ACES Payload
The ACES payload is designed for launch in the unpressurised cargo bay of Dragon free flying transfer vehicle. Once in orbit, ACES, transferred from the Dragon using the Space Station robotic systems, will be attached to the Columbus Laboratory Earth-facing external payload platform.
The payload has a volume of about 1 m3 and a mass of ~362 Kg. The key instruments are the two atomic clocks:
- PHARAO (Projet d'Horloge Atomique par Refroidissement d'Atomes en Orbit) is a primary frequency standard based on samples of laser cooled cesium atoms. PHARAO is funded and developed by the French National Space Agency (CNES). The PHARAO instruments consists of 6 separate elements.
PHARAO’s concept is very similar to ground based atomic fountains, but with a major difference: PHARAO will be operated under microgravity conditions. Atoms, launched in free flight along the PHARAO tube, cross a resonant cavity where they interact twice with a microwave field tuned on the transition between the two hyperfine levels of the caesium ground state. In a microgravity environment, the velocity of the atoms along the ballistic trajectories is constant and can be continuously changed over almost two orders of magnitude (5-500 cm/s), allowing the detection of atomic signals with sub-Hz linewidth.
- SHM (Space H-Maser) is an active hydrogen maser for space applications developed in Switzerland by Spectratime under ESA contract.
The maser operates on the hyperfine transition of atomic hydrogen. H2 molecules are dissociated in a plasma discharge and the resulting beam of H atoms is state-selected and sent in a storage bulb. The bulb is surrounded by a microwave cavity that, tuned on the atomic resonance, induces the maser action.
The performances of the two clocks are combined to generate an onboard timescale using the excellent short-term stability of SHM and the long-term stability and accuracy of the cesium clock PHARAO.
|
1. PHARAO Cesium Tube 2. PHARAO Laser Source 3. PHARAO computer 4. XPLC 5. MWL 6. GNSS Antenna |
7. Space hydrogen Maser 8. Heat pipes 9. Laser corner cube reflector 10. MWL antennae 11. CEPA 12. ELT |
The payload has a volume of about 1m3 and a mass of ~362 kg.
The key instruments
The key instruments are the two atomic clocks:
PHARAO (Projet d'Horloge Atomique par Refroidissement d'Atomes en Orbit) is a primary frequency standard based on samples of laser cooled cesium atoms. PHARAO is funded and developed by the French National Space Agency (CNES).
PHARAO’s concept is very similar to ground based atomic fountains, but with a major difference: PHARAO will be operated under microgravity conditions. Atoms, launched in free flight along the PHARAO cesium tube, cross a resonant cavity where they interact twice with a microwave field tuned on the transition between the two hyperfine levels of the caesium ground state. In a microgravity environment, the velocity of the atoms along the ballistic trajectories is constant and can be continuously changed over almost two orders of magnitude (5-500 cm/s), allowing the detection of atomic signals with sub-Hz linewidth.
For more information on PHARAO:
http://www.cnes.fr/web/CNES-en/4488-pharao.php
http://smsc.cnes.fr/PHARAO/index.htm
http://www.cnes.fr/web/CNES-en/8223-aces-the-time-measuring-super-machine.php
- SHM (Space Hydrogen Maser) is an active hydrogen maser for space applications developed in Switzerland under ESA contract with funding provided by the Swiss Space Office (SSO).
The maser operates on the hyperfine transition of atomic hydrogen. H2 molecules are dissociated in a plasma discharge and the resulting beam of H atoms is state-selected and sent to the hydrogen storage bulb. The bulb is surrounded by a microwave cavity that, tuned on the atomic resonance, induces the maser action.
The performances of the two clocks are combined to generate an onboard timescale using the excellent short-term stability of SHM and the long-term stability and accuracy of the cesium clock PHARAO.
Last update: 29 October 2012
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