end. At that time the Cassini mission, with the second Mariner Mark II spacecraft, would be in its Saturnian-tour phase. Spacecraft design Mariner Mark II class spacecraft developed for NASA by JPL were a new design approach advocated by NASA's Solar System Exploration Committee and were intended for flights in the 1990s to the outer planets and primitive bodies, such as comets and asteroids. CRAF was to be the first Mariner Mark II mission. The second mission, called Saturn Orbiter Titan Probe or SOTP (later Cassini–Huygens), was a Saturn orbiter with a probe designed to plunge into the atmosphere of the ringed planet's largest satellite, Titan. CRAF and SOTP were to use identical Mariner Mark II spacecraft, but each was to carry unique science instruments. Instrumentation All of the phenomena associated with comets were to be examined by CRAF's instruments. And because of the long duration of the planned rendezvous — almost three years — it was expected to fill in many of the major gaps in scientific understanding of the strange objects. The mission's scientific payload was selected in October 1986. It was to include: Cameras to photograph the nucleus, coma and tail, and changes that occur as Kopff orbits the Sun. Photos also would help scientists determine the comet's size and structure, the location of its poles, its rotation rate and geological structure. A surface penetrator-lander to be fired into Kopff's nucleus. The instruments aboard the penetrator-lander would collect a sample of cometary ices, study how they change when heated, and perform a chemical analysis of the gases released from the ice. The penetrator would bury its tip, which will contain a gamma-ray spectrometer measuring abundances of as many as 20 chemical elements, up to one meter (three feet) below the comet's surface. The penetrator was to carry accelerometers to determine Kopff's surface strength and its resistance to puncture, and thermometers to measure temperatures beneath the surface. The penetrator/lander would radio its findings to the spacecraft, which will then relay them to Earth. Mass spectrometers to study composition of gases released by the nucleus and the cloud of plasma (ionized gas) surrounding the nucleus. Dust counters, collectors and analyzers to capture samples of the comet's dust and study them on board. The information would help scientists determine the chemical elements that make up the dust and ice. In addition, the mass, size, shape and composition of individual dust