Star Trek: Phase II was set to air in 1978 as the flagship series of a proposed Paramount television network, and 12 episode scripts were written before production was due to begin. This series would have put most of the original crew back aboard the Enterprise for a second five-year mission, except for Spock, because Leonard Nimoy did not agree to return; a younger full-blooded Vulcan named Xon was planned as a replacement, although it was still hoped that Nimoy would make guest appearances. Sets were constructed and several minutes of test footage were filmed. However, the risks of launching a fourth network and the popularity of the then-recently released film Star Wars Episode IV: A New Hope led Paramount to make a Star Trek film instead of a weekly television series. The first script of this aborted series formed the basis of Star Trek: The Motion Picture, while two others were eventually adapted as episodes of Star Trek: The Next Generation.