When the spacecraft Kitty Hawk returned from Fra Mauro on February 9, 1971, the preliminary stage of lunar exploration ended. Project Apollo, severely truncated in the budget cuts of 1970, entered its last phase as NASA prepared to exploit the potential of earth-orbital manned flight. Skylab, an earth-orbiting laboratory scheduled for three long-duration missions between 1973 and 1974, would lay the groundwork. Shuttle, the new reusable spacecraft that carried NASA's hopes for a continuing manned program, had yet to receive the blessing of the Nixon administration's budget officials and appeared to be facing stiff opposition in Congress. After that, it would face a long period of development that seemed likely to push the next set of manned missions into the late 1970s or early 1980s.
Apollo's mission planners, looking ahead to only three more lunar missions, intended to make them as scientifically productive as the limitations of the system allowed. Modifications to the lunar module were under way and the first flight model of the lunar rover was undergoing tests. Landing sites for the next two missions had been selected and a group of sensors for remote sensing of the moon from lunar orbit was under development [see Chapter 12].