Fillable Printable Template for Scientific Poster
Fillable Printable Template for Scientific Poster
Template for Scientific Poster
Motivation
With the goal of landing high-mass cargo or
crewed missionson Mars,NASAhas been aiming
todevelopnew thermal protection technologies
with enhanced capability and reducedmass
comparedtotraditional approaches.
[5]
Astudy was
conducted on a dual layer thermalprotection
system (TPS) toidentify sensitivities in
performance touncertainties inmaterial properties
and aerothermalenvironments.Aperformance
metricwhich isindependentof the system
construction was developed inorder todirectly
comparethe resultsofthe traditional, dual layer
and eventually, flexible thermalprotection
systems.
Quantifying
Performance
One ofthe primary goals ofthis study was to
develop a metric toquantify andcompare the
performance ofnot justa dual layer ortraditional
TPS, but any thermalprotectionsystem.The
purpose ofdeveloping such a performancemetric
istoassessTPSdesign efficiency while including
characteristics ofthe trajectory rather than simply
using the masses ofthe systems.Inorder to
capture theability of a thermalprotection system
inregardtoboth the trajectories itcan fly and the
mass required todo so, a new TPSperformance
metricwas established.This metric, Specific Heat
Load (Q
SP
),isa ratioof the total integratedheat
load seen bythe TPS tothe required areal mass to
successfullyfly that trajectory while protectingthe
vehicle.
Performancevs. TotalIntegrated
Heat Load
When looking atresults from only one reference
node, asinFigure 7, one can seehow changes in
each variable impact the performance oftheTPS.
However, when this data isshown along with data
from other heating conditions,conclusionsabout
the relationship between heatload, overall
performance, andsensitivity can bedrawn. In
Figure 8, this data isshown inthe same form asin
Figure 7, withthe performance variationsfor due
toeach variable displayed.InFigure 9, the Root-
Sum-Square ofthe all the sensitivitiesfor each
heating node isplotted topresent a sense ofoverall
variabilityinthe system performance asa function
of heat load.
Performance Characterization, Sensitivity and Comparison
of a Dual Layer Thermal Protection System
Literature cited
1) K.T. Edquist, et. al.“Aerothermodynamic Design of the Mars
Science Laboratory Heatshield,” AIAA Paper 2009-4075. AIAA
Thermophysics Conference, San Antonio, Texas, June 2009.
2) J. Heinemann, et. al. Silica Impregnated Refractory Ceramic
Ablator (SIRCA) Arc Jet Test Report,” November 2006.
3) Y.K. Chen & F.S. Milos, “Ablation and Thermal Response
Program for Spacecraft Heatshield Analysis,” Journal of
Spacecraft andRockets, Vol. 36, No. 3, 1999, Pp. 475-483.
4) “Entry, Descent and Landing Systems Analysis Study: Phase
1 Report”, NASA/TM-2010-216720
5) M.K. McGuire, “Dual Heat Pulse, Dual Layer Thermal
Protection SystemSizing Analysis and Trade Studies for Human
Mars Entry Descent and Landing,” AIAA-2011-343-463
6) Wright M., “CEV Thermal Protection System (TPS) Margin
Management Plan,” NASA-ARC, C-TPSA-A-DOC-7005, Rev.
2.0, Nov. 12, 2009.
Fig. 1.Schematic ofthe
Dual Layer TPS
construction.From top to
bottom:ablator, insulator
(LI-900shuttle tile), Room
TemperatureVulcanized
(RTV) adhesive, a strain
isolation pad(SIP), a
second RTV layer, anda
titanium alloy backshell
Ablator
LI-900
Insulator
RTV
SIP
Ti Alloy
Fig. 3. Three step sizing process showing heat load
experienced by the vehicle vs. time, the layer being
sized in the material stack, and the constraining
allowable temperature for each step.
TPS Sizing Approach
Todetermine the required thicknessofeach layer
for a given node on the vehicle, a three step sizing
process was usedforthe dual layer system.First,
only the entry portionof the trajectory was run
with the insulator asthe only protectingmaterial
ensuring that the RTVreaches exactly its
allowable temperature (560 K). Next, keeping this
thicknessofthe insulator, the entire aerocapture
and entry trajectory issimulated with anablator on
top ofthe insulator. Inthis case, the ablator is
sized such that the maximum temperature ofthe
insulator surface isequal toitsmaximum specified
temperature(1700 K for LI-900).Finally, the
whole trajectory issimulatedagain with the
optimized thicknessofthe ablatornow remaining
constantwhile the insulator isresized until its
thicknessis again optimalfor keeping the RTV
maximum temperature atits threshold.
Trajectory Investigated
The test case used for thisstudy consisted ofa mid
L/D rigidaeroshell vehicle on a dualheat pulse
trajectory.The first pulse would slow the vehicle
from itshyperbolicapproach trajectorytoa
parking orbitvia aerocapture within Mars’
atmosphere.Followinga long on-orbit cool off
period, the vehiclewould then perform anentry
maneuverthrough the atmosphere and down tothe
Martian surface.
Fig. 2. Events leading from the hyperbolic approach
trajectory to touchdown on the Martian surface.
[3]
Fig. 4. Flow diagram depicting the computational tools
used and the flow of information in the sizing process
Computational
Approach
The ablation and thermal analysis toolused inthe
study was the Fully ImplicitAblationand
ThermalResponse Program (FIAT).Inorderto
carry out the high volume of input file
modifications,FIATsimulations,data
organization, andpost-processing, a custom
MATLAB™architecture was constructed around
FIAT.
Fig. 5. LI-900 Surface Temperature vs. Time for the
entry portion of the trajectory with varying PICA density.
The temperature peak seen after full ablation is
constrained to 1700 K to calculate optimal thickness of
the ablator.
Table 1. Summary of the areal mass variations due to
+/- 3 sigma changes in system variables. The
highlighted rows are the variables to which the system
was most sensitive to.
Results
The TPS sizing method was used toperform
sensitivity analyses and performance
characterizationon a Mid L/D vehicle atfive
different locations correspondingtofive different
values for the totalintegrated heat load seen
throughoutthe aerocapture + entry trajectory.
This wasdone with both dual layer andtraditional
TPS.
Fig. 6.The mid L/D rigid aeroshell vehicle with
contours of total integrated heat load shown. The five
circled heat loads represent the heat loads investigated
in this study.
[5]
Key Parameters
Animportantmilestone inthis study was the
identification of the variables towhich the areal
mass ofthe TPS was most sensitive.This
sensitivity analysis was conducted on a node subject
to85% of thetotal heat load for both TPS
constructions with PICA(Phenolic Impregnated
Carbon Ablator) as the ablator ineach case.
Dual Layer: Most important variables for 85% Heat Load
Rank
Layer
Sized
Trajectory
Variable
Min Areal Mass
(% of nominal)
Max Areal Mass
(% of nominal)
1
PICA
A&E
Surface Roughness
85.70%
114.14%
2
PICA
A&E
LI-900 Allowable Temp
81.90%
103.92%
3
LI-900
A&E
LI-900 Density
99.21%
100.81%
4
PICA
A&E
PICA Conductivity
99.46%
100.38%
5
PICA
A&E
PICA Density
99.68%
100.16%
Single Layer: Most important variables for 85% Heat Load
Rank
Layer
Sized
Trajectory
Variable
Min Areal Mass
(% of nominal)
Max Areal Mass
(% of nominal)
1
PICA
A&E
Surface Roughness
89.73%
110.27%
2
PICA
A&E
RTV Allowable Temp
95.48%
104.52%
3
PICA
A&E
PICA Conductivity
96.72%
103.28%
4
PICA
A&E
PICA Density
98.35%
101.65%
Fig 7. Variations in Q
SP
for variations in key parameters
from their -3σ to +3σ uncertainty values.Note that
surface roughness and allowable temperature induce
the greatest performance variation and the nominal
performance of the dual layer is 16% greater than the
traditional monolithic TPS.
Performance Sensitivities
After identifyingthe key sensitivities inthe
problem, the performanceofboth the duallayer
and traditional TPS was compareddirectlyusing
specific heatload, the parameter established inthis
study, asthe metric ofinterest.Boththe absolute
performance and its sensitivity tochanges inthe
variablespreviously identifiedwere investigated.
Below isa plot ofspecific heat load atthe 85%
node.Thered and green lines are the nominal
values for the dual and singlelayer constructions,
respectively.The verticalbars indicate the range
of variationinQ
SP
due to+/- 3 sigma changes in
eachof the variables of interest.
Conclusions
Astudy was conducted with a new duallayer
thermal protection system and the traditional
single layer TPS toidentify sensitivitiesin
performance touncertainties inmaterial properties
and aerothermalenvironments.Aperformance
metric,Specific HeatLoad, was developed in
order todirectly compare theresults ofthe
traditional, dual layer and eventually,flexible
systems. Overallsensitivityinperformance
increased with increasingheat load forboth
systemsaswellasabsolute performance. The
relative benefit ofthe dual layer system over the
traditional TPSissubstantial across the board,but
decreases asthe heatload increases.Atthelowest
heat load investigatedhere, the relative
improvement was 36% and atfullheatloadthe
benefit was 14%.
Fig 8. Variations in Q
SP
for variations in key parameters
- all nodes. Note that sensitivities increase with heat
load.
Fig 9. RSS Variations in Q
SP
for variations in key
parameters - all nodes. Note that the relative benefit of
the dual layer system is highest in the low heating
environment.
Cole D. Kazemba -Georgia Tech Space Systems Design Laboratory
Advisors: Dr. Robert Braun and Dr. Ian Clark
Co-Authors: Mary Kathy McGuire & Austin Howard – NASAAmes Research Center
