An additional Academy study, chaired by Francis S. Johnson of the University of Texas at Dallas and published in 1971, was even more specific: “An extensive study of the outer solar system is recognized by us to be one of the major objectives of space science in this decade. This endeavor is made particularly exciting by the rare opportunity to explore several planets and satellites in one mission using long-lived spacecraft and existing propulsion systems. We recommend that [Mariner-class] spacecraft be developed and used in Grand Tour missions for the exploration of the outer planets in a series of four launches in the late 1970s.” Thus the stage was set to initiate the Outer Planets Grand Tours. NASA’s timetable called for dual launches to Jupiter, Saturn, and Pluto in 1976 and 1977, and dual launches to Jupiter, Uranus, and Neptune in 1979, at a total cost over the decade of the 1970s of about $750 million. A necessary step was to obtain from the scientific community the best possible set of instruments to fly on the spacecraft. Following its initial internal studies, NASA turned for its detailed scientific planning to an open competition in which any scientist or scientific organization was invited to propose an investigation. In October 1970 NASA issued an “Invitation for Participation in the Mission Development for Grand Tour Missions to the Outer Solar System,” and a year later it had selected about a dozen teams of scientists to formulate specific objectives for these missions. At the same time, an advanced spacecraft engineering design was carried out by the Caltech Jet Propulsion Laboratory (JPL), and studies were also supported by industrial contractors. In fiscal year 1972, plans called for an appropriation by Congress of $30 million to fund these developments, leading toward a first launch in 1976. Even as the scientific and technical problems of the Grand Tour were being solved, however, political and budgetary difficulties intervened. The Grand Tour was an ambitious and expensive concept, designed in the enthusiasm of the Apollo years. In the altered national climate that followed the first manned lunar landings, the United States began to pull back from major commitments in space. The later Apollo landings were canceled, and in fiscal year 1972 only $10 million of the $30 million needed to complete Grand Tour designs was appropriated. It suddenly became necessary to restructure the exploration of the outer planets to conform to more modest space budgets.