The ACES experiment will be situated on the Columbus External Payload Facility (CEPA) on the International Space Station (ISS).
ACES is an ESA scientific mission that provides a stable and highly accurate timescale that can be used for space-to-ground as well as ground-to-ground comparisons of frequency standards. This is achieved by combining the long term frequency stability of a laser cooled Caesium clock (PHARAO) with the short term stability of a Space Hydrogen Maser (SHM).
As a sub-contractor of Kayer-Threde Inc., the TZR develops hardware components as well as software for the FCDP and MWL systems of the ACES project.
The 100 MHz signals delivered by PHARAO and SHM are collected and compared in both frequency and phase.
In the FCDP part developed by TZR, from the acquired raw data of the atomic clocks, the frequency and phase values are determined that are needed for the measurement and control of the atomic clocks. Instantaneous values of phase and frequency and the phase noise spectrum are calculated and preprocessed for scientific analysis. Furthermore, housekeeping data for the system control are acquired and compiled.
These parts developed by the TZR do not run on a microprocessor as software, but the algorithms are implemented directly into an FPGA as hardware structures using the Celoxica ESL-Compiler Handel-C. This enables the parallel processing of independent algorithms with the full speed of the system clock as well as direct control of external hardware in real time.
MWL is a key element of the ACES mission. It ensures stable frequency transfer for direct comparison of atomic clocks both space-to-ground as well as ground-to-ground.
For the MWL, TZR develops software based on an EPSON CARD PC. To comply with the tight real time requirements, QNX is used as operating system. The tasks of the MWL are executed by independent processes that are managed and controlled by a specially developed task manager.