The British Skylark (83) and French Centaure (64) were the main rockets utilised for the programme. The American Arcas (14), French Bélier (4) and Dragon (2), British Petrel (1) and German/Swiss Zenit (1) were also used. In total, the program oversaw the launch of 168 sounding rockets with an average success rate of 75%. During the course of the programme, the size and payload of the sounding rockets used by ESRO increased from 2.7 to 5.55 m (in length) and from 140 to 310 kg respectively.