SOHO Sun watcher celebrates 8 years in space
Posted: December 2, 2003

Since its launch on 2 December 1995, the Solar and Heliospheric Observatory (SOHO) has provided an unparalleled breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, and out to the solar wind. SOHO has continued to revolutionize our understanding of the Sun with its 24 hour per day observations of our daylight star. The SOHO spacecraft was nearly lost in space in 1998. Thanks to one of the most amazing rescue operations in space ever, the satellite is still in very good shape and continues to deliver excellent science data.

The main objectives of the SOHO mission was to study the structure and dynamics of the solar interior, the heating of the solar corona, and the acceleration of the solar wind. Five years later, science teams from around the world have made great strides toward answering these "big three" questions. At the same time, SOHO's easily accessible, spectacular data and basic science results have captured the imagination of the space science community and the general public alike. This presentation will summarize some of the scientific highlights and illustrate how SOHO acts like a a watchdog for solar storms. Furthermore, accurate monitoring the energy output from the Sun is important for understanding any natural valiability of the Earth's climate.

Recently 23.990 people participated in selecting the most popular SOHO image. The winning images was this:

SOHO has an impressive and unique list of achievements. Some of the key results include:

  • Revealing the first images ever of a star's convection zone (its turbulent outer shell) and of the structure below sunspots.

  • Providing the most detailed and precise measurements of the temperature structure, the interior rotation, and gas flows in the solar interior.

  • Measuring the acceleration of the slow and fast solar wind. Identifying the source regions and acceleration mechanism of the fast solar wind in the magnetically "open" regions at the Sun's poles.

  • Discovering new dynamic solar phenomena such as coronal waves and solar tornadoes.

  • Revolutionising our ability to forecast space weather, by giving up to three days notice of Earth-directed disturbances, and playing a lead role in the early warning system for space weather.

  • Monitoring the total solar irradiance (the 'solar constant') as well as variations in the extreme ultra violet flux, both of which are important to understand the impact of solar variability on Earth's climate.

However, during eight years of operation, the team has had to face several heart-stopping moments. But with extraordinary team spirit, skill and competence, they turned these episodes into remarkable success stories. In June 1998, control of the spacecraft was lost and the team fought for three months before regaining contact with the spacecraft. Then all three on-board gyroscopes failed. Again, the team rose to the challenge by reprogramming the spacecraft to completely eliminate the reliance on gyroscopes. In doing so, they crossed another frontier in space - SOHO became the first three-axis stabilized spacecraft to be operated without gyroscopes.

In May 2003, the East-West pointing mechanism of SOHO's high-gain antenna started showing signs of a possible breakdown. With this threat to the mission's lifeline, many people feared once again that the mission was in danger. After a long and arduous diagnostic process and a careful analysis of all options, the team decided to park the antenna in an "ideal" position, where data losses are minimised by rotating the spacecraft 180 deg every three months. In addition, new procedures and larger ground antennas (when available) can be used to all but eliminate the impacts to normal science operations.

At all times of the mission, the team continued to produce excellent science, and SOHO has revolutionised the way scientists think about the Sun and how it might affect Earth's environment. More than 1500 papers, representing the work of more than 1500 scientists, have been published based on SOHO data. And with SOHO still going strong, the success story is set to continue.

Prestigious award for SOHO
The SOHO team has been presented with the prestigious Laurels for Team Achievement Award of the International Academy of Astronautics (IAA).

The award recognises both the outstanding achievements in designing, building and operating the mission, as well as the science it has performed. It is a tribute to a team that has contributed to one of the most successful space missions in history.

The International Academy of Astronautics (IAA) presents the Laurels for Team Achievement Award in recognition of extraordinary performance and achievement by teams of scientists, engineers and managers in the field of astronautics. This honour has been awarded only twice before - to the Russian Mir Space Station Team and the US Space Shuttle Team. Now the SOHO team joins this select group.

The citation of the award for the SOHO team reads: "To the team of scientists, engineers, and managers for the development and operation of a world class mission leading to substantial advancements in understanding the Sun and the solar-terrestrial relationshipFor the development and operation of a world-class mission leading to substantial advancements in understanding the Sun and the solar-terrestrial relationship. Mankind's knowledge and understanding of the dynamic processes within and around the Sun and the solar-terrestrial interactions have multiplied manifold since SOHO began its operations in 1995."

The SOHO project is the result of an international effort. Fourteen European countries, led by the European Space Agency and prime contractor Astrium (formerly Matra-Marconi), built the SOHO spacecraft. It carries twelve instruments (nine European-led and three American-led) and was launched by an American Atlas 2AS rocket on 2 December 1995. The spacecraft was designed for a two-year-mission but its spectacular success has led to two extensions of the mission, first until 2003, and then again until March 2007.