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In-situ Exploration and Sample Return: Entry, Descent, and Landing

Entry, descent, and landing technologies ensure precise and safe landings.

Animation of MER Entry, Descent and Landing on Mars
Watch the animation MER Entry, Descent and Landing on Mars
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Entry, Descent, and Landing Innovations for the Mars Exploration Rover Mission:

Engineers faced the daunting task of slowing the Mars Exploration Rover spacecraft from about 12,000 miles per hour when they entered the atmosphere to about 12 miles per hour when they hit the surface of Mars.

Better Parachutes and Airbags

Inside of the world's largest wind tunnel at NASA's Ames Research center, the Mars Exploration Rover parachute is fully deployed.  The parachute went through many design iterations to perfect it for use by the rovers in January, 2004.  The rover chute is a narrow, conical design topped by minimal white fabric bands.
A test of the Mars Exploration Rover parachute.

For entry, descent, and landing, the mission inherited much from its martian predecessors, Viking and Mars Pathfinder. In order to slow the spacecraft down, the mission uses inherited parachute technology from the Viking missions of the late 1970s, which translated well for 1997's Mars Pathfinder mission. For the much heavier Mars Exploration Rover mission, the parachute's basic design remained the same but is 40% larger in area than Pathfinder's parachute.

The same cluster of airbags that softened Pathfinder's landing also cushioned the Mars Exploration Rovers. Twenty-four lobes that, when fully inflated, look like a massive bunch of white grapes, surrounded the lander, with the rover cradled inside. The airbags are made from a very durable, synthetic material called Vectran. On the human spaceflight side of NASA, this same material is used to make spacesuits. Again, the weight increase from 1997's mission called for a re-design of the airbags. Multiple drop tests proved that the additional mass was causing serious abrasions and tears. Engineers designed a double-bladder airbag that resisted these mission hazards, caused by the high speeds at which the rover package lands and rocks and other geological features it may encounter.

Looking like a giant cluster of white grapes or a bouquet of beach balls, a set of Mars Exploration Rover airbags sit, fully inflated, in a test facility.  The image, demonstrating how massive they are, features two men on a very large ladder that only makes it about three-quarters of the way up the airbags 18-foot (5.5-meter) height.
The fully inflated Mars Exploration Rover airbags stand about 18 feet (5.5 meters) high.
Against a stark white background in a cleanroom at Kennedy Space Center in Florida, the Opportunity rover is undergoing final preparations before launch.  The rover itself is not visible in this image because it is stowed inside its tetrahedral lander.  Packed tightly to the lander and just peeking out of protective silver fabric are the durable airbags that cushioned the rover landings.
The Opportunity rover undergoing final preparations before launch. The durable airbags are packed tightly against the tetrahedral lander.

Rocket Firings to Slow the Rover Down During Landing

This black and white image shows the pockmarked martian surface that Spirit encountered on its descent to Gusev Crater. The picture is taken at an altitude of 1,433 meters (about 4,701 feet). These images help the onboard software to minimize the lander's horizontal velocity before its bridal is cut, and it falls freely to the surface of Mars.
This image, taken by the descent image motion estimation system (DIMES) camera located on the bottom of the Mars Exploration Rover Spirit's lander, shows a view of Gusev Crater as the lander descends to Mars.

To slow the rover package before it hits the surface, three rocket-assisted descent (RAD) motors were designed for use if necessary. A radar system on the lander was able to detect distance from the surface. When the craft were about 2.4 kilometers (or about 1.5 miles) above the surface, the radar system alerted the Descent Image Motion Estimation Subsystem (DIMES). This camera took three pictures of the ground about four seconds apart and automatically analyzed them to estimate the spacecraft's horizontal speed. Moments later, a secondary propulsion system that was new to the Mars Exploration Rover mission fired during Spirit's descent. As predicted, Gusev Crater winds were fierce and moving Spirit from side to side, impeding a safe landing. The Transverse Impulse Rocket System (TIRS) counteracts horizontal movement, thereby making the craft more stable for landing. Windy conditions were not predicted for Opportunity's Meridiani Planum landing site, so Opportunity did not fire its TIRS system.

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