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ACE (Explorer 71)


The objective of the ACE (Advanced Composition Explorer) is to collect observations of particles of solar, interplanetary, interstellar, and galactic origins, spanning the energy range from that of wind ions to galactic cosmic ray nuclei up to 600 MeV/nucleon.

Definitive studies will be made of the abundances of essentially all isotopes from H to Zn (Z = 1-30), with exploratory isotope studies extending to Zr (Z = 40). The ACE payload includes six high resolution spectrometers, each designed to provide the optimum charge, mass, or charge-state resolution in its particular energy range. Each spectrometer has a geometry factor optimized for the expected flux levels, so as to provide a collecting power greater by a factor of 10-1000 times that of previous or planned experiments. The payload also includes three additional instruments of standard design to monitor energetic electrons, H and He ions, and a magnetometer. It has 9 instruments:

  • CRIS (Cosmic Ray Isotope Spectrometer)
  • SIS (Solar Isotope Spectrometer)
  • ULEIS (Ultra Low Energy Isotope Spectrometer)
  • SEPICA (Solar Energetic Particle Ionic Charge Analyzer)
  • SWIMS (Solar Wind Ion Mass Spectrometer)
  • SWICS (Solar Wind Ion Composition Spectrometer)
  • EPAM (Electron, Proton, and Alpha Monitor)
  • SWEPAM (Solar Wind Electron, Proton, and Alpha Monitor)
  • MAG (Magnetometer Instrument)

The ACE spacecraft is based on the design of the CCE (Charge Composition Explorer), built at JHU/APL for the Active Magnetospheric Particle Tracer Explorer (AMPTE) program. The spacecraft spin axis is pointed towards the Sun to within +/- 20 degrees, and it occupies a halo orbit about the L1 Earth-Sun libration point. Powered by solar cells, the spacecraft has a design life of at least five years, and it returns data in daily tape recorder dumps, received through NASA JPL's Deep Space Network and initially processed at NASA-GSFC. The average data telemetry rate is 6.7 Kbs.

Nation: USA
Type / Application: Research
Operator: NASA
Contractors: Johns Hopkins University Applied Physics Laboratory (APL)
Configuration: spin stabilzed, sunpointing
Propulsion: ?
Power: 4 deployable fixed solar arrays, batteries
Lifetime: +5 years
Mass: 785 kg
Orbit: Sun-Earth Lagrange point L1 halo orbit
Satellite COSPAR Date LS Launch Vehicle Remarks
ACE (Explorer 71) 1997-045A 25.08.1997 CC LC-17A Delta-7920-8


  • NSSDC Master Catalog: ACE
Further Explorer missions:

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