This course will cover an overview of the Entry Systems and Technology Division (TS) at NASA Ames Research Center (ARC) and descriptions of the extensive arc jet testing complex managed within the branch. After a quick look at the Earth and Planetary Entry projects supported by TS, along with the inventions and software developed within the division, a description of the entry environments to which thermal protection systems (TPS) are exposed will be discussed. The question of "How do we insure TPS survival?" will be answered with descriptions of the various test facilities across the agency and beyond and their applicability. The Ames Arc Jet Complex will then be described, starting with how an arc heater works, adding in the associated infrastructure required to run an arc heater, and the capabilities of each of the test tunnels. Finally, examples of TPS test articles will round out the course

Beck, Robin A.

NASA Technical Reports Server

National Aeronautics and 
Space Administration
Entry Systems and Technology Division
Ames Research Center
Arc Jet Testing
A Short Course
Presented by
Robin A. S. Beck
At TFAWS-2019
Newport News, VA
Aug 27, 2019
https://ntrs.nasa.gov/search.jsp?R=20190030274 2019-09-26T19:55:12+00:00Z
Outline
• Overview of the Entry Systems and Technology Division (TS) at 
NASA Ames Research Center (ARC) 
• Quick look at the Earth and Planetary Entry projects supported 
by TS and the inventions and software developed within the 
division
• A description of the entry environments to which thermal 
protection systems (TPS) are exposed
• How we insure TPS survival will be addressed with descriptions 
of the various test facilities across the agency and beyond and 
their applicability
• The Ames Arc Jet Complex will then be described
- how an arc heater works
- the associated infrastructure required
- capabilities of each of the test tunnels
• Examples of TPS arc jet test articles
2
Mission
3
Entry Systems and Technology Division (TS) at 
NASA Ames Research Center deals with 
Hypersonic entry into an atmosphere
Entry Systems & Technology Division
• Four branches under Entry Systems & Technology 
Division (Code TS) – D. Hash
https://www.nasa.gov/ames/exploration-tech/entry-systems
- Aerothermodynamics (TSA) – J. Hill
https://www.nasa.gov/archive2/content/aerothermodynamics-branch
- Thermophysics Facilities (TSF) – S. Eddlemon
https://www.nasa.gov/centers/ames/thermophysics-facilities-home
- Thermal Protection Materials and Systems (TSM) – M. 
Stackpoole
https://www.nasa.gov/content/thermal-protection-materials-branch
- Entry Systems & Vehicle Development (TSS) – K. Zarchi
https://www.nasa.gov/centers/ames/entry-systems-vehicle-development/index.html
4
TS Division Overview
• The TS division (Entry Systems and Technology Division) 
includes people who: 
- Help design spacecraft for different exploration missions
- Analyze the environments around a spacecraft
- Invent new materials that can protect a spacecraft
- Figure out how those materials will behave on a spacecraft and 
how thick they need to be
- Plan and perform tests on those materials and spacecraft designs 
to prove they will fly successfully
- Instrument vehicles in order to get flight data on the materials
- Build and launch demonstration vehicles
5
PHOENIX
NASP
X-33
X-34
X-37
SHARP 
B1 & B2  
MERCURY
GEMINI
APOLLO
SPACE SHUTTLE
PIONEER-VENUS
STARDUST & GENESIS 
MARS 
PATHFINDER
1960 1970 1980 1990 2000 2010 2020
BLUNT 
BODY 
CONCEPT* 
(1951)
ORION EFT-1 / 
EM-1 / DFI 
LOFTID
ADEPT SR-1
VIKING
GALILEO
MSL / MEDLI
PAET
COMMERCIAL CREW
MER
OSIRIS-REx
INSIGHT
M2020 / MEDLI2
NASA Entry Projects Supported by Ames
MARS  DS-2
MSR
* H. Julian Allen and Al Eggers, “A Study of the Motion 
and Aerodynamic Heating of Ballistic Missiles Entering 
the Earth’s Atmosphere at High Supersonic Speeds,” 
NACA-RM-A53D28, 1953 / NACA-TR-1381, 1958.
ORION TPS ADP
AFE
MARS 
SURVEYOR
SHUTTLE RTF
HEEET
6INSIGHT
1960 1970 1980 1990 2000 2010 2020
Blunt Body 
Concept* 
(1951)
NASA Ames Entry Systems Innovations 
TUFROC
PICA
SIRCAConstricted
Arc Heater
3DMATRCG
LI-2200
FRCI
AFRSI
AETB
TUFI
HEEET
ADEPT
FIAT
Advanced Entry 
Heating Simulator
Laser-Enhanced IHF
7
High Energy Heatshield Environments
Courtesy M. J. Wright 8
Backface
Temperature 
~250C)
Radiant heating 
from wake
(2000-6000 K)
(1000-3000 K)
How Do We Insure TPS Survival?
• We test!
• We get as many property measurements as possible
- Material compositions – virgin, char, pyrolysis gas
- Density, density degradation with temperature 
- Heats of combustion – helps to derive the heats of formation
- Specific heat vs temperature for virgin and charred material
- Thermal conductivity vs temperature for virgin and charred material
• Evaluate entry environments and test facility 
environments
• Try to match relevant environment parameters (𝑞𝑞,𝑝𝑝,ℎ, 𝜏𝜏) 
in test facilities
- Usually this must be done piece-wise
• Combine measured properties and thermal response 
during tests to develop material response model
• Predict response during entry 
9
Philosophy
• What is the test objective?
- Screening several candidate ablative materials for comparative 
performance
- Evaluating ablation performance over broad range of conditions
- Evaluating performance limits of a material (failure threshold)
- Developing data base for thermal modeling
- Developing data base for reliability assessment (design margin)
- Validating performance of material interfaces (gaps, seals, 
penetrations, etc.)
• The test objective dictates the test approach, and drives 
the selection of:
- Test facility
- Test article design
- Test conditions
- Instrumentation
- Post-test evaluation
10
Test Facilities - 1
Radiant Heating Facilities (JSC)
• Useful for evaluating insulation performance of 
complex TPS configurations
- Relatively low heat fluxes (<100 W/cm2)
- Large test articles
• Only meaningful if surface-boundary layer interaction 
effects are negligible, i.e., effects of surface catalycity, 
surface oxidation, transpiration, atmospheric 
composition, etc. are well-understood
- Primary objective is to evaluate heat conduction (2-D, 3-D)
- Must be cognizant of potential pressure effects on 
conduction
• Requires very accurate knowledge of:
- Heat flux distribution across test article (diagnostics)
- Spectral distribution of radiant energy (diagnostics)
- Spectral (and directional) optical properties of test material
 Can use surface coatings with known optical properties (if they 
won’t blow off)
• For complex test article geometry, must be aware of 
potential for shadowing
11
Test Facilities - 2
Radiant Heating Facilities -- CW and Fiber lasers 
(LHMEL)
• Primary application is to obtain very high heat fluxes not 
attainable in other ground test facilities
• Requires very accurate knowledge of:
- Heat flux distribution across test article (diagnostics)
- Spectral optical properties of test material at the laser wavelength
 Most materials are opaque at 10.6µm (CO2 lasers)
 Many materials are NOT opaque at 1.7 µm (Fiber lasers)
• Tests with small spots are misleading (cavity effects)
- Avoid spots smaller than ≈ 25 mm diameter
• Cannot simulate surface-boundary layer interaction effects
- Many facilities employ a (cold) cross-flow across the target area
 Primary purpose is to sweep ablation products out of the beam 
path, which is important to avoid complications of beam attenuation 
due to gas phase absorption
• Useful for studying potential spallation phenomena at very 
high heat fluxes
• NASA has developed mechanisms for thermostructural
testing (laser environments with specimens under load) at 
LHMEL 
12
Schematic of LHMEL Structural Panel Test
LOAD LOAD
LOAD LOAD
LASER
N2N2
HEEET
Composite
Gapfiller
Specimen
Graphite Shield
Loadpoints Loadpoints
N2 Spreader Bar
Fixed Frame
5
Test Facilities - 3
Radiant Heating Facilities – National Solar Thermal 
Test Facility
• Primary application is to obtain moderately high heat 
fluxes on very large specimens
- 100-ton capacity elevating module for lifting experiments to the 
top of the tower
- Water glycol cooling systems and air coolers to provide heat 
removal from experiments
- Rotating platform and shutter system to protect experiments 
while system sets up
• Requires very accurate knowledge of:
- Heat flux distribution across test article (diagnostics)
- Optical properties of test material at the solar 
wavelengths
• Cannot simulate surface-boundary layer interaction 
effects
- Can employ (cold) cross-flow across the target area
 Primary purpose is to sweep ablation products out of the beam 
path, which is important to avoid complications of beam 
attenuation due to gas phase absorption
- All tests at 1-atm, in air
13
1.0-m diameter heatshield tested 
by ARA at 150 W/cm2 for 200s
Test Facilities - 4
Combustion Facilities (LaRC)
• Useful for testing TPS materials in motor 
applications
- Rocket nozzles, combustor liners
- Well-suited for full scale systems-level tests
• Very limited utility for studying TPS performance in 
hypersonic flight at Mach > ≈ 7
- Cannot simulate many important environmental 
parameters
- Limitations in total temperature of combustion 
products (little flexibility)
 Maximum gas temperature set by theoretical 
combustion limits (≈ 2800 K)
- Chemical composition of test gases (gas-surface 
chemical reactions are not representative)
- Absence of dissociated species (due to gas 
temperature limits) precludes use of such facilities for 
studies of surface catalycity of oxidation
14
Test Facilities - 5
Arc Plasma Facilities (ARC, LaRC, AEDC, LCAT)
• Have been used for over 50 years to study TPS 
material performance
- Two classes:
 Lower enthalpy, high pressure, high heat flux (high β vehicles)
 Higher enthalpy, low pressure, low-moderate heat flux (lifting 
entry, aeroassist, aerocapture, planetary entry, etc. – low β
vehicles)
• Significant flexibility
- Pressure: nozzle geometry, test article design, gas mass 
flow rate
- Enthalpy: gas mass flow rate, electrical power
- Gas composition: most facilities operate with air, but tests 
have been conducted with N2, CO2, H2/He, etc. gas streams
• Amenable to sophisticated diagnostics
- Surface visibility (film or video), surface pyrometry, PLIF, 
etc.
• Capability to simultaneously simulate conditions 
representative of flight (e.g.,            ) is rare. Requires 
strategic test planning.
• Few can simulate time-varying conditions (trajectories)
pqH ,, 
15
AEDC H2 Test Chamber
Boeing LCAT Facility
Testing TPS for Extreme Environments
• Requires piecemeal testing at various facilities to cover 
the environments
16
NASA Ames ArcJet Complex
NASA Ames Research Center – 17 May, 2016
Thermophysics Facilities Branch
Entry Systems and Technology Division 17
TS Testing
• The Ames Arc Jet Complex has a rich heritage of over 55 years in 
Thermal Protection System (TPS) development for every NASA 
Space Transportation and Planetary program
- Apollo, Space Shuttle, Viking, Pioneer-Venus, Galileo, Mars Pathfinder, 
MER heatshield, Stardust, NASP, X-33, X-34, SHARP-B1 and B2, X-37 
WLE TPS, Orion heatshield development and MSL TPS
• The arc jets are used for the three major areas of TPS development: 
selection, validation and qualification
18
Proving the System – Arc Jet Testing
An arc jet produces an electrically heated, high speed gas 
flow onto a test article – matching key parameters of high 
speed entry from space into an atmosphere
19
How it works
• Under vacuum, add argon gas; connect a high-voltage (10 MW- 75 
MW) “car battery” across electrodes to breakdown argon; and we 
have a flow of electrons inside the arcjet tube.
• Air flow collides with electrons in this “lightening bolt”→ dissociated 
air at high temperatures (> 9000º F)
• Expand dissociated air out a nozzle to hypersonic conditions and 
into a chamber at altitude conditions matching peak heating
• When conditions are correct, insert test sample and see what 
happens!
20
Oh Yes, And All That Other Stuff
EJECTOR/
CONDENSER
DC POWER SUPPLY
ARC JET 
HEATER CORE
COOLING WATER
PUMPS & COOLING TOWERS
COMPRESSED AIR/Argon SUPPLY
CONTROLS, 
ENGINEERING, DATA 
ACQUISITION
TEST SAMPLE AND 
INSTRUMENTATION
STEAM 
PLANT
COMMON FACILITY INFRASTRUCTURE
21
Power supplies: 150 MW & 20 MW continuous
Steam Vacuum System: 10 lbs/sec, 0.1 psi
Steam Generator: 250 000 lbs/hr
Approximately 1.5 mi pipe/ductwork
Not pictured:
•Arc heater coolant circulation: 12 500 gpm
•High pressure air storage; 1.2M CF
•Independent 20 MW power supply
•Control and isolation systems
1 MW = 750 homes
TFD/20
AHF/20
Pollution Control
Ejector-Condenser System
Steam Generator SVS Cooling
IHF/60
PTF/20
150 MW Power Supply
GPF/100
NASA Ames ArcJet Complex Overview
Four Active Test Legs, One set of shared Utilities
Air compressors
22
Panel Test Facility
20 MW - TPS Panel Testing
Aerodynamic 
Heating Facility
20 MW - TPS Free Jet Testing
10 MW – TP3 (from JSC)
Interaction Heating
Facility
60 MW - TPS Free Jet and Panel 
Testing
Laser Enhanced 
Arcjet Facility
Adds up to 4 50-kW IR lasers to 
provide radiant flux to panels
2”x9” Turbulent Flow 
Duct
20 MW - TPS Panel Testing
23
IHF
• 60-MW Ames-designed constrictor arc heater
• Nozzle exit sizes from 76.2 mm (3”) to 1 m (36”)
• 3-arm fully programmable model insertion system, fully water-
cooled 
• Stagnation, free jet wedge, small sphere cones or flat panel 
test configurations
• Stagnation pressure from 1 to 600 kPa (0.01 to 6 atm)
• Heat fluxes from 0.5 to > 6000 W/cm2 (0.4 to >5200 Btu/ft2-s)
- As nozzle size and/or model size increases, heat fluxes decrease
- As model size decreases, 2- and 3-D effects make evaluation difficult
• Enthalpies 7 to 47 MJ/kg (3000 – 20,000 Btu/lb)
• Power supply capable of delivering 75 MW continuously and 
up to 150 MW for a 15 second duration
• Test times up to one hour demonstrated at lower conditions
24
LEAF
• Radiative laser heating facility added to the IHF
• 1 to 4 50-kW CW IR lasers can be used
- Provides up to 390 W/cm2 (~350 Btu/ft2-s) radiative heating on   
152 mm x152 mm (6” x 6”) wedge model or 100 W/cm2 (88 Btu/ft2-
s) on a 432 mm x 432 mm model (17” x17”)
• Nearly uniform across illuminated surface (variation < 
6%)
• Wavelength 1.07μm
25
AHF
• Air, Nitrogen and Oxygen gases
• 3 heaters available 
- 20-MW Ames-designed constrictor arc heater
- 20 MW Huels arc heater
- 10 MW constrictor arc heater (relocated from JSC)
• Nozzle exit sizes from 127 mm (5”) to 1016 mm (40”)
• Samples sizes up to 356 mm (14”) diameter or 660 by 660 mm (26” 
by 26”) wedge 
• Surface or stagnation pressures from 0.5 to 30 kPa (0.005 to 0.3 atm) 
dependent on the arc heater and nozzle
• Heat fluxes from less than 0.1 W/cm2 (0.08 Btu/ft2-s) on a flat plate, to 
over 300 W/cm2 (288 Btu/ft2-s) on a 102mm (4”) diameter 
hemisphere 
• 5-arm fully programmable model insertion system (limited by test 
model design) 
26
PTF/TPTF
• PTF
- 20-MW Ames-designed constrictor arc heater
- Semi-elliptic Mach 3.5 nozzle
- Test samples up to 355 mm by 355 mm (14-in by 14-in)
- -4 to +8 degree inclinations of the surface of test sample to the flow
- Run durations up to 30 minutes possible
- Cold wall, full catalytic heat flux from 0.6 to 40 W/cm2 (0.5 to 30 Btu/ft2-s)
- Surface pressures from 66 to 4700 Pa (0.0006 to ~0.05 atm)
• Truncated PTF (TPTF) 
- Shortens the PTF nozzle for higher surface conditions on smaller test 
articles
- 20-MW Ames-designed constrictor arc heater
- Semi-elliptic nozzle
- Test samples up to 100 mm by 100 mm (4-in by 4-in)
- -5 to +4 degree inclinations of the surface of test sample to the flow
- Cold wall, fully catalytic heat flux from 20 to 200 W/cm2 (18 to 180 Btu/ft2-s)
- Surface pressures to ~28 kPa (0.28 atm)
27
TFD
• Air or nitrogen gases
• Linde (Huels) free-length arc heater (12-MW)
• Test samples of 203 mm wide by 508 mm long (8” by 20”)
• Surface pressure from 2 to 15 kPa (0.02 to 0.15 atm)
• Cold wall heat fluxes from 2 to 70 W/cm2 (1.8 to 63 
Btu/ft2-s)
• Surface pressures to 28 kPa (0.28 atm)
28
Examples of Ground Test Articles
Stagnation 
(AHF or IHF)
• Arc jet test model samples
29
Panel (PTF)
Wedge
(AHF or IHF)
Small probe w/ 
multiple heating 
regimes (IHF or AHF)
• There are many test facilities that are necessary for 
evaluating the different aspects of the behavior of a 
thermal protection system during a mission
• But, to best understand materials in hypersonic flowfields, 
the arc jet test facilities provide the closest match to the 
environmental conditions (chemistry and physics) that 
TPS materials will face
• The capabilities vary from tunnel to tunnel, however, by 
combining their use, we can understand the material 
response over the extent of the mission parameters. 
30
Summary
WITHOUT US, YOUR HEATSHIELD IS TOAST
31
National Aeronautics and 
Space Administration
Ames Research Center – Silicon Valley
Entry Systems and Technology Division


Arc Jet Testing: A Short Course

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