Complex sentence: Budget constraints led to the merger of these projects into a single multi-national program in the early 1990s which is managed by the five participating space agencies, NASA, the Russian RKA, the Japanese JAXA, the European ESA, and the Canadian CSA.
Split into simpler sentences: Budget constraints led to the merger of these projects into a single multi-national program in the early 1990s. As mentioned it is a joint project between the five participating space agencies, NASA, the Russian RKA, the Japanese JAXA, the European ESA, and the Canadian CSA.