The MEDLI2 sensor package on the "Perseverance" rover not only collects data for future missions; it also shows how to use commercial off-the-shelf components in the space .
Last week, NASA successfully landed the Persistent rover in the Jezero Crater on Mars.
A high-level description of how the Entry, Descent, and Landing (EDL) system can safely land on the surface of Mars. Image courtesy of NASA/JPL California Institute of Technology
because of NASA The main goal of this mission is to obtain unknown data about the atmospheric conditions, landforms and microbial life of Mars. For example, NASA equips the rover A series of sensors, many of which are off-the-shelf commercial components.
The set of sensors on the "Perseverance" heat shield is called MEDLI2 and is designed to measure the entry, descent and landing (EDL) of the lunar rover to better assist future missions.
Space design challenges
We recently discussed the design challenges of powering the Perseverance Mars rover from a distance. However, flight sensors also encountered their own challenges during space travel and landing.
In space, sensors need to survive extreme temperature fluctuations, random vibrations, shocks, vacuum, and ionizing radiation. For these reasons, components specifically manufactured for spacecraft must be tested and qualified by performing applicable environmental tests.
Inertial measurement unit (IMU), gyroscope, magnetometer, thermocouple and pressure sensor is a commonly used sensor in deep space probes. NASA engineers must conduct extensive environmental and life cycle testing to verify its reliability and durability in the space environment. Generally, the design of the system is also conservative, with safety margins and spare/redundant units to improve reliability and minimize risks.
The design and manufacture of space-grade avionics is significantly different from commercial products.For example, printed circuit boards cannot use pure tin-based solder in a vacuum, which can cause catastrophic mechanical stress. In addition, tin-based solder may produce "tin whiskers", which are conductive and may cause arcing. Once the payload is launched, if there is no ability to replace PCBs, tin whiskers are particularly dangerous in spacecraft.
Images of different shapes and characteristics of metal or tin whiskers. Image used by NASA
However, NASA is still able to use some commercial components in MEDLI2 without any consequences. Details of
MEDLI2
MEDLI2 is the second version of NASA's entry, descent and landing instrument. The instrument package includes three types of sensors, located on the rear housing and constant force heat shield, including 17 pressure sensors, 17 glow plugs and 3 heat flow sensors. Its purpose is to obtain data on key aerodynamics, aero-thermodynamics and thermal protection system ( TPS ) performance parameters during EDL.
collect flight data
Prior to the MSL mission, the initial Medley did not measure the heat flux of the rear shell, so the flight data at this stage is the first of many of this new mission. The new MEDLI can collect the following data:
- reconstruction of aerodynamic drag
- vehicle attitude
- on-site atmospheric density
- aerothermal heating
- turbulence transition
- depth TPS performance/TPS ablation_ul
MEDLI2 includes sensors, electronics and wiring harnesses installed on the Mars 2020 heat shield. Image used by NASA/JPL California Institute of Technology
These data will allow researchers to compare flight data with predicted data.And update the analysis model.
is ready to deal with heat flow
Heat flow sensor is susceptible to high mechanical stress and thermal stress, which seriously affects its function. MEDLI2 tested the accuracy and survivability of commercial heat flux meters. Candidates for sensor kits include Gardon gauges, thermopile and Schmidt-Boelter gauges.
MEDLI2 heat shield and the position of various sensors on the rear housing. Image used by NASA
NASA has conducted a bench test (aerodynamic heat load environmental test) on the function and ecological impact of each instrument. Engineers ultimately chose Schmidt-Port pressure gauges because of their performance in the test.
targets the hypersonic pressure sensor
The hypersonic stagnation pressure is measured with a pressure sensor, ranging from 0-35000 Pa, spanning the entire test cycle, including the peak dynamic pressure environment.
One of the key findings of MEDLI is that during supersonic flight, the hypersonic pressure sensor cannot provide sufficient accuracy at lower pressures. Therefore, in MEDLI2, it is necessary to include a set of separate ultrasonic sensors with an accuracy in the range of 0-7000 Pa. Another 700 Pa pressure sensor is located on the other low pressure sensor.
Learn MEDLI2 for future missions to Mars
How did MEDLI2 perform when the Perseverance debuted last week? NASA reported that the probe successfully displayed the heating and pressure dynamics when it entered the Martian atmosphere of . MEDLI2 continues to collect data after the spacecraft reaches peak heating (up to 1300°C) and peak pressure. In the last 100 seconds of entering, the aircraft was still in the supersonic flight phase.
Comparison of instrument sensors used in MEDLI and MEDLI2. The picture is used by NASA
Then, according to the wind speed, the MEDLI2 pressure sensor collects data about direction and vehicle performance. MEDLI2 also uses many other sensors to obtain more relevant data based on details lost in past missions. NASA hopes that the insights gained from this mission will ultimately drive the design of a manned mission to Mars.
JPL (Jet Propulsion Laboratory) recently stated that some of the high-definition cameras used commercial off-the-shelf (COTS) parts in this mission, which opened up the possibility of commercial sensor applications in future missions. In other future projects, NASA may also balance radiation resistance and COTS components.
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