Protection for the Deep Space Journey
If you think landing a spacecraft on another planet is hard, did you ever consider how that precious cargo is protected through the vastness of space? Lockheed Martin built the system, called an aeroshell, that has protected every Mars-bound NASA spacecraft.
The next mission heading to the Red Planet is Mars 2020, which will be one of the most challenging entry, descent, and landing (EDL) sequences ever attempted on Mars.
The rover will touch down in the treacherous Jezero Crater area, a region filled with boulders, rocky cliffs and shifting sand dunes. But ahead of the hazards of landing, the spacecraft must first survive a seven-month journey through deep space.
Protecting against the extremes of space travel is critical to the success of any mission. We successfully completed the flight hardware structure of the heat shield, validating the physical integrity with a final static test after exposing it to flight-like thermal conditions. The heat shield is half of the large and sophisticated two-part aeroshell that Lockheed Martin is designing and building to encapsulate NASA JPL’s Mars 2020 rover from the punishing heat and friction of entry through the Martian atmosphere.
About Mars 2020
Mars 2020 will spend at least two Earth years (one Mars year) around the Jezero Crater, once the site of an ancient lake. The mission’s goals include:
- Looking for indications of past microbial life
- Seeking evidence of past habitable conditions
- Investigating the region’s geographic diversity
- Drilling, collecting and caching core samples for future return
- Demonstrate technologies that could aid human exploration
Aeroshell Form and Function
Aeroshells consist of two parts: the heat shield and the backshell. Together, they encapsulate the spacecraft, including its science instruments, descent stage and other operational equipment. For example, the Mars 2020 rover will also hold the Multi Mission Radioisotope Thermoelectric Generator (MMRTG) used to power the lander once it’s on the surface of Mars.
The aeroshell’s toughest and main job begins with entry, decent and landing (EDL). The heat shield and Thermal Protection System (TPS) keeps the spacecraft from burning up in the extreme heat generated during the initial descent through a planet’s atmosphere. On Mars, those temperatures are around 2,700 degrees Fahrenheit and even higher depending on the weight of the spacecraft.
In addition, the heat shield’s aerodynamics serves as a “brake” to help slow the spacecraft. That’s essential for a spacecraft that enters the thin atmosphere of Mars at 12,000 mph (19,300 kph) or higher.
The cone-shaped backshell structure, which is also covered with TPS, protects the spacecraft during entry. In addition, the backshell supports the parachute and other mechanisms needed for EDL, including electronics and batteries, and has holes for the small engines that help keep the spacecraft oriented correctly. For Mars 2020, the backshell also provides support for the sky crane that will lower the rover to the surface of Mars for a soft landing.
The basic geometry and materials of the aeroshell haven’t changed much since the days of the Viking landers in the 1970s. That’s because the technology works.
The aeroshell (combined heat shield and backshell) consists of an aluminum honeycomb structure sandwiched between graphite-epoxy face sheets. The backshell and heat shield are held together with nine spring-loaded separation mechanisms.
With the Mars Science Laboratory (MSL) in 2012 and now Mars 2020, the spacecraft enters the Martian atmosphere at an angle. This type of entry requires a modification to allow for precision steering during EDL. Engineers added two types of mass ejection mechanisms on either side of the aeroshell. Ejecting the weights slightly tips the aeroshell and makes guiding the spacecraft easier.
Though similar, the Mars 2020 heat shield – the largest heat shield ever built for a robotic mission measuring at 14.9 feet (4.5 meter) – has a different ablative thermal protection material than what’s used on other smaller landers. Called PICA, or Phenolic Impregnated Carbon Ablator, this thermal protection system (TPS) proved its hardiness on the MSL rover mission in 2012. A gap filler is used between the PICA tiles that expands with thermal loads. A thin, aluminized mylar blanket on the inside of the heat shield protects the rover from the cold of deep space.
Lockheed Martin, along with NASA’s Jet Propulsion Laboratory, will integrate a sophisticated EDL instrument suite into the Mars 2020 aeroshell. MEDLI2, or Mars Entry, Descent and Landing Instrumentation 2, will monitor the Mars 2020 entry vehicle during entry and descent. The data the instruments collect on the aerothermal, thermal protection system and aerodynamic performance characteristics of the landing vehicle will help engineers improve future Mars missions.