In June 2011, in collaboration with the French Centre National d’Etudes Spatiales (CNES), the CODALEMA team suspended an autonomous station from a static balloon held 400 m above the Nançay Observatory.
A CODALEMA autonomous station in the sky.
The goal was to detect in temporal coincidence cosmic events between the ground (array of autonomous stations) and the station in the sky. Setting antennas in altitude above the ground array would allow sampling of the electric field along the complete shower path, thus giving a true and incomparable image of the shower development (a kind of 3D reconstruction of the showers), as well as an enlargement of the physical scope for the study of cosmic rays.
The idea we proposed to the CNES was to maintain similar autonomous radio detection stations over the existing ground field, at various altitudes allowing sampling of the electric field along the shower path. This suggested using captive balloons with a rather long link to the ground (from a few hundred meters to 5 km), each balloon handling several radio stations on this link (or line), every 200 m for instance. Several balloon lines should sample the volume above the existing antenna and particle detector arrays.
At that time, the CNES was reinvestigating its balloon activity for Earth and Space sciences. Our project was accepted and a first attempt of launching was made on the site of Nançay, at a limited (400 m) altitude. The technical constraints were many and strong, the challenge was great. During the first trial, a WiFi link had been exceptionally set up at the Nançay Observatory to collect data from the station in flight.
The balloon has been maintained over the CODALEMA array for 2 weeks, requiring the permanent presence of a CNES technical team and round-the-clock monitoring. Unfortunately, the first data collected were disappointing, as the data acquisition system of the suspended station was designed for the ground and as soon as it was elevated above the treetops, with its view of the horizon, the acquisition was completely saturated by far more numerous and powerful anthropogenic emissions than we had envisaged. Several technical problems related in particular to the balloon’s tethering and its use in stormy conditions also occurred, leading CNES to terminate the mission. In addition, the legal constraints for issuing the necessary authorizations for the release of several of these imposing balloons above the Observatory would probably have prohibited the deployment of the configuration initially envisaged. However, the experience feedback was important and consequent, both for the CNES and for the CODALEMA team, delighted to have lived this extraordinary scientific adventure.
A CODALEMA autonomous station in the sky.
