The specific reason most of these instruments are used is because the provide information on one of these topics: information on the atmosphere, information on the planet's composition, information on the planet's magnetic sphere, or information on the planets particles. These instruments are also very light weight. Millions of dollars are spent to get these light weight materials to be used for these types of missions.
Cassini Instruments and Huygens Probe
Ulysses Space Mission and Instruments: