空间甚长基线干涉测量(Very Long Baseline Interferometry,VLBI)由于基线更长,在相同的观测频率下,可获得比地基甚长基线干涉测量更高的分辨率.我国正在推进空间甚长基线干涉测量科学与技术研究.俄罗斯RadioAstron空间甚长基线干涉测...空间甚长基线干涉测量(Very Long Baseline Interferometry,VLBI)由于基线更长,在相同的观测频率下,可获得比地基甚长基线干涉测量更高的分辨率.我国正在推进空间甚长基线干涉测量科学与技术研究.俄罗斯RadioAstron空间甚长基线干涉测量项目于2018年结束,其成功经验可以借鉴.该项目采用不同于常规地面甚长基线干涉测量的专用数据格式RDF(RadioAstron Data Format)记录观测数据,利用配备的星载或地面上行氢原子频标提供频率基准,数据经采集量化后传输至地面站,打上时标并记录于硬盘.为处理RadioAstron数据,分析了RDF格式,完成了RDF数据解码及相关处理,然后对比分析了Mark5B、VDIF等地面甚长基线干涉测量通用数据格式和RDF格式的特点,为我国未来空间甚长基线干涉测量数据格式设计与处理积累经验.展开更多
The concept for space interferometry from Polar or Equatorial Circular Medium Earth Orbits(the PECMEO concept) is a promising way to acquire the image of the"shadow"of the event horizon of Sagittarius A*with...The concept for space interferometry from Polar or Equatorial Circular Medium Earth Orbits(the PECMEO concept) is a promising way to acquire the image of the"shadow"of the event horizon of Sagittarius A*with an angular resolution of circa 5 microarcseconds. The concept is intended to decrease the size of the main reflector of the instrument to about 3 m using a precise orbit reconstruction based on Global Navigation Satellite System (GNSS) navigation, inter-satellite range and range-rate measurements, and data from the Attitude and Orbit Determination System (AODS). The paper provides the current progress on the definition of the subsystems required for the concept on the basis of simulations, radio regulations, and available technology. The paper proposes the requirement for the localization of the phase centre of the main reflector. The paper provides information about the visibility of GNSS satellites and the needed accuracies of the AODS. The paper proposes the frequency plan for the instrument and its Inter-Satellite Links (ISLs).The concepts for measurement of range and range-rate using ISLs (as well as for the data exchange at these ISLs) are presented. The block diagram of the interferometer is described and its sensitivity is estimated. The link budget for both ISLs is given as well as their critical components. The calculated measurement quality factors are given. The paper shows the expected performance of the sub-systems of the interferometer. The requirements for the localization of the main reflectors and the information about the availability of the GNSS satellites are based on the simulations results. The frequency plan is obtained according to the PECMEO concept and taking into account the radio regulations. The existing technology defines the accuracies of the AODS, both the link budgets and the fundamental measurement accuracies for ISLs, and the sensitivity of the instrument. The paper provides input information for the development of the orbit reconstruction filter and the whole PECMEO system展开更多
A space-based Very Long Baseline Interferometry (VLBI) program, named as the Cosmic Microscope, is proposed to involve dual VLBI telescopes in the space working together with giant ground-based telescopes (e.g., Squar...A space-based Very Long Baseline Interferometry (VLBI) program, named as the Cosmic Microscope, is proposed to involve dual VLBI telescopes in the space working together with giant ground-based telescopes (e.g., Square Kilometre Array, FAST, Arecibo) to image the low radio frequency Universe with the purpose of unraveling the compact structure of cosmic constituents including supermassive black holes and binaries, pulsars, astronomical masers and the underlying source, and exoplanets amongst others. The operational frequency bands are 30, 74, 330 and 1670 MHz, supporting broad science areas. The mission plans to launch two 30-m-diameter radio telescopes into 2 000 km×90 000 km elliptical orbits. The two telescopes can work in flexibly diverse modes,(i) Space-ground VLBI. The maximum space-ground baseline length is about100 000 km; it provides a high-dynamic-range imaging capacity with unprecedented high resolutions at low frequencies (0.3 mas at 1.67 GHz and 20 mas at 30 MHz) enabling studies of exoplanets and supermassive black hole binaries (which emit nanoHz gravitational waves),(ii) Space-space single-baseline VLBI. This unique baseline enables the detection of flaring hydroxyl masers, and more precise position measurement of pulsars and radio transients at mas level.(iii) Single dish mode, where each telescope can be used to monitor transient bursts and rapidly trigger follow-up VLBI observations. The large space telescope will also contribute in measuring and constraining the total angular power spectrum from the Epoch of Reionization. In short, the Cosmic Microscope offers astronomers the opportunity to conduct novel, frontier science.展开更多
Based on the relativistic time-space theory, we derived the space VLBI time delay and delay rate calculation models with an accuracy of 1 ps and 10^(-3) ps/s, respectively. The longest suitable baseline of the models ...Based on the relativistic time-space theory, we derived the space VLBI time delay and delay rate calculation models with an accuracy of 1 ps and 10^(-3) ps/s, respectively. The longest suitable baseline of the models is 4×10~5 km (Earth-Moon distance).展开更多
在我国探月工程四期中,将利用地面望远镜和月球轨道射电望远镜共同组成的超长基线,开展X频段空间VLBI试验.由于地月基线长达400000 km, UV覆盖不均匀,不适合开展常规的VLBI成图观测,相关科学研究应充分利用地月基线高角分辨率的特点并...在我国探月工程四期中,将利用地面望远镜和月球轨道射电望远镜共同组成的超长基线,开展X频段空间VLBI试验.由于地月基线长达400000 km, UV覆盖不均匀,不适合开展常规的VLBI成图观测,相关科学研究应充分利用地月基线高角分辨率的特点并充分考虑其基线灵敏度.该试验中的空间望远镜口径仅为4.2 m,相应的中国VLBI网所属X频段射电望远镜均为25–65 m的中等口径,且地月基线长度远超过地球直径.为尽可能提高地月基线灵敏度,本文提出利用国内多面中等口径地基VLBI望远镜参与地月基线观测,通过对相关处理机输出的各条地月基线VLBI互功率谱进行综合,将各个中等口径VLBI望远镜信号进行合成,达到一个100 m级的地基大口径望远镜与月球轨道小口径望远镜进行VLBI干涉的效果.本方法基本思路为,基于软件相关处理机的输出结果,通过对齐各基线的相位,补偿基线时延,对各条地月基线的互功率谱进行相干合成,从而达到提升信噪比的目的.基于此方法,我们利用火星探测器"天问一号"实测数据进行信号合成VLBI试验.结果表明,通过进行基线的互功率谱合成,可以使基线信噪比有明显提升.此方法也可应用于未来其他有类似需求的空间VLBI数据处理.展开更多
文摘空间甚长基线干涉测量(Very Long Baseline Interferometry,VLBI)由于基线更长,在相同的观测频率下,可获得比地基甚长基线干涉测量更高的分辨率.我国正在推进空间甚长基线干涉测量科学与技术研究.俄罗斯RadioAstron空间甚长基线干涉测量项目于2018年结束,其成功经验可以借鉴.该项目采用不同于常规地面甚长基线干涉测量的专用数据格式RDF(RadioAstron Data Format)记录观测数据,利用配备的星载或地面上行氢原子频标提供频率基准,数据经采集量化后传输至地面站,打上时标并记录于硬盘.为处理RadioAstron数据,分析了RDF格式,完成了RDF数据解码及相关处理,然后对比分析了Mark5B、VDIF等地面甚长基线干涉测量通用数据格式和RDF格式的特点,为我国未来空间甚长基线干涉测量数据格式设计与处理积累经验.
文摘The concept for space interferometry from Polar or Equatorial Circular Medium Earth Orbits(the PECMEO concept) is a promising way to acquire the image of the"shadow"of the event horizon of Sagittarius A*with an angular resolution of circa 5 microarcseconds. The concept is intended to decrease the size of the main reflector of the instrument to about 3 m using a precise orbit reconstruction based on Global Navigation Satellite System (GNSS) navigation, inter-satellite range and range-rate measurements, and data from the Attitude and Orbit Determination System (AODS). The paper provides the current progress on the definition of the subsystems required for the concept on the basis of simulations, radio regulations, and available technology. The paper proposes the requirement for the localization of the phase centre of the main reflector. The paper provides information about the visibility of GNSS satellites and the needed accuracies of the AODS. The paper proposes the frequency plan for the instrument and its Inter-Satellite Links (ISLs).The concepts for measurement of range and range-rate using ISLs (as well as for the data exchange at these ISLs) are presented. The block diagram of the interferometer is described and its sensitivity is estimated. The link budget for both ISLs is given as well as their critical components. The calculated measurement quality factors are given. The paper shows the expected performance of the sub-systems of the interferometer. The requirements for the localization of the main reflectors and the information about the availability of the GNSS satellites are based on the simulations results. The frequency plan is obtained according to the PECMEO concept and taking into account the radio regulations. The existing technology defines the accuracies of the AODS, both the link budgets and the fundamental measurement accuracies for ISLs, and the sensitivity of the instrument. The paper provides input information for the development of the orbit reconstruction filter and the whole PECMEO system
基金Supported with funding from the Ministry of Science and Technology of China(2018YFA0404600)the Chinese Academy of Sciences(114231KYSB20170003)
文摘A space-based Very Long Baseline Interferometry (VLBI) program, named as the Cosmic Microscope, is proposed to involve dual VLBI telescopes in the space working together with giant ground-based telescopes (e.g., Square Kilometre Array, FAST, Arecibo) to image the low radio frequency Universe with the purpose of unraveling the compact structure of cosmic constituents including supermassive black holes and binaries, pulsars, astronomical masers and the underlying source, and exoplanets amongst others. The operational frequency bands are 30, 74, 330 and 1670 MHz, supporting broad science areas. The mission plans to launch two 30-m-diameter radio telescopes into 2 000 km×90 000 km elliptical orbits. The two telescopes can work in flexibly diverse modes,(i) Space-ground VLBI. The maximum space-ground baseline length is about100 000 km; it provides a high-dynamic-range imaging capacity with unprecedented high resolutions at low frequencies (0.3 mas at 1.67 GHz and 20 mas at 30 MHz) enabling studies of exoplanets and supermassive black hole binaries (which emit nanoHz gravitational waves),(ii) Space-space single-baseline VLBI. This unique baseline enables the detection of flaring hydroxyl masers, and more precise position measurement of pulsars and radio transients at mas level.(iii) Single dish mode, where each telescope can be used to monitor transient bursts and rapidly trigger follow-up VLBI observations. The large space telescope will also contribute in measuring and constraining the total angular power spectrum from the Epoch of Reionization. In short, the Cosmic Microscope offers astronomers the opportunity to conduct novel, frontier science.
文摘Based on the relativistic time-space theory, we derived the space VLBI time delay and delay rate calculation models with an accuracy of 1 ps and 10^(-3) ps/s, respectively. The longest suitable baseline of the models is 4×10~5 km (Earth-Moon distance).
