Additional studies of the atmosphere, similar to those of Voyager, can be carried out from the Galileo Orbiter. Television pictures, ultraviolet and infrared spectra, and measurements of the polarization of reflected light will all be obtained with the same scan platform instruments that are used to study the surfaces of the satellites. A full battery of fields and particles instruments is planned for the Galileo Orbiter. Many of these are direct descendants of Voyager instruments. In general, their capabilities have been improved, particularly their ability to determine the composition of charged particles. There is a steady progression from Pioneer to Voyager to Galileo: The early measurements were concentrated on particle energies, but more sophisticated instruments yield the composition of the ions and the details of their motion. Many of the advances expected from Galileo in magnetospheric studies result from the Orbiter’s ability to explore many parts of the environment of Jupiter. The Pioneer and Voyager spacecraft made single cuts through the magnetosphere, and often it was difficult to distinguish temporal from spatial effects. Galileo will repeatedly swing around Jupiter, sampling conditions at many distances from the planet over a time span of two years or more. In addition, it is planned to adjust the orbit of Galileo to swing out into the magnetotail, the turbulent region of the magnetosphere that stretches “downwind” from Jupiter for hundreds of Jupiter radii. No flybys can reach the magnetotail; an orbiting spacecraft is required. The Galilean satellites naturally will be a primary focus of Galileo science, particularly after Voyager. It is planned to have as many as a dozen individual encounters, most of them at much closer range than the Voyager flybys. To take advantage of these opportunities, the Galileo scan platform will carry two new remote sensing systems. [Illustration: The Orbiter section of the Galileo spacecraft will carry both remote sensing and direct measuring instruments for the study of Jupiter, its satellites, and its magnetosphere. Several remote sensing instruments—an imagery system, a near infrared mapping spectrometer, an ultraviolet spectrometer, and a photopolarimeter/radiometer—will be mounted on a scan platform. The particles and fields instruments will be on a spinning section of the spacecraft. The Orbiter is expected to operate for at least two years around Jupiter, providing one close flyby of Io and several each of Europa, Ganymede, and Callisto. [P-20772]]