Enabling Distributed Low Radio Frequency Arrays - Results of an Analog Campaign on Mt. Etna

Abstract

Measurement of the red-shifted 21-cm signal of neu-tral hydrogen, and thus observing The Dark Ages is expected to be the holy grail of 21-cm Cosmology. A Radio-telescope to observe low radio frequency signals is needed, but radio interfer-ence on Earth and Earth's ionosphere blocking these signals are limiting science investigations in this field. Hence, such a radio-telescope composed of dozens to hundreds of antennas shall be deployed on the lunar far side. Such arrays are shielded from interference from Earth and Earth's ionosphere blocking very low radio frequencies is not present. Within the Helmholtz Future Topic Project Autonomous Robotic Networks to Help Modern Societies (ARCHES) we developed necessary technologies for autonomous robotic de-ployment of antenna elements, modular payload box design, and robust radio-localization to enable such distributed low-frequency arrays. In particular the antennas' positions must be determined accurately, such that the array can be operated as phased array. Our developments lead to the execution of an analog-demonstration on the volcano Mt. Etna, Sicily, Italy, in June and July 2022 over the course of four weeks. We successfully demonstrated the autonomous robotic deployment of antenna elements and our decentralized real-time radio-localization system to obtain the antenna element positions. Ad-ditionally, we showed a proof-of-concept operation of the phased array comprising four antenna elements: estimating the signal direction of arrival of a radio-beacon with unknown position, and the beamforming capabilities itself, for a carrier frequency of 20 MHz. In this paper, we give insights into our developed technologies and the analog-demonstration on the volcano Mt. Etna, Sicily, Italy. We show results of the successfully executed mission and give an outlook how our developed technologies can be further used for lunar exploration.