The objective of Solar A or Yohkoh (Japanese for sunbeam) is to study the high-energy radiations
from solar flares (hard and soft X-rays and energetic neutrons) as well as quiet
structures and pre-flare conditions. The mission is a successor to Hinotori,
a previous Japanese spacecraft flown at the previous solar activity maximum in 1981.
Yohkoh is a three-axis stabilized observatory-type satellite in a nearly-circular Earth
orbit, carrying four instruments: two imagers and two spectrometers. The spacecraft is a
rectangular solid about 2 m square and 4 m long. The imaging instruments have almost
full-Sun fields of view, to avoid missing any flares on the visible disk of the Sun.
- The hard X-ray telescope (HXT) is a multi-grid synthesis type with a spatial resolution
of 7 arcsec, operating in the 20 - 80 keV.range.
- The soft X-ray telescope uses grazing-incidence optics and achieves 4 arcsec spatial
resolution, operating in the 0.1 - 4 keV.range and using 1024 × 1024-pixel CCDs. US solar
physicists at Lockheed Palo Alto Research Laboratory are collaborating in the soft X-ray
telescope production and data analysis.
- a wide band spectrometer for X-rays and gamma-rays from 3 keV.to 20 MeV (also sensitive
to neutrons) and
- a Bragg crystal spectrometer for the X-ray lines Fe XXV, Fe XXVI, Ca XIX, and S XV.
Approximately 50 MB of data are accumulated per day, and stored on an on-board tape
recorder with 10.5 Mbyte capacity. The Yohkoh mission is a cooperative mission of Japan,
the US, and the United Kingdom.
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