In spite of their apparent simplicity, however, the Voyager photopolarimeters were plagued with troubles almost from the moment of launch. A succession of mechanical failures on Voyager 1 led to the sticking first of the polarization wheel and then of the filter wheel. Even when repeated commands from Earth managed to free the wheels, their behavior was erratic. Ultimately an electronic failure also took place, leading to the reluctant decision to shut down the Voyager 1 photopolarimeter. On Voyager 2, similar mechanical problems greatly restricted the ability of the instrument to carry out its observations. The photopolarimeter thus was unable to contribute its share to unraveling the mysteries of Jupiter and its satellites. [Illustration: Charles W. Hord, photopolarimeter Principal Investigator] [Illustration: James W. Warwick, planetary radio astronomy Principal Investigator] Planetary Radio Astronomy The final Voyager remote sensing instrument is designed to measure radio emission from Jupiter and Saturn over a wide range of frequencies. These emissions, which sound like hiss or static if played through an audio receiver, result from interactions of charged particles in the magnetospheres and ionospheres of the giant planets. The planetary radio astronomy (PRA) Principal Investigator is James W. Warwick, an astronomer in the Department of Astro-Geophysics of the University of Colorado at Boulder. Eleven colleagues from the United States and France participate as Co-Investigators. Warwick has been studying Jupiter longer than any other Voyager Principal Investigator. He has monitored its radio emissions since the 1960s, and he played a central role in the discovery that Io influenced these emissions. Jupiter emits many kinds of radio radiation, ranging from bland thermal emission at short (centimeter) wavelengths, to synchrotron emission from energetic electrons at intermediate (decimeter) wavelengths, to erratic, extremely intense bursts at long (meter and decameter) wavelengths. The origin of these latter, nonthermal emissions constitutes one of the major unsolved problems of the Jovian system, and, more generally, of the physics of plasmas. One of the most important advantages of the Voyager PRA for studying Jovian radio emission lies in its proximity to Jupiter and hence its ability to locate the sources of different kinds of radio bursts.