NASA’s Mars 2020 mission will have an autopilot that helps guide it to safer landings on the Red Planet.Credit: NASA/JPL-Caltech

The view of the Sea of Tranquility rising up to meet Neil Armstrong during the first astronaut landing on the Moon was not what Apollo 11 mission planners had intended. They had hoped to send the lunar module Eagle toward a relatively flat landing zone with few craters, rocks and boulders. Instead, peering through his small, triangular commander’s window, Armstrong saw a boulder field—very unfriendly for a lunar module. So the Apollo 11 commander took control of the descent from the onboard computer, piloting Eagle well beyond the boulder field,to a landing site that will forever be known as Tranquility Base.

“There had been Moon landings with robotic spacecraft before Apollo 11,” said Al Chen, entry, descent and landing lead for NASA’s Mars 2020 mission at the Jet Propulsion Laboratory in Pasadena, California. “But never before had a spacecraft on a descent toward its surface changed its trajectory to maneuver out of harm’s way.”

Chen and his Mars 2020 colleagues have experience landing spacecraft on the Red Planet without the help of a steely-eyed astronaut at the stick. But Mars 2020 is headed toward NASA’s biggest Martian challenge yet. Jezero Crater is a 28-mile-wide (45-kilometer-wide) indentation full of steep cliffsides, sand dunes, boulders fields and small impact craters. The team knew that to attempt a landing at Jezero—and with a rover carrying 50% more payload than the Curiosity rover, which landed at a more benign location near Mount Sharp—they would have to up their game.

“What we needed was a Neil Armstrong for Mars,” said Chen. “What we came up with was Terrain-Relative Navigation.”