The SP slit is 0.16” x 164”. Spectra areexposed and read out continuously 16times per rotation of the PMU (1.6 s).

Raster scans are made by stepping the slitacross the FOV using the slit scan mirrorshown below. Nominal step size is 0.16”.

The SP can scan across a 164” x 320”FOV while the CT and Filter FOV’s arefixed. In normal mode, the SP scans 1.6”in 50 sec or 160” in 83 min. Fast mapmode is faster by x 2.8, hence 164” in 30min.

Spectrograph Fields of View

320”

164”

I Q U V

~3 A at 21.5 mA sampling

164”

0.

16”

sam

plin

g

SP Slit scanning mirror

Filtergraph Fields of View• NFI Common 2048 x 4096 pixel CCD with BFI. 0.08” pixels ⇒full NFI FOV is 320” x 120”

Shown in blue on the MDI magnetogram at right.

320”

160”

The large rectangle is the full NFI CCD projected on the Sun: 2048 x 409612 µm pixels with a plate scale of 0.08” per pixel.The inner square is the 160” x 160” active region core subframe readout.Other modes: 8”, 16” (2x2), 32” (4x4) x 160” for 10 s Stokes IQUV maps.

• BFI Common 2048 x 4096 pixel CCD with NFI. 0.054” pixels ⇒full NFI FOV is 218” x 109”

Shown in green on the MDI magnetogram at right.

218”109”

FPP Mechanical Design

BFI/NFI CCD Radiator

BFI/NFI CCD Electronics

SP CCD Radiator

SP CCD Electronics

NFI Lyot Filter

CT CCD Electronics

SP Littrow MirrorSP Littrow Grating

SP Slit

BFI Filterwheel

BFI Shutter

NFI Shutter

BFI/NFI Beam Combiner

SP Slit Scanner

NFI Filterwheel

Beam Distributor

NFI FocalplaneMask

Polarization Modulator

Folding Mirror

2048 x 4096 CCD

Polarizing BS

Birefringent FilterFilterwheel Field Mask

Field lens

Shutter

X2 Mag lens

Folding Mirror

Folding Mirror

Telecentric lenses

X3 Mag lens

Shutter

Field lens

Filterwheel

Litrow Mirror

Polarizing BS

Folding Mirrors

Slit

Preslit

Grating

Folding Mirror

Image Offset Prisms

Demag lens

50 x 50 CCD Secondary

Primary

CLU

Tip Tilt Mirror

Reimaging Lens

Beam Distributor

Color Coding

OTA

Common Optics

CT

NFI

BFI

SP

Dual 256 x 1024 CCD

FPP Optical schematic including the Correlation Tracker (CT) which drives the tip-tilt mirror.

The Solar-B Mechanical Test Model (MTM) showing the relative positions and scales of the satelliteinstruments. The solar arrays are folded just aft of the FPP.

FPP

EIS

OTA

XRT

The Solar-B Mission

Solar-B is the third solar physics satellite of JAXA/Institute of Space and Astronautical Science (ISAS) which wasapproved as a successor to the highly successful Japan/US/UK YOHKOH (Solar-A) collaboration.

The SOLAR-B satellite will launch in Summer 2006. It will be placed in a polar, sun-synchronous orbit about the earth bya M-V-7 launch vehicle from the Kagoshima Space Center (KSC). This will keep the instruments in continuous sunlight,with no day/night cycling for nine months each year. The satellite weighs approximately 900 kg (dry) with some 170 kg ofthruster gas for maintaining a sun-synchronous orbit for more than two years.

The mission consists of a coordinated set of optical, X-ray and EUVtelescopes.

• The Solar Optical Telescope (SOT) is a 0.5 m Gregorian design which consists of the Optical Telescope Assembly (OTA) and the Focal Plane Package (FPP) instrument. It measures intensity, velocity, and magnetic fields in the photosphere and chromosphere.

• The X-ray Telescope (XRT) images the high temperature (0.5 – 10 MK) corona with a resolution of approximately 1 arcsecond.

• The Extreme Ultraviolet Imaging Spectrometer (EIS) measures temperature, density, velocity and other plasma parameters in the corona and transition region.

The Solar-B SOT/FPP Science Mission

The Focal Plane Package (FPP)The FPP consists of three main science instruments:

•Narrowband Filter Imager (NFI)• Tunable Lyot filter• Temperature calibrated, no active thermal control• 70-100 mA spectral resolution• EFL = 3100 cm, 0.08” pixels• Polarization precision 0.1%• Spatial resolution = 0.25”• Temporal cadence = 3.4s including CCD readout• 2048 x 4006 130 Ke- full well frame transfer CCD, shared with BFI• Intensity, Stokes, and Doppler images in 6 spectral regions

• Broadband Filter Imager (BFI)• 6 Interference filters in selectable filterwheel• 1-10 A spectral resolution• EFL = 4650 cm, 0.054” pixels• Spatial resolution = 0.2”• Temporal cadence = 3.4s including CCD readout• 2048 x 4006 130 Ke- full well frame transfer CCD, shared with NFI• Highest spatial and temporal resolution images from FPP

• Spectropolarimeter (SP)• Fe I 6301.5 and 6302.5 A spectral lines• 21 mA spectral resolution• Simultaneous orthogonal state images, 10-3 precision Stokes polarimetry• Spatial resolution = 0.32”• Temporal resolution = 4.8 s integrations at each slit position• 1024 x 448 130 ke- full well split framereadout CCD• Slit-scanned vector magnetogram maps

The optical layout of the FPP is shown above left. The mechanical design of theFPP is shown at left.

The FPP optics box is 1629 x 652 x 198 mm in size. The optical bench structureis aluminum honeycomb. Total weight of the FPP is 47.5 kg.

The Optical Telescope Assembly (OTA)The OTA (Figure 2) is a 0.5 m diameter Gregorian design. It is designed byJAXA/ISAS and manufactured by the Mitsubishi Electric Company (MELCO).

• 0.5 meter clear aperture• 562 mm diameter Zerodur primary mirror• 262 mm diameter Zerodur secondary mirror• Linear central obscuration 0.344• Axisymmetric design for minimal instrumental polarization

• Effective focal length = 4527 mm

• Spatial resolution = 0.2 – 0.3” in wavelength range 388 – 668 nm.

• 361” x 197” diffraction limited field-of-view (FOV) , defined by the heat stop rejection mirror at the Gregorian focus.

• Exit beam 30 mm diameter, collimated by the Collimator Lens Unit (CLU).

• UV and IR rejection coatings on the CLU limit the heat load passed to the FPP instrument.• Carbon fiber and invar structural elements for maximum thermal stability.

Side door

Collimator Lens Unit

Tip-tilt mirror

Polarization modulator: rotating quartzwaveplate, 0.625 Hz

Primary mirror

CFRP truss structure

Heat dump mirror

Secondary mirror

Top door

Figure 2. The Solar-B OTA.

Spectropolarimeter Observables

• Spectra of two Fe lines at 630.15 and 630.25nm and nearby continuum are exposed, with a0.16 x 164 arcsecond slit

– Spectra are exposed and read outcontinuously, 16 times per rotation of thePolarization Modulator.

• 2 spectra taken simultaneously in orthogonallinear polarizations

– Removes crosstalk polarization due to imagejitter.

– High accuracy can be archived: S/N=103 ormore in normal map mode.

• Raw spectra are added & subtracted into 4memories to demodulate, forming StokesParameters I, Q, U, V

– Single observation is 2 sets of IQUV spectrafrom each of the 2 linear polarizations.

• The slit can move between observations tomap a finite area

– A wide single scan moves 320” in 2000 stepsto map an entire active region.

– Repeated narrow scans study small featureswith high time resolution.

• Processing on the ground produces maps ofmagnetic field vectors, Doppler shifts, andthermal properties on the Sun

Example SP data product taken with the DLSPat Sac Peak Observatory.

Spectropolarimeter Observables, cont.

Normalmapping

Fastmapping

Dynamics DeepMag.

Time perposition

4.8s(3 rot.)

3.2s(1+1 rot.)

1.6s(1 rot.)

Many rot.

FOV alongslit

164” 164” 32” 164”

Effectivepixel size

0.16”x0.16”

0.32”x0.32”

0.16”x0.16”

0.16”x0.16”

PhotometricS/N

~103 ~103 ~580 >103

Data size 191Kpix/s 127Kpix/s 120Kpix/s ---

Time for 160”wide map

83 min 30 min --- ---

Time for 1.6”wide map

50 s 18 s 18 s ---

Four SP observing modes and their characteristics. All four produce Stokes I/Q/U/V maps.

The Solar-B SOT consists of two major components

• The Optical Telescope Assembly (OTA)• The Focal Plane Package (FPP)

These elements are described below:

Solar-B Science ObjectivesSolar-B as a whole will enable us to explore the origins of the Sun’s outer atmosphere and thecoupling between the fine-scale magnetic structure in the photosphere.

The SOT/FPP instrument in particular will provide high spatial and temporal resolution images ofconvection and magnetic fields. Magnetic field emergence, evolution, and interaction in thephotosphere and chromosphere will be mapped using vector polarimetry, Doppler imaging, andfiltergrams.

The main science objectives of Solar-B are as follows:

• Origin and evolution of the Sun’s magnetic field.Magnetic fields determine all aspects of the outer solar atmosphere dynamics. The fields aregenerated by dynamo action deep in the convection zone and possibly in a near surface shearlayer. SOT/FPP will provide the most continuous view of magnetic field emergence, evolution,and decay ever seen. Operating over the rising phase of Cycle 24, SOT/FPP will provide deepinsights into the nature of the 22 year magnetic cycle through high spatial and temporal resolutionmagnetograms, Dopplergrams, and filtergrams of the photosphere and chromosphere.

• Modulation of the Sun’s Irradiance.The recent discovery that the Sun varies in total irradiance in step with the magnetic cycleremains poorly understood. It is known that sunspots and pores decrease irradiance on short timescales but the source of the overall increase in irradiance during sunspot maximum is unclear.Most, and possibly all, of the increase is due to faculae and network magnetic elements, but othereffects may be at work. SOT/FPP will have the resolution and continuous viewing capabilities toexplore facular and network irradiance mechanisms with unprecedented detail, contributing to theimportant study of solar effects on the Earth’s climate.

• Heating of the outer atmosphere - generation of UV and X-Radiation.The Sun is a powerful and highly variable source of UV, X-rays, and energetic particles which are known tohave a great effect on the Earth’s atmosphere. Solar UV radiation in the 200 nm range is largely responsiblefor the ozone balance in the stratosphere. The source of this radiation must be due to the annihilation ofmagnetic energy in the Sun’s chromosphere, transition region, and corona. The broad complement ofinstruments on Solar-B will allow the first detailed look at magnetic field emergence in the photosphere andits subsequent interaction through magnetic reconnection and wave dissipation. The SOT/FPP vectormagnetograms will provide measurements of field orientation, electric currents, and velocities that willenable detailed studies of the mechanisms of outer atmospheric heating.

•Eruption and expansion of the Sun’s atmosphere.The million-degree corona continually expands outward in the form of the solar wind which buffets theEarth’s geomagnetic field and energizes the Earth’s upper atmosphere. In addition, coronal mass ejectionscause major geomagnetic disturbances that can lead to satellite failures and power outages on the ground.Solar-B is uniquely suited to studying these transient events using the X-ray imaging of XRT, detailedtemperature, density, and velocity measurements in the corona from EIS, and vector magnetic field andvelocity measurements in the lower atmosphere from SOT/FPP. The rapid cadence imaging and vectormagnetic field measurements of SOT/FPP will be particularly useful in studying the initiation phase oftransient events.

Filtergraph Spectral RegionsThe tunable Lyot filter of the NFI can take filtergrams or Stokes images (IQUV) in any line from the tablebelow at any wavelength offset. Vector magnetograms are possible in the 630.2 and 517.3 nm lines.

Ion λ,nm geff Purpose

Mg Ib 517.27 1.75 Low chromosphere magnetograms &dopplergrams

Fe I 524.71 2.00 Photospheric magnetogramsFe I 525.02 3.00 Used with 524.71 line for ratio analyses.Fe I 525.06 1.50 “

Fe I 557.61 0.00 Photospheric dopplergrams

Na D 589.60 Very weak fields, Hanle effect polarization Chromospheric magnetic fields

Fe I 630.15 1.67 Photospheric magnetogramsFe I 630.25 2.50 Photospheric magnetogramsTi I 630.38 0.92 Sunspot umbral magnetogram line

H I 656.30 H-alpha chromospheric filtergram anddopplergram line.

The BFI uses interference filters to take filtergrams in the wavelength regions listed below. The BFI willobtain the highest possible spatial and temporal resolution time series.

Center l, nm FWHM, nm Purpose

388.3 0.7 CN molecular bandhead: chromospheric network.396.8 0.3 Ca II H-line: magnetic elements in low chromosphere.430.5 0.8 G-band CH molecular bandhead: magnetic elements in

photosphere, convection flow mapping.450.5 0.4 Blue continuum for irradiance and temperature.555.0 0.4 Green continuum.668.4 0.4 Red continuum.

Frame size 4Kx2K, 2Kx2K, 1Kx1K, or 0.5Kx0.5K

Summing 1x1, 2x2, or 4x4 pixel

Readout time 3.4sec (1x1 summing), 1.7sec (2x2), 0.9sec (4x4)Partial readout for faster cadence

Reconfigure time <2.5 sec (for changing filter wheels etc)

Frame size 2K x1K, 1Kx1K, or 0.5Kx0.5K

Summing 1x1, 2x2, or 4x4 pixel

Duration 12.8 sec (4 images, 2x2 summing, 0.8sec exposure)

Filtergraph Observables: 1. Filtergrams• Snapshot image from a single exposure

– All bands of the BFI– All lines and nearby continuum for the NFI

• Combination of frame size and pixel summing for reduced data rate

• Fast cadence• Typically < 6 seconds for all bands

Horizontal velocity in thephotosphere derived fromcorrelation tracking on G-bandtime series.

Filtergraph Observables: 2. Dopplergrams• Map of line-of-sight velocity

– Derive central wavelength from 4 NFI filtergrams uniformly spaced throughFe I 557.6 nm line: F1…F4. R = ( F1 + F2 – F3 – F4 )/( F1- F2 - F3 + f4 )– On-board memory processing to make numerator and denominator– Velocity = V(R) implemented on ground in look-up table.– 1-sigma noise = 30 m/s for 2x2 summing 0.16” pixels, 0.8 sec exposure

I

Q

V

Δλ = -114 -38 +38 +114 mA

SOHO/MDI Ni I 676.8 nm Stokes component Filtergram imaging. MDI can’t make Stokes U but NFI can.

0.1 sec exposureIQUV measured simultaneously

5.3 x 164 arcsec 0.08 arcsec (1x1)14.7 x 164 arcsec 0.16 arcsec (2x2)

35 x 164 arcsec 0.32 arcsec (4x4)0.2 sec exposureIQV or IU, measured separately

10.7 x 164 arcsec 0.08 arcsec (1x1)29 x 164 arcsec 0.16 arcsec (2x2)70 x 164 arcsec 0.32 arcsec (4x4)

0.4 sec exposureIV only

21 x 164 arcsec 0.08 arcsec (1x1)58 x 164 arcsec 0.16 arcsec (2x2)

140 x 164 arcsec 0.32 arcsec (4x4)

Filtergraph Observables: 4. Stokes I Q U V images

• Stokes IQUV maps are made onboard fromNFI filtergrams. The maps can be inverted togive vector magnetic fields in the same way asthe SP.

• Two ways of Stokes imaging:

Shuttered– Combination of frame size and pixelsumming as in longitudinal magnetogram.– 0.4 sec exposures in synch with PMU.– Additional noise sources due to timebetween frames and cross-talk betweenpolarization states will occur.

Shutterless– Gives high cadence (1.6-4.8s) of stokesdata. Requires focal plane mask

Instrument Control and Data Transmission• Instrument control is formatted into Sequences of Observables. Sequences arerun from Observing Tables in the Mission Data Processor (MDP).

– Separate tables for SP and BFI/NFI Filtergraph.– Each table is a list of Macro-commands that describe a given observable(magnetogram, Stokes map, filtergram).

• FPP science data compression is performed by the MDP to reduce datavolume in telemetry. Compression is done by a custom ASIC chip in the MDP.

– CCD raw pixel depth is 16 bits.– Step 1: bit compression from 16 to 12 bits. 8 on-board look-up tables.– Step 2: choose either

• 12 bit JPEG (DCT) lossy compression• ~3 bits/pixel for typical BFI/NFI filtergram data.• ~1.5 bits/pixel for typical SP data.

• 12 bit DCPM lossless compression• 6-8 bits/pixel depending on image or spectral content.

• Data is stored on-board by the Data Recorder (DR).– Capacity = 8 Gbits.– The DR is shared by all Solar-B experiments (FPP, XRT, EIS).– Allocation is adjustable. Baseline: FPP 70%, XRT/EIS 30%.– Maximum telemetry rates for compressed FPP data:

• ~1.3 Mbit/sec (nominal)• ~1.8 Mbit/sec (FPP dominant mode)• ~70 minutes of continuous observations fills 5.6 Gbit allocation. Therest of the 90 minute orbit would be idle.

• Telemetry to ground stations– 96 min orbit– 4 Mbit/sec X-band transmission.– ~2.4 Gbits of data (all instruments) per 10 minute station pass.– Up to 20 downlinks per day:

• Kagoshima: 4• Wallops: 1• Svalbard: 15

• Data rate average over 24 hours:• 48 Gbit• ~6 Gbytes for all instruments

Example Observing Program:Small-scale Magnetic Flux Cancellation

Objective: measure opposite polarity cancellation in plage or network. Quantifyflux loss as a function of time and effect on upper atmosphere such asreconnection heating in the chromosphere.

SP: Dynamics mode0.16” x 64” (1 x 400 pixel) slit readout1.6 sec integration (1 rotation of PMU)Data rate: 56 kpix/sec to MDP

84 kbit/sec to DR at 1.5 bits/pixel compressionVector field map: 64” x 64” in ~10 min.

FG: 1024 x1024 pixel CCD readout: 55” x 55” BFI82” x 82” NFI

BFI: G-band, Ca II H-line1x1 non-binned pixels0.4 sec CCD readout at 2.5 Mpix/secG expose = 0.05 s, 2.5 s filter change, H exp = 0.4 s, CCD read 0.8Total cycle time = 3.75 sData rate: 280 kpix/sec to MDP

840 kbit/sec to DR at 3 bits/pixel compressionNFI: 630.25 nm magnetogram, 557.6 nm Dopplergram, Hα wing image1x1 non-binned pixels: maximum spatial resolutionHα exp 0.1s, 2 s filter tune, 4x1.6s mag exp, 2 s filter tune, 4x1.6s DopTotal cycle time = 16.9 sData rate: 558 kpix/sec to MDP

1.67 Mbit/sec to DR at 3 bits/pixel compression

Total FG cycle time = 21 s. Idle for 9 s to give 30 s mean cadence.

Total FPP data rate = 1.7 Mbit/sec to DR over 30 s cadence period. ~55 min tofill 5.6 Gbit DR allocation.

T. Berger1, D. Elmore2, B. Lites2

T. Shimizu3, T. Tarbell1, A. Title1

S. Tsuneta3

and the SOT/FPP Team

1 Lockheed Martin Solar and Astrophysics Lab2 High Altitude Observatory, UCAR3 National Astronomical Observatory of Japan

Flight model FPP. View looking towards the SP grating in the upper left.

Frame size 2Kx1K, 1Kx1K, or 0.5Kx0.5K

Summing 1x1, 2x2, or 4x4 pixel

Duration 12.8 sec for 1Kx1K with 2x2 summing~21 sec for 2Kx1K with 1x1 summing

Filtergraph Observables: 3. Longitudinal Magnetogram • Map of Stokes V / Stokes I

• Derived from multiple NFI filtergrams in a spectral line.• On-board memory processing to make numerator anddenominator:

• 630.25 nm magnetogram with 1x1 summing has RMS noise of1015 Mx per pixel.

• Comparison to SP 630.25 and 630.15 nm high precisionlongitudinal magnetograms allows high accuracy calibration ofNFI imaging magnetograms.

2/1,1,0,

)(

)(

1

1

±±=

=

∑

∑

=

=

orbawhere

Ib

VaMgram

ii

n

iii

i

n

ii

λ

λ

Longitudinal magnetogram in Fe I630.2 nm line taken with the 50 cmSwedish Vacuum Solar Telescopeon La Palma. The SOT/FPP willproduce movies of such images witha diffraction limited spatial resolutionof about 230 km.