The Advanced Composition Explorer (ACE) is a mission designed to study the elemental and isotopic composition of particles from solar, interplanetary, interstellar, and galactic sources. ACE will observe particles spanning a wide energy range, from solar wind energies (1 keV/nucleon) to galactic cosmic ray energies (several hundred MeV/nucleon). The mission aims to determine the abundance of isotopes from hydrogen to zinc (Z = 1 to 30), with exploratory studies extending to zirconium (Z = 40). The ACE payload includes six high-resolution spectrometers, each optimized for its energy range and designed to provide superior charge, mass, or charge-state resolution. Additional instruments will monitor solar wind and magnetic field conditions, as well as energetic particle fluxes. The scientific objectives of ACE include investigating the elemental and isotopic composition of matter, the origin and evolution of elements, the formation of the solar corona and acceleration of the solar wind, and particle acceleration and transport in nature. ACE will compare the composition of distinct samples of matter, including solar, interplanetary, and galactic sources, to study the origin and evolution of solar system and galactic material. The mission will also investigate the acceleration and transport of particles in space, using data from various instruments to test theoretical models. The ACE spacecraft is based on designs from previous missions and will be launched to the Earth-Sun libration point, L1. It will provide data on solar and interplanetary conditions, with data collected and transmitted to ground stations for analysis. The mission will use advanced spectrometers with large collecting power and unprecedented resolution to make significant advances in understanding the elemental and isotopic composition of solar, interplanetary, and interstellar particles over a wide energy range. The ACE data plan will allow correlations of various data sets to address outstanding scientific problems in the areas of the origin of elements, the formation of the solar corona, and particle acceleration and transport in nature.The Advanced Composition Explorer (ACE) is a mission designed to study the elemental and isotopic composition of particles from solar, interplanetary, interstellar, and galactic sources. ACE will observe particles spanning a wide energy range, from solar wind energies (1 keV/nucleon) to galactic cosmic ray energies (several hundred MeV/nucleon). The mission aims to determine the abundance of isotopes from hydrogen to zinc (Z = 1 to 30), with exploratory studies extending to zirconium (Z = 40). The ACE payload includes six high-resolution spectrometers, each optimized for its energy range and designed to provide superior charge, mass, or charge-state resolution. Additional instruments will monitor solar wind and magnetic field conditions, as well as energetic particle fluxes. The scientific objectives of ACE include investigating the elemental and isotopic composition of matter, the origin and evolution of elements, the formation of the solar corona and acceleration of the solar wind, and particle acceleration and transport in nature. ACE will compare the composition of distinct samples of matter, including solar, interplanetary, and galactic sources, to study the origin and evolution of solar system and galactic material. The mission will also investigate the acceleration and transport of particles in space, using data from various instruments to test theoretical models. The ACE spacecraft is based on designs from previous missions and will be launched to the Earth-Sun libration point, L1. It will provide data on solar and interplanetary conditions, with data collected and transmitted to ground stations for analysis. The mission will use advanced spectrometers with large collecting power and unprecedented resolution to make significant advances in understanding the elemental and isotopic composition of solar, interplanetary, and interstellar particles over a wide energy range. The ACE data plan will allow correlations of various data sets to address outstanding scientific problems in the areas of the origin of elements, the formation of the solar corona, and particle acceleration and transport in nature.