The objective of 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 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 x 1024-pixel CCDs. US solar physicists at Lockheed Palo Alto Research Laboratory are collaborating in the soft X-ray telescope production and data analysis. There is also a continuum 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.

The Solar Data Analysis Center (SDAC) at NASA/GSFC can provide small quantities of data, by request to gurman@sdac.nascom.nasa.gov. Sample data from the SXT images may be obtained via the World Wide Web from the SDAC at:

http://umbra.nascom.nasa.gov/

The Yohkoh analysis guide is available in PostScript form in three parts from:

ftp://umbra.nascom.nasa.gov/pub/yohkoh/doc/iguide.ps

ftp://umbra.nascom.nasa.gov/pub/yohkoh/doc/rguide.ps

ftp://umbra.nascom.nasa.gov/pub/yohkoh/doc/uguide.ps