NASA - National Aeronautics and Space Administration

The weather conditions that NASA's Advanced Composition Explorer (ACE) reports won't change our plans about going to the beach. But the information it provides will help scientists understand how events on the Sun have the ability to disrupt Earth's communications, overload power grids, present a hazard to astronauts, and affect weather patterns. We call this effect on Earth "space weather."

The Earth is continually bombarded with accelerated particles from the Sun and other galactic sources. ACE gives scientists the ability to study these energetic particles and further their understanding of the formation and evolution of the Solar System. The information ACE provides also helps to develop ways to protect the planet from their effects, including space weather.

The spacecraft is about five feet across and three feet high, not including the four solar arrays and the magnetometer booms attached to two of the solar panels. At launch, it weighed 785 kg, which included hydrazine fuel for orbit insertion and maintenance.

So what is happening on the Sun that can cause serious effects on Earth? The Sun has an 11-year cycle of increasing and decreasing sunspots and solar storms. In one of the biggest types of storms, a Coronal Mass Ejection (CME), up to 100 million tons of solar material can be ejected from the Sun's surface at speeds greater than two million miles per hour. This amount of material is comparable to the amount of water in the Mediterranean Sea. As CMEs leave the Sun, they can accelerate particles to nearly the speed of light.

When a CME reaches Earth, it can transfer its energy to Earth’s magnetic field and disable satellites. As a result, spacecraft sometimes feel the effects of major increases in "killer" electrons and other particles energized by the storms. The high-energy particles from the CME can penetrate the walls of the International Space Station and other near-Earth spacecraft and pose a health hazard for NASA's astronauts. High electric currents can also be generated in Earth's power grids, which can destroy large transformers and temporarily shut down neighboring power grids.

ACE is stationed between our planet and the Sun one million miles from the Earth.

The spacecraft carries nine instruments, each designed to observe different aspects of the solar and galactic neighborhood. ACE detects information about the energy, speed and magnetic field of each solar disturbance that is headed toward Earth, and it transmits radio warnings to us up to an hour before they arrive.

The National Oceanic and Atmospheric Administration (NOAA) makes ACE data available on the Web within minutes. It is used by space agencies, the military, electric power and communication industries, and universities around the world. With enough warning, the damaging effects of these disturbances can be decreased.

The Advanced Composition Explorer was launched from Kennedy Space Center, Fla., in August 1997. ACE is managed by NASA's Goddard Space Flight Center and the Agency's Office of Space Science Mission and Payload Development Division.

For further information, visit:
http://www.srl.caltech.edu/ACE/
NASA's John F. Kennedy Space Center and Goddard Space Flight Center