The Solar and Heliospheric Observatory (SOHO)

The Spacecraft: SOHO is made up of two modules. The Service Module forms the lower portion of the spacecraft and provides power, thermal control, pointing and telecommunications for the whole spacecraft and support for the solar panels. The Payload Module sits above it and houses all the scientific instruments.

DIMENSIONS

height, breadth, width ............ 4.3 x 2.7 x 3.65 m
width with solar array deployed ... 9.5 m

MASS

total at launch ................... 1850 kg[/br] payload ........................... 610 kg

TELEMETRY

during real-time operation ........ 200Kbits/s
during on-board storage mode ..... 40Kbits/s

An Uninterrupted View of the Sun: SOHO is designed to study the internal structure of the Sun, its extensive outer atmosphere and the origin of the solar wind, the stream of highly ionized gas that blows continuously outward through the Solar System.

SOHO is helping us understand the interactions between the Sun and the Earth's environment better than has been possible to date. Its legacy may enable scientists to solve some of the most perplexing riddles about the Sun, including the heating of the solar corona, the acceleration of the solar wind, and the physical conditions of the solar interior. It will give solar physicists their first long term, uninterrupted view of the mysterious star that we call the Sun.

That view of the Sun is achieved by operating SOHO from a permanent vantage point 1.5 million kilometers sunward of the Earth in a halo orbit around the L1 Lagrangian point. SOHO was designed to observe the Sun continuously for at least two years. All previous solar observatories have orbited the Earth, from where their observations were periodically interrupted as our planet `eclipsed' the Sun.

The Mission: SOHO was launched on December 2, 1995. The SOHO spacecraft was built in Europe by an industry team led by Matra, and instruments were provided by European and American scientists. There are nine European Principal Investigators (PI's) and three American ones.

The SOHO (Solar & Heliospheric Observatory) project is being carried out by the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA) as a cooperative effort between the two agencies in the framework of the Solar Terrestrial Science Program (STSP) comprising SOHO and CLUSTER, and the International Solar-Terrestrial Physics Program (ISTP), with Geotail (ISAS-Japan), Wind, and Polar.

SOHO is commanded from NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Maryland (USA). Its data is retrieved via the NASA Deep Space Network (DSN) and routed to the Experimenters' Operations Facility (EOF) located at GSFC. There the SOHO experimenters are able to display on their workstations the images and measurements that are being produced by their instruments. From the EOF the experimenters point the instruments aboard SOHO to a particular region of the Sun, or change the operating mode of the instruments. The SOHO scientists use their instruments very much as an observer would at a ground-based observatory.

The EOF is the forum where the experimenters coordinate their observations within SOHO and/or with ground based solar observatories. Electronically accessible data catalogs and data banks have been established at the EOF and at several participating institutes, both in the USA and in Europe. A sample Mosaic forms interface for the SOHO data catalog is accessible here.

SOHO instruments produce a data stream of 200 kilobits per second, that can be transmitted continuously to the DSN stations of Goldstone (USA), Canberra (Australia) and Madrid (Spain), when each is visible from SOHO due to the daily rotation of the Earth.