The first major step in the L-SAT programme was the publication by ESA in 1979 of the report ESA/EXEC (79) 3, (known as the ‘Blue Book’) which identified the market potential for a ‘large’ communication spacecraft and many of the essential features required to service the market needs. One of these features was the desirability for a multi-purpose platform which is now the basis of the overall L-SAT programme and the prime objective of the L-SAT 1 mission.