Complex sentence: Aerobraking was first used during the extended Venus mission of the Magellan spacecraft to circularize the orbit in order to increase the sensitivity of the measurement of the gravity field.
Split into simpler sentences: Aerobraking was first used during the extended Venusian mission of the Magellan spacecraft. It was used to circularize the orbit of the spacecraft in order to increase the precision of the measurement of the gravity field.