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NASA NTRS2007

The Roles of Verification, Validation and Uncertainty Quantification in the NASA Standard for Models and Simulations

The National Aeronautics and Space Administration (NASA) recently issued an interim version of the Standard for Models and Simulations (M&S Standard) [1]. The action to develop the M&S Standard was identified in an internal assessment [2] of agency-wide changes needed in the wake of the Columbia Accident [3]. The primary goal of this standard is to ensure that the credibility of M&S results is properly conveyed to those making decisions affecting human safety or mission success criteria. The secondary goal is to assure that the credibility of the results from models and simulations meets the project requirements (for credibility). This presentation explains the motivation and key aspects of the M&S Standard, with a special focus on the requirements for verification, validation and uncertainty quantification. Some pilot applications of this standard to computational fluid dynamics applications will be provided as illustrations. The authors of this paper are the members of the team that developed the initial three drafts of the standard, the last of which benefited from extensive comments from most of the NASA Centers. The current version (number 4) incorporates modifications made by a team representing 9 of the 10 NASA Centers. A permanent version of the M&S Standard is expected by December 2007. The scope of the M&S Standard is confined to those uses of M&S that support program and project decisions that may affect human safety or mission success criteria. Such decisions occur, in decreasing order of importance, in the operations, the test & evaluation, and the design & analysis phases. Requirements are placed on (1) program and project management, (2) models, (3) simulations and analyses, (4) verification, validation and uncertainty quantification (VV&UQ), (5) recommended practices, (6) training, (7) credibility assessment, and (8) reporting results to decision makers. A key component of (7) and (8) is the use of a Credibility Assessment Scale, some of the details of which were developed in consultation with William Oberkampf, David Peercy and Timothy Trocano of Sandia National Laboratories. The focus of most of the requirements, including those for VV&UQ, is on the documentation of what was done and the reporting, using the Credibility Assessment Scale, of the level of rigor that was followed. The aspects of one option for the Credibilty Assessment Scale are (1) code verification, (2) solution verification, (3) validation, (4) predictive capability, (5) technical review, (6) process control, and (7) operator and analyst qualification.

Zang, Thomas A.↗

NASA NTRS2018

Qualifying Bulk Metallic Glass Gear Materials for Spacecraft Applications

NASA is evaluating bulk metallic glass (BMG) gears for extreme environment (cryogenic) applications; e.g., Europa Lander. The main purpose of this report is to recommend a quality assurance (QA) protocol for the production of consistent and reliable gear castings. Currently, there are two, separate manufacturers involved; Materion Corporation produces re-melt stock and Visser Precision Cast, Inc. produces BMG castings. Division of the existing alloy specifications document into material supplier-specific documents is proposed. Until a composition-based specification is established, processability- and performance-based methodologies may be an option during manufacturing development. It is recommended that each of the documents has a distinct focus; the processing behavior of crystalline feedstock, and the mechanical behavior of amorphous castings. The report addresses the “gray area” in QA testing between these materials suppliers by outlining an equitable division of responsibilities. The use of a number of dedicated reference dies to produce witness materials for physical and mechanical property evaluation is strongly recommended. Allocation of QA tests between screen testing of gear castings, and formal testing of witness materials, including cryogenic properties, is also proposed. The most effective suite of tests for both physical and mechanical property determination are down-selected from available national and international standards. The contents of this report create a solid basis for selection of QA tests, thereby setting the stage for negotiations between the materials suppliers and the customer.This technical paper:a) provides recommendations to advance materials specifications document JPL D-56223,Rev. A from “draft” to “preliminary” status;b) proposes division of the current document into two supplier-specific documents;c) separates testing methods by “ingots/castings” and “witness materials”;d) classifies test methodology based on “processability” and “performance”;e) assembles candidate ASTM specifications for “screen testing” and “formal testing”;f) identifies standard tests compatible with evaluation of BMG flexspline gears;g) suggests division of responsibilities for processability and performance testing; andh) addresses the QA “gray area” between production of ingots and castings.The report recommends that:a) processability- and performance-based QA methods might be used in lieu ofcompositional specifications during manufacturing development only;b) reference dies be designed for “acceptance” and “qualification” castings;c) witness materials provide physical and mechanical property data;d) formal testing be conducted at ambient and cryogenic temperatures; ande) processing/properties be correlated with compositional variations.

Hales, Stephen J.↗

NASA NTRS2013

NASA Activity Update for the 2013 Unmanned Vehicle Systems International (UVSI) Yearbook

This year s report offers a high level perspective on some of the UAS related activities in which NASA is involved, both internal and external to the agency. Internally, NASA issued UAS operational policy on certification of NASA UAS and aircrew. A team of NASA UAS experts and operators analyzed all current procedures and best practices to design the policy. An update to the agencies Aircraft Operations Management Manual incorporated a new chapter to address UAS planning, preflight operations, flight operations, flight crew requirements, airworthiness and flight safety reviews. NASA UAS are classified into three categories based on weight and airspeed. Aircrews, including observers, are classified by how they interface with the UAS, and the policy defines qualifications, training, and currency. The NASA flight readiness approval process identifies risks and mitigations in order to reduce the likelihood and/or consequence of the risk to an acceptable level. The UAS operations process incorporates all aspects of airworthiness, flight standards and range safety exactly the same processes used for NASA manned aircraft operations. NASA has two internal organizations that routinely operate UAS. The Science Mission Directorate utilizes UAS as part of its Airborne Science Program and is the most frequent operator of NASA UAS in both national and international airspace. The Aeronautics Research Mission Directorate conducts UAS flight operations in addition to conducting research important to the UAS community. This past year the Science Mission Directorate supported the Hurricane and Severe Storm Sentimental (HS3) Mission with two NASA Global Hawk platforms. HS3 is a five-year mission specifically targeted to investigate the processes that underlie hurricane formation. During the 2012 portion of this mission the Global Hawk overflew hurricanes Leslie and Nadine in the Atlantic Ocean completing 6 flights and accumulating more than 148 flight hours. Another multi-year mission was initiated last year when the Sensor Integrated Environmental Remote Research Aircraft (SIERRA) UAS began surveying faults in California s Surprise Valley. A team of scientists and engineers from the United States Geological Survey (USGS), NASA Ames Research Center, Central Washington University, and Carnegie Mellon University will measure magnetic fields using ground surveys and the SIERRA to map the geophysics below the surface of Surprise Valley. The data collected will be used to generate 3D maps of the geophysical data of the area. The Aeronautics Mission Directorate continues its collaboration with Boeing to conduct UAS flight operations of the X-48C, a modified version of the X-48B originally built by Cranfield Aerospace, United Kingdom. The Aeronautics Mission Directorate utilizes vehicles of this size for a wide variety of research studies. Most of these operations are conducted within restricted airspace. The Aeronautics Research Mission Directorate also sponsors the UAS in the National Airspace System (NAS) Project, which is working in close cooperation with the Federal Aviation Administration (FAA) to address critical challenges associated with routine UAS operations in civil airspace. The project is focused on separation assurance and collision avoidance systems and algorithms, command and control for non-military operations including spectrum allocation requirements, human system interaction issues, and safety and certification topics.

Bauer, Jeffrey E.↗