Mission phase: C/D

Period: since 2010

Initial TRL: 5

CSRC contribution: development and manufacturing of the EM and FM, support in integration

Partners: FJFI CVUT Prague, EADS Astrium GmbH

  ACES is an ESA ultra-stable clock experiment, a time and frequency mission to be flown on the Columbus module of the ISS (International Space Station), in support of fundamental physics tests. The mission objectives are of great interest both scientifically and technologically. The fundamental aspects of ACES deal with the physics of a cold atom clock. For the first time cold atoms will be operated in conditions which are not realizable on Earth in order to perform fundamental physics tests (relativity, possible drift of fundamental constants with time).

  At the same time, a number of new technologies needed by the science community, will be validated. Furthermore, the science community could take advantage worldwide of the ACES frequency stability by using ground stations to download the ACES time reference. These aspects will become increasingly important with future developments of navigation and positioning systems, new "matter-wave" inertial sensors and fundamental physics tests in solar orbit.

  ELT is an optical link that will be part of the ACES mission; the ELT flight model is developed by the Czech Space Research Center in cooperation with EADS Astrium and Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague. The on-board hardware of ELT consists of a CCR (Corner Cube Reflector), a SPAD (Single-Photon Avalanche Diode), and an event timer board connected to the ACES time scale. Light pulses fired towards ACES by a laser ranging ground station will be detected by the SPAD diode and time tagged in the ACES time scale. At the same time, the CCR will re-direct the laser pulse towards the ground station providing precise ranging information.

  The laser link will perform comparison of distant clocks, both space-to-ground and ground-to-ground, to frequency uncertainty levels well below 1 x 10-16 after a few days of integration time. Because of the high stability of the ACES clock signal, non-common view comparisons of clocks across intercontinental distances will be possible with ELT. The optical link also finds interesting applications in the distribution of the ACES time reference and in the synchronization of geodetic observatories. Combined with MWL performance, ELT will contribute to the characterization and cross-comparison of two different time transfer and ranging systems. Optical versus dual-frequency microwave measurements also provide useful data for the study of atmospheric propagation delays and for the construction of mapping functions at three different wavelengths.