太空|TAIKONG ISSI-BJ Magazine - No. 5 January 2015 - The International Space Science Institute
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国际空间科学研究所
太空|TAIKONG
ISSI-BJ Magazine
No. 5 January 2015
FOREWORD
The International Space Science that the ASO-S mission has
Institute in Beijing (ISSI-BJ) complementary objectives to
successfully organized a two- existing or future solar missions,
day Forum on “Exploring Solar e.g. SOHO, Solar Orbiter, or
Eruptions and their Origins” in the Interhelioprobe. Therefore, the
framework of the Space Science ASO-S mission is an additional
Strategic Pioneer Project of the excellent example of how the
Chinese Academy of Sciences Chinese Space Science program
IMPRINT (CAS), in Beijing on October 30-31,
2014. ISSI-BJ Forums are informal
is innovative and challenging,
and complementary to existing
and free debates, brainstorming missions. This offers significant
太空 | TAIKONG meeting, among some twenty-five opportunities for cooperation
ISSI-BJ Magazine high-level participants on open through mission coordination and
questions of scientific nature. In scientific analysis that places
total 27 leading scientists from ASO-S and China in a central
eight countries participated in this position due to its unique objectives
Forum. and technology. It is also suggested
that ASO-S should provide some
Address: NO.1 Nanertiao, The Forum’s main aims were routine tools to the community or
Zhongguancun, Haidian District, to discuss the current status of high-level products of magnetic
Beijing, China the research progress on the field.
Postcode: 100190 relationships among magnetic
Telephone: +86-10-62582811 fields, solar flares and coronal The scientists concluded the very
Website: www.issibj.ac.cn mass ejections and to identify fruitful meeting with defining the
relevant results acquired by current mission to be successful with a
Main Authors missions. The debate mainly broad international interest. This
focused on the Advanced Space- TAIKONG magazine provides an
Weiqun Gan and Li Feng, Purple based Solar Observatory (ASO-S), overview of the scientific objectives
Mountain Observatory, CAS, China its key science goals and mission and the overall design of the ASO-S
definition, as well as some of the project, including spacecraft and
Editors key technological issues. ASO-S instrumentation discussed during
is one of the candidate missions the Forum.
Sabrina Brezger for advanced studies in the space
Maurizio Falanga science program of the Chinese I wish to thank the conveners and
Academy of Science, with regard organizer of the Forum Weiqun
to complementary missions. Gan (PMO, CN), Säm Krucker
(FHNW, CH / UC Berkeley, US),
After starting with recognizing Haimin Wang (NJIT, US), Yihua
the key scientific objectives for Yan (NAOC, CN). I also wish to
exploring solar eruptions, the thank the ISSI-BJ staff, Sabrina
Forum continued with an overview Brezger, Lijuan En, and Xiaolong
of the achievements of current Dong, for actively und cheerfully
relevant missions like Solar Orbiter supporting the organization of
and Solar Dynamics Observatory. the Forum. In particular, I wish to
Furthermore, new possibilities thank Weiqun Gan and Li Feng,
for observations of solar active who with dedication, enthusiasm,
phenomena were being discussed and seriousness, conducted the
Front Cover among the experts, in order to finally whole Forum and the editing of this
This image artistically illustrates review the planed instruments report. Let me also thank all those
ASO-S observing the eruptions of and satellites for ASO-S. The who participated actively in this
the Sun. participants recognized the very stimulating Forum.
high scientific value of the mission
and raised constructive comments
and suggestions on the mission Prof. Dr. Maurizio Falanga
concept, payloads key techniques, Beijing
and data product. They concluded January 2014
2 太空|TAIKONG
INTRODUCTION and CMEs, which are the major engineering implementation is
scientific objectives of ASO-S. expected to start in 2016. Aiming
A two-day forum on the mission The forum also had intensive at the 25th solar activity maximum,
of the Advanced Space-based discussions on the optimization ASO-S is planned to launch in 2021.
Solar Observatory (ASO-S) was of the scientific objectives and
held at the International Space payloads, synergy between This TAIKONG magazine presents
Science Institute in Beijing (ISSI- ASO-S and other ground and an overview of the ASO-S mission,
BJ). Approximately thirty scientists space observations, and potential its major scientific objectives, the
and engineers from China, France, international cooperation in the three payload elements onboard,
Germany, Italy, Russia, Switzerland, future. and the outcome from the
UK and USA attended this meeting. discussions during the forum
The forum was sponsored by ISSI- The primary concept of the ASO-S
BJ with some support from the mission was proposed in 2009 or
Purple Mountain Observatory, earlier. It partially inherited the MISSION OVERVIEW
Chinese Academy of Sciences. Sino-French joint Small Explorer for
Solar Eruptions (SMESE) mission. ASO-S could be the first Chinese
Solar flares and coronal mass The concept's phase A study was solar space observatory, if selected
ejections (CMEs) are the two most finished in March 2013. ASO-S is in 2016. It is a small or middle-
powerful eruptive phenomena currently undergoing scientific and scale mission to understand the
on the Sun. The energies of these engineering background studies physical processes involved in
eruptions are believed to originally (phase B) from January 2014 to solar eruptions, especially solar
December 2015, in the framework
come from the solar magnetic flares and CMEs. Table 1 gives an
field. The forum overviewed of the Space Sciences Strategic overview of the mission.
latest research progress on the Pioneer Project of the Chinese
solar magnetic field, solar flares, Academy of Sciences. If selected,
ASO-S MISSION SUMMARY
• Simultaneously observe non-thermal images of flares in hard
X-rays, and formation of CMEs, to understand the relationships
between flares and CMEs.
• Simultaneously observe full-disc vector magnetic field, energy
build up and release of solar flares, and the initiation of CMEs, to
Top level scientific objectives
understand the causality among them.
• Observe the response of solar atmosphere to eruptions, to
understand the mechanisms of energy release and transport.
• Observe solar eruptions and the evolution of magnetic field, to
provide early warning and physical clues for forecasting space
weather.
• FMG: Full-disc vector MagnetoGraph
Payloads • LST: Lyman-alpha Solar Telescopes
• HXI: Hard X-ray Imager
• launch vehicle: Long March 2D
• Orbit: solar synchronous orbit
Mission profile
- Altitude: 720 km
- Inclination: 98.2 degree
Spacecraft platform • candidates: SAST1000 or ZY-1
Data downlink • 220 GB/day
Launch year • 2021
Mission duration • > 4 years
Table 1: ASO mission overview.
太空|TAIKONG 3
SCIENTIFIC are often associated with CMEs, configuration.
however, a causal relationship
OBJECTIVES has not been established. The In this complicated development,
energies of these eruptions are we can discern four major
A solar flare is detected as a sudden believed to come from the solar observational goals:
flash of brightness observed over magnetic field, with comparable
the solar surface or at the solar amounts appearing as radiation 1) Simultaneously observe non-
limb. Solar flares can affect all and mass motions. Therefore, thermal images of flares in hard
layers of the solar atmosphere. The the simultaneous observations X-rays, and the formation of CMEs,
plasma temperature can reach tens of the solar magnetic field, solar to understand the relationships
of millions of Kelvins. Electrons, flares, and CMEs, are of particular between flares and CMEs.
protons, and heavier ions are importance in the study of their
accelerated to relativistic energies relationships. The origin and initiation of solar
and produce radiation across flares and CMEs remain unsolved
the electromagnetic spectrum at The ASO-S mission is specifically and are still a hot topic in solar
wavelengths from radio waves to proposed to understand the physics. It is generally accepted that
gamma rays. Ionization produced physical processes involved in flares originate locally, but CMEs
by flare emissions may produce solar flares, CMEs, and the solar can originate either in small scale
radio blackouts and disrupt magnetic field evolution. Its or in large scale. The relationship
communications. major scientific objectives could between flares and CMEs is still in
be abbreviated as ‘1M2B’: one debate. Is there any cause-effect
A CME is a large-scale release of magnetism plus two bursts (flares relationship between flares and
mass and magnetic field from the and CMEs). Figure 1 is an artistic CMEs? Does a flare trigger a CME
Sun. This process is a major cause view of a solar flare, a CME, and a or vice-versa, or is there no link
of geomagnetic storms. Flares possible associated magnetic field between them? Statistically there
is a rough 70% link. Why are some
flares accompanied by CMEs,
and others not, and how is this
behavior determined? The Sun
has an activity cycle of 11 years.
It is predicted that cycle 25 would
eventually start from 2020 and peak
around 2022 to 2025. Close to the
solar maximum, the occurrence of
flares and CMEs is more frequent.
ASO-S is planned to launch in 2021
and to make imaging observations
of the source region of these two
types of eruptions in white light,
UV, X-ray, and γ-ray. ASO-S will be
able to follow the eruptions from
the photosphere to the corona
and from their initiation to full
development.
2) Simultaneously observe
full-disc vector magnetic field,
energy build up and release of
solar flares, and the initiation of
CMEs, to understand the causality
among them.
Fig. 1: An artistic view of a solar flare, a CME, and a possible magnetic field A consensus has been reached that
configuration in white (modified from NASA's Solar Sentinels STDT report). solar flares and CMEs are driven by
4 太空|TAIKONG
between the magnetic field
complexity and the productivity
of CMEs? Are CME triggered locally
(e.g., by magnetic reconnection)
or globally on a large scale (e.g.,
by ideal MHD instabilities or loss of
equilibrium)? The full-disk vector
magnetograph onboard ASO-S
will provide detailed information
on the magnetic context of
eruptions. HXI is dedicated for
flare observations, LST for CME
observations. Simultaneous
observations of solar magnetic
field, solar flares, and CMEs
will help us to disentangle the
relationships among them, and
most importantly to establish
quantitative relationships
Fig. 2: Possible mode of Lyman-alpha observations of LST. The coronagraph between the magnetic field and
image taken by SOHO/UVCS (UltraViolet Coronagraph Spectrometer) is similar the eruptions.
to the future observations of LST/SCI, and full disk image observed by MSSTA
(Multi-Spectral Solar Telescope Array) is in analogue to the future observations 3) Observe the response of solar
of LST/SDI.
atmosphere to eruptions, to
the magnetic field, and the energy the most important issues in solar understand the mechanisms of
involved in these two eruptions physics. For example, the following energy release and transport.
comes from gradual build-up questions need to be answered.
of stresses (the "non-potential What roles do the magnetic When flares and CMEs occur, huge
energy") stored in the coronal field shearing and magnetic flux numbers of energetic electrons
magnetic field. The question emergence play to store the and ions are accelerated. These
‘What magnetic configuration pre-flare energy and to trigger accelerated particles can travel
is favorable for producing flares eruptions? What quantitative swiftly in the direction of the
and CMEs?’ remains to be one of relationship can we establish magnetic field, penetrate the lower
Fig. 3: Left: a full disk magnetogram observed by HMI. FMG will be a successor of HMI. Right: Magnetic field topol-
ogy and X-ray sources of a flare. The magnetic field can be derived from FMG observations, and hard X-ray sources
can be obtained from HXI measurements after the launch of ASO. (The image is adopted from the RHESSI website.)
太空|TAIKONG 5
Instrument Mass (kg) Size (mm) Power (W) Data rate(GB/day) FMG 85 1200×600×450 55 140 HXI 50 1200×400×400 70 5 LST 60 880×600×420 80 75 Structure 25 Sum 220
corresponding parameters of the telescopes observing in Lyman- and is formed all through the
magnetograph of PHI (Polarimetric alpha and white light: SDI (solar disk chromosphere and the bottom of
and Helioseismic Imager) onboard imager), SCI (solar coronagraph the transition region. Comparing
Solar Orbiter are listed in Table imager), and WST (full-disk white- with the conventional white-light
3. FMG consists of an imaging light solar telescope) for the coronagraph images, Lyman-alpha
optical system, a polarization purpose of calibration. WST can coronagraph observations will
optical system, and a CCD image also be used to observe white- provide new discoveries of CMEs.
acquisition and processing system. light flares, a fundamentally The light ray-tracing diagrams of
Its optical system is delineated in important aspect of flare physics. the SCI and SDI are delineated in
Figure 5. SDI works in the same wavelength the left and right panels of Figure
band as the HRI (High Resolution 7 , respectively.
• Hard X-ray Imager Imager) of EUI (Extreme Ultraviolet
Imager) onboard Solar Orbiter;
HXI aims to image the full solar And SCI shares some common ORBIT, SPACECRAFT
disk in the high-energy range features with METIS (Multi
from 30 keV to 300 keV, with Element Telescope for Imaging PLATFORM AND
good energy resolution and high and Spectroscopy) onboard ALTITUDE CONTROL
time cadence. It is designed for Solar Orbiter. The key parameters
flare observations. The principle of these four instruments are ASO-S has a solar synchronous
of HXI is the same as HXT (hard presented in Table 5. orbit at an altitude of ~ 700 - 750
X-ray telescope) on board km. The selection of the altitude
YOHKOH using indirect imaging The hydrogen Lyman-alpha line takes into account both the particle
of spatial modulation. Unlike HXI is the brightest line in the UV background along the orbit for HXI
and HXT, another high energy
imaging mission RHESSI adopts
the indirect imaging technique
by rotational modulation. STIX
(Spectrometer Telescope for
Imaging X-rays) onboard Solar
Orbiter takes the indirect imaging
of spatial modulation as well. The
key parameters of HXI and STIX
are summarized in Table 4. The
telescope structure including
collimators, detector, and
electronics box, etc., is presented
in Figure 6.
• Lyman-alpha Solar Telescopes
To observe CMEs continuously
from solar disk to a few solar
radii, another payload LST will
be on board. It comprises three Fig. 5: Optical system of FMG.
FMG PHI/HRT PHI/FDT
Wavelength Fe I 532.4nm Fe I 617.3±0.06nm Fe I 617.3±0.06nm
Accuracy BLOS≈5G BLOS
and the scattered light level for DISCUSSION AND made by ASO-S will be able to
LST. It has an inclination angle of monitor the Sun with much higher
around 98° . RECOMMENDATION data rate. Together also with the
• One candidate of the satellite Russian mission Interhelioprobe
platform is the FengYun During the two-day forum, there and many ground-based
series SAST1000 from were many insightful discussions. telescopes, scientists can benefit
Shanghai Academy of Space They are classified into three hugely from multi-perspective,
Technology. Another is ZY-1 following categories: multi-wavelength observations of
from China Academy of Space commonly observed phenomena.
Technology. 1. MISSION CONCEPT
• The altitude control uses the ASO-S plans call for a launch
three-axes stability technology. The participants intensively in around 2021 for selection at
The platform attitude pointing discussed the synergy between the end of 2015. Some of the
accuracy is designed to be ≤ ASO-S and Solar Orbiter. Thanks participants worried about such
0.01° , measurement accuracy to the different orbits of the two a tight schedule and expressed
≤ 1″, stabilization accuracy ≤ missions, stereoscopic studies can that some delay is completely
0.0005° /s. The payload attitude be made. For instances, FMG and acceptable. However, after
pointing accuracy is designed PHI can work together to solve comprehensively considering
to be ≤ 20″, and stabilization the 180º ambiguity problem of the status of key technology, the
accuracy ≤ 0.25″/30s for FMG transverse magnetic field in a novel participants found that the time
and 1-2″/10s for LST. and extremely attractive manner; scheme is attainable. For FMG,
HXI and STIX can be used to the team has worked on the
study the anisotropy of energetic magnetograph for tens of years,
electrons and the 3D geometry and the key technology is already
of flare loops; LST and EUI/METIS there. For HXI, the team has done a
can reveal the 3D context of the good part of work. Further through
features observed in Lyman-alpha, international collaborations, the PI
such as prominences. The remote- of STIX onboard Solar Orbiter was
sensing instruments onboard confident that the key technology
Solar Orbiter have only a limited of HXI could be solved in time. LST
duty cycle, while the observations inherits the Lyman-alpha telescope
HXI STIX
Energy range 30-300 keV 4-150 keV
Energy resolution 3%@662keV ~1 keV, less at higher energies
Angular resolution < 6” 7”
Field of view 1° 2.5° for spectroscopy,
1.5° for imaging
Temporal resolution 0.5 s Up to 0.1 s
Effective area 100 cm2 ~6 cm2
Table 4: Key parameters of HXI and STIX.
LST/SCI METIS LST/SDI EUI/HRI
Wavelength 121.6±10nm visible: 580-640nm 121.6±5nm H I Ly α 121.6nm
HI Ly α 121.6±10nm 17.4 nm
Field of view 1.1 – 2.5 R 1.4 -2.9 Rʘ (0.27 AU) 0.0 – 1.2 Rʘ 1000’’*1000’’
2.1 -4.35Rʘ (0.4AU)
Spatial resolution 4.6” 20’’(2*2 binning) 1.12” 1’’
Temporary resolu- 4 - 10s Visible: 5 min 1-5s can reach sub
tion UV/EUV: 15-20 min second
Table 5: Key parameters of LST/SCI, METIS, LST/SDI, and EUI/HRI.
8 太空|TAIKONGdesigned for the Sino-French left and half for right)
mission SMESE. It was proposed will be collected for one
about 10 years ago. Therefore, magnetogram. Such
we have already accumulated huge data absolutely
some experience from the SMESE need real-time onboard
mission and can also benefit from data acquisition and
the techniques applied to Lyman- processing. On the other
alpha telescopes onboard other hand, within 32s (for
missions, e.g., SOHO. Dr. Jean- obtaining 512 frames)
Claude Vial suggested us to make the pointing should be
good use of the time before the stabilized at least within
last round of the mission selection. half pixel, say 0.”25. For
All the participants expressed that a birefringent-filter-
even if a few years delay happens, based magnetograph,
there is no major influence on the temperature control
scientific goals of ASO-S. accuracy of filter should
be better than 0.01° C. Fig. 6: Design of the HXI structure.
Fig. 7: Ray-tracing diagrams of SCI (left) and SDI (right).
milliseconds possible. This is really
2. PAYLOADS KEY TECHNIQUES All of these issues should be paid
new, since such a time is just
more attention at this key stage of
the order of magnitude for the
The participants extensively the project.
electrons travelling from the top of
discussed the key technologies
the loop to the footpoints, and HXI
involved in payloads. • HXI
can for the first time resolve these
motions. A big issue for hard X-ray
• FMG The main discussions on HXI are
telescopes is the calibration. The
about the energy range, absolute
HXI team and STIX team plan to sit
The key techniques of FMG calibrations, cross talk problem
together in the future to compare
discussed include: data acquisition between different subcollimators,
the absolute values observed by
and real-time onboard processing, background measurement, etc.
HXI and STIX. The gain calibration
image stabilization, temperature It is found that the upper limit
was also briefly discussed. Proper
control (or compensation), and of the energy band of 300 keV
alignment of front and rear
oil sealing. In order to get higher is better than 150 keV that STIX
subcollimator pairs needs to
accuracy, FMG uses multi-frame- has. Another new aspect of HXI
be done to avoid the cross talk
add mode. In normal mode of is the high time cadence, which
problem and to ensure the optical
observation, 512 frames (half for makes the image with tens of
太空|TAIKONG 9performance. To measure the coronal magnetic field, the
background, one can remove the 180-degree disambiguation of the
grids in front of some detector transverse field in the photosphere,
elements. and surface flow maps. Probably in
the future, the Q-maps quantifying
• LST the magnetic topology could be
included as well. It is better to start
LST led to quite a number of preparation for work early in the
discussions. The FOV of LST program.
onboard ASO-S is more beneficial
in observing the inner corona
than METIS onboard Solar SUMMARY
Orbiter. The cleanness of the
spacecraft is very crucial to
The participants reached an
Lyman-alpha measurements.
agreement after this two-
Another fundamental issue for
day meeting: ASO-S has well-
coronagraphs is to decrease the
defined scientific objectives
stray light, especially that from
and will measure fundamental
the first mirror. It is recommended
and important parameters of
to quantify the stray light as a
solar magnetic field, solar flares,
function of radial distance. It
and CMEs. The mission is not
is also recommended to add a
overloaded and still is ambitious.
white-light channel to increase
It has focus and is in good
the science outcome of LST, by
balance between the advanced
implementing filter wheels in
scientific objectives and resources.
the optical path. The participants
Therefore, the mission is very
also suggested including a
probable to be successful. The
capability for measuring Lyman-
director of Kiepenheuer-Institute
alpha polarization to obtain the
for Solar Physics in Germany Prof.
horizontal component of the
Oskar von der Luehe stimulatively
coronal magnetic field, and the
asked the ASO-S team to “go for it”!
possibility of a Lyman-alpha
And in the future, some workshops
spectrometer to retrieve more
will be set up to work on the
physical quantities. As a result, the
calibration of hard X-ray telescope
LST team will seriously consider
on different missions, etc. It is also
these possibilities and envisage
planned to frame ASO-S into the
the technical feasibility. During the
NASA’s Living with a Star Program.
meeting, the contrast of Lyman-
alpha images and the contribution
of geocorona to the Lyman-alpha
signal were also discussed.
3. DATA PRODUCT
Another aspect is the data product.
It is suggested that ASO-S should
not only provide measurements
but also some routine tools to the
community. In particular for FMG,
the team was asked to provide
high-level products of magnetic
field. Borrowing the experiences
from HMI, the high-level product
may include the extrapolated
10 太空|TAIKONG太空|TAIKONG 11
太空|TAIKONG Participants Sergey Bogachev LPL, Russia Yuanyong Deng National Astronomical Observatories, CAS, China Mingde Ding Nanjing University, China Maurizio Falanga International Space Science Institute - Beijing, China Cheng Fang Nanjing University, China Li Feng Purple Mountain Observatory, CAS, China Weiqun Gan Purple Mountain Observatory, CAS, China Hugh Hudson UC Berkeley, USA/ Uni. Glasgow, UK Haisheng Ji Purple Mountain Observatory, CAS, China Eduard Kontar University Glasgow, UK Säm Krucker FHNW, CH / UC Berkeley, USA Vladimir Kuznetsov IZMIRAN, Russia Hui Li Purple Mountain Observatory, CAS, China Jun Lin Yunnan Astronomical Observatory, CAS, China Yang Liu Stanford University, USA Oskar von der Lühe KIS, Germany Eckart Marsch Kiel University, Germany Marco Romoli University Firenze, Italy Brigitte Schmieder LESIA, France Albert Shih GSFC, USA Yingna Su Purple Mountain Observatory, CAS, China Jean-Claude Vial IAS, France Jingxiu Wang National Astronomical Observatories, CAS, China Ji Wu National Space Science Center, China Jian Wu Purple Mountain Observatory, CAS, China Yihua Yan National Astronomical Observatories, CAS, China Mei Zhang National Astronomical Observatories, CAS, China Haiying Zhang Nanjing Institute of Astronomical Optics & Technology, CAS, China Yiqian Zhou SSA, China
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