Advanced Composition Explorer
The Earth is constantly bombarded with a stream of accelerated particles arriving not only from the Sun, but also from interstellar and galactic sources. The study of these energetic particles is the aim of the Advanced Composition Explorer (ACE) and this will contribute to our understanding of the formation and evolution of the solar system as well as the astrophysical processes involved. The 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 experiments.
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.
Instrument for satellite
Solar Energetic Particle Ionic Charge Analyzer (SEPICA)
launch: 25. August 1997
actual status: active; at L1
end of mission t.b.d.
(The spacecraft has enough propellant on board to maintain
an orbit at L1 until ~2024.)