The Mysteries of Real Materials

The presentation will consist of showing arc jet data mysterious to the modelers. It will show pictures from an arc jet test where a material (unidentified) exhibited a failure mode that nobody understands followed by thermocouple data from arc jet tests on another (unidentified) material of interest in which the T/Cs exhibit repeatable, consistent, fascinating yet frustrating response characteristics that have the modelers stumped. This all happens between RT and 200 F. Unless we figure out what the responsible phenomenology is and can model it, we can't size the TPS with any confidence

Thermal Protection System (TPS) Design and the Relationship to Atmospheric Entry Environments

This presentation was part of the session : Short CoursesSixth International Planetary Probe Worksho

Two-Dimensional Finite Element Ablative Thermal Response Analysis of an Arcjet Stagnation Test

The finite element ablation and thermal response (FEAtR, hence forth called FEAR) design and analysis program simulates the one, two, or three-dimensional ablation, internal heat conduction, thermal decomposition, and pyrolysis gas flow of thermal protection system materials. As part of a code validation study, two-dimensional axisymmetric results from FEAR are compared to thermal response data obtained from an arc-jet stagnation test in this paper. The results from FEAR are also compared to the two-dimensional axisymmetric computations from the two-dimensional implicit thermal response and ablation program under the same arcjet conditions. The ablating material being used in this arcjet test is phenolic impregnated carbon ablator with an LI-2200 insulator as backup material. The test is performed at the NASA, Ames Research Center Interaction Heating Facility. Spatially distributed computational fluid dynamics solutions for the flow field around the test article are used for the surface boundary conditions

Rotating Arc Jet Test Model: Time-Accurate Trajectory Heat Flux Replication in a Ground Test Environment

Though arc jet testing has been the proven method employed for development testing and certification of TPS and TPS instrumentation, the operational aspects of arc jets limit testing to selected, but constant, conditions. Flight, on the other hand, produces timevarying entry conditions in which the heat flux increases, peaks, and recedes as a vehicle descends through an atmosphere. As a result, we are unable to "test as we fly." Attempts to replicate the time-dependent aerothermal environment of atmospheric entry by varying the arc jet facility operating conditions during a test have proven to be difficult, expensive, and only partially successful. A promising alternative is to rotate the test model exposed to a constant-condition arc jet flow to yield a time-varying test condition at a point on a test article (Fig. 1). The model shape and rotation rate can be engineered so that the heat flux at a point on the model replicates the predicted profile for a particular point on a flight vehicle. This simple concept will enable, for example, calibration of the TPS sensors on the Mars Science Laboratory (MSL) aeroshell for anticipated flight environments

Test Case Series 1

A simple one-dimensional test case is defined for the purpose of inter-code comparison. This year the focus is set on in-depth physics and chemistry. Material properties, boundary conditions, and output format are provided

Development and Test Plans for the MSR EEV

The goal of the proposed Mars Sample Return mission is to bring samples from the surface of Mars back to Earth for thorough examination and analysis. The Earth Entry Vehicle is the passive entry body designed to protect the sample container from entry heating and deceleration loads during descent through the Earth s atmosphere to a recoverable location on the surface. This paper summarizes the entry vehicle design and outlines the subsystem development and testing currently planned in preparation for an entry vehicle flight test in 2010 and mission launch in 2013. Planned efforts are discussed for the areas of the thermal protection system, vehicle trajectory, aerodynamics and aerothermodynamics, impact energy absorption, structure and mechanisms, and the entry vehicle flight test

Arcjet Testing of Woven Carbon Cloth for Use on Adaptive Deployable Entry Placement Technology

This paper describes arcjet testing and analysis that has successfully demonstrated the viability of three dimensional woven carbon cloth for dual use in the Adaptive Deployable Entry Placement Technology (ADEPT). ADEPT is an umbrella-like entry system that is folded for stowage in the launch vehicle s shroud and deployed in space prior to reaching the atmospheric interface. A key feature of the ADEPT concept is its lower ballistic coefficient for delivery of a given payload than those for conventional, rigid body entry systems. The benefits that accrue from the lower ballistic coefficient include factor of ten reductions of deceleration forces and entry heating. The former enables consideration of new classes of scientific instruments for solar system exploration while the latter enables the design of a more efficient thermal protection system. The carbon cloth now base lined for ADEPT has a dual use in that it serves as ADEPT s thermal protection system and as the "skin" that transfers aerodynamic deceleration loads to its umbrella-like substructure. The arcjet testing described in this paper was conducted for some of the higher heating conditions for a future Venus mission using the ADEPT concept, thereby showing that the carbon cloth can perform in a relevant entry environment. The ADEPT project considered the carbon cloth to be mission enabling and was carrying it as a major risk during Fiscal Year 2012. The testing and analysis reported here played a major role in retiring that risk and is highly significant to the success and possible adoption of ADEPT for future NASA missions. Finally, this paper also describes a preliminary engineering level code, based on the arcjet data, that can be used to estimate cloth thickness for future missions using ADEPT and to predict carbon cloth performance in future arcjet tests

Selection and Certification of TPS: Constraints and Considerations of Venus Missions

This presentation was part of the session : Probe Missions to the Giant Planets, Titan and VenusSixth International Planetary Probe WorkshopThe science community currently has interest in planetary entry probe missions to improve our understanding of the atmosphere of Saturn [1], missions to Venus and also sample return missions from comets and asteroids. In addition, the In-Space Propulsion Program has completed aerocapture mission design studies that have defined the requirements for the Thermal protection System (TPS) to Venus, Mars, Titan and Neptune. There have been investments in new TPS materials and to revive flight qualified materials such as PICA (used on Stardust and currently baselined for MSL and Orion) and Carbon-Phenolic, the TPS material of choice for Venus and Outer Planet missions. Mission studies have shown the heating rates for the "shallow" Saturn probes are in the range of (2 - 5) KW/cm2 in its H(2)/He atmosphere. Venus entry probes will experience heat fluxes in the similar range of (3 - 7) kW/cm(2) in CO2. High-speed Earth reentry missions from comets and asteroids will experience heating of the range of (1 - 5) kW/cm(2) and at pressures equal to or higher than Stardust. Aerocapture during Venus missions will experience heat fluxes in the range of (2 - 4) kW/cm(2) in CO2. Titan aero-capture missions will experience far smaller heating fluxes in the N2/methane atmosphere. Since the flight times are longer during aerocapture missions, TPS design requirements involve much larger heatloads at relatively lower heat-fluxes compared to those for direct entry probe missions. It is clear that qualification and certification of the heritage ablative materials or the development of new, ablative Thermal Protection System (TPS) materials for entry or aerocapture probe missions is needed [2] and the challenges are in testing, especially in the appropriate atmospheric gases. NASA Ames has nearly completed the construction of a small, low cost, 5 MW arc jet facility, called the Development Arcjet Facility (DAF) that will permit testing of small models at high heat fluxes and in different gases. This paper will review the entry conditions from a collection of mission studies to various solar system destinations, the testing needs of both newer as well as heritage TPS for each destination and provide the approach, we at NASA Ames plan to adopt, in testing and analysis by making use of both existing arc jet facilities as well as an affordable, small 5 MW arc jet that can be used for TPS development in test gases appropriate for the Neptune, Titan, Saturn, Venus or Earth applications. [1] Atreya, S. K., et. al. "Formation of Giant Planets and Their Atmospheres: Entry Probes for Saturn and Beyond; 5 th International Planetary Probe Workshop, June 25-29, Bordeaux, France. [2] Venkatapathy, E. and Laub, B. "Requirements for Development of Thermal Protection Systems for Multiple Missions: 5th International Planetary Probe Workshop, June 25-29, Bordeaux, France.NASA In-Space Propulsion Progra

Technology for Entry Probes

A viewgraph describing technologies for entry probes is presented. The topics include: 1) Entry Phase; 2) Descent Phase; 3) Long duration atmospheric observations; 4) Survivability at high temperatures; and 5) Summary

High quality organic resources are most efficient in stabilizing soil organic carbon: Evidence from four long-term experiments in Kenya

In sub-Saharan Africa, long-term maize cropping with low external inputs has been associated with the loss of soil fertility. While adding high-quality organic resources combined with mineral fertilizer has been proposed to counteract this fertility loss, the long-term effectiveness and interactions with site properties still require more understanding. This study used repeated measurements over time to assess the effect of different quantities and qualities of organic resource addition combined with mineral N on the change of soil organic carbon concentrations (SOC) over time (and SOC stocks in the year 2021) in four ongoing long-term trials in Kenya. These trials were established with identical treatments in moist to dry climates, on coarse to clayey soil textures, and have been managed for at least 16 years. They received organic resources in quantities equivalent to 1.2 and 4 t C ha&minus;1 per year in the form of Tithonia diversifolia (high quality, fast turnover), Calliandra calothyrsus (high quality, intermediate turnover), Zea mays stover (low quality, fast turnover), sawdust (low quality, slow turnover) and local farmyard manure (variable quality, intermediate turnover). Furthermore, the addition or absence of 240 kg N ha&minus;1 per year as mineral N fertilizer was the split-plot treatment. At all sites, a loss of SOC, rather than gain, was predominantly observed due to a recent conversion from permanent vegetation to agriculture. The average reduction of SOC concentration over 19 years in the 0 to 15 cm depth ranged from 42 % to 13 % of the initial SOC concentration for the control and the farmyard manure treatments at 4 t C ha&minus;1 yr&minus;1, respectively. Adding Calliandra or Tithonia at 4 t C ha&minus;1 yr&minus;1 limited the loss of SOC concentrations to about 24 % of initial SOC, while the addition of saw dust, maize stover (in 3 of 4 sites) and sole mineral N addition, showed no significant reduction in SOC loss over the control. Site specific analyses, however, did show, that at the site with the lowest initial SOC concentration (about 6 g kg&minus;1), the addition of 4 t C ha&minus;1 yr&minus;1 farmyard manure or Calliandra plus mineral N led to a gain in SOC concentrations. All other sites lost SOC in all treatments, albeit at site specific rates. While subsoil SOC stocks in 2021 were little affected by organic resource additions (no difference in 3 of 4 sites), the topsoil SOC stocks corroborated the results for SOC concentrations. The relative annual change of SOC concentrations showed a higher site specificity in high-quality organic resource treatments than in the control, suggesting that the drivers of site specificity in SOC buildup (mineralogy, climate) need to be better understood for effective targeting of organic resources. Even though farmyard manure showed the most potential for reducing SOC loss, our results clearly show that maintaining SOC with external inputs only is not possible at organic resource rates that are realistic for small scale farmers. Thus, additional agronomic interventions such as intercropping, crop rotations or strong rooting crops may be necessary to maintain or increase SOC.</p