Complex sentence: On 27 August 1962, Mariner 2 was launched by Atlas-Agena B 179D, the first spacecraft conduct a successful flyby of another planet when it flew past Venus on 14 December 1962.
Split into simpler sentences: On 27 August 1962, Mariner 2 was launched by Atlas-Agena B 179D. It later became the first spacecraft conduct a successful flyby of another planet, when it flew past Venus on 14 December 1962.