MEDLI2, the Sensors That Monitored the Perseverance Rover’s Landing on Mars – News – All About Circuits

Last week, NASA successfully landed the Perseverance rover in theJezero Crater on Mars.

Because NASA's key goals with this mission are to acquire data on the unknowns of Marsatmospheric conditions, landscape, and microbial life, for instanceNASA outfitted the rover with a host of sensors, many of which are commercial-off-the-shelf components.

One kit of sensors on Perseverance's heatshield, known as the MEDLI2, is designed to measure the entry, descent, and landing (EDL) of the rover to better aid future missions.

We recently discussed the design challenges of powering the Perseverance rover from afar. But flight sensors experience their own challenges during space travel and landing.

In space, sensors need to survivefluctuating extreme temperatures, random vibrations, shock, vacuum, and ionizing radiations. For these reasons, components purpose-built forspacecraft must be tested and qualified by performing applicable environmental tests.

Inertial measurement units (IMU), gyroscopes, magnetometers, thermocouples, and pressure transducers are commonly-used sensors in deep space probes. NASA engineers must conduct extensive environmental and lifecycle testing to validate their reliability and ruggedness for the space environment. Typically, the systems are also designed conservatively with safety margins and backup/redundant units in place to increase reliability and minimizerisk.

Designing and manufacturing space-grade avionics can be notablydifferent from commercial products. For instance, printed circuit boards cannot use pure tin-based solderin the vacuum ofspace, which could induce catastrophic mechanical stress. Further, tin-based solder mayproduce "tin whiskers," which are electrically-conductive and can cause arcing.Tin whiskers can be especially hazardous inspacecraft without the ability toreplace the PCBs once the payload launches.

Still, NASA was able to use some commercial components in MEDLI2 without consequence.

MEDLI2 is the second version of NASA'sentry, descent, and landing instrumentation. This instrumentation package includesthree types of sensors located on the backshell and heatshield of Perseverance, including 17 pressure transducers, 17 thermal plugs, and 3 heat flux sensors. Its purpose is to gain data on critical aerodynamic, aerothermodynamic, and thermal protection system (TPS) performance parameters during the EDL.

Previouslyduring the MSL mission, the original MEDLI did not measure heat flux in the backshell, so flight data for this phase was among the many firsts with this new mission. The new MEDLI can collect data on:

This data will allow researchers to compare flight data with predicted data and update analytical models.

Heat flux sensors are vulnerable to high mechanical and thermal stress, which can severely affect their functionality. MEDLI2tested commercially-available heat flux gauges for accuracy and survivability. The candidates for the sensor kitincluded Gardon gauges, a thermopile, and Schmidt-Boelter gauges.

NASA performedbenchtop tests (environmental tests with aerothermal loads) on thefunctionality and ecological impact of each of these gauges. The engineers ultimately chose Schmidt-Boelter gauges because of their performance during testing.

Hypersonic stagnation pressure is measured using a pressure transducer for the 035,000 Pa range that spans the entire test period, including the peak dynamic pressure environment.

One of the key findings from MEDLI was that the hypersonic pressure transducers do not provide sufficient accuracy at lower pressures during supersonic flight. Therefore, in MEDLI2,it was necessary to include a separate set of supersonic transducers that are accurate over the 07000 Pa range. Another pressure transducer is located on the vehicle's backshell to measure low pressures of 0-700 Pa.

How exactly did the MEDLI2 fare during Perseverance's entry last week? NASA reports that thesensors successfully indicated heating and pressure dynamics as the entry vehicle passedthrough the Martian atmosphere. MEDLI2 continued collecting data after the spacecraft reachedpeak heating (up to 1300C) and peak pressure. During the final 100 seconds of the entry, the vehicle remainedin the supersonic flight phase.

From the wind speed, the MEDLI2 pressure transducers then collected data on direction and vehicle performance.MEDLI2 usedmany othersensors to gain more relevant data based on the missing details from past missions as well. NASA hopes insights obtained from this mission will eventually drive the design of crewed missions to Mars.

JPL (Jet Propulsion Laboratory) recently stated that some of the high-definition cameras used in this mission were commercial-off-the-shelf (COTS) parts, which opens the possibility of commercial sensors being used in future missions. It's possible that NASA maybalance radiation-hardened and COTS components in other future projects as well.

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MEDLI2, the Sensors That Monitored the Perseverance Rover's Landing on Mars - News - All About Circuits