Goddard Space Flight Center
Greenbelt, MD

Dec. 8, 1999


NASA today announced selections of four investigations to be flown on the Solar TErrestrial RElations Observatory (STEREO) mission, planned for launch in 2004. The STEREO mission will be a multilateral international collaboration involving participants from France, Germany, the United States, and United Kingdom. STEREO is the third mission selected for NASA's Solar-Terrestrial Probe (STP) Program, under the Agency's Sun- Earth Connections Theme.

STEREO will for the first time unveil the Sun in three dimensions. Its objective is to address the origin, evolution and interplanetary consequences of one the most massive disturbances in our solar system called the coronal mass ejection (CME). This will be achieved by sending two identically instrumented spacecraft, both at 1 AU orbit around the Sun, but one flying well ahead of the Earth and one behind.

The instrument suite for STEREO will characterize the CME plasma all the way from the solar surface to the orbit of the Earth. These instruments will measure physical characteristics of CME's with remote sensing and local sensing instruments, allowing scientists to determine solar origins of CME's, their propagation into the interplanetary medium and ultimately their consequences on Earth's magnetic field.

By viewing CME's in three dimensions, STEREO will be able to pinpoint their speed and distance from Earth, and thus more accurately time the arrival of the plasma cloud. The planned 2004 launch date will enable STEREO to make observations during the simpler, declining phase of the current activity cycle, which is expected to reach solar maximum around the year 2000.

"Existing spacecraft only provide a limited picture of these huge solar eruptions, called CME's, which can hurl up to ten billion tons of electrically charged gas toward Earth at more than one million miles per hour," said STEREO co-investigator Dr. Barbara Thompson of NASA's Goddard Space Flight Center (Greenbelt, MD). "By placing two spacecraft off the Sun-Earth line, STEREO will reveal details about CME structure and dynamics that have been impossible to obtain."

The investigations selected by NASA are:

"This selection forms the final link of a powerful partnership between the international science community, NASA and Johns Hopkins University Applied Physics Laboratory," said STEREO Mission Manager Abby Harper of Goddard. "I am eager to work with such an experienced team, as STEREO will produce out-of-this-world class science and space weather data for a relatively low cost."

The two STEREO spacecraft will be built by Johns Hopkins University Applied Physics Laboratory (Laurel, Md.). STEREO is a $150 million development mission (phase C/D real year cost), which equates to $64 million for instruments and $86 million for the two spacecraft. Mission operations and data analysis cost is about $45 million. Development is scheduled to begin January 2001. Goddard will provide mission management and control of STEREO.

For additional information about the STEREO mission and its payload, go to:



6 April 1998


Solar physicists from the UK and other European countries are urging the European Space Agency (ESA) to build a new spacecraft to orbit the Sun. The Solar Orbiter would circle much closer to the Sun than any previous spacecraft, approaching the within 20 million km of the Sun's surface - 3 times closer than the innermost planet, Mercury. Following a special workshop sponsored by ESA and organised by Professor Eric Priest of the University of St Andrews, the scientists are suggesting that the Solar Orbiter project should be part of a coordinated international approach to learning more about the Sun. It would follow up the success of Ulysses and SOHO, two spacecraft currently being used to study the Sun.

The Sun is an important subject for research by ESA. As our nearest star, the Sun is of great significance for astronomy as a whole and provides the best opportunity for astronomers to study basic cosmical processes in great detail. In addition, it affects Earth's environment and can cause damage to satellites and disrupt electricity supplies.

A hundred of the world's leading solar physicists met at the ESA workshop, held at the Instituto de Astrofisica de Canarias on the Spanish island of Tenerife at the end of March. They considered various solar space missions being planned by different groups of scientists around the world and concluded that the Solar Orbiter, provided by ESA in collaboration with other space agencies, would be a key part of a coherent international programme.

"Space missions take many years to plan" says Professor Priest. "From time to time we have to stand back and decide what key scientific questions we should try to answer in the future. In what direction should we head? What might be technologically feasible in 10 or 20 years from now? Such exciting ideas for studying the Sun are on offer, it is hard to choose between them."

In addition to the Solar Orbiter, workshop participants looked at three other proposed space missions:

STEREO is a proposal to send several spacecraft to different positions in the Solar System. By viewing the Sun from different directions they could build up 3-D pictures (stereoscopic or tomographic). These would reveal clearly, for the first time, the complex contortions of gas and magnetic fields involved in solar eruptions. The consequences include solar flares and the mass ejections of gas which, arriving at the Earth, can cause satellite failures and power black-outs.

SOLAR-NET is a rival scheme, aiming to inspect the stormy surface and atmosphere of the Sun in much sharper detail. A combination of three telescopes in an interferometer could achieve a clarity of vision 40 times better than that of the present instruments in space. The immense magnetic explosions responsible for heating the Sun's atmosphere and for sparking solar flares occur in regions too small to be clearly resolved by available telescopes.

PROBE is a scheme to send a spacecraft into the Sun's hot atmosphere, where it could sample its atoms directly and measure the magnetic fields. Probe would fly by the Sun at a distance of only 2 million kilometres from the surface, compared with 150 million kilometres for the Earth-Sun distance. Remarkable heat shields would have to maintain the spacecraft at an operable temperature in sunshine 2500 times stronger than at the Earth.

After a lively debate, the following consensus emerged. A coherent international programme of missions should be set up. Stereo and Probe are likely to be realized within NASA's programme, but it was agreed that they would benefit greatly by participation of European scientists with ESA endorsement. Solar-Net was recognized to be of high scientific interest and was considered suitable for a small demonstration mission. Solar Orbiter was recommended as the main ESA element in the programme.

In contrast to Probe, which would fly right past the Sun in less than a day, Solar Orbiter would remain above the same region of the Sun for several days and would continue to orbit the Sun many times. At a later stage the aim would be to observe in detail, for the first time, the mysterious polar regions of the Sun. And Solar Orbiter would be able to see the regions through which Probe was flying.

Commenting on the choice of Solar Orbiter, Professor Priest said, "What tipped the scales was the exciting new science, its key role in the overall international programme, and the broad backing of the world's solar scientists. By selecting Solar Orbiter as the project for which we will all now be pressing, we can be certain that Europe will create a fitting successor to SOHO, which is already revolutionizing solar science.

As with any proposal like this, Solar Orbiter will have to go through ESA's procedures for mission selection before it can be authorised. Assessments by expert committees and detailed studies of the science, engineering and costs are required. Any collaboration with other space agencies has to be negotiated. However, the support of the specialists in solar physics helps strengthen the case for Solar Orbiter as ESA's next solar project, to be considered for possible launch between 2005 and 2010.


Images to support this story can be found at the following internet location


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