To go from hypersonic space capsule to naked, wheels-down  rover, "the vehicle reconfigures itself seven times," said mechanical-systems engineer Tommaso Rivellini, who helped design the landing procedure for Curiosity, formally known as the Mars Science Laboratory.

(Pictures: Mars Rover's "Crazy" Landing, Step by Step.)

"There are many things that have to go right. If any one thing goes wrong, we've pretty much lost the vehicle," added Rivellini of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

Among those make-or-break moments, two stand out as particularly likely to keep engineers on the edge of their seats, Rivellini and JPL spokesperson Steve Ebelhar said.

(Related: "Sky Show Sunday—Planets to Align for Mars Rover Landing.")

After Curiosity—encased in upper and lower heat shields—breaches the