MARINER 10- By the early seventies NASA had launched many many probes to the planets, but no one had yet visited tiny Mercury. NASA wished to do so but could not afford a Titan rocket needed for a direct approach. Instead, NASA took its highly successful Mariner Spacecraft Bus, added a sunshield and new cameras, and launched it on a stock Atlas-Centaur. Utilizing a "reverse" gravity assist, Mariner 10 flew by Venus, using its influence to slow the spacecraft and deflect it deeper into the Solar System for a Mercury flyby.Â