NASA has successfully developed a new and innovative Heatshield for Extreme Entry Environments Technology, or HEEET, which, at a Technology Readiness Level (TRL) of 6, is ready for use in Ice Giant missions. HEEET is not just a replacement for the legacy full-density carbon-phenolic (FDCP) material, which was used in NASA's Pioneer-Venus and Galileo missions; it is also a more mass efficient and robust alternative, and a technology that has a sustainable manufacturing base. HEEET is a dual-layer, 3-dimensionally woven material. It has a dense outer layer, made of pure carbon fibers, that comes into contact with and protects against extreme entry environments. Below this layer is an integrally woven, lower density insulating layer, made of a blend of carbon and phenolic yarn, that reduces heat-conduction to the carrier structure. The present paper describes development of this material, its thermal, structural, and aerothermal testing, production of an engineering test unit at flight scale, and maturation for infusion into missions to various planetary destinations, with a focus on Ice Giant in situ missions. Finally, for representative entry velocities at Uranus and Neptune, and a range of entry masses and flight path angles, margined thicknesses of HEEET are computed. When the limits of heat fluxes and pressures that can be achieved in ground-test facilities, and loom limits, are imposed on these thickness estimates, it is shown that several atmospheric entry missions are possible at the two destinations.

Spatially-resolved nitric oxide (NO) planar laser-induced fluorescence (PLIF) rotational thermometry was performed on a Mach 5 non-equilibrium flow around a blunt-body specimen in the Hypersonic Materials Environmental Test System (HyMETS) arc-heat wind tunnel at the NASA Langley Research Center. Transitions within the (0,0) band in the A2Sigma+ - X2Pi system of NO were excited with a 10 Hz pulsed ultra-violet laser. A multi-line fitting algorithm was applied to the PLIF spectra and transitions were filtered based on an iterative method that maximizes thermometry accuracy. NO PLIF thermometry results are compared to non-equilibrium computational fluid dynamics (CFD) simulations reported in the literature. Differences between the experiment and CFD are quantified for the free-stream, post-shock, shear-layer, and expansion-fan regions of the flow. Potential sources of error, applicable to both the CFD and experiment, are discussed.

This poster provides an overview of the requirements, design, development and testing of the 3D Woven TPS being developed under NASAs Heatshield for Extreme Entry Environment Technology (HEEET) project. Under this current program, NASA is working to develop a Thermal Protection System (TPS) capable of surviving entry into Saturn. A primary goal of the project is to build and test an Engineering Test Unit (ETU) to establish a Technical Readiness Level (TRL) of 6 for this technology by 2018. Poster also discusses use of HEEET TPS for probe missions to the Ice Giants, Uranus and Neptune.

Ballistic coefficient range: 200–350 kg/m2 (in steps of 50 kg/m2) Inertial entry flight path angle range that covers deceleration loads between 50 and 200 g • Uranus: -16.5° to -36.5° Neptune: -16° to -26° • no pressure and/or heat flux constraints imposed Inertial entry velocity: Uranus: 23 km/s Neptune: 26 km/s Stagnation point convective heating estimates obtained from correlations based on freestream density and velocity; radiative heating likely to be small at both destinations All trajectories terminated at flight Mach number of 0.8 (heatshield jettison) • Step #2: Size HEEET using FIAT [4] to stagnation point aerothermodynamic environments estimated in Step #1 Planet-specific B’ tables for material thermal response, and a margins policy [5] that accounts for uncertainty in environments & material properties Thicknesses determined with: (a) initial temperature of -10°C, and (b) a maximum allowable back face temperature of 250 °C • Step #3: Adjust stagnation point sizing from Step #2 to margin against turbulent heating on the conical flank Flank heating can be as high as stagnation point heating, but at a lower (≈50%) pressure level – increased material recession Current solution: Scale up stagnation point recession layer thickness by 1.2, and scale down insulation layer thickness by 1.2 • Step #4: Add manufacturing margins to estimates of flank thicknesses (recession and insulation layers) Manufacturing margins: 0.51 cm for the insulation layer, and 0.38 cm for the recession layer References: [1] Hwang, H., et al., (2018), 15th IPPW, Boulder, CO, June 11–15. [2]Ice Giants: Pre-Decadal Survey Mission Study Report (2017), JPL D-100520. [3] Allen, G. A., Jr., Wright, M. J., and Gage, P. J. (2005) NASA/TM-2005-212847. [4] Milos, F. S. and Chen, Y.-K. (2013) J. Spacecraft and Rockets, 50(1), pp.137-149. [5] Mahzari, M. and Milos, F. (2018), 15th IPPW, Boulder, CO, June 11–15. Heatshield for Extreme Entry Environment Technology (HEEET) TPS for Ice Giants Probe Missions D. Ellerby§, T. Boghozian*, D. Driver§, J. Chavez-Garcia*, M. Fowler$, P. Gage#, M. Gasch§, G. Gonzales*, C. Kazemba, C. Kellermann$, S. Langston%, J. Ma§, M. Mahzari §, F. Milos§, O. Nishioka§, G. Palmer*, K. Peterson §, C. Poteet%, D. Prabhu*, S. Splinter%, M. Stackpoole§, E. Venkatapathy§ , J. Williams*, and Z. Young§ §NASA ARC; %NASA LaRC; $NASA JSC; *AMA.-Moffett Field, CA; #NEERIM Corp.-Moffett Field, CA

Starting in 2013 and completing in 2019, the Heatshield for Extreme Entry Environment Technology (HEEET) project has been working to mature a 3-D Woven Thermal Protection System (TPS) to Technical Readiness Level (TRL) 6 to support future NASA missions to destinations with extreme entry environments such as Venus, Saturn, Uranus, Neptune and high-speed sample return missions to Earth. A key aspect of the project has been the building and testing of a 1-meter base diameter Engineering Test Unit (ETU) representative of what could be used for a Saturn probe. This paper provides a high-level overview of the HEEET project including 1) manufacturing and testing of the ETU for structural model verification, 2) establish system capability and 3) verify manufacturing workmanship.

The Hypersonic Materials Environmental Test System arcjet facility located at the NASA Langley Research Center in Hampton, Virginia, is primarily used for the research, development, and evaluation of high-temperature thermal protection systems for hypersonic vehicles and reentry systems. To improve testing capabilities and knowledge of the test article environment, a detailed three-dimensional model of the arcjet nozzle and the freejet portion of the flowfield is developed. The computational fluid dynamics model takes into account nonuniform inflow state profiles at the nozzle inlet as well as catalytic recombination efficiency effects at the probe surface. The results of the numerical simulations are compared to the calibrated pitot pressure and the stagnation-point heat flux for three test conditions at low, medium, and high enthalpies. Comparing the results and the test data indicates a partially catalytic copper surface on the heat flux probe of about 10% recombination efficiency and a 2-3 kPa pressure drop from the total pressure measured at the plenum section in front of the nozzle. With these assumptions, the predictions are within the uncertainty of the stagnation pressure and heat flux measurements. The predicted velocity conditions at the nozzle exit are also compared and show good agreement with the radial and axial velocimetry data.

Spallation is a phenomenon in which solid particles are ejected off the surface of an ablative material in a high-enthalpy, high-shear flow field. The main contributor to this phenomenon in carbon-based heat shields is the mechanical erosion of carbon fibers weakened by oxidation decomposition. The dynamics of this phenomenon, which are poorly characterized in the literature, strongly affect the ablation rate of the material. In state-of-the-art codes, ablation by spallation is modeled using a "failure" ablation rate that is empirically determined. The present study aims at understanding the rate of ablation of low-density carbon materials. Results from a test campaign at the NASA Langley Hypersonic Materials Environmental Test System (HYMETS) arc jet facility are used to examine spallation. High-speed multi-camera imagery at 44,000 fps is used to generate velocity vectors of spalled particles emitted from carbon-fiber samples exposed to an arc jet airflow. The imagery recorded approximately 4 x 10(6) unique particles, indicating that spallation is a potentially non-trivial process. The velocities of the particles ejected from the surface were found to be between 10 m/s and 20 m/s, accelerating to velocities as high as 250 m/s further away from the sample surface. Although the particle diameters were not directly observable, estimates suggest anywhere from 0.06% to 5.6% of the mass loss from the sample occurred due to spallation.

D. M. Driver, D.T. Ellerby(Presenting Author), M. J. Gasch, M. Mahzari, F. S. Milos, O. S. Nishioka, K. H. Peterson, M. M. Stackpoole, E. Venkatapathy, Z. W. Young, P. J. Gage, T. Boghozian, J. F. Chavez-Garcia, G. L. Gonzales, G. E. Palmer, D. K. Prabhu, J. D. Williams, C.D. Kazemba, A. S. Murphy, S. L. Langston, C. C. Poteet, S. C. Splinter, M. E. Fowler, C. M. Kellermann, NASA Ames Research Center Moffett Field, CA 94035, Neerim Corp Moffett Field, CA 94035, Analytical Mechanics Associates, Inc. Moffett Field, CA 94035, Science and Technology Corp, Moffett Field, CA 94035, Millennium Engineering and Integration Co. Moffett Field, CA 94035,NASA Langley Research Center Hampton, VA 23681, NASA Johnson Space Center Houston, TX 77058, Jacobs Technology, Inc. Houston, TX 77058

A method of remotely measuring surface recession of a material sample in a plasma flow through emission spectroscopy of the post shock layer was characterized through experiments in the NASA Langley HYMETS arc jet facility. Different methods for delivering the seed products into the Phenolic Impregnated Carbon Ablator (PICA) material samples were investigated. Three samples were produced by seeding the PICA material with combinations of Al, Si, HfO2, VB2, Al2O3, SiO2, TiC, HfC, NaCl, and MgCl2 through infusing seed materials into a core of PICA, or through encapsulating seed material in an epoxy disk, mechanically bonding the disk to a PICA sample. The PICA samples seeded with the candidate tracers were then tested at surface temperatures near 2400 K under low pressure air plasma. The emission of Al, Ti, V, Na, and Mg in the post-shock layer was observed in the UV with a high resolution imaging spectrometer viewing the whole stagnation line from the side, and from UV to NIR with a fiber-coupled miniaturized spectrometer observing the sample surface in the wavelength range from 200 nm to 1,100 nm from the front through a collimator. Al, Na, and Mg were found to be emitting in the post-shock spectra even before the recession reached the seeding depth - therefore possibly characterizing the pyrolysis process rather than the recession itself. The appearance of Ti and V emission in the spectra was well correlated with the actual recession which was monitored through a video of the front surface of the sample. The applicability of a seed material as an indicator for recession appears to be related to the melting temperature of the seed material. Future parametric studies will be carried out in low power plasma facilities at the University of Kentucky.

The spallation phenomenon was studied through numerical analysis using a coupled Lagrangian particle tracking code and a hypersonic aerothermodynamics computational fluid dynamics solver. The results show that carbon emission from spalled particles results in a significant modification of the gas composition of the post-shock layer. Results from a test campaign at the NASA Langley HYMETS facility are presented. Using an automated image processing of short exposure images, two-dimensional velocity vectors of the spalled particles were calculated. In a 30-s test at 100 W/cm2 of cold-wall heat flux, more than 722 particles were detected, with an average velocity of 110 m/s.

Emission spectroscopy measurements in the post-shock layer in front of low density ablative material samples of different shapes were obtained in the NASA Langley HYMETS arcjet facility. A horizontal line of measurement positions was imaged on the entrance slit of the spectrometer allowing detection of the entire stagnation line in front of the samples. The stagnation line measurements were used to compare the post-shock layer emission signatures in front of PICA and FiberForm. The emission signatures of H, NH, and OH are characteristic for pyrolysis gases and consequently were only observed in front of the PICA samples. CN and C were found in front of both materials and are mainly due to interactions of the carbon fibers with the plasma. In all tests with instrumented samples, the emission of Mn, Cr, and Ni was observed when the thermocouple temperatures reached or exceeded ~1,500 K, strongly indicating erosion of the molten thermocouple tips. Temperatures in the post-shock layer were estimated from comparing the CN band emission to spectral simulation. The resulting rotational and vibrational temperatures were on the order of 7,000 to 9,000 K and close to each other indicating a plasma condition close to equilibrium. In addition to the stagnation line configurations, off-axis lines of observation were investigated to gather information about spalled particles in the flow. From a comparison of measured continuum emission with simulated Planck radiation, average particle temperatures along the measured line of observation were determined for two cases. Particle temperatures between 3,500 and 2,000 K were found. A comprehensive investigation of the entire amount of data set is ongoing.

This poster provides an overview of the requirements, design, development and testing of the 3D Woven TPS being developed under NASAs Heatshield for Extreme Entry Environment Technology (HEEET) project. Under this current program, NASA is working to develop a Thermal Protection System (TPS) capable of surviving entry into Saturn. A primary goal of the project is to build and test an Engineering Test Unit (ETU) to establish a Technical Readiness Level (TRL) of 6 for this technology by 2017.

This poster provides an overview of the requirements, design, development and testing of the 3D Woven TPS being developed under NASA's Heatshield for Extreme Entry Environment Technology (HEEET) project. Under this current program, NASA is working to develop a Thermal Protection System (TPS) capable of surviving entry into Venus or Saturn. A primary goal of the project is to build and test an Engineering Test Unit (ETU) to establish a Technical Readiness Level (TRL) of 6 for this technology by 2017.

Future NASA robotic missions utilizing an entry system into Venus and the outer planets, results in extremely high entry conditions that exceed the capabilities of state of the art low to mid density ablators such as PICA or AVCOAT. Previously, mission planners had to assume the use of fully dense carbon phenolic heatshields similar to what was flown on Pioneer Venus or Galileo. Carbon phenolic is a robust TPS material, however, its high density and relatively high thermal conductivity constrain mission planners to steep entries, with high heat fluxes and pressures and short entry durations. The high entry conditions pose challenges for certification in existing ground based test facilities and the longer-term sustainability of CP will continue to pose challenges. NASA has decided to invest in new technology development rather than invest in reviving carbon phenolic. The HEEET project, funded by STMD is maturing a game changing Woven Thermal Protection System technology. HEEET is a capability development project and is not tied to a single mission or destination, therefore, it is challenging to complete ground testing needed to demonstrate a capability that is much broader than any single mission or destination would require. This presentation will status HEEET progress. Near term infusion target for HEEET is the upcoming New Frontiers (NF-4) class of competitively selected Science Mission Directorate (SMD) missions for which it is incentivized.

A novel series of ablative composites containing a hyperbranched polyazomethine synthesized inside a carbon fiber preform (HyPAZA) were prepared, which have similar density to phenolic impregnated carbon ablators (approximate to 0.3g/cc). A novel method of synthesizing strong hyperbranched polyazomethine thermosets has been developed, enabling polyazomethines to be studied in ablators for the first time. Several formulations of HyPAZA perform better than the phenolic impregnated carbon ablator in terms of polymer char yield, composite mechanical strength, CO2 laser ablation tests at heat fluxes of 550 and 1100W/cm2, and small-scale arcjet testing at a heat flux of 400W/cm2. Char yields of hyperbranched polyazomethines were as high as 79% at 1000 degrees C by thermogravimetric analysis. This is one of the highest char yields ever reported for a fully organic polymer. Some HyPAZA composites are over 10 times stronger than the carbon fiber preform, as determined by compression tests. Specimens were also tested in an arcjet facility at 400W/cm2. Several formulations exhibited better performance than the phenolic impregnated carbon ablator in terms of ablation rate by a factor of 1.2 to 1.7. In addition, HyPAZA composites impregnated with aerogel show a lower rate of increase of back wall temperature, and therefore a lower thermal conductivity.

The development of durable bonded joint technology for assembling composite structures is an essential component of future space technologies. While NASA is working toward providing an entirely new capability for human space exploration beyond low Earth orbit, the objective of this project is to design, fabricate, analyze, and test a NASA patented durable redundant joint (DRJ) and a NASA/Boeing co-designed fluted-core joint (FCJ). The potential applications include a wide range of sandwich structures for NASA's future launch vehicles. Three types of joints were studied -- splice joint (SJ, as baseline), DRJ, and FCJ. Tests included tension, after-impact tension, and compression. Teflon strips were used at the joint area to increase failure strength by shifting stress concentration to a less sensitive area. Test results were compared to those of pristine coupons fabricated utilizing the same methods. Tensile test results indicated that the DRJ design was stiffer, stronger, and more impact resistant than other designs. The drawbacks of the DRJ design were extra mass and complex fabrication processes. The FCJ was lighter than the DRJ but less impact resistant. With barely visible but detectable impact damages, all three joints showed no sign of tensile strength reduction. No compression test was conducted on any impact-damaged sample due to limited scope and resource. Failure modes and damage propagation were also studied to support progressive damage modeling of the SJ and the DRJ.

Planar laser-induced fluorescence of naturally occurring nitric oxide has been used to provide insight into baseline flow conditions of the Hypersonic Materials Environmental Test System 400 kW arc-heated wind tunnel at NASA Langley Research Center via radial and axial velocity measurements and instantaneous flow-visualization images. This represents both the first flow-tagging velocity measurements and the first application of nitric-oxide planar laser-induced fluorescence flow visualization in an arcjet facility. Results are presented at selected facility run conditions, including some in a simulated Earth atmosphere (75% nitrogen, 20% oxygen, 5% argon) and others in a simulated Martian atmosphere (71% carbon dioxide, 24% nitrogen, 5% argon) for specific bulk enthalpies ranging from 6.5 to 18.4 MJ/kg. Flow-visualization images reveal the presence of large-scale unsteady flow structures and indicate nitric-oxide fluorescence signal over more than 70% of the core flow for specific bulk enthalpies below about 11 MJ/kg but over less than 10% of the core flow for specific bulk enthalpies above about 16 MJ/kg. Axial velocimetry was performed using molecular tagging velocimetry. Axial velocities of about 3 km/s were measured along the centerline. Radial velocimetry was performed by scanning the wavelength of the narrowband laser and analyzing the resulting Doppler shift. Radial velocities of +/- 0.5 km/s were measured.