SOLAR-C Plan-A Mission
H. Hara (NAOJ)
SOLAR-C WG
2008 Nov 18

Outline• Science• Scientific payload• Orbit (presentation by Dr. Kawakatsu)• A spacecraft system• Output from this meeting Target orbit inclination to achieve science goal

• SummaryMission Description• Exploration of the Sun (and heliosphere)with spacecraft in an out-of-ecliptic
interplanetary orbit from 1AU distanceScientific Objectives• How are magnetic fields created in the sun?
– Obtain missing information on angular rotation speedand meridional flows in high-latitude and polarregions– Can we discover a difference of a large-scaleconvective motion between the equator and poles?
– Explore the magnetic flux tube at the tachocline• Understand how polar fields are reversed• Understand what causes the high coronal activity inpolar regions• Understand how the fast solar wind is accelerated• Measure the solar irradiance variation as a function oflatitude to understand the variability of sun-like stars• Study influence of the sun to heliosphere
Dr. Yokoyama presents his view on the Science Objectivesof SOLAR-C plan-A, mainly on the solar dynamo.

Solar Magnetic Activity Cycle• How are magnetic fields created in the sun? (Dynamo)

1980

1990

2000

YearDr. Rempel provides a presentation on the solar dynamo.

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 up
for 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Rotation and Meridional Flows• Basic quantities to understand the solar dynamo• cannotbe determinedfromshowobservations
Dr. Kosovichev
and Dr. Gizon
the sciencein
topic
eclipticplane for high-latitude
regionsof helioseismology
and helioseismic
technique forPlan-Aout-of-eclipticmission.
• Needhelioseismic observations tofill up for all latitude regions Surface magnetic field transport
North Pole

Submergence ofmagnetic field？	

Meridional flow speed
20m/s

Angular velocity

South Pole-20m/s

Meridional flow

-60 deg Latitude 60 deg

Flux tube search at depth oftachocline
P-mode ray path

SOLAR-C S/C• Intense magnetic flux tube isthought to be created at thetachocline.
• Search of magnetic flux tube
near tachocline may be possible
by a large skip angle method oflocal helioseismology.

Tachocline
Convection zone

Dr. Sekii presents his estimate onwhether the signature of magnetic flux is detected at tachocline.

Polar Magnetic Fields
New observation from Hinode SP
Tsuneta et al. (2008)

70 deg758085• What is the shape of global polar fields?
• How are polar fields reversed near solar maximum?
• What is the source of ubiquitous horizontal fields?

Polar Magnetic Fields
New observation from Hinode SPTsuneta et al. (2008)

70 deg758085• Knowledge from recent Hinode observations and science
topic of SOLAR-C plan-A by Dr. Tsuneta• Comments on polar fields from SOLIS obs. by Dr. Harvey• Polar magnetic flux budget and dynamo by Dr. Schrijver

Polar Coronal Activity••••

Dynamic polar regions of the sun
Highly transient jets
More stable plumes in EUV images
Source of high-speed solar wind

Hinode XRTDr. Cirtain shows a presentation on the science topic ofcoronal activity from out-of-ecliptic orbit.

Solar Wind
• How is the high-speed solar windfrom polar coronal holes
accelerated?
• Measurement of global magnetic
fields in polar coronal holes,
flows in transition region and low
corona, and the wind speed may
provide the linkage between sun
and inner heliosphere.

Ulysses First Orbit
near Solar Min

Dr. Sakurai and Dr. Imada show
their views on the acceleration ofsolar winds and what should bedone by SOLAR-C
McComas et al. (2003)

Ulysses Second Orbit
near Solar Max

Total Solar Irradiance (TSI)from out-of-ecliptic plane• Understand the sun as astar• Solar irradiance TSI cycle
variation ~0.1%• Larger amplitude ofvariation for other sun-likestars• Interesting to measure
TSI from an orbit
inclination >40 deg
Dr. Schmutz shows presentation on
TSI instrument and its science.
Figure from PMOD WRC homepage

CME

Stereoscopic view from STEREOSTEREO
COR2-ASTEREO
COR2-B

Seen from normalof equatorial plane

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

STEREO
HI1-B

Spacecraft(SOLAR-C)

Sun
Howard & Tappin (2008)

Dr. Culhane mentions on the sun-earth
connection by SOLAR-C

Ecliptic planeCMEEarthModel Payload• Visible-light Imager– Photospheric Doppler velocity and magnetic field– Need a wide range tunable filter to first observe features in polar
regions in various wavelengths. ↔ different from MDI and HMI• Coronal Imager• High-throughput EUV Imaging spectrometer– High-throughput and smaller (lighter) than Hinode EIS will bepossible.

• Optional (as treated in the SOLAR-C WG proposal, 2007)– Total irradiance monitor– Heliospheric imager– In-Situ instruments(not discussed with interplanetary physics group)• Total weight ~100 kg• Total data recording rate ~100 kbps ave. (not easy)

Presentation on Payload
suitable for SOLAR-C Plan-A• Visible-light Imager by Dr. Apporchaux– Photospheric Doppler velocity and magnetic field– Need a wide range tunable filter to first observe features in polar
regions in various wavelengths. ↔ different from MDI and HMI• Coronal Imager by Dr. Auchere• High-throughput EUV Imaging spectrometer by Dr. Davila– High-throughput and smaller (lighter) than Hinode EIS will be possible.

• Optional (in the SOLAR-C WG proposal, 2007)– Total irradiance monitor by Dr. Schmuts– Heliospheric imager by Dr. Vourlidas– In-Situ instruments (not discussed with interplanetary physics group)
Probably something mentioned by Dr. Sakurai and Dr. Culhane• Total weight ~100 kg• Data recording rate ~ 100 kbps ave.

Candidate Orbit (1)• Methodology to achieve an out-of-eclipticorbit
 Planet-gravity assisted Swing-bylike Ulysses Interplanetary cruise by ion engine
like ISAS HAYABUSA, NASA DAWN,…

Heritagein previousmissions

 Solar sail, not discussed in this talk
POLARIS/SPI is introduced by Dr. Appourchaux and Dr. Alexander

For the feasibility of Mission (spacecraft and payload),Sun-spacecraft distance ↔ thermal design
and Earth-spacecraft distance ↔ telemetry conditionneed to be considered in selecting the Plan-A orbit.

Candidate Orbit (2)Except for No.2 case, the distance between the spacecraft
and the sun is generally long.
No. MethodProperty

1

Jupiter swing-byUsed in Ulysses mission:
long orbital period > ~6 years

2

Earth and Venus swing-by

Planned for Solar Orbiter:
Concern in huge heat load near the sun~25 times solar radiation at 0.2 AU

3Jupiter swing-by and earth
swing-by

Reduction of orbital period by earth
swing-by
Investigated in SOLAR-C WG

4Jupiter swing-by andpowered earth swing-by

Reduction of orbital period by earth
swing-by
Investigated in SOLAR-C WG

Candidate Orbit (3)No. Method

Property5

Use of ion engine for orbit of - Stable heat load
1AU distance from the Sun - Low spacecraft weight for highinclination orbit
Investigated in SOLAR-C WG

6

Use of ion engine and Earthswing-by for ellipsoidal orbitof 0.7-1.3 AU distance fromthe Sun

7

Use of ion engine and Earth - Double heat load at ~0.7 AU& Venus swing-by forcompared to 1AU condition.
ellipsoidal orbit of 0.7-1.3 AU - Limited launch window
distance from the Sun
may be Investigated by SOLAR-C WG

8

Between case 5 and 6- Double heat load at ~0.7 AU
compared to 1AU condition.
Investigated by SOLAR-C WG

Various types of orbit control
Jupiter swing-byEarth swing-by

Jupiter swing-by

SunSunearthearth

powered Earth swing-bySunearth

Details are shown by Dr. Kawakatsu.

Jupiter swing-by

Current status for JGA orbit study
Advantage:• High-inclination orbit i > 60 deg is possible.
• There is a possibility of larger payload weight than orbit
design by use of ion engine
Disadvantage for solar observations:• 4 years after launch or orbit points far from the sun:probably no solar observations• Distance between Sun and spacecraft > 1 AUpoor spatial sampling for 2D solar imaging• SOLAR-C WG has not done the feasibility study ofspacecraft for the JGA orbit cases.

Ion Engine
Asteroid ‘Itokawa’
Ion Engine µ10
Ion production

Electro-staticacceleration neutralization

Injection
velocity

propellant
Ion source

ScreenGridAccel.
GridDecel.
GridElectric
potential

HAYABUSA

Note: Permanent magnets are used in ion engines.

Ion Engine µ20
•
••
•
•
•

Beam diameter 200mm
Specific impulse 2800 s
Thrust28mN
Microwave Power 100W
System Power 1050 W
Simultaneous use of 4 sets ofthis engine is currently assumedin Plan-A.

Endurance test under wayµ20 and Dr. Nishiyama

Two Practical Cases• Dr. Kawakatsu show two orbit cases using ion engines.
• Leverage 7.25 deg tilt of solar rotation axis by selecting
launch window• (1) Spacecraft can see the sun at 45 deg view angle
from the solar equatorial plane.
– Earth swing-by is used.
– 0.7-1.3AU Sun-S/C distance in the early phase– 1AU Sun-S/C distance at the final orbit.

• (2) An orbit keeping 1AU distance.
– Spacecraft can reach a moderate inclination orbit in a shortspacecraft life
– A possibility to go to higher inclination slowly if a long spacecraft
life is allowed.

How is appearance of solar poles
as a function of inclination?
i: inclination angle between solar equatorial plane

i = 60 deg

i = 50 deg

i = 40 deg

i = 30 deg

i = 20 deg

A Candidate Orbit with Earth Swing-by• Use of ion engine– 3000 s specific impulse– Simultaneous use of 4 engines,
each having 30mN max thrust• H2A + KM-V2 kick motor
Ecliptic plane• 1200 kg initial wet S/C mass
• Accelerated in orbit plane byion engine• Step-like change of the orbitinclination by the earth
gravity assist (swing-by)• Eccentricity = 0.3 for early
Coordinate:
Orbital plane of Earth is in X-Y plane. phase and 0.0 for the final.

A Candidate Orbit with Earth Swing-byView of S/C orbit from edge-on direction of earth’s orbit

Ecliptic plane

Ecliptic plane

Ecliptic plane

View of S/C orbit from face-on direction of earth’s orbit

Sun-S/C & Earth-S/C Distance
Earth Swing-by
1.5

1.0

0.5

0.00123456Year

Sun-S/C distance
Earth-S/C distance

Thermal design
Telemetry rate7Inclination angle
from Solar equatorial plane
Ion engine duty (%)

7169

Spacecraft Weight (kg) 1200

1127

711052

Earth Swing-by

6264
97590208310831

A Simplified Orbit
View of S/C orbit from edge-on direction of earth’s orbit

Ecliptic plane

Ecliptic plane

Ecliptic plane

View of S/C orbit from face-on direction of earth’s orbit

Sun-S/C & Earth-S/C Distance
1.5

Ion Engine only
No Earth Swing-by

1.0

0.5

0.00

123456Year

Sun-S/C distance
Earth-S/C distance

Thermal design
Telemetry rate

7Inclination angle
from Solar equatorial plane
Ion engine duty (%)

61

61Spacecraft Weight (kg) 1200

1123

671046Ion Engine only
No Earth Swing-by71

70
963

876

60
789

0713

Solar Orbiter

From a figure in Dr. Woch’s presentation at MPS

From a figure in Dr. Woch’s presentation
at MPS45

assumeJun 2016

SO

SOLAR-C:
Earth Swing-by case

Mass budget(very preliminary)
Subsystem

Weight (kg)

Fuel

Weight (kg)Communication50

Chemical (N2H4)

40

Data handling12

Ion engine (Xe)

400

Attitude control

72

Total (Fuel)

440

Electrical harness

15

Structure

100

Dry S/C+ Fuel1139

Thermal control

20Electrical power

160

Total with margin

1200

RCS

30

Ion Engine System

140

Mission payload

100Dry spacecraft mass

699

SOLAR-C Plan-A Systema network system by Spacewire
Mission Instr.-1
DataHandlingUnit

ITRSAPgimbalIon EngineSystem
PowerControl
Unit

To eachcomponent

Mission Instr.-3
RouterRouterAttitudeControl
SystemDR

Router
AOCS
actuators

Mission Instr.-2

AOCS
sensors

RCS

HeaterControl
Unit

COMHGAMGA

gimbalgimbalLGA

Actuator Control Unit

Communication System (1)• Low-weight High Gain Antenna (HGA) needed.
• Ground support antenna required at both northern andsouthern hemisphere• ~100 kbps (TBD) data recording rate needs 400 kbps
(800 kbps) telemetry speed for 6 (3) hour downlink timeper day• For the science data transfer X-band is better than Kaband for a weather (rainy) condition, and Ka-band isbetter for the HGA antenna on S/C to be small.

Communication System (2)• X-band, 1.5mφ HGA, 50W transmission power,JAXA Usuda 64mφ ground station, 0.7AU distance:~200 kbps telemetry rate possible= 50 kbps ave. recording rate for 6 hours downlinkduration per day will need higher telemetry rate for helioseismic
observations (a question to helio-seismologists)• cf. 750 kbps telemetry rate for STEREO at 0.5 AU:– X-band, 1.2 φ HGA, 60W transmission power– DSN ground stationsElectrical Power System• Distance between the sun and S/C = 0.7-1.3AU
 Switching regulator system• Solar Array Panel (SAP)
GaAs triple junction solar cell arrays assumed.
5 – 6 kW power required  24 – 30 m2 area
2.0 m
6.0 – 7.5 m×2• BAT: Li-ion battery 23AH

Impact in Thermal Design• Thermal environmental condition is much better
than SO, but Plan-A S/C needs a treatment forhuge internal heat dissipation.
• There are three major heat sources:– High-speed communication system• 50 – 100 W: high-density heat source– Ion engine• ~500 W dissipation near ion engine thruster• ~500 W dissipation near microwave power supply• ~400 W dissipation near DC power supply• Use of heat pipe is mandatory.
• Thermal design is feasible when no direct solar illumination
at radiators. Feasibility study in a selected orbit condition isnecessary.

– Others (spacecraft bus components)

Attitude Control• Three axis stabilized• No external disturbance in the interplanetary space
except for disturbance due to photon pressure andinternal disturbance in the spacecraft.
• The accumulated torque is released by thruster impulsethat will probably happen once per day. This will becomea noise in the helioseismic observations.
Periodic unloading every day should be prohibited.
• There will not be a problem in S/C pointing stability
because the requirement is less severe than that inHinode.

Model Spacecraft
Solar array panel

Telescopes
Sun sensors

HGAStar sensors~1.2m

Ion engines
~1.5m
~1.5m

~2.0m
Panels act as radiators.

Output after this meetingTarget Orbit Inclination
to the solar equatorial plane
The following table needs to be filled during this meeting.
Science Target

TargetInc.
(deg)
Magnetic field measurements at high latitudes##(Lat. > 50o)

Rotation profile at high latitudes (Lat. > 50o)##

Meridional flow at high latitudes (Lat. > 50o)##

Super granulation pattern at high latitudes##High-speed solar wind##

Total solar irradiance variation with inclination##In-situ measurements##

Imaging of Helioshphere

##

Note

Summary• SOLAR-C plan-A is a mission to look at the sun from ahigh-inclination out-of-ecliptic orbit.
• We will observe features all over the latitudes on the sun
and a wide rage of latitude in heliosphere at ~1AU:
Magnetic fields, convection, internal rotation, meridionalflows from direct or helioseismic observations, activity ofupper atmosphere, source region of solar wind, andinterplanetary in-situ measurements.
• There is a practical solution for a spacecraft to enter ahigh-inclination orbit using ion engine.
• Higher inclination is better, but the target inclinationneeds to be clearly defined from science objectives.
• Effort to increase the total weight of payload has been
continued. Better estimate in weight is required for ion
engine system, power supply system, andcommunication system which are coupled with theselection of orbit.

Jupiter Gravity Assist••••

Orbital period of a final orbit >~6 years
High inclination (i >60 deg) is possible.
Not good for long-period observations of the sun
Need a large solar array paddle ~27 times larger thannear-earth spacecraft• RTG was used in Ulysses as electrical power supply
RTG (Radioisotope Thermoelectric Generators):
power through the natural radioactive decay of plutonium• Ulysses: a = 3.37 AU, i = 79.1 deg, P=6.2 years
weight: 367 kg including 55 kg payload
Jupiter swing-by

Jupiter Gravity Assist (JGA)• H2A202+KM_V2 (kick-motor)• Solar observations starts
at ~4 years after launch.
• Sleep mode in the S/Ccold condition required.
• Feasible S/C plan will bein an orbit of Sunspacecraft distance >1AU
Looking at the final orbit
from the normal to the orbital plane.

JGA + Earth Gravity Assist• H2A202+KM_V2 (kick-motor)• Orbital period of the
final orbit becomesshorter.
• The final weight ofspacecraft is almost
the same as thecases of JGA only.
Looking at the final orbit
from the normal to the orbital plane.

JGA + Powered EGA• H2A202+KM_V2 (kick-motor) + additional
engine for powered earth swing-by• Orbital period of the final orbit becomes shorter
than the cases of JGA+EGA, but we could not
find a solution to have a circular orbit of 1AU
distance from the sun.
• Reduction of payload weight due to theadditional engine and its fuel cannot be ignored.