. A radio signal passes from the orbiting component of the instrument to the component on the comet surface and is then immediately transmitted back to its source, the idea being to establish a radio link that passes through the comet nucleus. The varying propagation delay as the radio waves pass through different parts of the cometary nucleus is used to determine the dielectric properties of the nuclear material. Many properties of the comet nucleus is examined as its overall structural homogeneity, the average size of the sub-structures (Cometesimals) and the number and thickness of the various layers beneath the surface. Instrument References: [KOFMANETAL0000] COS