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MEDLI2 was one of the crucial technologies aboard the rover’s protective hull that helped document the entry, descent and landing of the spacecraft.
“Tango Delta, landing confirmed, Perseverance safely on the surface of Mars, ready to start looking for signs of past life.” For more than six years, the Mars Entry, Descent, and Landing Instrumentation 2 (MEDLI2) team have been waiting to hear these words.
On February 18, 2021, the Perseverance rover successfully landed and began its robotic exploration of the Red Planet. MEDLI2 was one of the crucial technologies aboard the rover’s protective hull that helped document the entry, descent, and landing (EDL) of the spacecraft.
The role of MEDLI2 was to collect critical data on the harsh environment as Perseverance entered the planet’s atmosphere. It included three types of sensors – thermocouples, heat flow sensors, and pressure transducers – that measured extreme heat and pressure upon input. It also contained electronic components and hardware to record the thermal and pressure loads experienced during entry and during the deployment of the parachute.
MEDLI2 used its pressure, temperature and heat flow measurements to determine the heating that occurred on the heat shield and rear shell. Together, these two components make up the aeroshell, which housed the Perseverance rover.
MEDLI2 was powered up five hours before the “7 Minutes of Terror” to land on Mars. This provided the initial conditions before input as well as time for the MEDLI2 electronics to stabilize the temperature before collecting critical input data. The MEDLI2 team was relieved to receive the indication that MEDLI2 was successfully activated. The team continued to monitor incoming data throughout this five-hour coastal phase prior to entry.
The majority of the MEDLI2 sensors and primary electronics were mounted on the March 2020 heat shield. Approximately 10 seconds after the deployment of the supersonic parachute, MEDLI2 was last de-energized because it had completed its work. As it is essential that the heat shield be separated to allow the Perseverance rover to be extracted from the entry vehicle, it was necessary that MEDLI2 be turned off a few seconds before separation to avoid any power supply problems. The harness connecting the heat shield and the rear shell was then severed by firing a pyro-cutter, and the heat shield was abandoned.
“We didn’t find any issues with the separation,” said Henry Wright, MEDLI2 project manager at NASA’s Langley Research Center in Hampton, Virginia. “The March 2020 heat shield has been cleanly separated from the March 2020 entry vehicle. The MEDLI2 material is clearly visible on the March 2020 heat shield as it falls towards the surface of Mars. Good job!”
All MEDLI2 data has been stored on Perseverance for return to Earth after a successful landing. Perseverance also returned what is known as real-time “critical event data” during the EDL. This data included a subset of the MEDLI2 data which allowed observation of what the entry vehicle was experiencing upon entry. Three days after the successful landing of Perseverance, the MEDLI2 data was sent back to Earth and the next phase of the project began: data analysis and performance reconstruction.
“The data returned was magnificent in its depth, complexity and clarity, which allowed the MEDLI2 team to make immediate and interesting observations,” said Wright.
The data collected from MEDLI2 also provides measurements that will be used to determine the properties of the atmosphere traversed by the entry vehicle from March 2020. MEDLI2 provides EDL observational data essential for understanding the remaining margin on the Perseverance input as well as data that will be used to improve models and prediction tools for future missions.
Further examination of the data
Heat shield insulation temperatures were recorded throughout the full entry phase and were in line with entry expectations. The maximum measured temperature of the insulation upon entry was 1,830 degrees Fahrenheit, or 1,000 degrees Celsius, which corresponds to an estimated maximum surface temperature of around 2,550 degrees Fahrenheit, or 1,400 degrees Celsius.
MEDLI2 also used its built-in thermocouples to determine the extent to which the protective insulation of the heat shield has burned, which is called ablation. All thermocouples survived the input heating pulse, indicating that the heat shield ablation was less than expected. This observation could be used to re-evaluate the amount of insulation needed on a heat shield to potentially reduce the overall mass of the input vehicle.
Surface pressures were also measured throughout the same phase with a peak heat shield surface pressure matching the team’s input predictions. MEDLI2 focused on heat shield surface pressure measurement to capture the full range of maximum surface pressures. The other six heat shield pressure measurements had a pressure range to emphasize conditions during supersonic flight regime (about five times the speed of sound on Mars thanks to the deployment of the supersonic parachute). This information helps to better understand the performance of the input vehicle when the impacts of variations in atmospheric density, winds, etc. are more pronounced. MEDLI2 pressure data will be used to improve the modeling approach for future EDL missions.
MEDLI2 included sensors on the rear shell of the March 2020 entry vehicle, an area that has had limited sightings. Surface pressure, insulation temperature and direct surface heating measurements included the aft hull sensor suite. Knowledge of the surface pressure at the rear of the input vehicle contributes to a reduction in the size of the landing footprint. The rear hull insulation temperature data was within initial predictions, which can be used to reduce modeling uncertainty. As with heat shield insulation, understanding the temperature performance of the rear shell insulation could lead to a reduction in the mass of the rear shell insulation. Direct measurements of the rear hull surface heating also help reduce the uncertainty of predictive models.
Now that the MEDLI2 team has its flight data and supporting data from March 2020, the MEDLI2 team will continue to analyze this data for the next six months.
Contacts for news media
Kristyn damadeo
NASA Langley Research Center, Hampton, Va.
757-755-0366
[email protected]
Andrew Good
Jet Propulsion Laboratory, Pasadena, California.
818-393-2433
[email protected]
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