N° 4–1996: SOHO, an early start, a long lifetime

SOHO currently cruises through space towards its station near the so-called first Lagrange point 1.5 million km towards the Sun where it will be in uninterrupted daylight and where the gravitational pull of the Sun and the Earth are balanced. The spacecraft is now expected to arrive at its station on 14 March 1996, two weeks earlier than originally planned.
Coincidentally, this is the tenth anniversary of another space milestone, the encounter of ESA's Giotto probe with Comet Halley!

An optimised orbit-shaping manoeuvre on 4 January, further refined SOHO's trajectory. Enough fuel remains on board to maintain SOHO's position in space for at least twenty instead of the planned six years.

All systems of the 1850 kg spacecraft designed and built by European industry have been checked after launch and are in excellent shape. Their nominal performance has allowed an early and uninterrupted start of the commissioning of the scientific payload.

SOHO's 12 scientific instruments* are currently being tested. Scientists are studying the first images and calibrating their instruments for the scheduled start of operations in late March. The craft's particle detectors investigating "in situ" the solar wind streaming around SOHO at its vantage point near Lagrange point 1, have been operational for some time and SOHO's first image of the Sun was taken on 19 December 1995. "All those who have worked tirelessly on the SOHO payload, spacecraft and ground-segment are to be congratulated on their excellent work and for having developed the most remarkable tool to help us understand the Sun and its environment, the heliosphere" said Roger Bonnet, ESA's Director of Science.

According to present plans one month of early science is scheduled to begin around end of March and scientists hope to present their initial findings to the wide public by early May. SOHO is a project of international cooperation between ESA and NASA. The mission is led and coordinated by ESA who also procured the spacecraft; NASA provided the launch and operates the satellite. The European scientists who designed nine of the observatory's instruments and their US colleagues who built a further three are all present at Goddard Space Flight Center, where they jointly plan the optimum scientific use of the satellite.

The spacecraft is part of the international Solar-Terrestrial Science Programme, the next member of which is Cluster, a flotilla of four spacecraft that will study how the Sun affects Earth and surrounding space. Cluster is scheduled for launch in May 1996 on the first Ariane 5 rocket. It will be the second mission belonging to the first "Cornerstone" of ESA's long- term scientific programme "Horizon 2000".

Photos available :

LASCO Experiment : Coronal mass ejection

The first Dopplergrams obtained from the Michelson Doppler Imager (MDI) experiment of the Solar Oscillations Investigation (SOI) on SOHO :

Part I

Part II

Complete list of all SOHO experiments and their Principal Investigators.

Scientific Instruments

1.	SUMER	Solar Ultraviolet Measurements of Emitted Radiation	PI : K. Wihelm MPAe, Lindau, Germany
2.	CDS	Coronal Diagnostic Spectrometer	PI : R.A. Harrison DRAL, Chilton, UK
3.	EIT	Extreme Ultraviolet Imaging Telescope	PI : J.P. Delaboudinière IAS, Orsay,France
4.	UVCS	Ultraviolet Coronagraph Spectrometer	PI : J.L. Kohl SAO, Cambridge, USA
5.	LASCO	Large-angle Sectroscopie Coronagraph	PI : G.E. Brueckner NRL, Washington DC, USA
6.	SWAN	Solar Wind Anisotropics	PI : J.L. Bertaux CNRS, Verrières le Buisson, France
7.	CELIAS	Charge, Element and Isotope Analysis System	PI : D. Hovestadt MPE, Garching, Germany
8.	COSTEP	Comprehensive Supra-thermal and Energetic Particle Analyser	PI : H. Kunow University of Kiel, Germany
9.	ERNE	Energetic and Polativistic Nuclei and Electron Experiment	PI : J. Torsti University of Turku, Finland
10.	GOLF	Global Oscillations at Low Frequence	PI : A. Gabriel IAS, Orsay, France
11.	VIRGO	Variability of Solar Irradiance and Gravity Oscillations	PI : C. Fröhlich PMOD, Davos, Switzerland
12.	SOI/MDI	Solar Oscillations Investigation / Michelson Doppler Image	PI : P.H. Sherrer CSSA, Stanford University, USA

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