Atomic Clock Ensemble in Space
Atomic Clock Ensemble in Space (ACES) is an ESA-led fundamental-physics experiment mounted outside the International Space Station’s Columbus laboratory. It combines PHARAO, a CNES laser-cooled caesium clock, with the Space Hydrogen Maser. PHARAO supplies long-term accuracy while the maser supplies short-term stability. Microwave and laser time-transfer links connect the ensemble with precise clocks on Earth, supporting tests of gravitational redshift, comparisons between distant clocks and relativistic geodesy.
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Identity
- Aliases
- Atomic Clock Ensemble in SpaceACES
- Name
- Atomic Clock Ensemble in Space
- Status
- active
Details
- Astronauts
- -
- Description
- Atomic Clock Ensemble in Space (ACES) is an ESA-led fundamental-physics experiment mounted outside the International Space Station’s Columbus laboratory. It combines PHARAO, a CNES laser-cooled caesium clock, with the Space Hydrogen Maser. PHARAO supplies long-term accuracy while the maser supplies short-term stability. Microwave and laser time-transfer links connect the ensemble with precise clocks on Earth, supporting tests of gravitational redshift, comparisons between distant clocks and relativistic geodesy.
- Outcome
- ACES launched to the International Space Station on 21 April 2025 and was installed outside Columbus on 25 April. Its experiment plan combines clock characterization and time-transfer measurements with comparisons of ground and space clocks to test fundamental physics.
- Programs
- -
- Start Date
- 2025-04-21
- Vehicle Families
- -
Links
Assets & Meta
- Creation Time
- August 14, 2026 at 06:55:33 UTC
- Updated Time
- October 29, 2026 at 15:28:37 UTC
Other
- Affiliations
- Space Stations
- Vehicles
- -