The Advanced Composition Explorer (ACE) is a mission selected for development and launch in the mid-1990s to study particles from solar, interplanetary, interstellar, and galactic sources. The mission aims to observe particles spanning a wide energy range, from the solar wind (~1 keV/nucleon) to galactic cosmic rays (several hundred MeV/nucleon). ACE will provide definitive studies of nearly all isotopes from hydrogen to zinc (1≤Z≤30) and exploratory studies up to zirconium (Z = 40). The payload includes six high-resolution spectrometers designed to optimize charge, mass, or charge-state resolution and collecting power, which is 10 to 1000 times greater than previous or planned experiments. Additional instruments will monitor solar wind, magnetic fields, and energetic H, He, and electron fluxes. The scientific objectives of ACE include: 1. **Elemental and Isotopic Composition**: Determining the elemental and isotopic composition of various samples of matter. 2. **Origin and Evolution of Elements**: Investigating the origin and evolution of solar system and galactic material. 3. **Solar Corona and Solar Wind**: Studying the formation of the solar corona and the acceleration of the solar wind. 4. **Particle Acceleration and Transport**: Understanding particle acceleration and transport processes in nature. The ACE spacecraft is based on designs from previous missions like AMPTE/CCE and SIMPL, with a two-deck, irregular octagon body. It will be launched by a Multi-purpose Launch Vehicle (MLV) to the Earth-Sun L1 point, where it will maintain an orbit with a 10-degree inclination. Data will be collected on tape and transmitted to the Deep Space Network for analysis and distribution. ACE's advanced spectrometers and large collecting power will enable significant advancements in our understanding of the elemental and isotopic composition of particles over a wide energy range, addressing key scientific questions in the origin of elements, solar corona formation, and particle acceleration.The Advanced Composition Explorer (ACE) is a mission selected for development and launch in the mid-1990s to study particles from solar, interplanetary, interstellar, and galactic sources. The mission aims to observe particles spanning a wide energy range, from the solar wind (~1 keV/nucleon) to galactic cosmic rays (several hundred MeV/nucleon). ACE will provide definitive studies of nearly all isotopes from hydrogen to zinc (1≤Z≤30) and exploratory studies up to zirconium (Z = 40). The payload includes six high-resolution spectrometers designed to optimize charge, mass, or charge-state resolution and collecting power, which is 10 to 1000 times greater than previous or planned experiments. Additional instruments will monitor solar wind, magnetic fields, and energetic H, He, and electron fluxes. The scientific objectives of ACE include: 1. **Elemental and Isotopic Composition**: Determining the elemental and isotopic composition of various samples of matter. 2. **Origin and Evolution of Elements**: Investigating the origin and evolution of solar system and galactic material. 3. **Solar Corona and Solar Wind**: Studying the formation of the solar corona and the acceleration of the solar wind. 4. **Particle Acceleration and Transport**: Understanding particle acceleration and transport processes in nature. The ACE spacecraft is based on designs from previous missions like AMPTE/CCE and SIMPL, with a two-deck, irregular octagon body. It will be launched by a Multi-purpose Launch Vehicle (MLV) to the Earth-Sun L1 point, where it will maintain an orbit with a 10-degree inclination. Data will be collected on tape and transmitted to the Deep Space Network for analysis and distribution. ACE's advanced spectrometers and large collecting power will enable significant advancements in our understanding of the elemental and isotopic composition of particles over a wide energy range, addressing key scientific questions in the origin of elements, solar corona formation, and particle acceleration.