SOLAR-C Mission
Option-A (Plan-A)
H. Hara（NAOJ)
JAXA SOLAR-C WG
2010 Oct 10
3rd SOLAR-C Science Definition MeetingInterim Report

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
Convection in polar regions
Search of tachocline regarded as a source region of strong
magnetic fields＜Exploration from Vantage Point＞• Global and local evolution of polar upper atmosphere fromnew viewpoints• Total irradiance measurements from out-of-ecliptic orbit• Solar wind measurement in polar CH and Alfven wave
detection from inclined views• Imaging of CMEs and solar wind/CIR shock structures• Others
TSI(W m-2)

Option-A Target Final Orbit
SOLAR-C

EarthSun

The target orbital period of 1 yr, synchronized with EarthIssues on Solar Dynamofrom Interim Report (IR)• Q1) What physical processes dominate the generation ofglobal-scale poloidal magnetic fields and where do theyoperate?
• Q2) How does the transformation between the poloidal(polar) and toroidal (active regions) magnetic fluxes
occur? How does this regulate the cyclic magnetic
activity?
• Q3) What are the structure and the evolution of the solar
differential rotation, and the mean, large-scale meridional
flow, how are they maintained and how do they vary withthe solar cycle?
• Q4) What is the dynamical origin of photospheric activeregions? What is the role of the tachocline?
• Q5) How can we predict sunspot cycles and periods ofhigh solar activity?

Prime Measurement Targets in S-C
for understanding Solar Dynamo• T1) Differential rotation and meridional flow in thepolar regions and the deep convection zone
• T2) Photospheric magnetic flux distribution andevolution in the polar regions• T3) Dynamical coupling between magnetic fieldsand flows• T4) Structure and evolution of solar convectionObs.of upper solar atmospherecurrently described in IR• Formation/evolution of coronal structures– Global-scale coronal structure in polar points– Plume– Small-scale bright points• Solar wind
– Spectroscopic detection of Alfven waves by different
view angles– Restrict the range of T⊥/T// in O v 1032 observations
for the inner corona by different view angles– No description on the in-situ solar windmeasurements on S-C

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?
This will be answered by TSI observations from S-C out-of-ecliptic orbit.
Chromospheric variation

Photometric variation

SunSunLockwood et al. 2007, ApJS,171, 260

Optional targets
when we can have payload mass
• CME/CIR imaging from out-of-ecliptic points• Monitoring cosmic rays,
which relates to generation of cosmogenic isotopes (14C, 10Be, ..), tounderstand the transport processes in the heliosphere [ This is justan idea, need to consider more for justification. ] A quick scan ofheliosphere in the solar cycle may give a new hint to understand thediscrepancy between the model and Ulysses results.

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– In-situ instruments (CR detector, magnetometer?, etc.; not defined)• Total mass 130 kg (tentative allocation for design activity)• Detailed optical layout studies not described in IRRequirements for S/C System Design• Duration >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)

Disc center

Virtual View of Solar North Poleat 7 deg from solar equatorial plane

Data from a single FITS data of HMI/SDO 45s-cadence Longitudinal Magnetic Field

Disc center

Virtual View of Solar North Poleat 20 deg from solar equatorial plane

Data from a single FITS data of HMI/SDO 45s-cadence Longitudinal Magnetic Field

Disc center

Virtual View of Solar North Poleat 30 deg from solar equatorial plane

Data from a single FITS data of HMI/SDO 45s-cadence Longitudinal Magnetic Field

Disc center

Virtual View of Solar North Poleat 40 deg from solar equatorial plane

Data from a single FITS data of HMI/SDO 45s-cadence Longitudinal Magnetic Field

Requirement
for average data recording rate
• Data Recording Rate: ~100 kbps (Total)• Estimation for a model case (preliminary)– Helioseismology/B-field observations ~ 50kbps• Global helioseismology– 512×512(pixels) ×3(bit/pixel)/60(s)/1024(kbps/bps) = 13 kbps ave.

• Local helioseismology– 1024 ×1024 ×3 (bit/pixel) /60(s)/1024 = 51 kbps ave.

• Magnetic (B) field– LOS B: 1024 ×1024 ×3(bit/pixel)/300s/1024 = 10 kbps
– Vec. B:2048 ×2048 ×3(b/pix) × 16img /7200(s)/1024 = 28 kbps

– EUV imaging spectroscopy ~20 kbps ave.
– EUV/X-ray imaging ~20 kbps ave.
– TSI monitor: ~1 kbps
– Heliospheric imager ~ 1kbps by on-board summing– Others: probably negligible

Mission Requirements for Orbit Formation– To reach Solar Lat. 40°by early 2020’s.
– Mass of Science instruments > 130kg.
– Data transmission rate > 300kbps @ 0.6AU.

Challenge to Solar Lat. 40°• Rough Estimation of the Launch Energy∆v

C3 = (v∞)2 ≈ (20km/s)2 ≈ 400km2/s2(cf. C3 for the Jupiter Transfer ≈ 80km2/s2)

Techniques to Overcome the Challenge• Trajectory Manipulation Techniques Available–Geometric Relation
Take advantage of the tilt of the Solar equatorial plane against the ecliptic
plane (about 7deg.). Choice of the appropriate launch date is important.

–Launcher Capacity
Launch energy is still the most contributing part. Launch a small
spacecraft with a heavy launcher yields large launch energy.

–Gravity Assist (Swingby)
The most efficient trajectory manipulation method in the interplanetarycruise, which is widely used in various planetary missions.

–Propulsion
Usage of high efficiency propulsion system enables large velocity
increment with less propellant.

Possible Options of the Trajectory Sequence• Venus option (optionally surveyed)• Jupiter option• SEP option

Option-A orbit• Near-Earth orbit using ion engine & Earth swing-by– Higher-priority orbit for Solar Physics, if technically feasible– 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 plane
Cruise by Ion engine
Rocket: H-II A-202 in a shorter durationcompared with SO
Ballistic orbit ~5 years for final orbit
Venus & Earth of a=1.0AU, 1yr period
Swing-by~3 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
1Earth-S/C
045
30
Angle from
15Solar
0Equatorial-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

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 @0.6AU 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

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

Window for observations
8Timing of Jupiter/Earth swing-by

Low power condition

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

04530
Angle from15
Solar
0Equatorial-15
Plane (deg)-30-451000
Telemetry
100Rate (kbps)

Low telemetry rate

1024hr/day linkassumed
1
2018

2019

2020

2021

2022

2023

2024

2025

2026

2027

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

Jupiter Option Summary• Compliance to the Mission Requirements– Reaches Solar Lat. 30°in 2022 (assumes launch in 2018), and finally achieves 40°.
– Spacecraft’s mass budget permits instruments > 130kg.
– Data transmission rate > 300kbps @ high Lat. region (> 30°) (from 2025).

• Advantage– Conservative sequence which does not require electric propulsion system.

• Disadvantages– Long duration before the observation starts (> 4 years). Far from both Sun and Earthduring the transfer.
– Frequent observation of Solar Polar region (every a half year) starts from 2025.
– Good launch opportunity (to reach 40°) may be infrequent.
(the next launch window in 2019 achieves Solar Lat. 37°with the similar sequence)Key Technologies for SEP Option
Ultra-Lightweight Solar Panelµ20 ion engine system

Conceptual Image ofSEP option spacecraft
Ka/X Communication System(also required in Jupiter option)

Ka/X Communication System (1)• System concept–X-band system
Mission requirement (300kbps @ 0.6AU telemetry) is achieved byredundant X-band system. It is equipped and well demonstrated in
HAYABUSA, KAGUYA, etc.

–Ka-band system
To enhance the scientific achievements, a single Ka-band system isadditionally equipped.

–Link budget

Item

X-bandKa-band

Unit

8400

32300

MHz

40.0
36.5

20.0
48.2

W
dBi

0.56
300k

0.56
1MAUbps

Link Margin

1.0

2.0

dB

Receive C/N0
Required C/N0

59.3
58.4

64.6
62.6

dBHz
dBHz

Frequency
Transmitter Power
Transmit Antenna Gain
Communication Distance
Bit RateKa/X Communication System (2)• System Configuration
Ka-TX (EM)X/Ka Feeder (New Development)
KaTWT

X/Ka HGA
X/Ka HGA

KaEPC

Ka-band

HGA Control Unit
X/Ka Feeder

S/X HGA(KAGUYA)KaSW-1XEPC-1DIP-1

XTWT-1HYB

XSW-4

X LGA-1

XEPC-2

XTWT-2

XTRP-1

XSW-3
DIP-2

XSW-2

KaTX-1

KaTX-2
XSW-5

XTRP-2XSW-1

XLGA-2

X-bandImprovements
Improvementsin
ingroundgroundsegments
segments
also
alsoininprogress.
progress.

X-TRP (AKATSUKI)
X-TWT (AKATSUKI)

SEP Option Summary• Compliance to the Mission Requirements– Reaches Solar Lat. 30°in 2020 (assumes launch in 2017), and finallyachieves 40°.
– Spacecraft’s mass budget permits instruments > 130kg.
– Data transmission rate > 300kbps @ high Lat. region (> 30°) (from 2022).

• Advantages– Satisfy the most of the mission requirements.
– Frequent launch windows (every half year).

• Disadvantage– Requires advanced technologies (electric propulsion system, etc.).

Trade-off Issues• First Cost Estimate
SEP ( kick-motor + IES ) > Jupiter ( kick-motor ) > Venus ( no engines )• Mission life: not clearly set, life-cost relation not yet investigated• New development for orbit formation (assumption; use of H-IIA)
SEP (kick-motor+IES), Jupiter (kick-motor), Venus (0.7AU test)• Mission readiness
SEP option may need an ENG mission using µ20 ion engine
before SOLAR-C.
• Final latitude degree:
40 deg (SEP) ~ 40 deg (Jupiter) > 25(2017L)-30(2020L) deg (Venus)• Payload mass:
130 kg (SEP) ~ 130 kg (Jupiter) << > 400 kg (Venus)• Time for final orbit formation (1AU distance from the Sun)
Jupiter (7 yr) > SEP (5 yr) > Venus (3yr)• Others

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 areHereSOLAR
Orbiter40200Year

11 yr

11 yr

Synergy among multiple spacecrafts
3D Scanning of Heliosphere by Multiple Spacecrafts

Figure 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.
Restriction: Instrument wavelengths need to be the same
SEP
OptionBallistic
Jupiter
OptionSolar Orbiter

Solar Latitude

Summary• SOLAR-C Option-A is a mission to look at the Sun froman 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 magnetic 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. No updates sinceMarch.
• 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. Due to thisengineering issues, selecting the prime orbit for Option-A
is not decided. Discussion is still going on.