GAN Weiqun

Space Solar Physics in China*

GAN Weiqun

(210033)

The activities of Chinese space solar physics in 2018–2020 are going on smoothly. Besides the missions of ASO-S and CHASE which are in the engineering phases, there are quite a number of projects which are in the pre-study stage (conception study) or have finished the pre-study stage, constituting a rich pond for the selection of next solar mission(s). This paper describes in brief the status of all these related projects.

Space astronomy, Solar physics

1 Missions Undertaken

Mission-level solar projects in China have gone a long way[1-8]. Unprecedentedly, there are two solar missions in engineering phases currently: the Advanced Space- based Solar Observatory (ASO-S), and Chinese H- alpha Solar Explorer (CHASE).

ASO-S is a mission proposed for the 25th solar maximum by the Chinese solar community[9,10]. The scientific objectives are to study the relationships among solar magnetic field, solar flares, and coronal mass ejections (CMEs). Three payloads are Full-disk Magnetograph (FMG)[11,12], Lyman-alpha Solar Te-lescope (LST)[13-15], and Hard X-ray Imager (HXI)[16,17], respectively. ASO-S has a solar synchronous orbit at an altitude of 720 km with an inclination angle of around 98.2o. Since the formal approval at the end of 2017, ASO-S underwent the official Phase-B study from January 2018 to April 2019. Then from May 2019, ASO-S has been undertaking the Phase-C study. The Phase-D study (flight model) is expected to start at August 2020. ASO-S is planned to launch either at the end of 2021 or in early 2022.

CHASE[18]is a unique science payload onboard a new experimental platform. It is designed to spectrally image the whole Sun at lines of H-alpha (6562.8 ?) and FeI (6569.2 ?). A scheme of grating spectrometer plus scanning mirrors is used in its optical system. Total weight of the telescope is about 35 kg. Now the mission is under engineering study and the expected launch date is in early 2021.

2 Pre-study Projects: Finished

In the report for 2016–2018[8], we listed some proposals which were selected into the first batch of pre-study projects supported by the CAS’s Strategic Priority Program on Space Science during the 13th five-year plan. Two years later, a few of them have finished their pre-studies, which are as follows.

(1) Multi-scale Solar Spectral Observatory (MSSO) (January 2018 to December 2019): As expe-cted, this project finished all the works on time at the end of 2019. Being a mission conception it proposed in fact a comprehensive framework: a full waveband radiation monitor plus a multi-wave band spectral imaging of coronagraph. The former, taking the Sun as a star, aims at observing the whole radiation from the infrared to gamma-rays by using several individual detectors, so as to study the long time variation of the Sun and the short time influence like the influence by the solar flares. The latter would like to observe with unprecedently high resolution the corona from 1.5 to 90 solar radii by using a group of spectrometers and imagers, so as to study how the solar wind, CMEs, shock-waves, and energetic particles evolve from the Sun to the Earth.

(2) Dual observations at solar polar orbit (Jan-uary 2018 to December 2019): This mission conception was also finished its study on time at the end of 2019. The idea is to use two identical satellites at conjugate positions of solar polar orbit (the perihelion and aphelion is comparable to the Sun-Earth distance), so as to observe the whole Sun always, especially for the solar polar regions. The proposed payloads include temporally the full disk magnetograph, ultraviolet polarized telescope, wide field coronagraph, and in-situ detectors for the solar wind. The proposers believe that this mission could make a break-through in understanding the origin of solar magnetic field besides monitoring the Sun globally.

(3) Solar Transition region Observation and Re--search Mission (STORM) (January 2018 to Decem-ber 2019): The completed mission concept includes both a EUV telescope (diameter 20 cm; Ne VII 465 ?, FOV 250?×250?) and a spectrometer (400~475 ?, 745~795 ?, 995~1045 ?), in order to observe for the first time the connections from the lower atmosphere continuously to the upper transition region and corona, so as to provide a better understanding for the mech-anism of coronal heating and the origin of solar wind.

(4) Close observation on solar eruptions (Jan-uary 2018 to December 2019): Close to the Sun to make both in-situ and remote observations is certainly an exciting task. Differing from Solar Orbiter and Park Solar Probe, this mission proposes to measure the magnetic reconnection region directly, like the current sheet which leads to solar flares and CMEs. The proposed payloads consist of detectors for measuring energetic particles, electric field, ma-gnetic field, EUV coronal spectrometers (for measu-ring high temper-ature plasma), and so on.

Obviously, these finished pre-study projects are being improved at present and looking for opportunities to do further studies.

3 Pre-study Projects: Undertaking

In 2019 the second batch of pre-study projects supported by the CAS’s Strategic Priority Program on Space Science during the 13th five years plan is started. Furthermore, there are also several projects supported by other sources. They are summarized as follows.

(1) The Formation Flying of Focused Solar Hard X-ray Telescope: it is a conception study, which plans to propose a feasible mission with two spacecraft sep-a-r--ated about 150 m. The front one is the focused grazing telescope, while the rear one is the detector, so as to get unprecedently high spacial resolution in solar hard X-ray imaging. This proposal has gotten financial supports from both CAS and NNSFC. The key of the study is around the feasibility.

(2) Solar Observatory at L5: in fact there are two independent proposals for the solar and terrestrial observations at L5. One is proposed by NSSC, paying more attention to the space weather domain; and the other by Nanjing University, emphasizing more on solar physics. Both proposals are more or less similar in the payload deployments, including obviously a couple of in-situ and remote instruments.

(3) Solar Observation at L2: this proposal is proposed also by NSSC and has gotten pre-study support from CAS. The idea is to launch a mission working at L2, to observe the solar corona through a natural coronagraph,., using the Earth as a nat-ural shelter for the Sun. Both scientific and technical issues are the topic to be studied.

(4) Space Weather Mission at L1: for quite a time it was heard that National Satellite Meteorological Center would build a space weather mission working at L1. But no more information has been publicly released so far. Therefore no progress can be reported. However, their Fengyun-3E mission will be launched in 2020, on which an X (0.6~8.0nm, 0.6~ 6.0nm, 0.6~5.0nm, 0.6~2.0nm, 0.6~6nm, 0.6~1.2 nm) and EUV (19.5 nm) telescope will make a routine observation of the Sun.

(5) Three-dimensional Imaging for Inner Helio-sphere: this proposal proposes to launch a group of 6 identical spacecraft into the Earth orbit, two of which work together as a sub-group and separate from other sub-groups by 120o. This kind of distributions is believed to be able to make some key observations on the solar structures and the eruptions.

(6) Close Imaging the Sun: it is another proposal proposed by the different affiliations from what in Section 2. A series of technical and scientific issues are being studied with the supports by CAS and NNSFC.

(7) A New Kind Telescope for Solar Hard X-rays and Gamma-rays: the traditional high energy solar telescopes use either spatial or temporal modulation. This proposal proposes a new kind of telescope based on a new principle, so-called double modulations.

(8) Solar Observatory on the Moon: it seems to be long term envision and no real progress has been made so far, although it is proposed in response to the call by the Chinese Lunar Program.

(9) Some proposal candidates for the Space Station: in response to the call issued by the Chinese space station, several solar proposals are submitted, like Multi-waveband and Wide-Field EUV Spectral Imaging, the EUV Polarization Observation, Wide- field X-ray Telescope/Coronagraph, Super-wide Dy-na-mic Frequency Spectrometer in Millimeter Wave-band, and so on. At the moment, it is still unknown which one could be selected.

4 Conclusions

We have seen from the above that the zero-break-through of the first Chinese Solar spacecraft will soon be realized either in 2021 or 2022. The scientific researches on the data from ASO-S and CHASE are intensively being prepared. On the other hand, quite a number of pre-study mission concepts have been proposed. It is really a good situation for the Chinese solar physics community. However, at the moment it is still unclear where and what is the real chance for the next solar mission. Furthermore, how to select the mission from so many proposals is another challenge. Anyway, with the launch of ASO-S and CHASE, the second Chinese solar spacecraft will soon be put on the agenda.

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GAN Weiqun. Space Solar Physics in China., 2020, 40(5): 726–728. DOI:10.11728/cjss2020.05.726

* Supported by Chinese Academy of Sciences (XDA15052200) and by National Natural Science Foundation of China (U1731241, 11921003 and U1931138)

February 13, 2020

E-mail: wqgan@pmo.ac.cn