In the same period NASA carried out studies of two possible orbiter and probe missions. Working through the Ames Research Center, a scientific panel chaired by James Van Allen explored the adaptation of the Pioneer 10 and 11 spinning spacecraft to carry a probe to Jupiter and to carry out an orbiter mission emphasizing magnetospheric studies. William B. Hubbard of the University of Arizona chaired a JPL-based panel investigating the use of a Mariner-class fully stabilized spacecraft similar to Voyager to carry out a satellite-oriented orbiter mission. In 1976 these concepts were combined in a study, again chaired by Dr. Van Allen, of a Voyager-type orbiter with probe-carrying capability. This mission concept was given the name JOP, for Jupiter Orbiter Probe, and lead responsibility was assigned by NASA to JPL, with Ames carrying out the design of the probe.
In 1977, as Voyager activity was building toward autumn launch, a struggle was underway in Washington to obtain approval for the new Jupiter orbiter and probe mission. Budgeting authority was requested in the President’s Fiscal Year 1978 budget, but only after extensive testimony and several Congressional votes was the mission approved. The official new start for JOP, soon to be renamed Galileo, was set for July 1, 1977, and the scientific investigators and their instruments were selected in August.
At JPL, many members of the Voyager Team made a smooth transition to the Galileo Project. Much of the knowledge that had gone into the design of the Voyager spacecraft and its subsystems was now incorporated into Galileo. Similarly, at Ames the knowledge gained from the design of the Pioneer Venus probes, which were launched to Venus in 1978, a year after Voyager launch, was applied to design of a Jupiter probe. Among the individuals who brought their Voyager experience to Galileo were John Casani, who left the position of Voyager Project Manager to become Galileo Project Manager, and Torrence Johnson of the Voyager Imaging Team, who became Galileo Project Scientist.
The investigations of Jupiter and its system planned for the Galileo Project represented substantial advances over those carried out by Voyager. In part, this was the result of new spacecraft capabilities, particularly the atmospheric entry probe. It also represented increasing sophistication in scientific instrumentation over the seven-year interval between the selection of the payloads for the two missions.