The next-generation space solar observatory:

The SOLAR-C Mission�

K. Watanabe & H. Hara ISAS/JAXA & NAOJ

SOLAR-C WG 2015 Feb 27�

ISSI#Coronal#Rain#�

Basic#Problems##in#Helio(Physics�1.#Origin#of#large8scale#

explosion�

2.#Hea=ng#of#chromosphere#and#corona,#

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3.#Magne=c#cycle#

Planned##satellite##Solar#observatory#prepared#by#JAXA##SOLAR8C#W.G.�

First#determines#3D#magne=c#structures#from#unprecedented#observa=ons#for##elucida=ng#basic#problems#in#Helio8Phys.##

Keywords:##8#Chromospheric#B#measurements##8#0.1”#–#0.3”#spa=al#resolu=on##8#�1s#high8cadence#observa=ons##8#high#resolu=on#spectroscopy�

SOLAR-C�

(0.1”#=#70#km)�

Science#Objec=ves#Observations of All from photosphere to corona seamlessly

as a system�

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drive#short8=me#geo8space#variability#

•  Mechanisms#responsible#for##–  hea=ng#and#dynamics#of#chromosphere#&#corona#

–  accelera=on#of#solar#wind#•  Fundamental#physical#processes#

–  Magne=c#reconnec=on,#MHD#waves,#shocks,#etc.#

•  Fine8scale#magne=sm#and#associated#solar#spectral#irradiance#

SOLAR8C#will#determine�

EPIC: European Participation in Solar-C 4 MISSION CONFIGURATION AND PROFILE

SUVIT/IUSUVIT/UBIS

SUVIT/SPSUVIT/FG

HCI

Startracker

UltrafineSun Sensor

+Z

+Y

+X

Telemetry Antenna

SUVIT/TA

EUVST

Telescope Door

+Z

+Y

+X

Heat Dump WindowStartracker

Telemetry AntennaSolar Array Panel

Apogee Kick EngineThrusters

SUVIT/TAHCI

Optical Bench Unit

Telemetry AntennaBus Module

Inertial Reference Unit(Gyros, part of Bus Module)

Figure 26: Solar-C Spacecraft; source: NAOJ. The scientific payload also includes the Irradiance Monitor (IM).

vide the downlink of science data to ground via X-bandcommunication channels (see Section 4.5). The Iner-tia Reference Unit (IRU), not visible in Figure 26) willbe established by a fibre-optic gyro system with low-est possible drift rates. The startrackers and the IRUwill have considerable heritage from and achieve per-formance levels as those in Alphasat, Sentinel-2 andEDRS-C.

Instruments and spacecraft structures that are essen-tial for stability and accuracy, are equipped with heatersto provide a stable thermal environment. In addition, in-struments will have emergency heaters to keep them in asafe state in case of malfunctions of the bus system. Theheating power requirements are the result of a detailedthermal analysis which will be carried out as part of thedesign phase.

Two solar array panels are deployed from the twosides of the spacecraft body and are designed to generateabout 5 000 Watt of electrical power. A possible reduc-tion of the panel size or of the number of solar cells willbe based on the more accurately determined power re-quirements available after the definition phase. The sizeof the spacecraft body (telescopes and bus module) isroughly 3.7 ⇥ 3.2 ⇥ 7.1m3, excluding the solar arrays.This size fits in the fairing envelope of the H-IIA 4Srocket. The estimate for the total mass is about 4 met-ric tons, which consists of 2.3 ton dry mass and 1.7 tonpropellant, which requires efforts on reduction for a H-IIA launch, but the mass constraint may be relaxed withthe new H-III rocket (first flight expected in 2020).

The model specification of the spacecraft system issummarised in Table 6.

38

SOLAR-C Spacecraft�

Hinode�

SUVIT#TA#1.4#m#diameter#telescope�

EUVST#(EUV#Spectroscopic#Telescope)�

HCI#(High#Resolu=on#########Coronal#Imager)�

SUVIT:#Solar#UV8Visible8IR#Telescope#

50cm#dia.#telescope�

Chromospheric#magne=c#fields#measurements�

EPIC: European Participation in Solar-C 3 PROPOSED SCIENTIFIC INSTRUMENTS

Figure 24: The opto-mechanical layout of HCI. The layout resembles that of the EUV imagers TRACE, SDO/AIA and Hi-C.

10 Hz bandwidth cutoff and will allow smooth operationof the image motion compensation system.

In terms of resources, the instrument occupies avolume of 430 ⇥ 70 ⇥ 40 cm3, has a mass of 155 kg(including 15 % margin) and requires 68 W power (ofwhich 24 W for operational heaters).

3.4 High Resolution Coronal Imager (HCI)

The HCI is a normal-incidence EUV telescope con-sisting of primary and secondary mirrors in Ritchey-Chretien configuration. It will perform high-resolutionimaging in the EUV pass-bands described in Sec-tion 2.4: 30.4 nm containing the He II resonance line asdiagnostic of the transition region, 17.1 nm containinglines of Fe IX and Fe X showing 1 MK coronal struc-tures at high contrast, and 9.4 nm containing Fe XVIIIwith emission in very hot outburst features.

Table 5 summarises key design features of HCI.The primary and secondary mirrors are both dividedinto three sectors, with each sector coated with differentmulti-layer coatings for high reflectance in the pertinentpassband. The sectors have different areas to accommo-date expected count rates (17.1 nm 33%, 30.4 nm 17%,9.4 nm 50%, respectively).

The primary mirror will have a clear aperture of32 cm diameter. Wavelength selection will be done witha filter wheel as in SDO/AIA.

The optics will give an effective focal length of20 m. Combined with a 10µm pixel back-thinned CCD(4k⇥4k format) this gives 0.100/pixel sampling.

The secondary mirror will have an active mount thatis actuated to remove instrument pointing errors and fo-cus the system, as in TRACE and SDO/AIA. As in these

instruments, HCI will have a guide telescope for Sun-tracking to feed the image stabiliser. This system willincorporate spacecraft pointing information to achievethe required pointing accuracy and stability.

Entrance filters will reject visible light. An aper-ture door protects them during launch, as in TRACE andSDO/AIA. A mechanical shutter near the focal planecontrols the exposure time. Typical exposure times (asfor the comparable channels of SDO/AIA) will rangefrom 0.1 s for flares to 100 s for dark quiet-Sun targets.

The analog output from the single CCD will be con-verted into 14 bits. In standard observing, the readoutarea will cover only one quarter of the full FOV (2k⇥2kpixels or 20500⇥20500) at an exposure cadence of 10 s.The planned data rates for normal-cadence observationsare 5.9 Mbps (raw), 2.9 Mbps (lossless) and 1.3 Mbps(lossy). In lossless compression each pixel value corre-sponds to 7 bits; in lossy compression only 3 bits. In fastsmall-area sampling 1024 ⇥ 1024 pixels (10000⇥10000)readout can reach 1 s cadence with lossy compression.

HCI will use large heritage from the comparableEUV imagers on-board TRACE and SDO/AIA. How-ever, as the instrument will have 5–6 times better an-gular resolution, the following issues will be assessedduring the definition phase:– mirror micro-roughness, i.e., optimising multi-layer

reflectance and minimising wide-angle scattering;.– effect of multi-layer coatings on effective area after

masking;– stabilisation at twice the resolution of IRIS;– vibration from moving elements (as the filter wheel);– effect of hits by energetic particles.

36

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•  Optics: single off-axis mirror (30cmφ, f=360cm)

and a grating •  Telescope length: 430cm �

With low scattering optics, for exploring low EM regions (MR and CH).�

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(30cmφ, f=360cm) and a grating •  Telescope length: 430cm �

AR (log T/K < 6.2) - 1s exposureAR (log T/K > 6.2) - 1s exposure

log (T/[K])4 5 6 7

FeIX

FeX/XI

MgX

FeXII

FeXIII

FeXIV

SiXII CaXIV

CaXV

CaXVI

CaXVII

FeXVIII

FeXIX

FeXIX

FeXIX

FeXX

FeXXIII

FeXXIIFeXXIV

FeXXI

Slit assembly�

With low scattering optics, for exploring low EM regions (MR and CH).�

EPIC: European Participation in Solar-C 3 PROPOSED SCIENTIFIC INSTRUMENTS

Figure 24: The opto-mechanical layout of HCI. The layout resembles that of the EUV imagers TRACE, SDO/AIA and Hi-C.

10 Hz bandwidth cutoff and will allow smooth operationof the image motion compensation system.

In terms of resources, the instrument occupies avolume of 430 ⇥ 70 ⇥ 40 cm3, has a mass of 155 kg(including 15 % margin) and requires 68 W power (ofwhich 24 W for operational heaters).

3.4 High Resolution Coronal Imager (HCI)

The HCI is a normal-incidence EUV telescope con-sisting of primary and secondary mirrors in Ritchey-Chretien configuration. It will perform high-resolutionimaging in the EUV pass-bands described in Sec-tion 2.4: 30.4 nm containing the He II resonance line asdiagnostic of the transition region, 17.1 nm containinglines of Fe IX and Fe X showing 1 MK coronal struc-tures at high contrast, and 9.4 nm containing Fe XVIIIwith emission in very hot outburst features.

Table 5 summarises key design features of HCI.The primary and secondary mirrors are both dividedinto three sectors, with each sector coated with differentmulti-layer coatings for high reflectance in the pertinentpassband. The sectors have different areas to accommo-date expected count rates (17.1 nm 33%, 30.4 nm 17%,9.4 nm 50%, respectively).

The primary mirror will have a clear aperture of32 cm diameter. Wavelength selection will be done witha filter wheel as in SDO/AIA.

The optics will give an effective focal length of20 m. Combined with a 10µm pixel back-thinned CCD(4k⇥4k format) this gives 0.100/pixel sampling.

The secondary mirror will have an active mount thatis actuated to remove instrument pointing errors and fo-cus the system, as in TRACE and SDO/AIA. As in these

instruments, HCI will have a guide telescope for Sun-tracking to feed the image stabiliser. This system willincorporate spacecraft pointing information to achievethe required pointing accuracy and stability.

Entrance filters will reject visible light. An aper-ture door protects them during launch, as in TRACE andSDO/AIA. A mechanical shutter near the focal planecontrols the exposure time. Typical exposure times (asfor the comparable channels of SDO/AIA) will rangefrom 0.1 s for flares to 100 s for dark quiet-Sun targets.

The analog output from the single CCD will be con-verted into 14 bits. In standard observing, the readoutarea will cover only one quarter of the full FOV (2k⇥2kpixels or 20500⇥20500) at an exposure cadence of 10 s.The planned data rates for normal-cadence observationsare 5.9 Mbps (raw), 2.9 Mbps (lossless) and 1.3 Mbps(lossy). In lossless compression each pixel value corre-sponds to 7 bits; in lossy compression only 3 bits. In fastsmall-area sampling 1024 ⇥ 1024 pixels (10000⇥10000)readout can reach 1 s cadence with lossy compression.

HCI will use large heritage from the comparableEUV imagers on-board TRACE and SDO/AIA. How-ever, as the instrument will have 5–6 times better an-gular resolution, the following issues will be assessedduring the definition phase:– mirror micro-roughness, i.e., optimising multi-layer

reflectance and minimising wide-angle scattering;.– effect of multi-layer coatings on effective area after

masking;– stabilisation at twice the resolution of IRIS;– vibration from moving elements (as the filter wheel);– effect of hits by energetic particles.

36

High#Resolu=on#Coronal#Imager#(HCI)�8#He#II#304#8#Fe#IX#171#8#Fe#XVIII#94�

HCI�

EPIC: European Participation in Solar-C 4 MISSION CONFIGURATION AND PROFILE

SUVIT/IUSUVIT/UBIS

SUVIT/SPSUVIT/FG

HCI

Startracker

UltrafineSun Sensor

+Z

+Y

+X

Telemetry Antenna

SUVIT/TA

EUVST

Telescope Door

+Z

+Y

+X

Heat Dump WindowStartracker

Telemetry AntennaSolar Array Panel

Apogee Kick EngineThrusters

SUVIT/TAHCI

Optical Bench Unit

Telemetry AntennaBus Module

Inertial Reference Unit(Gyros, part of Bus Module)

Figure 26: Solar-C Spacecraft; source: NAOJ. The scientific payload also includes the Irradiance Monitor (IM).

vide the downlink of science data to ground via X-bandcommunication channels (see Section 4.5). The Iner-tia Reference Unit (IRU), not visible in Figure 26) willbe established by a fibre-optic gyro system with low-est possible drift rates. The startrackers and the IRUwill have considerable heritage from and achieve per-formance levels as those in Alphasat, Sentinel-2 andEDRS-C.

Instruments and spacecraft structures that are essen-tial for stability and accuracy, are equipped with heatersto provide a stable thermal environment. In addition, in-struments will have emergency heaters to keep them in asafe state in case of malfunctions of the bus system. Theheating power requirements are the result of a detailedthermal analysis which will be carried out as part of thedesign phase.

Two solar array panels are deployed from the twosides of the spacecraft body and are designed to generateabout 5 000 Watt of electrical power. A possible reduc-tion of the panel size or of the number of solar cells willbe based on the more accurately determined power re-quirements available after the definition phase. The sizeof the spacecraft body (telescopes and bus module) isroughly 3.7 ⇥ 3.2 ⇥ 7.1m3, excluding the solar arrays.This size fits in the fairing envelope of the H-IIA 4Srocket. The estimate for the total mass is about 4 met-ric tons, which consists of 2.3 ton dry mass and 1.7 tonpropellant, which requires efforts on reduction for a H-IIA launch, but the mass constraint may be relaxed withthe new H-III rocket (first flight expected in 2020).

The model specification of the spacecraft system issummarised in Table 6.

38

Hinode�

SUVIT#TA�

EUVST#(EUV#Spectrograph)�

SUVIT#SPP�

HCI#(Coronal#imager)�

International Collaboration�

ESA & EUVST consortium �

NASA�

NASA�

JAXA+α�

JAXA+α�

Launch vehicle: JAXA Spacecraft: JAXA�

A planned case of task share that world-wide solar physicists desire�

-  Proposed to US Heliophysics Decadal Survey -  EUVST: proposed to ESA Cosmic Vision II -  Submitted to JAXA-AO�

α:#European#countries�

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Coordinated Observations�

Credit:#ESA/AOES�

Solar*Orbiter�

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Solar*Dynamic*Observatory*or*a*mission*of*full9disk*observa<ons�

SOLAR8C�

Summary�•  SOLAR-C is a mission to understand the causal

linkage between solar magnetic fields and active phenomena on the Sun and in the heliosphere.

•  SOLAR-C equips three major payloads to elucidate fundamental problems in Helio-physics

by high-resolution (0.1”−0.3”) imaging & spectroscopy with temporally stable chromospheric magnetometry.

•  All telescopes of the SOLAR-C have capability to observe coronal rains with enough spatial resolution, enough cadence, and enough coverage of temperature.