What went wrong: Long before the Spirit, Opportunity, and Curiosity rovers began exploring the surface of Mars, there were the Viking landers. In 1975, a pair of orbiter-lander spacecraft were launched to the red planet. The first lander, Viking I, safely touched down on July 20, 1976, followed shortly after by the Viking II lander. Expected to operate for 90 days, with a goal of photographing and analyzing the Martian surface and searching for signs of life, both landers (and their orbiters) continued to operate for years. Viking II's mission ended in April 1980 when its batteries failed. Viking I, however, was still going on November 19, 1982 when, in an effort to correct an issue with its own on-board batteries, mission controllers sent a series of commands with a new battery-charging sequence to the lander. Unfortunately, the new commands were written in the section of the lander’s memory used to store the pointing parameters for its high-gain antenna, preventing it from communicating with its controllers on Earth. After NASA engineers spent several months trying to reestablish contact, they gave up and declared the Viking I mission (and Viking program) over in March 1983.