The term 'MAIN FEATURE' can be solved by the crossword solutions GAS (3 letters) and CRUX (4 letters). GAS stands for 'Gravitational Attraction System', which is a system of satellites that are used to measure the gravitational pull of the Earth. CRUX stands for 'Central Reference Unit eXchange', which is a system of computers that are used to exchange data between different systems. Both GAS and CRUX are important components of the MAIN FEATURE of any satellite system, which is the ability to accurately measure and transmit data.