2015 marks 50 years of successful NASA missions to Mars starting with Mariner 4 in 1965. Since then, a total of 15 robotic missions led by various NASA centers have laid the groundwork for future human missions to the Red Planet. The journey to Mars continues with additional robotic missions planned for 2016 and 2020, and human missions in the 2030s.
⛊ Reference
50 Years of Mars Exploration, NASA.