Advanced Composition Explorer
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Advanced Composition Explorer(ACE) A NASA satellite, launched in 1997 to measure the isotope and element abundances in the solar corona and cosmic rays over a wide range of energies. It is in orbit around L1, one of the Lagrangian points of the Sun–Earth system, 1.5 million km nearer to the Sun than Earth is.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006