The Mars Experiment

DROP ZONE NASA scientists have developed a better way to get from space to the Martian surface: a “sky crane.” Bob Sauls

On August 5, NASA’s Mars Science Laboratory will reach the outer edge of the Martian atmosphere. The 8,500-pound craft will have traveled 352 million miles at speeds of up to 13,200 mph, but its real work will have only just begun. Over the next seven minutes it will plummet through 80 miles of atmosphere, withstanding temperatures of up to 3,800°F, and guide itself to a sudden halt in the massive Gale Crater.

The MSL is the most ambitious Mars project to date. Its rover, named Curiosity, is twice as long and five times as heavy as its predecessors, Spirit and Opportunity. Its 150-square-mile landing zone is a third of the size of that of previous missions, requiring unprecedented accuracy. And whereas the previous rovers traveled less than a mile during their three-month-long primary missions, Curiosity will drive up to 12 miles over the course of a full Martian year, which lasts 687 Earth-days.

The MSL’s objective is to determine if Mars has—or ever had—the conditions necessary to support life. And it will do so with the most advanced set of scientific tools included on any off-Earth expedition. The MSL is more than just a Mars mission, though. It is also a test of several newly developed devices and techniques that will drive NASA projects for decades to come, from expeditions to the Jovian ice moon Europa to manned missions to Mars.

SEVEN MINUTES OF TERROR

Five of the 11 missions that have reached the Martian atmosphere have failed during the entry, descent and landing (EDL) stage, which is why engineers nicknamed the process “seven minutes of terror.” For the MSL mission, researchers rethought how spacecraft undertake EDL. They replaced ballistic entry with a more accurate guided-entry system and developed a new landing method—the sky crane—that could become standard on large rover missions.

CURIOSITY ROVER:  Bob Sauls

ENTRY 0 minutes
As it begins entry stage, the MSL consists of four major components: a back shell, a heat shield, a descent module and the Curiosity rover. Just before reaching the Martian atmosphere, the MSL will jettison two 165-pound tungsten weights from its back shell. The shift in mass will tilt the craft relative to its direction of travel, generating lift and allowing for some navigational control. The MSL will use eight thrusters on its back shell to guide itself toward the landing zone. Over nearly four minutes, friction will slow the MSL to 1,000 mph, at which point the craft will jettison six more weights, rebalancing its tilt angle relative to its motion.

DESCENT 4 Minutes
Once the MSL slows to 900 mph, it will deploy a 51-foot nylon-and-polyester chute. Within a minute and a half, the craft will decelerate to 180 miles an hour. When the MSL’s radar indicates that it is five miles above the planet’s surface, the heat shield will drop away, and the Mars Descent Imager, a high-definition camera, will begin shooting video that scientists will later use to study the landing site and the surrounding area. About 80 seconds after the heat shield falls away, the MSL’s back shell will detach, and with it the parachute, leaving only the descent module and Curiosity to continue the landing.

LANDING 7 minutes
About a mile above the surface, eight retrorockets on the descent module will begin firing, slowing the MSL to 1.7 mph over 40 seconds. At about 65 feet above the ground, and still traveling at 1.7 mph, the descent module will begin to lower Curiosity on nylon cords in a maneuver called the sky crane. A computer in the rover will send commands to the descent module through a wire “umbilical cord.” Once the rover reaches the ground, the descent module, 25 feet above, will release the nylon cords and perform a flyaway, crashing 500 feet to the north. The rover will then switch from EDL to surface mode and begin its primary mission.