The Mars Science Laboratory (MSL) and its Curiosity rover – built by the Jet Propulsion Laboratory – will support the Mars Exploration Program’s strategy of “follow the water” and will have the science goals of determining whether the planet was ever habitable, characterizing the climate and geology of Mars, and preparing for human exploration.
The Mars Science Laboratory is the most ambitious Mars mission yet, and it involves a revolutionary terminal descent system utilizing an overhead powered-descent propulsion configuration and bridle assembly to gently land the large Curiosity rover directly on its wheels. This will be the first landed mission to ever fly such a configuration. The system architecture of the descent stage essentially separates the touchdown gear (whether wheels, legs, airbags, or pallets) from the terminal descent propulsion. Lockheed Martin designed and built the aeroshell system, which includes the composite load-carrying structure and the thermal protection system.
The aeroshell is a blunt-nosed cone that encapsulates and protects Curiosity during its deep space cruise to Mars, and from the intense heat and friction that will be generated as the system descends through the Martian atmosphere. Lockheed Martin has designed and built nearly every capsule flown by NASA for space exploration since Apollo, but none as large as the MSL aeroshell at about 15 feet (4.5 meters) in diameter. For comparison, the heatshields of the Spirit and Opportunity Mars Exploration Rovers measured 8.5 feet and Apollo capsule heatshields measured just less than 13 feet.
Designed to provide a more-precise landing than previous missions, the steering capability of the aeroshell is produced by ejecting ballast that off-sets the center-of-mass prior to entry into the atmosphere. This off-set creates lift that is used to guide the aeroshell using roll control and autonomous steering. This precision guidance will improve the accuracy of the landing ellipse from hundreds of kilometers to only 20 kilometers (12 miles).
The backshell is half of the large and sophisticated two-part aeroshell capsule. In addition to protecting the rover during cruise and descent, the backshell provides structural support for the parachute and unique sky crane, a system that lowers the rover to a soft landing on the surface of Mars. The biconic-shaped backshell is made of an aluminum honeycomb structure sandwiched between graphite-epoxy face sheets. It is covered with a thermal protection system composed of the cork/silicone super light ablator (SLA) 561V that originated with the Viking landers. SLA-561V has been used on the heatshields of all Mars landers mission of past, but this is the first time it will be used on the backshell of a Mars mission. Lockheed Martin used the proprietary ablator on the backshells of the successful Genesis and Stardust missions.
The heatshield is the forebody or ‘wind’ facing and the backshell is the lee side during entry of the aeroshell system. Because of the unique entry trajectory profile that has environments that are more extreme than previous Mars missions and will create external temperatures up to 3,500 degrees Fahrenheit, the heatshield uses a tiled Phenolic Impregnated Carbon Ablator (PICA) thermal protection system instead of the Mars heritage SLA-561V. This will be the first time PICA has flown on a Mars mission. Invented by NASA Ames Research Center, PICA was first flown as the monolithic thermal protection system on the heatshield of the Stardust Sample Return Capsule that is now in the Smithsonian Air and Space Museum.
Because of its large size, the aeroshell experiences tremendous entry loads primarily as a result of the dynamic pressures from the atmosphere. More specifically, the heatshield is subjected to approximately 105,000 pounds of compressive force distributed across its surface. This will cause the heatshield to deflect, creating thousands of pounds of bending and shear loads that must be reacted by the backshell.
The MSL Entry Descent and Landing Instrumentation (MEDLI) suite on the heatshield will measure heatshield temperatures, surface recession and atmospheric pressures as the aeroshell descends through the Martian atmosphere. MEDLI was developed by NASA Langley Research Center and NASA Ames Research Center.