The solar system is constantly bombarded by extremely energetic charged particles. These are called cosmic rays, although they are particles, not photons—“rays” are only produced when the particles strike something, such as the molecules of the Earth’s atmosphere, and give up their energy in a flash of x-rays and gamma-rays. One of the Voyager instruments is designed to study these galactic cosmic rays, particularly to look from beyond the orbit of Saturn, where the cosmic ray particles will be less affected by the solar magnetic field and solar wind than they are near Earth. The cosmic ray Principal Investigator is Rochus E. Vogt of the California Institute of Technology. Vogt has measured cosmic rays from the ground, from balloons, and from spacecraft for many years. During 1977 and 1978 he served as Chief Scientist at JPL, and then assumed the job of directing the physics, mathematics, and astronomy programs at Caltech. Among his six Co-Investigators is Ed Stone, the Voyager Project Scientist. Because the cosmic ray instrument was not directed principally toward measurements of the Jovian system, it is described only briefly. Like the LECP, it is designed to determine the energy and composition of individual electrons and positive ions. For electrons, the energy range is from 3 to 110 MeV, and for ions from 1 to 500 MeV per nucleon; the corresponding velocities are from about 10 percent to 99 percent of the speed of light. For the positive ions, composition can be determined for elements from hydrogen to iron. At Jupiter, this system could be used to determine the nature of the rare particles accelerated to very high energies in the Jovian magnetosphere. Radio Science The final Voyager science investigation is in the field of radio science. No special instrument was required for this study; rather, NASA selected members of a Radio Science Team who proposed investigations that could be carried out using the already existing spacecraft telecommunication system. The radio science Team Leader is Von R. Eshleman of the Center for Radio Astronomy at Stanford University. Eshleman is a radar physicist who has been interpreting spacecraft radio occultation data since the first such probe was carried out when Mariner 4 passed behind Mars in 1964. The Deputy Team Leader is G. Leonard Tyler, a colleague of Eshleman’s at Stanford. There are five other radio team members, four of them from JPL.