Advanced Composition Explorer

active Mission

Designed to collect and analyze particles from near and far, ranging from solar wind ions to galactic cosmic ray nuclei, ACE far exceeded its expected life span of five years and continues to provide data on space weather, and give advance warning of geomagnetic storms.




Aug. 25, 1997


Sun-Earth Interaction


Study spaceborne energetic particles
Experience Earth, our solar system, nearby asteroids, the universe, and the spacecraft exploring them with immersive real-time 3D web-based apps for Mac, PC and mobile devices.

NASA's Advanced Composition Explorer (ACE) collects and analyzes particles of solar, interplanetary, interstellar and galactic origins. The data contributes to our understanding of the Sun, its interaction with Earth, and the evolution of the solar system.

  • ACE continues to provide space weather reports and warnings of geomagnetic storms that can disrupt communications on Earth and harm astronauts in space.
  • The spacecraft has operated far beyond its expected lifetime.

United States of America (USA)
Sun–Earth L1 Lagrange Point
Spacecraft Mass
1,658 pound (752 kilograms)
Mission Design and Management
Launch Vehicle
Delta 7920-8 (no. D247)
Launch Date and Time
Aug. 25, 1997 / 14:39 UT
Launch Site
Cape Canaveral, Florida / Launch Complex 17A
Scientific Instruments
1. Solar Wind Ion Mass Spectrometer (SWIMS) and Solar Wind Ion Composition Spectrometer (SWICS)
2. Ultra-Low Energy Isotope Spectrometer (ULEIS)
3. Solar Energetic Particle Ionic Charge Analyzer (SEPICA)
4. Solar Isotope Spectrometer (SIS)
5. Cosmic Ray Isotope Spectrometer (CRIS)
6. Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM)
7. Electron, Proton, and Alpha-Particle Monitor (EPAM)
8. Magnetometer (MAG)
9. Real Time Solar Wind Experiment (RTSW)

Key Dates

Aug. 25, 1997: Launch

Jan 21, 1998: Spacecraft began operations

A Boeing Delta II expendable launch vehicle lifts off with NASA’s Advanced Composition Explorer (ACE) observatory at 10:39 a.m. EDT, on Aug. 25, 1997, from Launch Complex 17A, Cape Canaveral Air Station, Florida.

In Depth: ACE

NASA's Advanced Composition Explorer (ACE) spacecraft was designed to study spaceborne energetic particles from the Sun-Earth L1 Lagrange point, about 870,000 miles (1.4 million kilometers) from Earth.

Specifically, the spacecraft was launched to investigate the matter ejected from the Sun to establish the commonality and interaction between the Sun, Earth and the Milky Way galaxy.

In addition, ACE also provides real-time space weather data and advanced warning of geomagnetic storms. ACE’s nine instruments have a collecting power that is 10 to 10,000 times greater than anything previously flown.

After launch, the spacecraft’s Delta 2 launch vehicle’s second stage reignited after four hours to insert the satellite into a 110 × 851,000-mile (177 × 1.37 million-kilometer) orbit.

After reaching apogee a month after launch, ACE inserted itself into its Lissajous orbit around the L1 point. The spacecraft was declared operational Jan. 21, 1998.

As of 2015, it continued to provide near-real-time 24/7 coverage of solar wind parameters and to measure solar energetic particle intensities.

With the exception of the SEPICA instrument (data from which was no longer received after Feb. 4, 2005), all instruments on ACE remained operational as of mid-2017, and the propellant on the spacecraft could theoretically allow the mission to continue into 2024.

Additional Resources

Key Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.

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