SOLAR-C Mission
Option-A (Plan-A)
H. Hara（NAOJ)
JAXA SOLAR-C WG
2010 Mar 9
2nd SOLAR-C Science Definition Meeting

SOLAR-C Concept• Two options are under study:– Option-A (so-called Plan-A):
Exploration of origin of the solar magnetic activity cyclefrom an out-of-ecliptic orbit
by X-ray/magnetic field/helioseismic observations
Toward understanding the solar magnetic activity cycle– Option-B： high-spatial resolution observations of thedynamic Sun with enhanced spectroscopic andpolarimetric capabilities
Toward understanding the magnetic-field dissipation processes• Launched by JAXA H2A rocketSolar Magnetic Activity Cycle• How are magnetic fields created in the sun? (Dynamo)• Internal flows, behavior of polar magnetic fields, andpolarity reversal at poles from out-of-ecliptic observations
may be important.

1980

1990

2000

Year

Option-A

Exploration from out-of-ecliptic orbit＜Toward understanding the solar dynamo＞• Surface magnetic activity in polar regions• Surface/internal flow fields in polar regions• Search of tachocline regarded as a source regionof strong magnetic fields＜Exploration from Vantage Point＞• Search of solar winds in polar coronal holes• Total irradiance measurements from out-ofecliptic orbit; The Sun as a star
• Imaging of CMEs and solar wind/CIR shock
structures
TSI(W m-2)

Option-A Target Final Orbit
SOLAR-C

EarthSun

The target orbital period of 1 yr, synchronized with EarthRotation and Meridional Flows• Basic quantities to understand the solar dynamo• cannot be determined from observations in ecliptic plane
for high-latitude and polar regions• Need out-of-ecliptic helioseismic observations to fill upfor all latitude regions
North Pole

Submergence ofmagnetic field？

Surface magnetic field transport
Meridional flow speed

20m/s

Angular velocity

South Pole-20m/s

Meridional flow-60 deg Latitude 60 deg

Exploration of B at the base of CZ
P-mode ray path

• Many solar physicists believe
SOLAR-C S/C that magnetic flux tubes areproduced at tachocline.
• Exploration of magnetic flux
tube at tachocline byhelioseismic observations
EarthTachocline
Convection zone (CZ)

Internal angular rotation rate

Polar Coronal Activity

Hinode XRT••••

Dynamic polar regions of the sun
Highly transient jets
More stable plumes in EUV images
Source of high-speed solar windSolar Wind
Ulysses• How is the high-speed solar windfrom polar coronal holes
accelerated?
• Measurement of global magnetic
fields in polar coronal holes,
flows in transition region andlow corona, and the wind speed
may provide the linkage between
sun and inner heliosphere.
• We may be able to see theParker spiral of solar winds
by a heliospheric imaging.

Ulysses First Orbit
near Solar Min

McComas et al. (2003)

Ulysses Second Orbit
near Solar Max

Total Solar Irradiance (TSI)from out-of-ecliptic plane• Understand the sun as a star
• Solar irradiance TSI cycle
variation ~0.1% p-p

Figure from PMOD WRC homepage

Photometric variationof solar type stars• Solar type stars show larger amplitude photometricvariations, (though the number of sample is small…)• Is it due to a difference in viewing angle to activity belts?
Chromospheric variation

Photometric variation

SunSunLockwood et al. 2007, ApJS,171, 260

Total Solar Irradiance (TSI)from out-of-ecliptic plane• Interesting to measure TSI from an orbit
with inclination >40 deg
Latitudinal variation of TSI• Overall effects of sunspot blocking,facular brightening near the limb, andchange of activity-band location whenviewing from an out-of-ecliptic plane• Amplitude over the solar cycle willfrom Schatten 1993, JGR, 98, 18907
increase at the max viewing angle fromPlan-A S/C. How large? The Sun is a
special mild star for life to adjust its
irradiance change?
A view at latitude 40 deg from solar equatorial plane
and location of the activity belt (-30 < θ < 30 deg)Stereoscopic View of CME
Stereoscopic view from STEREOSTEREO
COR2-ASTEREO
COR2-B

B

A

Seen from normalof ecliptic plane

STEREO Can we see a signature of Parker-spiralHI2-Bstructures by an imaging observation?

STEREO
HI1-B

Spacecraft(SOLAR-C)

viewing direction
Sun

Ecliptic plane

Earth

Howard & Tappin (2008)

CME

otherspacecraft

Direct Imaging of Density Pattern
in Solar Wind Structures
Sun

STEREO-A

CIR structures detected by STEREO HI

α(P)

α=0°

HI-2

EarthαHI-1Seen from normalof ecliptic plane

α=90°
Vα

ACEN

Rouillard et al. 2008, GRL, 35, L10110

Direct Imaging of Density Patternin Solar Wind Structures
Density difference in SW structuresdetectable by a slightly-modified
STEREO HI from the Plan-A orbit

CIR detected by STEREO HI

HI-2

in ~4 σ significance level to thezodiacal-light background by
6 hours exposure (Preliminary)

HI-1

VACE

N

Solar-wind density structuresfrom MHD simulation
as observed at an out-of-ecliptic plane

Rouillard et al. 2008, GRL, 35, L10110

Other non-solar observations• Zodiacal light or interplanetary dusts– Photometric measurements have only been done
from Earth, near-Earth orbits, and inner-heliosphericorbits (by Helios) in the ecliptic plane.
– Photometric measurements in near-infrared
wavelength may access the age of re-ionization ofUniverse– An in-situ measurement of colliding dusts particles as
infrequent plasma detection (Ulysses, Japanese“Nozomi” mission, …)• Anomalous cosmic rays in Heliosphere– See Isobe-san’s presentation

Option-A：Model Payload
Each has a space heritage/a slightly modified version in missions that have been flown.

• Visible-light Magnetic-field and Doppler imager– full-disk observations– Internal flow structures, mag. fields, convection, .. in polar regions• X-ray/EUV telescope– Coronal dynamics in polar regions, synergy with coronal imagers,
observing the sun around the earth, in stereo-scopic views• EUV imaging spectrometer– Flow/wave structures in polar regions ( plume, solar wind )• Total irradiance monitor– Latitudinal distribution of surface irradiance• Others (Options at present)– Heliospheric imager: CME imaging, solar wind/CIR shock structures– Zodiacal-light photometer: distribution of interplanetary dust
– In-situ instruments (magnetometer, dust counter, …., etc.)• Total mass 130 kg (tentative allocation for design activity)Requirements for S/C System Design• Sojourn time >40 days (TBD) for a solar latitude of >30 deg (TBD)– Target of max. latitude : ~40 deg (higher is better, of course)– Need to define these numbers clearly from evaluation through helioseismic
model calculations• Distance to the Sun in the final orbit: 1.0 AU– Minimum distance to the sun is 0.7 AU from the thermal-design point of view
– Maximum distance to the sun is not defined because of a possibility ofballistic orbits by Jupiter swing-by• Use 7 deg tilt angle of the solar rotation axis to the ecliptic plane• Duration of cruise phase to the final orbit: ~5 years– Need 40-days (TBD) observations near perihelion/aphelion points
in the cruise phase• Payload weight: 130 kg• Data recording rate: >100 kbps ave.
• Mission life:
cruise phase N0~5 yr + N1 yr + extended duration N2 yr (total ~N3 yr)Orbit Design & Option-A Spacecraft• Dr. Kawakatsu explains candidate orbits
and spacecraft system for the Option-Amission.

Option-A orbit• Near-Earth orbit using ion engine & Earth swing-by– Higher-priority orbit for Solar Physics– High-data rate observations required for magnetic and helioseismic
research– Limited imaging observations of the Sun during the use of ion engine
if there is no active pointing mechanism on the payload– Launch opportunity: every 0.5 year
– 40° inclination from solar equatorial plane,1AU distance,synchronized with Earth– It takes ~5 yr to achieve the target orbit.

• Jupiter swing-by + Earth swing-by (ballistic orbit)– Lower-data rate observations and lower spatial resolution before
achieving target orbit– Observations are always possible except for swing-by operation– Launch opportunity: every ~1.1 yr– 36-40° inclination from solar equatorial plane,1AU distance,synchronized with Earth– Shorten the orbital period by Earth swing-by. It takes ~7 yr to achieve
the orbital period of 1 yr.

How is the solar poles seen
as a function of inclination angle?
i : inclination angle from solar equatorial planeRocket: H-II A-202

Cruise by Ion engine
in a shorter durationcompared with SO~5 years for final orbit
of a=1.0AU, 1yr period

i = 50 deg

Possible by
Earth swing-by
only

i = 40 deg

i = 30 deg

i = 20 deg

i = 60 deg
Ballistic orbit
Jupiter & Earthswing-by
of long-duration
cruise (>7 yr )Final period ~ 2 yr
H-II A-204

Ballistic orbit
by Jupiter & Earth Swing-by
H-II A-202~7 years for final orbit ofa=1.0AU, 1yr period

Ion engine + Earth swing-by
Timing of Earth swing-by

Window for observations
2cruise by ion engines

Distance (AU)Sun-S/C
1
Earth-S/C
045
30
Angle from
15Solar0
Equatorial-15
Plane (deg)
-30
-45
1000
Telemetry
100Rate (kbps)
1024hr/day link
assumed
1- Few occasions
for pointing to the Sun- Pointing disturbance level TBD

2017

2018

2019

2020

2021

2022

2023

2024

2025

2026

Priority in this case: reach max inclination as soon as possible

Jupiter + Earth swing-by
Sun-S/C distance > 2.5 AU

Window for observations
8

Timing of Jupiter/Earth swing-by

Low power condition

Distance (AU) 6Sun-S/C
4Earth-S/C
2Jupiter swing-by

04530
Angle from15Solar
0Equatorial-15
Plane (deg)
-30
-45
1000
Telemetry
100Rate (kbps)

Low telemetry rate

1024hr/day link
assumed
1
2018

2019

2020

2021

2022

2023

2024

2025

2026

2027

Priority in this case: reach max inclination as soon as possible

Technical Issues
in spacecraft system for SEP Option• Option-A - escaping from ecliptic plane– Kick-motor: no suitable kick motor for H II-A interplanetary mission– High power systems (~7 kW)• need high-efficiency power supply for operating ion engines towardfurther reduction of the S/C weight• need light weight solar array paddle (being developed in JAXA)– High telemetry rate in interplanetary space (~100 kbps data recording
rate @0.5AU set as minimal required level)• not a high rate for NASA’s S/C missions (slightly better in STEREO)• a key issue to enhance scientific return from helioseismology• needs downlink stations for deep space at both northern and southernhemispheres– High thrust ion engines (120 mN max)
• endurance test of ENG model being performed at JAXA/ISAS– Heat exhaust from high-heat-generating components• found to be little problems after a thermal design for a model orbit

Technical Issues
in spacecraft system for Jupiter Option• Option-A - escaping from ecliptic plane– Kick-motor: no suitable kick motor for H II-A interplanetary mission– High power systems (TBD kW) for operating at far Sun-S/C distance• needs high-efficiency power supply for operating ion engines towardfurther reduction of the S/C weight• needs light weight solar array paddle (being developed in JAXA)– High telemetry rate in interplanetary space (~100 kbps data recording
rate @0.5AU set as minimal required level)• not a high rate for NASA’s S/C missions (slightly better in STEREO)• a key issue to enhance scientific return from helioseismology• needs downlink stations for deep space at both northern and southernhemispheres– High thrust ion engines (120 mN max)
• endurance test of ENG model being performed at JAXA/ISAS– Heat exhaust from high-heat-generating components• found to be little problems after a thermal design for a model orbitProvisional Schedule• If Option-A needs to look at the polar polarity reversal in2020’s in a good observing condition, the launch of
2017/2018 is required in SEP option.
• In the baseline Jupiter option, the polar reversal may
occur before S/C reaches the maximum inclination.
Option-A Phase
Pre-A A B/C

Sunspot number

DSolarMax.
NASASDO2017
LaunchSolarMax.

Max. angle from
Solar Eq. (deg)SEP option

We areHere

SOLAR
Orbiter40200Year

11 yr

11 yr

Synergy among multiple spacecrafts
3D Scanning of Heliosphere by Multiple SpacecraftsFigure from Heber & Cummings (2001)

Synergy between Option-A and SO
3D Scanning of the Sun by Multiple Spacecrafts
One spacecraft cannot cover both polar regions at one time.

SEPOption

BallisticJupiter
OptionSolar Orbiter

Solar Latitude

Summary• SOLAR-C Option-A is a mission to look at the Sun froma high-inclination out-of-ecliptic orbit.
• We will observe features all over the latitudes on the sun
and a wide rage of heliospheric latitudes at ~1AU:
Magnetic fields, convection, internal rotation, meridionalflows from polarimetric and helioseismic observations,activity of upper atmosphere, source region of solar wind,
and interplanetary in-situ measurements.
• Science in Heliospheric Physics has not been welldiscussed with heliophysics group.
• There are practical solutions for a spacecraft to entera 40-deg inclination orbit with1-yr orbital period.
• The orbit with ion engines may be better at a glance,
but there need many technical challenges.