two successful crewed lunar landings. Many Americans lost interest afterward, feeling that since the country had accomplished President John F. Kennedy's goal of landing on the Moon by the end of the 1960s, there was no need for further missions. There was also a growing sentiment that the billions of dollars spent on the space program should be put to other uses. The Moon landings continued through 1972, but the near loss of the Apollo 13 mission in April 1970 served to further anti-NASA feelings. Plans for missions up to Apollo 20 were canceled, and the remaining Apollo and Saturn hardware was used for the Skylab space station program in 1973–1974, and for the Apollo–Soyuz Test Project (ASTP), which was carried out in July 1975. Many of the ambitious projects NASA had planned for the 1970s were canceled amid heavy budget cutbacks, and instead it would devote most of the decade to the development of the Space Shuttle. ASTP was the last crewed American space flight for the next five years. The year 1979 witnessed the spectacular reentry of Skylab over Australia. NASA had planned for a Shuttle mission to the space station, but the shuttles were not ready to fly until 1981, too late to save it. Meanwhile, the Soviets, having failed in their attempt at crewed lunar landings, canceled the program in 1972. By then, however, they had already begun Salyut, the world's first space station program, which began in 1971. This would have problems of its own, especially the tragic loss of the Soyuz 11 crew in July 1971 and the near-loss of the Soyuz 18a crew during launch in April 1975. It eventually proved a success, with missions as long as six months being conducted by the end of the decade. In terms of unmanned missions, a variety of lunar and planetary probes were launched by the US and Soviet programs during the decade. The most successful of these include the Soviet Lunokhod program, a series of robotic lunar missions which included the first unmanned sample return from another world, and the American Voyagers, which took advantage of a rare alignment of the outer planets to visit all of them except Pluto by the end of the 1980s. China entered the space race in 1970 with the launching of its first satellite, but technological backwardness and limited funds would prevent the country from becoming a significant