ACE

Explorer 71, Advanced Composition Explorer

Mission Profile

ACE (Advanced Composition Explorer, Explorer 71) is a NASA space physics satellite launched on 25 August 1997 aboard a Delta II to the Sun-Earth L1 Lagrange point, where it has monitored the composition and energy spectra of solar wind particles and cosmic rays for over 27 years. Its nine instruments measure the elemental, isotopic, and ionic charge state composition of particles arriving from the Sun and from galactic cosmic ray sources, providing an unprecedented catalog of solar wind variability and particle acceleration processes. ACE is also the primary source of real-time solar wind data used by NOAA's Space Weather Prediction Center for geomagnetic storm forecasting, providing up to 60 minutes advance warning of solar wind conditions about to impact Earth's magnetosphere. ACE continues operating as one of NASA's longest-lived solar observatories.