Advanced Composition Explorer (ACE) Project

Project Description
The Advanced Composition Explorer (ACE) is an Explorer mission
that was managed by the Office of Space Science Mission and
Payload Development Division of the National Aeronautics and
Space Administration (NASA).

The Earth is constantly bombarded with a stream of accelerated
particles arriving not only from the Sun, but also from
interstellar and galactic sources. Study of these energetic
particles will contribute to our understanding of the formation
and evolution of the solar system as well as the astrophysical
processes involved. The Advanced Composition Explorer (ACE)
spacecraft carrying six high-resolution sensors and three
monitoring instruments samples low-energy particles of solar
origin and high-energy galactic particles with a collecting
power 10 to 1000 times greater than past or planned experiments.

From a vantage point approximately 1/100 of the distance from
the Earth to the Sun ACE performs measurements over a wide range
of energy and nuclear mass, under all solar wind flow conditions
and during both large and small particle events including solar
flares. ACE provides near-real-time solar wind information over
short time periods. When reporting space weather ACE can provide
an advance warning (about one hour) of geomagnetic storms that
can overload power grids, disrupt communications on Earth, and
present a hazard to astronauts.

ACE orbits the L1 libration point which is a point of Earth-Sun
gravitational equilibrium about 1.5 million km from Earth and
148.5 million km from the Sun. With a semi-major axis of
approximately 200,000 km the elliptical orbit affords ACE a
prime view of the Sun and the galactic regions beyond.

For more information, link to http://www.srl.caltech.edu/ACE/