Apollo Soyuz Test Project represented the beginning of cooperation in space between the world's superpowers. The goal was to achieve a linkup between spacecraft launched by both the United States and the Soviet Union. Differences in technology was a major obstacle which had to be overcome. Because of the change requirements for the Soyuz, there was more to ASTP than just Apollo 18 and Soyuz 19.
There were two unmanned Soviet craft, Cosmos 638 and Cosmos 672, both launched in 1974. Soyuz 16 was a manned mission to test the modifications which had been made. In 1976, Soyuz 22, which was a surplus ASTP spacecraft, was modified for geological research with a camera replacing the universal docking adapter.
The cost to the United States for ASTP was USD 245 million (1975 dollars).