The physics requirement (muon threshold, up/down discrimination, calorimetry measurement...) will constrain the geometry of the array. Different geometries such as strings and more elaborate structures have been studied.
One must also be able to make electrical interconnection of the many substructures and be able to recover part of the detector for servicing. A few electro-optical cables for the whole detector are required to handle the rate and to insure redundancy.
We will focus, in the present phase of the project, on a simple string-like substructure of optical modules a few hundred meter high equipped with a few tens of photo-multipliers. More elaborate substructures will be considered for the future.
The detector as a whole should be aligned and the relative position of the different optical modules has to be monitored with an accuracy of 20 cm (see ).