Article III: Phasing and Scheduling 1. Phase B studies Based on present schedules, the Phase B (preliminary design) studies of the SL are expected to be completed around the end of 1973. 2. Phases C & D At the completion of the Phase B studies, the parties will mutually agree on a design for immediate implementation and development by ESRO in Phases C & D (final design and hardware development and manufacture). 3. Completion schedules It is currently planned that the first operational space flight of the Shuttle will occur in late 1979. To permit adequate time for experiment integration, check-out and compatibility testing, the SL flight unit shall be delivered to NASA about one year before the first operational Shuttle flight. 4. Schedule changes Each party will keep the other fully and currently informed of factors affecting the schedules of the Shuttle and the SL respectively and their potential effects on flight readiness.