Article 2 The programme referred to in article 1 above shall be broken down into two phases, a definition phase which has already been started and a design, development and construction phase. 1. The purpose of the definition phase (sub-phases B 1-B 3) of the Spacelab programme is to establish the configuration of the Spacelab in the light of the requirements of the users and to define the corresponding sub-systems. The results available at the end of sub-phase B 2 will serve as a basis for the preparation of a technical proposal and a development plan, together with a detailed cost analysis and an estimate of the cost of the design, development and construction phase. 2. The elements for the detailed analysis referred to in paragraph 1 of the present article shall be available to the Participants by 1 August 1973 and will also be notified to the other member States of the Organisation. 3. The decision to proceed to the design, development and construction phase shall be taken in conformity with the provisions of article 5 below.