Status of the flight model of the cold atoms space clock PHARAO

Abstract

PHARAO (Projet d'Horloge Atomique par Refroidissement d'Atomes en Orbite), which is being developed by the French space agency CNES, is the first Primary Frequency Standard (PFS) specially designed for operation in space. PHARAO is a main instrument of the ACES (Atomic Clock Ensemble in Space) mission. ACES is being developed by ESA and the payload will be installed on-board the International Space Station. The mission is based on comparisons with ground based clocks to perform fundamental physics experiments: gravitational redshift measurements, analysis of the stability of the fundamental constants and anisotropy of light. Planned duration of the mission is 18 months with a possible extension to 36 months. The frequency accuracy requirement for PHARAO is less than 3 x 10 -16 and the expected frequency stability is 10 -13 Tau -1/2. An engineering model of PHARAO has been constructed and fully tested to validate the clock architecture. Two sub-systems for the flight model FM) have been delivered: the cesium tube where the atoms are manipulated and the microwave source which generates the 9.2 GHz signals. The other sub-systems, the laser source and the computer, will be delivered this year. Some performances tests have been performed on the microwave source and on the cesium tube assembled with the other EM subsystems. The whole FM clock will be assembled in 2013.

PHARAO flight model: optical on ground performance tests

“…Gasc (1) , A. Ratsimandresy (1) , S. Béraud (1) , F. Buffe (1) , P. Torresi (1) , Ph. Larivière (1) , V. Bernard (1) , T. Bomer (2) , S. Thomin (2) , C. Salomon (3) , M. Abgrall (4) , D. Rovera (4) , I. Moric (4) , Ph. Laurent (4) .…”

“…A complete description of the setup and its operation is given in [2]. The PHARAO clock includes 4 subsystems: the laser source provides laser beams at 852 nm to the cesium tube to manipulate the atoms.…”

“…The number of ISS passes over a European ground station is 5 per day. The clock signal is obtained from the combination of two atomic clocks: a cold cesium clock PHARAO as a primary frequency standard [2] and an active hydrogen maser as a freewheel oscillator. The comparison with earth based clocks is performed by two way time transfer links operating in the microwave domain (MWL) and in the optical domain (ELT).…”

PHARAO laser source flight model: Design and performances

“…The mission is dedicated to fundamental physics through the time and frequency comparisons between the space clock and ground based clocks 2,3 . The clock signal of the space segment is generated from the combination of the PHARAO clock and an active hydrogen maser 4,5 . The expected performances in space are frequency accuracy better than 3×10 −16 and frequency stability of 10 −13 τ −1/2 , where τ is the integration time in seconds.…”