The Mars2020 entry vehicle is currently being developed by NASA to safely land its next rover on the Martian surface in 2021. The vehicle will be protected from entry aeroheating using three different TPS materials: PICA tiles on the forebody, SLA-561V on the backshell and Acusil-II on the parachute close-out cone (PCC) and its backshell interface plate (BIP). Mars2020's entry vehicle and TPS design is identical to the Mars Science Laboratory, NASA's last Mars lander; therefore, the purpose of this study is to assess the adequacy of the existing TPS design and thickness for Mars2020 predicted environments. This study focuses on sizing and margin assessment of Acusil-II TPS on the PCC and BIP. The methodology and analysis techniques that were used for assessing thermal margins are reviewed. Analysis assumptions and limitations are discussed in detail. Thermal sizing is performed at different locations and results are presented

Beck, Robin

Edquist, Karl

Hwang, Helen

Mahzari, Milad

White, Todd

Williams, Joseph

Wise, Adam

NASA Technical Reports Server

National Aeronautics and 
Space Administration
Entry Systems and Technology Division
Ames Research Center
Sizing and Margins Assessment of 
the Mars2020 Acusil-II Thermal 
Protection System
Milad Mahzari, Robin Beck, Joseph Williams*, Todd White, Helen Hwang
NASA Ames Research Center
*Analytical Mechanics Associates, Inc.
Karl Edquist, Adam Wise
NASA Langley Research Center
12th AIAA/ASME Joint Thermophysics and Heat Transfer Conference
2018-06-25 1
https://ntrs.nasa.gov/search.jsp?R=20180006860 2019-08-31T17:56:18+00:00Z
Outline2
• Mars2020 entry vehicle overview
- Need for TPS sizing
• PCC/BIP overview
• Heating environments
• TPS sizing methodology
- Analysis locations
- Margining process
- Sizing assumptions
• Sizing results
• Summary and conclusions
2
Introduction
• Mars2020 EDL sequence and entry 
vehicle design will be very similar 
to Mars Science Laboratory (MSL)
- Build-to-print with minor changes
- No change to the three Thermal Protection 
System (TPS) materials and thicknesses
- PICA on heatshield
- SLA-561V on the backshell
- Acusil-II on Parachute Closeout Cone 
(PCC) and Backshell Interface Plate (BIP) 
• Demonstrate that the as-built 
thickness of TPS materials is 
sufficient to withstand Mars2020 
aerothermal environments
- Perform TPS sizing as was done for MSL 
and show that the as-built thickness is 
greater than sized thickness
- Update environments and analysis 
assumptions as needed
- This talk focuses on Acusil-II sizing on 
PCC/BIP
- Heatshield and backshell sizing showed 
as-built PICA and SLA thicknesses have 
plenty of margin
3
MSL Entry Vehicle and Cruise Stage
PCC/BIP Overview
• BIP is the primary aeroshell structure that interfaces 
with the descent stage, cruise stage and parachute 
support structure 
• PCC houses the parachute assembly, multiple 
antennas and includes various closeouts for interfaces 
between aeroshell, rover and cruise stage
• Complex geometry, surface features and varying stack 
of substructure materials
• Aluminum doubler was installed on the windside of 
PCC in the regions of high heating
4
Acusil Installed on MSL PCC
PCC/BIP with TPS
PCC/BIP without TPS
Windside
Trajectory and Heating Environments
• TPS stressing trajectory (15-TPS-01)
- High entry velocity early in the arrival period
• Convective heating is simulated using NASA Langley’s CFD code 
LAURA (Laminar, non-catalytic)
- Impact of catalycity and turbulence quantified separately and accounted 
for in margins 
• Radiative heating is simulated using NASA Langley’s radiation 
code HARA (new for Mars2020)
• Primary simulations are done without antenna Radomes
- A few solutions are obtained on a grid with antenna Radomes
• MSL simulations are leveraged to quantify impact of RCS thruster 
plume impingement on PCC/BIP
- Peak convective heat flux is augmented for 8 seconds (estimated total 
firing time) 
5
Heat Pulse Augmentation due to 
RCS Plume Impingement
RCS Plume Impingement on PCC/BIP
Margined Heat Load from LAURA/HARA Simulations (No Radomes)
RadiativeConvective Combined
Windside
Need for Sizing at Many Locations
• We need to perform TPS sizing at multiple locations to ensure that as-built 
Acusil thickness is sufficient
- Varying aeroheating conditions
§ Significant radiative heating that peaks at a different location than convective heating
- Local heating augmentation due to RCS thruster plume impingement
- Complex geometry and features, varying Acusil-II thickness (smooth OML) 
- Varying substructure material stack and thickness
- Different bondline temperature limits 
- 1D modeling tools and validated 1D material models
6
Complex Geometry and Substructure Stack Margined Heat Load
Sizing Cases
• Investigated a total of 16 sizing 
cases
• PCC Cone (4 cases)
- Cone windside
- Cone leeside
- PUHF antenna
- Megacutter
• Radomes (4 cases)
- TLGA Radome
- Two points at TLGA base
- PLGA Radome
• BIP (3 cases)
- Leeside near PCC
- Leeside near backshell
- RCS augmentation location
• PCC Lid (5 cases)
- 1 case for the region with full 
thickness of substructure
- 4 cases for the region with tapered 
substructure
7
Margin Process
• Various independent sources of uncertainty are RSS’ed in a three-branch sizing process to 
avoid stacked conservatism
• True Factor of Safety (FOS) can be calculated for the as-built Acusil thickness
- As-built FOS = (As-built thickness– Manufacturing Tolerance) / Baseline Thickness
8Reference: Wright et al., JSR 2014
Sizing Assumptions
• Sizing is performed using NASA Ames ablative material response code 
FIAT (v3.1.1)
- Location-specific material stack
• Heat flux predictions from LAURA/HARA solutions are curve fitted in time 
and applied directly as surface heating in FIAT
- Convective heating margin: 3.0x (accounting for turbulence, uncertainties, biases)
- Radiative heating margin: 1.47x
• Acusil thermal response model updated based on limited absorptivity 
data
- Radiative heating was assumed negligible in MSL analysis
• Thermal response models for the various substructures (metallic and 
composite) and adhesives developed by MSL
• Initial temperature of 35 C for PCC 
and BIP
- Margined maximum value derived from 
thermal analysis (prior to entry)
• Bondline temperature limits mandated 
by structural requirements
- See table
9
Location Bondline Temperature Limit (℃)
PCC Cone 150
BIP 55
PUHF 180
Radomes 230
PCC Lid 230
Bondline Temperature Margin
• Bondline temperature margin (used in 3rd branch of sizing) is estimated by 
performing Monte Carlo analysis around FIAT
- 15,000-run Monte Carlo (16 Monte Carlo simulations for the 16 sizing cases)
- Material properties are varied in each run based on data and engineering judgement
- Max bondline temperature is recorded for each run; margin is calculated as 99.73% - mean (3σ)
10
Max. bondline 
temperature 
from each run
Nominal 
Environments
Applied 
Uncertainties
FIAT
Material
Stack
15,000 Monte Carlo Runs
Thermal Margin 
is set from
99.73% - mean
Material 
Response
Monte Carlo Inputs
Material Stack and Environments 
dependent on each location.
Gaussian Distribution 
used for inputs 
PCC Cone Sizing
• Windside Edge
- Highest combined heating location
- Aluminum doubler à more thermal mass but thinner TPS
• PUHF Antenna
- Reduced Acusil thickness but more thermal mass
- Higher bondline temperature limit
- Apply windside edge heating for sizing (conservative)
• Leeside Edge
- Highest heating for regions with maximum TPS thickness
- No doubler à less thermal mass but full Acusil thickness
• Megacutter
- Heating augmentation due to the RCS plume impingement
- Reduced Acusil thickness due to different substructure design
11
Leeside Edge
Windside Edge
PUHF
Megacutter
Sizing Case Windside Edge
Leeside 
Edge
PUHF 
Antenna
Mega
Cutter
Sized 
Thickness (cm) 0.93 1.58 0.76 1.24
As-Built 
Thickness (cm) 1.50 1.74 1.29 1.64
As-Built Factor 
of Safety (%) 79% 21% 90% 46%
Margined Combined Heat Load
TLGA and PLGA Sizing
12
• CFD solutions were obtained at 5 trajectory points 
on a grid with Radomes
- Conditions at maximum heat load location are used for sizing
• FIAT analysis is done using spherical geometry
• Radome structure is tolerant to a higher bondline 
temperature limit (230 C)
• Bondline temperature limit is enforced at parachute 
deploy for PLGA and backshell release for TLGA
• Sizing results show that the as-built thickness is 
more than adequate for Mars2020 environments
PLGA
TLGA
PLGA
TLGA
Convective Radiative Combined
Margined Heat Load Contours
Sizing Case TLGA PLGA
Sized Thickness (cm) 1.84 2.00
As-Built Thickness (cm) 2.50 2.50
As-Built Factor of Safety (%) 49% 37%
TLGA Base Sizing
• Need for sizing at TLGA base
- CFD solutions with Radomes showed areas of augmented 
heating at the base
- Radome structure overlaps with the PCC cone à reduced TPS 
thickness in that region
- Different substructure stack and bondline temperature 
requirements in this region (area with no Aluminum backing)
• Two sizing cases were investigated
- TLGA Lee Base: peak environments for the region with no 
Aluminum backing
§ 230 C temperature limit enforced at the top of Radome structure
- PCC Leeside of TLGA: peak environments for the region that 
has Aluminum backing
§ 150 C temperature limit enforced at the top of Aluminum
13
Sizing Case TLGA: Lee Base
PCC: 
Leeside of 
TLGA
Sized Thickness (cm) 0.60 0.83
As-Built Thickness (cm) 1.59 1.59
As-Built Factor of Safety (%) 199% 113%
Heat Load Contours Show Local Hot 
Spots at the Base of TLGA
BIP Sizing
• Peak heating occurs on the leeside
• RCS plume impingement near 3 o’clock 
location
• Varying Acusil thickness on the BIP from 
PCC to backshell
• 3 sizing cases were investigated
- BIP-near-PCC: peak environments for the thinnest 
region of Acusil
- BIP-near-Backshell: peak environments for the 
thickest region of Acusil
- BIP-RCS-Aug-Loc: local environments at the 3 
o’clock location augmented with RCS effects
14
BIP Cross Section Showing Varying 
Acusil Thickness
RCS Impingement on BIP Perimeter
Sizing Case BIP-near-PCC
BIP-near-
Backshell
BIP-RCS-
Aug-Loc
Sized Thickness (cm) 2.22 2.35 2.29
As-Built Thickness (cm) 2.45 3.97 2.45
As-Built Factor of Safety (%) 21% 87% 17%
PCC Lid
• Acusil thickness on the lid varies from 
0.74 cm to 1.06 cm
- Minimize lid mass due to parachute re-
contact risk
- Thickness was reduced in areas of low 
heating
• The lid substructure is made of 
Aluminum honeycomb and facesheet 
sandwich
- Tapered on the edge to only facesheet
• Doublers are applied on the tapered 
region for structural reasons
- Three zones of doubler thickness
- The region labeled as “outer” is guaranteed 
to have the thickest doubler configuration
- The region labeled as “inner” has the 
thinnest doubler configuration
• Varying material stack and thickness 
combined with varying environments 
necessitates sizing at multiple 
locations     
15
Lid Top View Showing Varying Acusil Thickness
Lid Side View Showing Substructure Tapering
Bottom View of Tapered Region Showing 
Three Thickness Zones for Doublers
Windside
Leeside
1.06 cm
0.74 cm
1.06 cm
0.74 cmCylindrical 
Ramp
Linear 
Ramp
Inner
Outer
PCC Lid Sizing
• Full Al-HC: Peak heating in the region with full 
thickness of Al-HC sandwich
- Acusil thickness varies from 0.74cm to 1.06cm
• Windside-Outer: Peak heating in the region with 
maximum thickness of doubler
- Acusil has its max thickness (1.06cm)
• Leeside-Inner: Peak heating in the region with 
minimum doubler thickness
- Acusil has its max thickness (1.06cm)
• Triangle-Outer: Peak heating in the regions that 
have max thickness of doubler and less-than-
max thickness of Acusil
• Triangle-Inner: Peak heating in the regions that 
have min thickness of doubler and less-than-max 
thickness of Acusil
16
Sizing Case Full Al-HC
Windside-
Outer
Leeside-
Inner
Triangle-
Outer
Triangle-
Inner
Sized Thickness (cm) 0.62 0.60 0.84 0.44 0.70
As-Built Minimum Thickness (cm) 0.74 1.06* 1.06* 0.74 0.74
As-Built Factor of Safety (%) 33% 98% 40% 90% 16%
PCC Lid Margined Heat Load Overlaid on 
Acusil and Substructure Thickness Boundaries
*Based on this analysis, Acusil as-built thickness was reduced from 1.06 cm to 0.96 cm to alleviate lid mass increase
Full 
Al-HC
Summary and Conclusions
• TPS sizing had to be performed at many locations due to:
- Varying aeroheating conditions
- Varying substructure material stack and thicknesses; Varying Acusil thickness
- Different bondline temperature limits
- Availability of only 1D thermal response model for Acusil-II
• Sizing results showed that the as-built Acusil-II on Mars2020 PCC and 
BIP has sufficient thickness to protect the underlying structure from 
aeroheating environments
- All locations have positive margin in case of future sizing threats
- Improved and more detailed analysis process compared to MSL
- Lid sizing was critical in reducing Acusil thickness to alleviate increase in lid 
mass due to parachute design changes
• Many sizing iterations were done to arrive at the final results shown 
in this talk
- Refined environments, techniques and assumptions to fit within the as-built 
thickness
• Multi-dimensional analysis capability and thermal response models 
would have significantly improved and simplified this sizing effort
- By taking advantage of in-plane conduction, we would have been able to 
show even greater sizing margins with multi-dimensional analysis
17
18
Questions?
Effect of Catalycity
• DPRL simulations were performed to 
determine the impact of catalycity on PCC and 
BIP environments
• A time-varying catalycity augmentation factor 
was derived by dividing the turbulent fully-
catalytic heating by the turbulent non-catalytic 
heating 
• Sizing was done at a few locations using the 
catalycity augmentation factor
- The impact on heat load and sizing is very small 
due to the fact that the augmentation factor 
approaches 1 around peak heat flux time
19
Time-varying Catalycity augmentation Factor
Heat Flux Ration from DPLR Simulations
Catalycity augmentation Factor Applied to the Heating 
Environment for PCC Leeside Sizing Location 
Blister Analysis
• Varying TPS thickness over the blisters
- Minimum TPS thickness is 2.6mm at the bottom of the blister
- Local minimum of 6mm near the top
• Heating augmentation up to 14 W/cm2 from RCS plume at the 3 o’clock 
blister
• MSL approach
- FIAT analysis was done assuming 2.5mm of Acusil using margined heating 
environments
- Peak bondline temperature of 360C was deemed acceptable
- Arcjet test was done to verify
- Measured temperatures at the backface of Aluminum was significantly lower than 
model predictions (conservative model)
• For Mars2020, we performed FIAT analysis and showed that blister 
bondline temperature is bounded by MSL analysis
20
Mars2020 FIAT Analysis with Margined EnvironmentsMSL FIAT Analysis with Margined Environments
National Aeronautics and 
Space Administration
Ames Research Center
Entry Systems and Technology Division


Sizing and Margins Assessment of the Mars2020 Acusil-II Thermal Protection System

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