The ET design study, supported by the European Commission from the May 2008 and the July 2011, delivered the conceptual design of a 3rd generation GW.
The ET design study has been organized in four technical working packages devoted to the major aspects of the design of a new GW observatory:

WP1: “Site Identification”

The main objectives were: Definition of the seismic requirements of an experimental site, selection between underground or surface site, definition of the requirements of the infrastructures, conceptual design of the main infrastructures and evaluation of their costs, site candidates listing.

WP2: “Suspension Requirements”

Main objectives: Definition of the requirements of the optics suspension in terms of seismic isolation, mechanical losses and thermal conduction. Conceptual design of the suspension.

WP3: “Topology Identification”

Main Objectives: Definition of the requirements in terms of quantum noise, identification of the detector topology, selection of the detector geometry.

WP4: “Astrophysics Issues”

Main Objectives: Definition of the detection capabilities requirements, Evaluation of the design driven Astrophysics potentialities of the detector, computational power requirements definition.