[Illustration: The Voyager spacecraft are among the most sophisticated, automatic, and independent robots ever sent to explore the planets. Each craft has a mass of one ton and is dominated by the 3.7-meter-diameter white antenna used for radio communication with Earth. Here Voyager undergoes final tests in a space simulator chamber. [373-7162AC]] CHAPTER 3 THE VOYAGER MISSION Genesis of Voyager Voyager had its origin in the Outer Planets Grand Tour, a plan to send spacecraft to all the planets of the outer solar system. In 1969, the same year in which the Pioneer Project received Congressional approval, NASA began to design the Grand Tour. At the same time, the Space Science Board of the National Academy of Sciences completed a study called “The Outer Solar System,” chaired by James Van Allen of the University of Iowa, which recommended that the United States undertake an exploration program: 1. To conduct exploratory investigations of the appearance, size, mass, magnetic properties, and dynamics of each of the outer planets and their major satellites; 2. To determine the chemical and isotopic composition of the atmospheres of the outer planets; 3. To determine whether biologically important organic substances exist in these atmospheres and to characterize the lower atmospheric environments in terms of biologically significant parameters; 4. To describe the motions of the atmospheres of the major planets and to characterize their temperature-density-composition structure; 5. To make a detailed study for each of the outer planets of the external magnetic field and respective particle population, associated radio emissions, and magnetospheric particle-wave interactions; 6. To determine the mode of interaction of the solar wind with the outer planets, including the interaction of the satellites with the planets’ magnetospheres; 7. To investigate the properties of the solar wind and the interplanetary magnetic field at great distances from the Sun at both low and high solar latitudes, and to search for the outer boundary of the solar wind flow; 8. To attempt to obtain the composition, energy spectra, and fluxes of cosmic rays in interstellar space, free of the modulating effects of the solar wind. The report also noted that “exceptionally favorable astronomical opportunities occur in the late 1970s for multiplanet missions,” and that “professional resources for full utilization of the outer-solar-system mission opportunities in the 1970s and 1980s are amply available within the scientific community, and there is a widespread eagerness to participate in such missions.”