Design and concepts for a 12m optical communication antenna

A team of scientists and engineers led by MT-Mechatronics has conducted a study for an OCA (optical communication antenna) for ESA (European Space Agency) under contract No. 4000117525/16/D/MB, ESOC in Darmstadt, Germany. The antenna/telescope on Earth shall be able to establish communication with a Mars-orbiting probe. Daytime operation is required to ensure highest availably time regarding downloading valuable data. The other requirements ask for a telescope with 100m 2 effective aperture, able to operate at worse seeing conditions, with very low photon flux and at a Sun-Earth-Probe angle of 5 degrees. Operation wavelengths shall be both 1064 nm and 1550 nm. Due to these challenges, the telescope design has some similarities to the solar observation telescopes. However, solar telescopes are working with an abundant flux of photons, whereas the photon flux from the probe reaching the OCA is extremely low. The developed design concepts consider Sunshades and solar rejection filters at the entrance pupil. The telescope's design also minimizes penetration of the stray light. The major challenge is to minimize the influence of turbulence which adds scattering photons and could degrade SNR (signal-to-noise ratio). This paper describes the development of the optical layout of the OCA, the telescopes mount and enclosure, optical design, spectral filter, the detector type selection, the pointing and tracking system and includes some cost estimations. Final outcome of the study was providing a collection of design concepts which are essential guide-lines for the OCA manufacturing. Further studies particularly in regard of risks and costs reduction and deeper detail system designs are planned as next steps.