOS II instruments were successfully deployed on the martian surface as payload elements of the NASA Mars Exploration Rover (MER) mission and have returned data since landing in January 2004. M?ssbauer spectroscopy has made significant contributions to the success of the MER mission, in particular identification of iron-bearing minerals formed through aqueous weathering processes. As a field-portable instrument and with backscattering geometry, MIMOS II provides an opportunity for non-destructive in-situ investigations for a range of applications. For example, the instrument has been used for analyses of archaeological artifacts, for air pollution studies and for in-field monitoring of green rust formation. A MER-type MIMOS II instrument is part of the payload of the Russian Phobos-Grunt mission, scheduled for launch in November 2011, with the aim of exploring the composition of the martian moon Phobos. An advanced version of the instrument, MIMOS IIA, that incorporates capability for elemental analyses, is currently under development.     

Tethered-Satellite system (TSS): Preliminary results on the active experiment core equipment

Summary The first Tethered-Statellite System (TSS-1) Electrodynamic mission has been launched aboard the Space Shuttle STS-46 on July 31, 1992, as a joint mission between the United States and Italy. A 500 kg spherical Satellite (1.6 m diameter) attached to the Orbiter by a thin (0.24 cm), conducting, insulated wire (Tether), has been reeled upwards from the Orbiter payload bay to a distance of 257 m when the Shuttle was at a projected altitude of 300 km. ASI, the Italian Space Agency, had the responsibility for developing the reusable Satellite, while NASA had the responsibility for developing the Deployer system and the Tether, integrating the payload and providing transportation into space. One of the main scientific goals of this first mission was to demonstrate the possibility of energy conversion from mechanical to electrical by using a long Tether orbiting through the Earth's magnetic field. ASI designed and developed an active experiment, referred to as Core Equipment, in order to carry out this demonstration. The experiment used two Electron Generator Assemblies (EGAs), located on the Orbiter, to re-emit into the ionosphere as an electron beam the electrons collected on the Satellite from the ionosphere. Each EGA had the capability to emit an electron beam with a programmed intensity from 10 mA up to 750 mA with a resolution of 3 mA. The perveance of each EGA was 7.2 microperv, and the beam energy, up to 3 kV, was provided as part of the e.m.f. induced across the TSS due to its motion through the Earth's magnetic field. Other instruments provided current, voltage, and ambient-pressure measurements, and allowed, via a series of switches, different electrical configurations of the TSS. Moreover, the Core Equipment provided a dynamic package, to study the TSS dynamics, as a first goal, and to verify the possibility of using the TSS Satellite as a platform for future experiments in the microgravity field. The expected voltage across the TSS was estimated to be 5 kV for a full Tether deployment of 20 km. During the mission, and due to unforeseenable reasons, the Tether deployment achieved was only of 257 m. Despite this limitation, there is evidence that the experiment was working nominally in the very low-voltage range across the TSS. This result strongly increases the confidence in the possibility of high-voltage operation of the electrodynamic TSS, as the Tether deployment will achieve the 20 km, as expected in the future reflight. The paper describes the experiment, and reports some preliminary results achieved during the first mission. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Mössbauer spectroscopy in space

Nearly 40 years after the discovery of the Mössbauer effect for the first time a Mössbauer spectrometer will leave our planet to explore in situ the surface of another solar system body: the red planet Mars [1]. We are currently developing a miniaturized Mössbauer spectrometer (MIMOS) which is part of the scientific payload of the Russian Mars96 mission, to be launched within the next 2–4 years [2,3]. To fulfill the requirements for a space mission to the planet Mars, all parts of the spectrometer had to be extremely miniaturized and ruggedized to withstand the space flight and Mars environmental conditions. The relevant parts (e.g. drive, detector system, electronics etc.) will be described in more detail and its characteristics compared to standard systems. Because of this new development there now is a growing interest to include a Mössbauer (MB) instrument in future space missions to other solar system bodies as for instance Venus, the terrestrial Moon, and a comet nucleus. Because of extremely different environmental conditions (e.g. nearly zero gravity on the surface of a comet nucleus, high pressure and temperature on the surface of Venus, etc.) different instrument designs and concepts are required for different missions. We will present some ideas for various types of missions, as well as the motivation for using Mössbauer spectroscopy in these cases.     

The future of gamma-ray astronomy

The field of gamma-ray astronomy has experienced impressive progress over the last decade. Thanks to the advent of a new generation of imaging air Cherenkov telescopes (H.E.S.S., MAGIC, VERITAS) and thanks to the launch of the Fermi-LAT satellite, several thousand gamma-ray sources are known today, revealing an unexpected ubiquity of particle acceleration processes in the Universe. Major scientific challenges are still ahead, such as the identification of the nature of Dark Matter, the discovery and understanding of the sources of cosmic rays, or the comprehension of the particle acceleration processes that are at work in the various objects. This paper presents some of the instruments and mission concepts that will address these challenges over the next decades.     

An overview of the laser ranging method of space laser altimeter

Space laser altimeter is an active remote sensing instrument to measure topographic map of Earth, Moon and planetary. The space laser altimeter determines the range between the instrument and laser footprint by measuring round trip time of laser pulse. The return pulse reflected from ground surface is gathered by the receiver of space laser altimeter, the pulsewidth and amplitude of which are changeable with the variability of the ground relief. Meantime, several kinds of noise overlapped on the return pulse signal affect its signal-to-noise ratio. To eliminate the influence of these factors that cause range walk and range uncertainty, the reliable laser ranging methods need to be implemented to obtain high-precision range results. Based on typical space laser altimeters in the past few decades, various ranging methods are expounded in detail according to the operational principle of instruments and timing method. By illustrating the concrete procedure of determining time of flight of laser pulse, this overview provides the comparison of the employed technologies in previous and undergoing research programs and prospect innovative technology for space laser altimeters in future.     

A new test of gravitational redshift using Galileo satellites: The GREAT experiment

We present the result of the analysis of the GREAT (Galileo gravitational Redshift test with Eccentric sATellites) experiment. An elliptic orbit induces a periodic modulation of the fractional frequency difference between a ground clock and the satellite clock, partly due to the gravitational redshift, while the good stability of Galileo clocks allows one to test this periodic modulation to a high level of accuracy. GSAT0201 and GSAT0202, with their large eccentricity and on-board H-maser clocks, are perfect candidates to perform this test. Satellite laser ranging data allows us to partly decorrelate the orbit perturbations from the clock errors. By analyzing several years of Galileo tracking data, we have been able to improve the Gravity probe A test (1976) of the gravitational redshift by a factor of 5.6, providing, to our knowledge, the first reported improvement since more than 40 years.     

空间引力波探测计划-LISA系统设计要点

为了验证广义相对论,世界各国竞相开展了空间引力波探测方面的研究。本文以欧洲空间引力波探测LISA(Laser Interferometer Space Antenna)计划为例,根据基线设计,对LISA系统有效载荷及主要组件的设计进行了分析和阐述。LISA主要探测和研究低频引力波辐射,其工作频段为10^-3~1 Hz,工作距离为5×10⁶ km,预计能探测到双致密星系统以及星系合并引起的超大质量并合等波源,测距精度达到pm量级。以上研究希望能对我国未来的空间引力波探测计划有一定启示。     

Overview to the Hard X-ray Modulation Telescope (Insight-HXMT) Satellite

As China's first X-ray astronomical satellite, the Hard X-ray Modulation Telescope (HXMT), which was dubbed as Insight-HXMT after the launch on June 15, 2017, is a wide-band(1-250 ke V) slat-collimator-based X-ray astronomy satellite with the capability of all-sky monitoring in 0.2-3 Me V. It was designed to perform pointing, scanning and gamma-ray burst(GRB)observations and, based on the Direct Demodulation Method (DDM), the image of the scanned sky region can be reconstructed.Here we give an overview of the mission and its progresses, including payload, core sciences, ground calibration/facility, ground segment, data archive, software, in-orbit performance, calibration, background model, observations and some preliminary results.     

"神舟"五号的空间环境保障

空间环境安全保障是载人航天器飞行安全和航天员生命安全保障的一个重要部分．文章从高层大气、高能辐射环境、流星体空间碎片和重大空间环境扰动事件等四个方面空间环境要素对载人航天的影响，介绍了空间环境预报中心为“神舟”五号载人飞行任务所作的空间环境保障工作．     

Electrodynamic Dust Shields on the International Space Station: Exposure to the space environment

Electrodynamic Dust Shields (EDS) have been in development at NASA as a dust mitigation method for lunar and Martian missions. An active dust mitigation strategy, such as that provided by the EDS, that can remove dust from surfaces, is of crucial importance to the planetary exploration program. We report on the development of a flight experiment to fully expose four EDS panels to the space environment. This flight experiment is part of the Materials International Space Station experiment X (MISSE-X), an external platform on the International Space Station that will expose materials to the space environment.     

Validation of the galactic cosmic ray and geomagnetic transmission models

A very high-momentum resolution particle spectrometer called the Alpha Magnetic Spectrometer (AMS) was flown in the payload bay of the Space Shuttle in a 51.65 degrees x 380-km orbit during the last solar minimum. This spectrometer has provided the first high statistics data set for galactic cosmic radiation protons, and helium, as well as limited spectral data on carbon and oxygen nuclei in the International Space Station orbit. First measurements of the albedo protons at this inclination were also made. Because of the high-momentum resolution and high statistics, the data can be separated as a function of magnetic latitude. A related investigation, the balloon borne experiment with a superconducting solenoid spectrometer (BESS), has been flown from Lynn Lake, Canada and has also provided excellent high-resolution data on protons and helium. These two data sets have been used here to study the validity of two galactic cosmic ray models and the geomagnetic transmission function developed from the 1990 geomagnetic reference field model. The predictions of both the CREME96 and NASA/JSC models are in good agreement with the AMS data. The shape of the AMS measured albedo proton spectrum, up to 2 GeV, is in excellent agreement with the previous balloon and satellite observations. A new LIS spectrum was developed that is consistent with both previous and new BESS 3He observations. Because the astronaut radiation exposures onboard ISS will be highest around the time of the solar minimum, these AMS measurements and these models provide important benchmarks for future radiation studies. AMS-02 slated for launch in September 2003, will provide even better momentum resolution and higher statistics data.     

空间紫外光学遥感技术与发展趋势

空间紫外光学遥感技术是除可见、近红外、热红外和微波遥感以外的一个具有突出优势的遥感领域,全球气候变化研究是目前国际上空间紫外-真空紫外光学遥感的热点课题。本文对空间紫外光学遥感的作用、国内外研究现状及发展趋势进行了综述和分析。介绍了一组紫外光学遥感仪器的功能和特点,给出了它们的主要性能参数;指出我国目前的工作重点是推进星载紫外光谱遥感仪器的应用、积累空间探测数据、建立反演算法等;而未来发展目标将是研制集天底、临边和掩星成像探测于一体的新一代紫外成像探测仪器,高精度观测全天候的整层大气密度和臭氧的三维分布,实时监测大气组分及化学成分（如O₂、N₂、NO、OH和O₃）的变化及变化趋势,以及进一步拓展我国紫外光学遥感仪器的应用领域。