The Mars Entry Descent and Landing Instrumentation 2 (MEDLI2) sensor suite will measure aerodynamic, aerothermodynamic, and TPS performance during the atmospheric entry, descent, and landing phases of the Mars 2020 mission. The key objectives are to reduce design margin and prediction uncertainties for the aerothermal environments and aerodynamic database. For MEDLI2, the sensors are installed on both the heatshield and backshell, and include 7 pressure transducers, 17 thermal plugs, and 3 heat flux sensors (including a radiometer). These sensors will expand the set of measurements collected by the highly successful MEDLI suite, collecting supersonic pressure measurements on the forebody, a pressure measurement on the aftbody, direct heat flux measurements on the aftbody, a radiative heating measurement on the aftbody, and multiple near-surface thermal measurements on the thermal protection system (TPS) materials on both the forebody and aftbody. To meet the science objectives, supersonic pressure transducers and heat flux sensors are currently being developed and their qualification and calibration plans are presented. Finally, the reconstruction targets for data accuracy are presented, along with the planned methodologies for achieving the targets

Bose, Deepak

Hwang, Helen H.

Karlgaard, Christopher D.

Kuhl, Christopher A.

Mahzari, Milad

Oishi, Tomomi

Pennington, Steven P.

Santos, Jose A.

Schoenenberger, Mark

Trombetta, Dominic

White, Todd R.

Wright, Henry S.

NASA Technical Reports Server

Mars 2020 Entry, Descent and Landing Instrumentation 2 (MEDLI2)

This paper introduces the Mars Entry Descent and Landing Instrumentation 2 (MEDLI2) concept for NASAs Mars 2020 mission. Mars 2020 is a flagship-class mission, scheduled for launch in 2020, with science and technology objectives to help answer questions about habitability of Mars as well as to demonstrate technologies for future human expedition. MEDLI2 is a suite of instruments embedded in the heatshield and backshell thermal protection systems (TPS) of the Mars 2020 entry vehicle. The objectives of MEDLI2 are to gather critical aerodynamics, aerothermodynamics and TPS (Thermal Protective System) performance data during the Entry Descent and Landing (EDL) phase of the mission

Oishi, Tomo

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Mars 2020 Entry, Descent, and Landing 
Instrumentation 2 (MEDLI2)
Helen H. Hwang1
MEDLI2 Principal Investigator
Deepak Bose,1 Todd R. White,1 Henry S. Wright,2 Mark Schoenenberger,2
Christopher A. Kuhl,2 Dominic Trombetta,2 Jose A. Santos,3 Tomo Oishi,4
Christopher D. Karlgaard,5 Milad Mahzari,6 and Steven P. Pennington7
1NASA Ames Research Center, Moffett Field, CA 
2NASA Langley Research Center, Hampton, VA
3Sierra Lobo, Inc., Moffett Field, CA
4Jacobs Technology, Inc., Moffett Field, CA
5Analytical Mechanical Associates, Inc., Hampton, VA
6Analytical Mechanical Associates, Inc., Moffett Field, CA
7Science Systems and Applications, Inc., Hampton, VA
June 2016
https://ntrs.nasa.gov/search.jsp?R=20190000379 2019-08-30T05:10:03+00:00Z
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Outline
• Intro
• Goals and Objectives
• Science Requirements
• Sensors and Development Challenges
– Pressure Transducers
– Thermocouples
– Heat Flux Sensors and Radiometer
• Sensor Testing: Qualification and Calibration
– Pressure Transducers
– Thermocouples
– Heat Flux Sensors and Radiometer
• System Architecture and Operation
• Reconstruction Targets
– Pressure Measurements
– Thermal Measurements
• Summary
1June 2016
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Background: Mars 2020 Entry Vehicle
• The Mars 2020 Entry, Descent, and Landing Instrumentation 2 (MEDLI2) 
is the EDL sensor suite for the flagship-class Mars 2020 mission
• The Mars 2020 mission is a rover mission utilizing investments in Mars 
Science Laboratory (MSL) technologies
– The entry vehicle, including the heatshield, is nearly “build to print”
– Entry environments will be similar, if not more benign, than for MSL
2June 2016
Backshell (SLA-561V)
Heatshield (PICA)
Parachute Close-out Cone 
(Acusil II)
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MEDLI2 Science Goals
• MEDLI2 goals are to acquire flight data, in order to:
– Define entry aerothermal environments and reduce aerothermal uncertainties
– Reduce entry vehicle thermal protection system (TPS) mass
– Improve future aerocapture and EDL performance
• MEDLI2 science objectives are to:
– Reduce design margins and prediction uncertainties for aerothermal environments 
and TPS response
– Reduce uncertainty and enable validation of the aerodynamic database
3June 2016
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MEDLI2 Science 
Objectives/Requirements
Aerothermal and TPS:
• Reconstruct forebody aerothermal heating
• Determine forebody TPS temperatures
• Reconstruct aftbody aerothermal heating
• Measure aftbody heat flux
Aerodynamics and Atmosphere:
• Reconstruct hypersonic and supersonic aerodynamic axial force 
coefficient
• Reconstruct wind relative vehicle attitude
• Reconstruct atmospheric density and winds
• Reconstruct vehicle Mach number
4June 2016
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MEDLI2 Expands Scope of 
Instrumentation
5June 2016
MEDLI on MSL (2012) MEDLI2 on Mars 2020
7 Hypersonic Pressure 
Transducers
7 Instrumented Plugs
• 4 Thermocouples
• 1 HEAT sensor
1 Sensor Support 
Electronics Box
1 Sensor Support 
Electronics Box
Pressure Transducers:
1 Hypersonic,
6 Supersonic, 
and 1 Backshell
11 Instrumented
PICA Plugs
6 Instrumented
SLA Plugs
3 Heat Flux Gauges
(including 1 Radiometer)
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MEDLI2 Instrumentation Layout
6June 2016
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MEDLI2 Forebody Pressure 
Measurement
• One pressure transducer to measure 
stagnation point pressure during hypersonic 
flight for reconstruction of atmospheric 
density, and CA
– MEDLI flight spare
– Target range: 1650 Pa – 35 kPa
– Target accuracy: 1% of reading
• Six pressure transducers measure surface 
pressure in the range relevant for supersonic 
flight
– Target range: 650 Pa – 7 kPa
– Target accuracy: 1% of reading
• The supersonic port locations are based on a 
constrained-optimization process to minimize 
error in the reconstruction of angles of attack 
and side-slip
7June 2016
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Supersonic Pressure Sensor Proof-of-
Concept
• Driving requirement:
– Heatshield during cruise phase 
estimated to be as low as −130 °C
– No commercially availably sensor can 
withstand the temperature range 
required
• Proof of concept sensor constructed
– Disassemble and remove foil-backed 
strain gauge
– Replace with COTS semiconductor 
piezoresistive unit
– 12-point calibration conducted
• Gain of more than 60 times of 
effective output signal compared to 
unmodified sensor
• Based on this concept, custom 
sensors will be assembled for flight
• Extensive testing and calibration 
scheduled for later this year
8June 2016
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MEDLI2 Aftbody Pressure 
Measurement
• Science Objectives: 
– Improve backshell pressure model
– Estimate backshell contribution to drag
• One pressure sensor in the afterbody
– Target Range: 40 – 700 Pa
– Target Accuracy: 4 Pa
• The current port location is defined 
based on available wind tunnel data 
and CFD analysis
• Further refinement of the location will 
occur based on the results of 
recently completed ballistics range 
test
9
From: John Van Norman
June 2016
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MEDLI2 Forebody Thermal 
Instrumentation
• Science objectives: Measure baseline heating, 
transition to turbulence, and turbulent heating 
footprint
• Forebody thermal instrumentation includes 11 
PICA plugs with embedded thermocouples
– Three plugs (1-3) with three thermocouples each to 
measure in-depth thermal response
– Eight plugs (4-11) with one thermocouple for 
aerothermal reconstruction
• A combination of Type R and Type K TCs
– Near surface:
• Type R: -50 to 1480 °C, for depths  < 0.1 inches
• Target Accuracy: ±15 W/cm2
– In-depth:
• Type K: -270 to 1260 °C, for depths ≥ 0.1 inches
• Target Accuracy: ±50 °C
10June 2016
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1920
MEDLI2 Aftbody Thermal 
Instrumentation
• Science objectives: 
– Aeroheating (both reconstructed and direct 
measurement)
– Measure radiative vs. total heating 
• Aftbody instrumentation includes 6 SLA-561V thermal 
plugs, 2 heat flux gauges, and 1 radiometer 
• Each plug will have 1 or 2 Type K thermocouple for 
aerothermal reconstruction
– Range: -270 to 1260 °C
– Target Accuracy: ±3 W/cm2
• Heat flux gauges will directly measure total heating
– Target Range: 0 – 15 W/cm2
– Target Accuracy: ±1 W/cm2
• Radiometer will measure radiative heating at location 
predicted to be have peak radiative component
– Target Range: 0 – 15 W/cm2
– Target Accuracy: ±1 W/cm2
11June 2016
SLA-561V Aerothermal Plug
Heatflux Sensor
Radiometer
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Heat Flux Sensors and Radiometer
12June 2016
• Heat flux sensors and radiometer are 
Schmidt-Boelter gauges
• Radiometer is a heat flux sensor with a 
sapphire window at the sensing element 
tip
– Sapphire blocks convective heating 
component
– Wide view angle (−150°) combined with 
highly radiating aftbody flowfield will lead to 
substantial signal
– Sapphire window optical properties will be 
measured
– Deposition of ablation products on window 
may alter readings—how large is this 
effect?
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Reconstruction Targets
13June 2016
Quantity of Interest Reconstruction Target Relevant Sensors 
Forebody Reconstructed Heating ±15 W/cm2 Forebody Thermocouples 
Boundary Layer Transition ±1 second Forebody Thermocouples 
In-depth Temperatures ±50 °C Forebody Thermocouples 
Aftbody Reconstructed Heating ±3 W/cm2 Aftbody Thermocouples 
Aftbody Heat Flux ±1 W/cm2 Heat Flux Sensor/Radiometer 
Axial Force Coefficient ±2% All Pressure Transducers 
Vehicle Attitude ±0.5 degrees Supersonic Pressure Transducers 
Atmospheric Winds ±10 m/s Supersonic Pressure Transducers 
Atmospheric Density ±5% Forebody Pressure Transducers 
Mach Number ±0.1 Forebody Pressure Transducers 
Aftbody Pressure ±4 Pa Aftbody Pressure Transducer 
 
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Pressure Measurements 
Reconstruction Methodology
• Algorithm is a weighted, least-squares (WLS) method to calculate best-
fit estimates of atmospheric conditions based on inertial state of 
vehicle and a model of surface pressure
• Linear covariance tool maps input uncertainties to nonlinear WLS 
algorithm to output uncertainties
– Predicts ability to meet science requirements for accuracy for angle of attack, 
density, Mach number, wind states, etc.
14June 2016
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Thermal Measurements Reconstruction 
Methodology
• Similar to MEDLI, plan is to utilize inverse techniques to reconstruct 
surface heating
– Whole-time domain least squares method that minimizes the sum of squared 
differences between TC data and predicted temperatures
– For MEDLI, surface chemistry calculations could not be included due to 
inaccuracies of the PICA equilibrium gas-surface chemistry model. Surface heating 
estimates assumed no recession
• Improvements to reconstruction methods include:
– Finite-rate chemistry model for PICA in CO2 (developed by NASA’s Entry System 
Modeling project) to estimate surface film coefficient as a function of time
– Characterization of variations in material properties in flight-lot PICA to better 
estimate heating (e.g., thermal conductivity)
– Merging multiple data sources for heating reconstruction in order to incorporate 
heat flux sensor measurements
15June 2016
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Summary (and some parting thoughts)
• MEDLI2 builds upon the success of MEDLI, and extends the scope of 
measurements significantly
– Aftbody measurements (pressure, near-surface thermal, direct heat flux, radiation)
– Supersonic pressure measurements 
– Increased number of forebody thermal near-surface measurements
• Reducing the design margins for future Mars missions will continue to 
be critical
– For small robotic missions, every kg counts, and being able to shave a few kg from 
the aftbody can result in increased delivered payload
– For human-scale missions, every kg counts, plus robustness is also an issue. Being 
able to predict how the entry vehicle will perform with greater accuracy will be 
necessary
• With a successful Mars 2020 mission, MEDLI2 will be able to impact 
future Mars missions by reducing margins, improving models, with a 
better understanding of the uncertainties and risk
16June 2016
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Questions?
17June 2016


Mars 2020 Entry, Descent and Landing Instrumentation 2 (MEDLI2)

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