Credit: NASA/JPL-Caltech

How to tame that “seven minutes of terror” the NASA Perseverance Mars mission will experience during its plunge through the Martian atmosphere?

Part of the answer comes early in the deep dive to the Red Planet thanks to the Mars Entry Descent and Landing Instrumentation 2, or MEDLI2 for short.

Credit: Lockheed Martin

NASA’s Mars 2020 mission is expected to pierce the thin Martian atmosphere on February 18 at around 12,500 mph, producing skyrocketing temperatures of 2,370°F before the spacecraft’s parachutes unfurl and aerodynamics slow the descent.

Ejection of ballast before entry into Mars’ atmosphere will offset the aeroshell’s center of gravity and creates lift that is used to guide this hardware through roll control and autonomous steering.

MEDLI2 is integrated into the Mars 2020’s heat shield and backshell. That instrument suite is designed to assess the spacecraft’s aerothermal, thermal protection system and aerodynamic performance during entry, descent and landing (EDL). Moreover, data collected will help improve future Mars lander missions – including those transporting humans to the surface.

MEDLI2 sensors are installed on the Mars 2020 heat shield and back shell prior that will protect NASA’s Perseverance rover on its journey to the surface of Mars.
Credit: NASA

Two-part aeroshell capsule

The Mars 2020 aeroshell measures about 15 feet (4.5 meters) in diameter, compared to just less than 13 feet (4 meters) for the Apollo capsules. Lockheed Martin in Denver, Colorado has designed and built every aeroshell flown by NASA to Mars – but none as large as the Mars 2020 aeroshell.

The biconic-shaped backshell is half of the large and sophisticated two-part aeroshell capsule. It is covered with super light ablator, a cork/silicone thermal protection system that was created by Lockheed Martin and originated with the NASA Viking Mars landers in the 1970s.

David Scholz was Lockheed Martin’s principal engineer for the Mars 2020 aeroshell. “The particular material used on Mars 2020 is called SLA-561V, with the S-L-A standing for ‘super light ablator.’ It was developed for Viking all the way back in the 1970s and has been used on numerous heatshields and backshells since then,” he said.

Credit: NASA/JPL-Caltech

Sensor system

MEDLI2 sensors are installed on the Mars 2020 heat shield and back shell. They will measure the environment surrounding the spacecraft and the performance of thermal protection system material during the atmospheric entry phase of the Mars 2020 Perseverance rover mission.

There are three types of sensors that comprise MEDLI2: thermocouples, heat flux sensors and pressure transducers. A data acquisition and signal conditioning unit (the Sensor Support Electronics Unit) records the heating and atmospheric pressure experienced during entry and through parachute deployment, and the harnessing between the sensors and the Sensor Support Electronics unit.

MEDLI2 builds on the first MEDLI suite, which flew on NASA’s Curiosity rover mission that landed in August 2012. That instrumentation is again being applied to the heat shield, but in a different configuration to better measure the flow characteristics.

This time instrumentation is being installed on the backshell as well to collect measurements of the heating and the surface pressure to aid in reducing the large uncertainty applied to the current predicted results.

Future humans to Mars expeditions will tap into entry, descent, and landing data collected earlier by robotic landers.
Credit: Bob Sauls – XP4D/Explore Mars, Inc. (used with permission)

Making certain about uncertainties

“Uncertainties in our ability to model and predict the performance of an entry vehicle and the associated thermal protection system mean that large margins (100% to 200%) need to be included in our predictions to ensure the entry vehicle can survive the worst case conditions,” said Henry Wright, MEDLI2 project manager at NASA’s Langley Research Center in Hampton, Virginia.

MEDLI2 is a Game Changing Development project led by NASA’s Space Technology Mission Directorate with support from the Human Exploration and Operations Mission Directorate and the Science Mission Directorate.

The project is managed at NASA Langley and was implemented in partnership with NASA’s Ames Research Center in California’s Silicon Valley and the Jet Propulsion Laboratory in Pasadena, California.

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