Solar-B Fact Sheet

ISAS | PPARC | NASA

Why Solar-B?
Solar-B will, for the first time, provide quantitative measurements of the full vector magnetic field on small enough scales to resolve elemental flux tubes. The field of view and sensitivity allow changes in the magnetic energy to be related to both steady state (coronal heating) and transient changes (flares, coronal mass ejections) in the solar atmosphere. Solar-B is an excellent opportunity for highly leveraged US participation in a major mission that will greatly advance our understanding of the crucial first link in the Sun-Earth connection. The estimated cost to NASA is about $65M, a quarter to a third of the total cost of the mission. Solar-B is planned to start in FY99, launch in FY04, and operate for at least 3 years.

Science Objectives:
1. Creation and Destruction of the Sun's Magnetic Field: Magnetic fields permeate all space and play an important role in shaping the universe on all scales. The fields are continuously being generated by dynamos in stellar interiors and swept out into space by stellar winds. The solar dynamo is sufficiently near and operates on a short enough period, 11 years, that it can be studied directly.

2. Modulation of the Sun's Luminosity: During the last decade observations from space have led to the profound discovery that the total output of energy from the Sun is not constant but varies in phase with the magnetic activity cycle. The amplitude of this variation, over the single cycle measured, though small was only a factor of three to five below the level required for a significant climatic response. Solar-B will make the first observations with resolution, wavelength coverage, and time span adequate to determine the mechanism for the magnetic modulation of solar luminosity.

3. Generation of UV and X Radiation: The Sun is a powerful and highly variable source of ultraviolet, X-rays and energetic particles, which are known to have major effects on our environment. This high energy radiation must be due to the annihilation of magnetic energy in the Sun's atmosphere, the chromosphere and corona. Due to its broad complement of instruments with high spatial and spectral resolution, Solar-B will be able to study processes such as magnetic reconnection and wave dissipation that are believed to be responsible for the conversion of magnetic energy into UV and X radiation.

4. Eruption and Expansion of the Sun's Atmosphere The million-degree corona continually expands outward, becoming a supersonic wind that blows past the Earth, buffeting the geomagnetic field and energizing the upper atmosphere. In addition, large parts of the corona are seen to erupt, blasting through the solar wind and causing major magnetic disturbances at Earth. Solar-B will provide accurate measurements of magnetic fields, electric currents, and velocity fields, thus revealing the root causes of the Sun's eruptions.

Key Spacecraft Characteristics:

Mission Characteristics:

Proposed Solar-B Instrument Complement

Solar Optical Telescope (SOT):
Gregorian or Cassegrain, 50cm aperture, light weight glass composite
Angular Resolution: Diffraction limited at 0.25" (175km on the Sun)
Wavelength Range: 480-650nm
Polarimetric Accuracy: 10e-4

Focal Plane Package (FPP) Vector Magnetograph:
Magnetic Lines: 525.0nm FeI; 630.2nm FeI, Continuum: 524.6nm, Velocity: 532.4nm FeI
Field of View: 164x164 arcsec squared
Magnetic Sensitivity: B(longitudinal) = 1-5G, B(transverse) = 30-50G
Temporal Resolution: 5 min., Detectable change in active region magnetic energy: 10e30 erg
Data: Time series of photospheric vector magnetograms, Doppler velocity and photospheric intensity

Focal Plane Package (FPP) Spectrograph:
Littrow type echelle. Spectral resolution 2.0nm
Data: Detailed Stokes line profiles of intensity and polarization

X-Ray Telescope (XRT):
Wavelength Range: 2,0 to 60.0 Å, Angular Resolution: 1.0 to 2.5 arcsec
Field of View: Full or partial disk, Data: Coronal Images at different temperatures

EUV Imaging Spectrograph (EIS):
Pixel Size: 1.5 arcsec x 0.002nm, Field of View: 400 arcsec
Wavelength Range: 25-29nm, Temperature Range: 1 x 10e5 - 2 x 10e7 K
Data: Doppler line widths and shifts and monochromatic images

Solar-B: An International Collaboration:
As the senior partnet ISAS has responsibility for the spacecraft and the optical telescope. The science instruments would be assembled under Japanese oversight by the international partners, the United States, Germany and the United Kingdom. NASA's contribution would include the development of the vector magnetograph (Estimated cost $35M) and contributions to the three other instruments, estimated at $10M each. Germany is expected to support the spectrograph and the UK the X-ray/XUV instruments.

Solar-B Responsibilities

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