... This implies that the scientific output be much larger than that from modern ground based observations in the same scientific field. ... In order to obtain a full picture of the variable structure of such objects with the very high angular resolution it is necessary to build in future multi-element space systems similar to ground arrays. ... 30,000 km) for objects within = ? ... structure and motion of extragalactic sources as a result of their lensing by extragalactic objects . ...