Results for “Staging Building” — Page 16

NASA NTRS2014

Low-Cost, Class D Testing of Spacecraft Photovoltaic Systems Can Reduce Risk

The end-to-end verification of a spacecraft photovoltaic power generation system requires light! Specifically, the standard practice for doing so is the Large Area Pulsed Solar Simulation (LAPSS). A LAPSS test can characterize a photovoltaic system's efficiency via its response to rapidly applied impulses of simulated sunlight. However, a Class D program on a constrained budget and schedule may not have the resources to ship an entire satellite for a LAPSS test alone. Such was the case with the Lunar Atmospheric and Dust Environment Explorer (LADEE) program, which was also averse to the risk of hardware damage during shipment. When the Electrical Power System (EPS) team was denied a spacecraft-level LAPSS test, the lack of an end-to-end power generation test elevated to a project-level technical risk. The team pulled together very limited resources to not only eliminate the risk, but build a process to monitor the health of the system through mission operations. We discuss a process for performing a low-cost, end-to-end test of the LADEE photovoltaic system. The approach combines system-level functional test, panel-level performance results, and periodic inspection (and repair) up until launch. Following launch, mission operations tools are utilized to assess system performance based on a scant amount of data. The process starts in manufacturing at the subcontractor. The panel manufacturer provides functional test and LAPSS data on each individual panel. We apply an initial assumption that the per-panel performance is sufficient to meet the power generation requirements. The manufacturer's data is also carried as the performance allocation for each panel during EPS system modeling and initial mission operations. During integration and test, a high-power, professional theater lamp system provides simulated sunlight to each panel on the spacecraft, thereby permitting a true end-to-end system test. A passing test results in a step response to nearly full-rated current at the appropriate solar array switch in the power system. A metal-halide bulb, infrared imagers, and onboard spacecraft measurements are utilized to minimize risk of thermal damage during test. Data is provided to support test results for both passing and marginal panels. Prior to encapsulation in the launch vehicle, each panel is inspected for damage by the panel manufacturer. Cracked cells or other damage is amended on-site. Because the photovoltaic test system is inexpensive and portable, each repaired panel can be re-verified immediately. Post-launch, the photovoltaic system is again characterized for per-panel deviations from the manufacturer's performance test. This proved especially tricky as the LADEE spacecraft performs only one current measurement on the entire array. The algorithm for Matlab tools to assess panel performance based on spacecraft attitude is discussed. While not as precise and comprehensive as LAPSS, the LADEE approach leverages minimal resources into an ongoing assessment program that can be applied through numerous stages of the mission. The project takes a true Class D approach in assessing the technical value of a spacecraft level performance test versus the programmatic risk of shipping the spacecraft to another facility. The resources required are a fraction of that for a LAPSS test, and is easy to repeat. Further, the test equipment can be handed down to future projects without building an on-site facility.

photovoltaic↗

NASA NTRS2004

E-beam-Cure Fabrication of Polymer Fiber/Matrix Composites for Multifunctional Radiation Shielding

Aliphatic polymers were identified as optimum radiation polymeric shielding materials for building multifunctional structural elements. Conceptual damage-tolerant configurations of polyolefins have been proposed but many issues on the manufacture remain. In the present paper, we will investigate fabrication technologies with e-beam curing for inclusion of high-strength aliphatic polymer fibers into a highly cross-linked polyolefin matrix. A second stage of development is the fabrication methods for applying face sheets to aliphatic polymer closed-cell foams.

Wilson, John W.↗

NASA NTRS2008

Amino Acid Degradation after Meteoritic Impact Simulation

Amino acids are among the most important prebiotic molecules as it is from these precursors that the building blocks of life were formed [1]. Although organic molecules were among the components of the planetesimals making up the terrestrial planets, large amounts of primitive organic precursor molecules are believed to be exogenous in origin and to have been imported to the Earth via micrometeorites, carbonaceous meteorites and comets, especially during the early stages of the formation of the Solar System [1,2]. Our study concerns the hypothesis that prebiotic organic matter, present on Earth, was synthesized in the interstellar environment, and then imported to Earth by meteorites or micrometeorites. We are particularly concerned with the formation and fate of amino acids. We have already shown that amino acid synthesis is possible inside cometary grains under interstellar environment conditions [3]. We are now interested in the effects of space conditions and meteoritic impact on these amino acids [4-6]. Most of the extraterrestrial organic molecules known today have been identified in carbonaceous chondrite meteorites [7]. One of the components of these meteorites is a clay with a composition close to that of saponite, used in our experiments. Two American teams have studied the effects of impact on various amino acids [8,9]. [8] investigated amino acids in saturated solution in water with pressure ranges between 5.1 and 21 GPa and temperature ranges between 412 and 870 K. [9] studied amino acids in solid form associated with and without minerals (Murchison and Allende meteorite extracts) and pressure ranges between 3 and 30 GPa. In these two experiments, the amino acids survived up to 15 GPa. At higher pressure, the quantity of preserved amino acids decreases quickly. Some secondary products such as dipeptides and diketopiperazins were identified in the [8] experiment.

Bertrand, M.↗

NASA NTRS2010

Human Exploration Beyond LEO by the End of the Decade: Designs for Long-Duration "Gateway" Habitats

For the past few years, designs have been developed that are intended to demonstrate that a long-duration habitation system beyond LEO is plausible within several years. Here we summarize a pair of designs with the overriding goal of development and operation beyond LEO before the end of the decade that also build upon experiments and lessons learned from ISS. Both concepts here have the goal of an expandable long-duration habitat at Earth- Moon L1 and/or L2. Both options require subsequent launches for the astronauts. If a heavy-lift launch vehicle is available this decade, an expandable 30.5 mt habitat and departure-stage propulsion system may be launched to E-M L1,2 in a single launch and will offer 575 cubic meter (roughly half the habitable volume of ISS) If existing (or near-future) EELVs are the available launch vehicles this decade, a 16 mt, 170 cubic meter design that uses a pair of launches of Delta IV H and LEO rendezvous/fuel transfer to reach E-M L1,2.

Thronson, Harley↗

NASA NTRSDate not supplied

Early Results from a Broad Compatibility Study of Various Materials with Ionic Silver Biocide

Ionic silver is baselined for microbial control in spacecraft potable water systems forfuture exploration missions, but materials compatibility analysis is required to evaluate thepassive depletion of ionic silver concentration onto wetted material surfaces over time.Various articles concerning such testing have been published that examine interactions withwater containing ionic silver biocide, but most tests have focused on only a couple ofmaterials each and comparing results of different evaluations to one another has provedchallenging.This paper reports the first results from static exposure testing of a large arrayof material coupons to a 400 parts per billion (ppb) aqueous silver fluoride (AgF) solution,using a surface to volume ratio of approximately 2 cm-1. The test is designed in two mainstages. Stage 1 is a one-week screening to evaluate silver uptake. Materials that performmodestly to well after that week are promoted to Stage 2, which is a longer test with periodicsampling to examine the silver uptake rates over time; these samples are evaluated for otherwater quality parameters in addition to the remaining silver concentration. In a tangentialinvestigation, select materials that take up some silver in Stage 1 may be “aged” by repeatingthe Stage 1 test to determine whether repeated exposure reduces silver uptake rate, andsuccessfully aged materials may then continue to Stage 2 testing. The materials under testinclude metallic and polymeric materials with various surface finishes, treatments, andcoatings, as well as select other materials historically used in spacecraft water systems. Thistest began in August 2019, and thus only includes early results; future follow-on papers willinclude additional results as the test progresses. The ultimate goal builds a broad, easilycomparable data set that can be used to guide material selections for silver biocide-compatible spacecraft water system design.

Silver Biocide↗

NASA NTRS2019

Requirements Development and Management on the Psyche Project

In January 2017, Psyche was one of two mission concepts selected by NASA for flight as part of the 14th Discovery mission competition. The project has been staffing up and maturing the spacecraft, instrument and mission system baseline designs on the path towards a 2022 launch. During much of 2018, the Project has been executing the lifecycle stage called Phase B, “Preliminary Design and Technology Completion,” one key element of which is the development and management of requirements at various levels. In the case of the Psyche project, this process has been particularly unique for several reasons. The project utilizes a Solar Electric Propulsion (SEP) Chassis from Space Systems Loral (SSL), a high volume manufacturer of commercial geostationary (GEO) telecom spacecraft based on the 1300 satellite bus. While SSL has an extensive, well-vetted set of requirements based on their very successful Earth-orbiting product line, translating that heritage to a deep space science mission required special care. In addition to the differences associated with the deep space environment and longer communication times, new interfaces had to be incorporated. While a substantial portion of the Flight System consists of the SEP Chassis, there were several new interfaces within various subsystems between SSL components and those provided by JPL and other contractors. Managing these interfaces through requirements at a relatively higher level than normally seen on internal or external builds proved challenging. Finally, the Psyche spacecraft plans to host the flight terminal of the Deep Space Optical Communications (DSOC) technology demonstration, which is itself a separate project with its own requirements that must be flowed down and managed. This paper will present an overview of the requirement development and management process for the Psyche project. It will discuss in detail the various challenges summarized above, the methods and decisions chosen to address them, and evaluate their overall effectiveness at this stage in the project.

Elkins-Tanton, Linda T.↗

NASA NTRS2024

The H-poor nature of incompletely melted planetesimals: The view from acapulcoites and lodranites

The abundance of H in planetary building blocks is of fundamental importance for constraining the evolution of the terrestrial planets. It is commonly assumed that chondrites are the principal sources of Earth’s H; however, recent studies have suggested that primitive achondrites and achondrites may retain a small complement of H. There are few constraints on the H budgets of primitive achondrites, which represent the transition from unmelted to melted planetesimals, but prior work suggests that bulk parent body H contents are several orders of magnitude lower than typical chondritic values. Therefore, to provide further constraints on H retention during the transition from unmelted to melted planetesimals, we have measured the H contents of olivine, orthopyroxene, clinopyroxene, and plagioclase from a suite of acapulcoite-lodranite clan meteorites. Acapulcoite-lodranite clan meteorites represent the “prototypical” primitive achondrite parent body and have bulk major element compositions more akin to the Earth than previously studied primitive achondrites (e.g., the ureilites). We find that the H 2 O contents of olivine (∼5–12 µg/g H 2 O), orthopyroxene (∼3–10 µg/g H 2 O), and clinopyroxene (∼5–8 µg/g H 2 O) are broadly similar, while plagioclase (∼2.5–5 µg/g H 2 O) tends to be offset to lower values. Using a simple, single-stage batch-melting model, we calculate a preferred maximum acapulcoite-lodranite parent body H 2 O content of 38 µg/g, which is similar to other estimates for primitive achondritic and achondritic parent bodies. Furthermore, assuming chondrite-like precursor materials, our data are consistent with efficient loss of H prior to or during the onset of melting of early-formed planetesimals. This requires that Earth’s H-budget was dominated by building blocks that underwent minimal thermal processing.

Primitive achondrite↗

NASA NTRS1991

High accuracy switched-current circuits using an improved dynamic mirror

The switched-current technique, a recently developed circuit approach to analog signal processing, has emerged as an alternative/compliment to the well established switched-capacitor circuit technique. High speed switched-current circuits offer potential cost and power savings over slower switched-capacitor circuits. Accuracy improvements are a primary concern at this stage in the development of the switched-current technique. Use of the dynamic current mirror has produced circuits that are insensitive to transistor matching errors. The dynamic current mirror has been limited by other sources of error including clock-feedthrough and voltage transient errors. In this paper we present an improved switched-current building block using the dynamic current mirror. Utilizing current feedback the errors due to current imbalance in the dynamic current mirror are reduced. Simulations indicate that this feedback can reduce total harmonic distortion by as much as 9 dB. Additionally, we have developed a clock-feedthrough reduction scheme for which simulations reveal a potential 10 dB total harmonic distortion improvement. The clock-feedthrough reduction scheme also significantly reduces offset errors and allows for cancellation with a constant current source. Experimental results confirm the simulated improvements.

Zweigle, G.↗

NASA NTRS1998

Applications of Artificial Neural Networks in Structural Engineering with Emphasis on Continuum Models

The use of continuum models for the analysis of discrete built-up complex aerospace structures is an attractive idea especially at the conceptual and preliminary design stages. But the diversity of available continuum models and hard-to-use qualities of these models have prevented them from finding wide applications. In this regard, Artificial Neural Networks (ANN or NN) may have a great potential as these networks are universal approximators that can realize any continuous mapping, and can provide general mechanisms for building models from data whose input-output relationship can be highly nonlinear. The ultimate aim of the present work is to be able to build high fidelity continuum models for complex aerospace structures using the ANN. As a first step, the concepts and features of ANN are familiarized through the MATLAB NN Toolbox by simulating some representative mapping examples, including some problems in structural engineering. Then some further aspects and lessons learned about the NN training are discussed, including the performances of Feed-Forward and Radial Basis Function NN when dealing with noise-polluted data and the technique of cross-validation. Finally, as an example of using NN in continuum models, a lattice structure with repeating cells is represented by a continuum beam whose properties are provided by neural networks.

Kapania, Rakesh K.↗

NASA NTRS2011

Visual Object Recognition and Tracking of Tools

A method has been created to automatically build an algorithm off-line, using computer-aided design (CAD) models, and to apply this at runtime. The object type is discriminated, and the position and orientation are identified. This system can work with a single image and can provide improved performance using multiple images provided from videos. The spatial processing unit uses three stages: (1) segmentation; (2) initial type, pose, and geometry (ITPG) estimation; and (3) refined type, pose, and geometry (RTPG) calculation. The image segmentation module files all the tools in an image and isolates them from the background. For this, the system uses edge-detection and thresholding to find the pixels that are part of a tool. After the pixels are identified, nearby pixels are grouped into blobs. These blobs represent the potential tools in the image and are the product of the segmentation algorithm. The second module uses matched filtering (or template matching). This approach is used for condensing synthetic images using an image subspace that captures key information. Three degrees of orientation, three degrees of position, and any number of degrees of freedom in geometry change are included. To do this, a template-matching framework is applied. This framework uses an off-line system for calculating template images, measurement images, and the measurements of the template images. These results are used online to match segmented tools against the templates. The final module is the RTPG processor. Its role is to find the exact states of the tools given initial conditions provided by the ITPG module. The requirement that the initial conditions exist allows this module to make use of a local search (whereas the ITPG module had global scope). To perform the local search, 3D model matching is used, where a synthetic image of the object is created and compared to the sensed data. The availability of low-cost PC graphics hardware allows rapid creation of synthetic images. In this approach, a function of orientation, distance, and articulation is defined as a metric on the difference between the captured image and a synthetic image with an object in the given orientation, distance, and articulation. The synthetic image is created using a model that is looked up in an object-model database. A composable software architecture is used for implementation. Video is first preprocessed to remove sensor anomalies (like dead pixels), and then is processed sequentially by a prioritized list of tracker-identifiers.

English, James↗

NASA NTRS2007

Human Space Exploration: The Moon, Mars, and Beyond

America is returning to the Moon in preparation for the first human footprint on Mars, guided by the U.S. Vision for Space Exploration. This presentation will discuss NASA's mission, the reasons for returning to the Moon and going to Mars, and how NASA will accomplish that mission in ways that promote leadership in space and economic expansion on the new frontier. The primary goals of the Vision for Space Exploration are to finish the International Space Station, retire the Space Shuttle, and build the new spacecraft needed, to return people to the Moon and go to Mars. The Vision commits NASA and the nation to an agenda of exploration that also includes robotic exploration and technology development, while building on lessons learned over 50 years of hard-won experience. Why the Moon? Many questions about the Moon's potential resources and how its history is linked to that of Earth were spurred by the brief Apollo explorations of the 1960s and 1970s. This new venture will carry more explorers to more diverse landing sites with more capable tools and equipment for extended expeditions. The Moon also will serve as a training ground before embarking on the longer, more difficult trip to Mars. NASA plans to build a lunar outpost at one of the lunar poles, learn to live off the land, and reduce dePendence on Earth for longer missions. America needs to extend its ability to survive in hostile environments close to our home planet before astronauts will reach Mars, a planet very much like Earth. NASA has worked with scientists to define lunar exploration goals and is addressing the opportunities for a range of scientific study on Mars. In order to reach the Moon and Mars within a lifetime and within budget, NASA is building on common hardware, shared knowledge, and unique experience derived from the Apollo Saturn, Space Shuttle and contemporary commercial launch vehicle programs. The journeys to the Moon and Mars will require a variety of vehicles, including the Ares I Crew Launch Vehicle, which transports the Orion Crew Exploration Vehicle, and the Ares V Cargo Launch Vehicle, which transports the Lunar Surface Access Module. The architecture for the lunar missions will use one launch to ferry the crew into orbit, where it will rendezvous with the Lunar Module in the Earth Departure Stage, which will then propel the combination into lunar orbit. The imperative to explore space with the combination of astronauts and robots will be the impetus for inventions such as solar power and water and waste recycling. This next chapter in NASA's history promises to write the next chapter in American history, as well. It will require this nation to provide the talent to develop tools, machines, materials, processes, technologies, and capabilities that can benefit nearly all aspects of life on Earth. Roles and responsibilities are shared between a nationwide Government and industry team. The Exploration Launch Projects Office at the Marshall Space Flight Center manages the design, development, testing, and evaluation of both vehicles and serves as lead systems integrator. A little over a year after it was chartered, the Exploration Launch Projects team is testing engine components, refining vehicle designs, performing wind tunnel tests, and building hardware for the first flight test of Ares I-l, scheduled for spring 2009. The U.S. Vision for Space Exploration lays out a roadmap for a long-term venture of discovery. This endeavor will inspire and attract the best and brightest students to power this nation successfully to the Moon, Mars, and beyond. If one equates the value proposition for space with simple dollars and cents, the potential of the new space economy is tremendous, from orbital space delivery services for the International Space Station to mining and solar energy collection on the Moon and asteroids. The Vision for Space Exploration is fundamentally about bringing the resources of the solar system within the economic sphere of humaind. Given the immense size of our solar system, the amount of available material and energy within it present an enormous economic opportunity.

Sexton, Jeffrey D.↗

NASA NTRS1993

Study of switching transients in high frequency converters

As the semiconductor technologies progress rapidly, the power densities and switching frequencies of many power devices are improved. With the existing technology, high frequency power systems become possible. Use of such a system is advantageous in many aspects. A high frequency ac source is used as the direct input to an ac/ac pulse-density-modulation (PDM) converter. This converter is a new concept which employs zero voltage switching techniques. However, the development of this converter is still in its infancy stage. There are problems associated with this converter such as a high on-voltage drop, switching transients, and zero-crossing detecting. Considering these problems, the switching speed and power handling capabilities of the MOS-Controlled Thyristor (MCT) makes the device the most promising candidate for this application. A complete insight of component considerations for building an ac/ac PDM converter for a high frequency power system is addressed. A power device review is first presented. The ac/ac PDM converter requires switches that can conduct bi-directional current and block bi-directional voltage. These bi-directional switches can be constructed using existing power devices. Different bi-directional switches for the converter are investigated. Detailed experimental studies of the characteristics of the MCT under hard switching and zero-voltage switching are also presented. One disadvantage of an ac/ac converter is that turn-on and turn-off of the switches has to be completed instantaneously when the ac source is at zero voltage. Otherwise shoot-through current or voltage spikes can occur which can be hazardous to the devices. In order for the devices to switch softly in the safe operating area even under non-ideal cases, a unique snubber circuit is used in each bi-directional switch. Detailed theory and experimental results for circuits using these snubbers are presented. A current regulated ac/ac PDM converter built using MCT's and IGBT's is evaluated.

Zinger, Donald S.↗

NASA NTRS2015

Area 3 Support Buildings (A3SB) H5-0992, H5-0996 PRL 218 Confirmatory Sampling Report

The Area 3 Support Buildings site (A3SB) consists of two separate areas located on the north side of Beach Road in the northern portion of Kennedy Space Center, Florida (KSC), outside the secured perimeter of KSC. The A3SB areas are approximately 0.6 miles apart, and were developed as Shiffler's Grocery Store and Service Station (west site) and as a residence (east site) prior to acquisition by the National Aeronautics and Space Administration (NASA) in 1963. Both areas were used by the Bendix Company in support of NASA as chemical laboratories from 1963 through 1969. Both of the buildings were demolished by 1987. The west portion of the site was used by the US Fish & Wildlife Service (F&W) in support of the Merritt Island National Wildlife Refuge (MINWR) for parking at the entrance to the Hammock Trails from 1969 to the present. The east portion of the site was used for intermittent suspect materials staging in the early 1990s and is still used as an apiary location, but is otherwise no longer active. In support of the NASA HSWA permit requirements, this site was identified as Potential Release Location (PRL) 218 and a Solid Waste Management Unit (SWMU) Assessment (SA) was conducted in 2013. Confirmatory Sampling (CS) was recommended and approved by the KSC Remediation Team (KSCRT). Three locations of concern (LOCs) were identified and sampled at the site. The LOCs include two former chemical labs and a former suspect staging area. The CS was conducted in March of 2015 at three locations by means of Direct Push Technology (DPT) groundwater sampling and at one location for soil sampling. The samples were collected and analyzed in accordance with the approved CS Work Plan. There were no exceedances of criteria detected in any of the samples from the three LOCs. The results of this investigation indicate that past and/or present operations have not negatively impacted environmental media at the A3SB. Based upon no confirmed groundwater detections above GCTLs and no soil impacts above applicable screening criteria no further investigation is warranted at the A3SB. A No Further Action (NFA) status for all locations was approved by the KSCRT at the June 2015 meeting.

Confirmatory sampling↗

NASA NTRS2020

Hardware Verification and Validation for a Navigation Sensor Software Model in Support of Flight Vehicle Performance Analysis

… or, “It’s in the details, how to make complicated software perform like complicated hardware.” In attempts to minimize development time and quickly build an operational vehicle, NASA’s Space Launch System (SLS) has had to be intentional about integrated testing. Constraints on budget and schedule have required balance between testing needs and the desire for an integrated flight vehicle as soon as possible. To provide key insights early in design and analysis cycles, a large amount of effort has shifted into maturing and validating models at the component level with integrated testing as a means to validate their integration. In terms of SLS Navigation, this, and the model-based design approach have pushed explicit requirements for sensor models to be validated against flight hardware to high precision. This paper covers the approach taken to verify and validate the models for the two key navigation sensors on the SLS vehicle, the Redundant Inertial Navigation Sensor and the Rate Gyro Assembly. These models are used in performance evaluation, fault detection, and operations development extensively. Using a mix of data from hardware vendor documentation and testing reports, limited in-house testing, and integration activities, these models were able to be validated against flight hardware at multiple levels, from the internal software design to statistical behavior at the raw sensor and integrated box levels. The high level of insight into the hardware elements is instrumental to support flight certification activities and building confidence in SLS Navigation capability. Focused testing enabled additional insight and validation that proved invaluable and the resulting insights were used to focus and mature models. Additionally, of having validated performance-based hardware models enables a wide breadth of activities including detailed fault detection studies and integration into future vehicle frameworks, such as an upper stage and provide a valuable asset to continued SLS analysis and design.

Evan J Anzalone↗

NASA NTRS2020

Hardware Verification and Validation for a Navigation Sensor Software Model in Support of Flight Vehicle Performance Analysis

… or, “It’s in the details, how to make complicated software perform like complicated hardware.” In attempts to minimize development time and quickly build an operational vehicle, NASA’s Space Launch System (SLS) has had to be intentional about integrated testing. Constraints on budget and schedule have required balance between testing needs and the desire for an integrated flight vehicle as soon as possible. To provide key insights early in design and analysis cycles, a large amount of effort has shifted into maturing and validating models at the component level with integrated testing as a means to validate their integration. In terms of SLS Navigation, this, and the model-based design approach have pushed explicit requirements for sensor models to be validated against flight hardware to high precision. This paper covers the approach taken to verify and validate the models for the two key navigation sensors on the SLS vehicle, the Redundant Inertial Navigation Sensor and the Rate Gyro Assembly. These models are used in performance evaluation, fault detection, and operations development extensively. Using a mix of data from hardware vendor documentation and testing reports, limited in-house testing, and integration activities, these models were able to be validated against flight hardware at multiple levels, from the internal software design to statistical behavior at the raw sensor and integrated box levels. The high level of insight into the hardware elements is instrumental to support flight certification activities and building confidence in SLS Navigation capability. Focused testing enabled additional insight and validation that proved invaluable and the resulting insights were used to focus and mature models. Additionally, of having validated performance-based hardware models enables a wide breadth of activities including detailed fault detection studies and integration into future vehicle frameworks, such as an upper stage and provide a valuable asset to continued SLS analysis and design.

Thomas Park↗

NASA NTRSDate not supplied

Thermo-Poro-Mechanical Modeling of RTV Intumescence

Room temperature vulcanizing (RTV) silicone is a high-temperature adhesive used as a gap-filler between heatshield tiles in numerous entry missions. Its propensity to intumesce, or swell upon exposure to heat, is a well-known effect that needs to be carefully quantified during design. At tile interfaces of charring ablators, intumescence, combined with differential recession, could cause the gap filler to protrude past the ablator outer mold line, forming a “fence”. Fencing can in turn cause transition to turbulence of the flow wetting the heat shield, leading to augmented surface heating. Recent experiments conducted at the Plasmatron X facility, the high enthalpy wind tunnel of the Center for Hypersonics and Entry Systems Studies, have shown prominent fencing of RTV gap fillers in PICA, under both nitrogen and air plasmas. Similar observations are well known in the arcjet literature. Further experiments under controlled environment, performed using in situ X-ray micro-computed tomography (micro-CT) at the Advanced Light Source (ALS), have shown heating rate-dependent swelling and shrinkage of RTV during pyrolysis. To simulate RTV intumescence, a novel model was introduced in the Porous Materials Analysis Toolbox based on OpenFOAM, PATO, to account for pore-pressure buildup within both closed- and open-pores. The governing equation for the thermo-poro-mechanical response were developed, assuming linear elasticity for the charring silicone. A new multi-pyrolysis model that tracks non-monotonic advancement of material properties with pyrolysis was proposed. This model addresses the limitations of state-of-the-art ablator models to capture the different stages of thermal degradation and coupled thermomechanics. Swelling of RTV was simulated using the new thermo-poro-mechanical model and compared against in situ micro-CT data. Results showed good agreement in intumescence height and temperature profiles at all heating rates, indicating that the key factor contributing to RTV swelling is the internal pressure build-up within closed- and open-pores. As RTV is cured into a soft (rubbery) compound with low-porosity and permeability, initial temperature increase and pyrolysis gas production cause a significant increase of internal pressure, causing a pronounced volume growth. As thermal degradation progresses, rigidization of the silicone occurs due to char hardening which counteract volume shrinkage after gas pressure relief. Overall, our model shows that accounting for changes in properties such porosity, permeability and key thermomechanical coefficients is crucial for capturing the RTV volume change during ablation and enable a predictive capability for heatshield tile interface response. A plan for future calibration of thermomechanical properties evolution during degradation is discussed, as a key next step to close the new model.

RTV↗

NASA NTRSDate not supplied

Thermo-Poro-Mechanical Modeling of RTV Intumescence

Room temperature vulcanizing (RTV) silicone is a high-temperature adhesive used as a gap-filler between heatshield tiles in numerous entry missions. Its propensity to intumesce, or swell upon exposure to heat, is a well-known effect that needs to be carefully quantified during design. At tile interfaces of charring ablators, intumescence, combined with differential recession, could cause the gap filler to protrude past the ablator outer mold line, forming a “fence”. Fencing can in turn cause transition to turbulence of the flow wetting the heat shield, leading to augmented surface heating. Recent experiments conducted at the Plasmatron X facility, the high enthalpy wind tunnel of the Center for Hypersonics and Entry Systems Studies, have shown prominent fencing of RTV gap fillers in PICA, under both nitrogen and air plasmas. Similar observations are well known in the arcjet literature. Further experiments under controlled environment, performed using in situ X-ray micro-computed tomography (micro-CT) at the Advanced Light Source (ALS), have shown heating rate-dependent swelling and shrinkage of RTV during pyrolysis. To simulate RTV intumescence, a novel model was introduced in the Porous Materials Analysis Toolbox based on OpenFOAM, PATO, to account for pore-pressure buildup within both closed- and open-pores. The governing equation for the thermo-poro-mechanical response were developed, assuming linear elasticity for the charring silicone. A new multi-pyrolysis model that tracks non-monotonic advancement of material properties with pyrolysis was proposed. This model addresses the limitations of state-of-the-art ablator models to capture the different stages of thermal degradation and coupled thermomechanics. Swelling of RTV was simulated using the new thermo-poro-mechanical model and compared against in situ micro-CT data. Results showed good agreement in intumescence height and temperature profiles at all heating rates, indicating that the key factor contributing to RTV swelling is the internal pressure build-up within closed- and open-pores. As RTV is cured into a soft (rubbery) compound with low-porosity and permeability, initial temperature increase and pyrolysis gas production cause a significant increase of internal pressure, causing a pronounced volume growth. As thermal degradation progresses, rigidization of the silicone occurs due to char hardening which counteract volume shrinkage after gas pressure relief. Overall, our model shows that accounting for changes in properties such porosity, permeability and key thermomechanical coefficients is crucial for capturing the RTV volume change during ablation and enable a predictive capability for heatshield tile interface response. A plan for future calibration of thermomechanical properties evolution during degradation is discussed, as a key next step to close the new model.

silicone intumescence↗

NASA NTRS2006

A New Heavy-Lift Capability for Space Exploration: NASA's Ares V Cargo Launch Vehicle

The National Aeronautics and Space Administration (NASA) is developing new launch systems in preparation for the retirement of the Space Shuttle by 2010, as directed in the United States (U.S.) Vision for Space Exploration. The Ares I Crew Launch Vehicle (CLV) and the Ares V heavy-lift Cargo Launch Vehicle (CaLV) systems will build upon proven, reliable hardware derived from the Apollo Saturn (1961 to 1975) and Space Shuttle (1972 to 2010) programs to deliver safe, reliable, affordable space transportation solutions. This approach leverages existing aerospace talent and a unique infrastructure, as well as the vast amount of legacy knowledge gained from almost a half-century of hard-won experience in the space enterprise. Beginning early next decade, the Ares I will launch the new Crew Exploration Vehicle (CEV) to the International Space Station (ISS) or to low-Earth orbit for trips to the Moon and, ultimately, Mars. Late next decade, the Ares V's Earth Departure Stage will carry larger payloads such as the lunar lander into orbit, and the Crew Exploration Vehicle will dock with it for missions to the Moon, where astronauts will explore new territories and conduct science and technology experiments. Both the Ares I and Ares V systems are being designed to support longer future trips to Mars. The Exploration Launch Projects Office, located at NASA's Marshall Space Flight Center, is designing, developing, testing, and evaluating both launch vehicle systems in partnership with other NASA Centers, Government agencies, and industry contractors. This paper provides top-level information regarding the genesis and evolution of the baseline configuration for the Ares V heavy-lift system. It also touches on risk-based management strategies, such as building on powerful hardware and promoting common features between the Ares I and Ares V systems to reduce technical, schedule, and cost risks, as well as development and operations costs. Finally, it gives a summary of several notable accomplishments over the past year, since the Exploration Launch Projects effort officially kicked off in October 2005, and looks ahead at work planned for 2007 and beyond.

Sumrall, John P.↗