Advanced Composition Explorer (ACE or Explorer 71) is a NASA Explorer program satellite and space exploration mission to study matter comprising energetic particles from the solar wind, the interplanetary medium, and other sources. Real-time data from ACE are used by the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC) to improve forecasts and warnings of solar storms. The ACE robotic spacecraft was launched on 25 August 1997, and entered a Lissajous orbit close to the Lagrange point (which lies between the Sun and the Earth at a distance of some from the latter) on 12 December 1997. The spacecraft is currently operating at that orbit. Because ACE is in a non-Keplerian orbit, and has regular station-keeping maneuvers, the orbital parameters in the adjacent information box are only approximate. , the spacecraft is still in generally good condition, and is projected to have enough propellant to maintain its orbit until 2024. NASA Goddard Space Flight Center managed the development and integration of the ACE spacecraft. History The Advanced Composition Explorer (ACE) was proposed in 1986 as part of the Explorer Concept Study Program. ACE is designed to make coordinated measurements of the elemental and isotopic composition of accelerated nuclei from H (Hydrogen) to Zn (Zinc) spanning six decades in energy per nucleon, from solar wind to galactic cosmic ray energies, with sensitivity and with charge and mass resolution much better than heretofore possible. Following a Phase-A definition study, ACE was selected for development in 1989, and began construction in 1994. On 25 August 1997, ACE was successfully launched from Cape Canaveral Air Force Station by a Delta II launch vehicle. The August 1997 launch was originally scheduled back in 1993. Science objectives ACE observations allow the investigation of a wide range of fundamental problems in the following four major areas: Elemental and isotopic composition of matter A major objective is the accurate and comprehensive determination of the elemental and isotopic composition of the various samples of "source material" from which nuclei are accelerated. These observations have been used to: Generate a set of solar isotopic abundances based on a direct sampling of solar material Determine the coronal elemental and isotopic composition with greatly improved accuracy Establish the pattern of isotopic differences between galactic cosmic ray and Solar System matter Measure the elemental and isotopic abundances of interstellar and interplanetary "pick–up ions" Determine the isotopic composition of the "anomalous