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Research into activity on the Sun by astronomers from Armagh Observatory, lead by Professor Gerry Doyle, have over the last six years used data from a spacecraft called SOHO (SOlar and Heliospheric Observatory). This is an international project between NASA and the European Space Agency to study the Sun, from its deep core to its outer atmosphere and the so-called solar wind, a stream of electrically charged particles which emanates from the Sun and pervades the whole solar system.

SOHO moves around the Sun in step with the Earth, by orbiting around a point approximately 1,500,000 kilometres from the Earth, that is to say, about four times the distance of the Moon, where the combined gravity of the Earth and the Sun keeps the spacecraft in an orbit locked to the Earth-Sun line.

In late June a problem was detected in the satellite's high-gain antenna, which is used to transmit the large amounts of data from SOHO's scientific observations to Earth. This was bad news not only for Armagh astronomers but for solar physicists world-wide. To transmit data, the antenna must rotate constantly to keep the Earth in its field of view as both Earth and SOHO orbit the Sun. If the problem is not solved, the Earth will remain outside the antenna's beam on a periodic basis, with similar blackouts occurring every three months.

However, following a series of tests over the last few days by SOHO engineers, the news may not be all bad. It is currently hoped to have full high-rate telemetry coverage to resume on or about 14th July 2003. To achieve this, they will make the spacecraft roll 180 degrees around the Sun-pointing axis in a manoeuvre currently planned for 8th July. If successful, this will be good news for the Armagh group who are en route to Goddard Space Flight Center in Washington for a scheduled joint observing run with SOHO and another orbiting satellite called TRACE to begin on 15th July for 4 days.

FOR FURTHER INFORMATION CONTACT: Gerry Doyle (jgd@arm.ac.uk) or John McFarland (jmf@arm.ac.uk) at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3755-7174

See also:
SOHO Regains High-rate Telemetry

Last Revised: 2003 July 17th
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