Engineering topics

McNelis, Anne M.

Publications and source records attributed to McNelis, Anne M..

30 records · Page 2

NASA NTRS2010

Statistical Analysis of a Large Sample Size Pyroshock Test Data Set Including Post Flight Data Assessment

The Earth Observing System (EOS) Terra spacecraft was launched on an Atlas IIAS launch vehicle on its mission to observe planet Earth in late 1999. Prior to launch, the new design of the spacecraft's pyroshock separation system was characterized by a series of 13 separation ground tests. The analysis methods used to evaluate this unusually large amount of shock data will be discussed in this paper, with particular emphasis on population distributions and finding statistically significant families of data, leading to an overall shock separation interface level. The wealth of ground test data also allowed a derivation of a Mission Assurance level for the flight. All of the flight shock measurements were below the EOS Terra Mission Assurance level thus contributing to the overall success of the EOS Terra mission. The effectiveness of the statistical methodology for characterizing the shock interface level and for developing a flight Mission Assurance level from a large sample size of shock data is demonstrated in this paper.

Hughes, William O.↗

NASA NTRS2005

Verification of a 2 kWe Closed-Brayton-Cycle Power Conversion System Mechanical Dynamics Model

Vibration test data from an operating 2 kWe closed-Brayton-cycle (CBC) power conversion system (PCS) located at the NASA Glenn Research Center was used for a comparison with a dynamic disturbance model of the same unit. This effort was performed to show that a dynamic disturbance model of a CBC PCS can be developed that can accurately predict the torque and vibration disturbance fields of such class of rotating machinery. The ability to accurately predict these disturbance fields is required before such hardware can be confidently integrated onto a spacecraft mission. Accurate predictions of CBC disturbance fields will be used for spacecraft control/structure interaction analyses and for understanding the vibration disturbances affecting the scientific instrumentation onboard. This paper discusses how test cell data measurements for the 2 kWe CBC PCS were obtained, the development of a dynamic disturbance model used to predict the transient torque and steady state vibration fields of the same unit, and a comparison of the two sets of data.

Ludwiczak, Damian R.↗

NASA NTRS2004

Ground Based Microgravity Emissions Testing Of Flight Hardware

To control microgravity environment on the International Space Station (ISS), NASA developed payloads have to meet the payload integration requirements of the Space Station Program, specifically a microgravity allocation plan. The Microgravity Emissions Laboratory (MEL) was developed at NASA Glenn Research Center (GRC) for verification of the payloads compliance with payload integration requirements. MEL is a 6 degree of freedom inertial measurement system capable of characterizing the microgravity emissions, generated by a disturber, down to a micro g. Microgravity Emissions tests provide a payload developer with a tool to assess payload's compliance with the requirements, i.e. forces and moments, generated by the payload at its center of gravity. Forces and moments are presented in time domain for both stationary and transient signals, and in frequency domain for the stationary signals. To date, MEL conducted over thirty tests of ISS hardware. The test results are being successfully used by the payload developers for design verification and improvement.

Samorezov, Sergey↗

NASA NTRS2003

Microgravity Emissions Laboratory Testing of the Light Microscopy Module Control Box Fan

The Microgravity Emissions Laboratory (MEL) was developed at the NASA Glenn Research Center for the characterization, simulation, and verification of the International Space Station (ISS) microgravity environment. This Glenn lab was developed in support of the Fluids and Combustion Facility (FCF). The MEL is a six-degrees-of-freedom inertial measurement system that can characterize the inertial response forces (emissions) of components, subrack payloads, or rack-level payloads down to 10 7g. The inertial force output data generated from the steady-state or transient operations of the test article are used with finite element analysis, statistical energy analysis, and other analysis tools to predict the on-orbit environment at specific science or rack interface locations. Customers of the MEL have used benefits in isolation performance testing in defining available attenuation during the engineering hardware design phase of their experiment s development. The Light Microscopy Module (LMM) Control Box (LCB) fan was tested in the MEL in June and July of 2002. The LMM is planned as a remotely controllable on-orbit microscope subrack facility that will be accommodated in an FCF Fluids Integrated Rack on the ISS. The disturbances measured in the MEL test resulted from operation of the air-circulation fan within the LCB. The objectives of the testing were (1) to identify an isolator to be added to the LCB fan assembly to reduce fan-speed harmonics and (2) to identify the fan-disturbance forcing functions for use in rack-response analysis of the LMM and Fluids Integrated Rack facility. This report describes the MEL, the testing process, and the results from ground-based MEL LCB fan testing.

McNelis, Anne M.↗

NASA NTRS2003

Light Microscopy Module Fan Disturbance Characterized Through Microgravity Emissions Laboratory Testing

A Light Microscopy Module (LMM) is being engineered, designed, and developed at the NASA Glenn Research Center. The LMM is planned as a remotely controllable on-orbit microscope subrack facility, allowing flexible scheduling and control of physical science and biological science experiments within Glenn s Fluids Integrated Rack on the International Space Station. The LMM concept is a modified commercial research imaging light microscope with powerful laser-diagnostic hardware and interfaces, creating a one-of-a-kind, state-of-the-art microscopic research facility. The microscope will house several different objectives, corresponding to magnifications of 10, 40, 50, 63, and 100. Features of the LMM include high-resolution color video microscopy, brightfield, darkfield, phase contrast, differential interference contrast, spectrophotometry, and confocal microscopy combined in a single configuration. Also, laser tweezers are integrated with the diagnostics as a sample manipulation technique. As part of the development phase of the LMM, it was necessary to quantify the microgravity disturbances generated by the control box fan. Isolating the fan was deemed necessary to reduce the fan speed harmonic amplitudes and to eliminate any broadband disturbances across the 60- to 70-Hz and 160- to 170-Hz frequency ranges. The accelerations generated by a control box fan component of the LMM were measured in the Microgravity Emissions Laboratory (MEL). The MEL is a low-frequency measurement system developed to simulate and verify the on-orbit International Space Station (ISS) microgravity environment. The accelerations generated by various operating components of the ISS, if too large, could hinder the science performed onboard by disturbing the microgravity environment. The MEL facility gives customers a test-verified way of measuring their compliance with ISS limitations on vibratory disturbance levels. The facility is unique in that inertial forces in 6 degrees of freedom can be characterized simultaneously for an operating test article. Vibratory disturbance levels are measured for engineering or flight-level hardware following development from component to subassembly through the rack-level configuration. The MEL can measure accelerations as small as 10-7g, the accuracy needed to confirm compliance with ISS requirements.

McNelis, Anne M.↗

NASA NTRS2001

Microgravity Emissions Laboratory Developed

The Microgravity Emissions Laboratory (MEL) was developed for the support, simulation, and verification of the International Space Station microgravity environment. The MEL utilizes an inertial measurement system using acceleration emissions generated by various operating components of the space station. These emissions, if too large, could hinder the science performed on the space station by disturbing the microgravity environment. Typical test components are disk drives, pumps, motors, solenoids, fans, and cameras. These components will produce inertial forces, which disturb the microgravity on-orbit station environment. These components, usually housed within a station rack, must meet acceleration limits imposed at the rack interface for minimizing the onboard station-operating environment. The NASA Glenn Research Center developed this one-of-a-kind laboratory for testing components and, eventually, rack-level configurations. The MEL approach is to measure the component's generated inertial forces. This force is a product of the full diagonal mass matrix including the test setup (the center of gravity, mass moment of inertia, and weight) and the resolved diagonal rigid-body acceleration determined from measurements using the 10 apparatus accelerometers. The mass matrix can be test derived. The bifilar torsional pendulum method is used to measure the moment of inertia for the test component.

Goodnight, Thomas W.↗

NASA NTRS2000

Investigation of Acoustic Fields for the Cassini Spacecraft: Reverberant Versus Launch Environments

The characterization and understanding of the acoustic field within a launch vehicle's payload fairing (PLF) is critical to the qualification of a spacecraft and ultimately to the success of its mission. Acoustic measurements taken recently for the Cassini mission have allowed unique opportunities to advance the aerospace industry's knowledge in this field. Prior to its launch, the expected liftoff acoustic environment of the spacecraft was investigated in a full-scale acoustic test of a Titan IV PLF and Cassini simulator in a reverberant test chamber. A major goal of this acoustic ground test was to quantify and verify the noise reduction performance of special barrier blankets that were designed especially to reduce the Cassirii acoustic environment. This paper will describe both the ground test and flight measurements, and compare the Cassini acoustic environment measured during launch with that measured earlier in the ground test. Special emphasis will be given to the noise reduction performance of the barrier blankets and to the acoustic coherence measured within the PLF.

Hughes, William O.↗

NASA NTRS1999

Pyroshock Environments Characterized for Spacecraft Missions

Pyrotechnic shock, or pyroshock, is the transient response of a structure to loading induced by the ignition of pyrotechnic (explosive or propellant activated) devices. These devices are typically used to separate structural systems (e.g., separate a spacecraft from a launch vehicle) and deploy appendages (e.g., solar panels). Pyroshocks are characterized by high peak acceleration, high-frequency content, and short duration. Because of their high acceleration and high-frequency, pyroshocks can cause spaceflight hardware to fail. Verifying by test that spaceflight hardware can withstand the anticipated shock environment is considered essential to mission success. The Earth Observing System (EOS) AM-1 spacecraft for NASA's Mission to Planet Earth is scheduled to be launched on an Atlas IIAS vehicle in 1999, and the NASA Lewis Research Center is the launch vehicle integrator for this NASA Goddard Space Flight Center spacecraft. The EOS spacecraft was subjected to numerous ground shock tests to verify that its scientific instruments and avionics components will withstand the shock-induced vibration produced when the spacecraft separates from the launch vehicle. Shock test data from these tests represent the third largest available pyroshock database in the United States. Future spacecraft missions will directly benefit from the knowledge gained from these tests. The payload separation system used for EOS is a new system that operates by firing six separation nuts. This system was tested to verify its functional operation and to characterize the resulting shock levels. The launch vehicle contractor (Lockheed Martin Astronautics) and spacecraft contractor (Lockheed Martin Missiles & Space) completed 16 separation test firings. This resulted in an unusually large amount of pyroshock data. Typically, only one or two pyroshock test firings are performed for a spacecraft mission. Because of the size of this separation system shock database, engineers were able to perform unique statistical analyses to characterize the distribution of the test data. For example, it was proven that the shock data follow a lognormal distribution, a concept often assumed but rarely proven. The test-to-test repeatability of the shock source level was analyzed, and the effects of various test configurations and separation nut production lots were examined and quantified. Engineers investigated the change in shock level as the shock traveled from the spacecraft separation interface to the avionics components of the upper stage and analyzed the effects of the structural fidelity (simulator versus real) of the components and their weight on vibrational response. In addition, the shock attenuation with distance and across joints was quantified and compared with concepts originally generated in 1970, and the effects of separation nut preload and firing sequences effects were examined. Because of this EOS shock testing and the analyses performed at NASA Lewis, a significant amount of new information on pyroshock and its characteristics is now available to the aerospace industry. We hope that this information will help future spacecraft test planners to perform better and cheaper spacecraft separation shock tests and to better understand their test data.

Hughes, William O.↗

NASA NTRS1998

Statistical Treatment of Earth Observing System Pyroshock Separation Test Data

The Earth Observing System (EOS) AM-1 spacecraft for NASA's Mission to Planet Earth is scheduled to be launched on an Atlas IIAS vehicle in June of 1998. One concern is that the instruments on the EOS spacecraft are sensitive to the shock-induced vibration produced when the spacecraft separates from the launch vehicle. By employing unique statistical analysis to the available ground test shock data, the NASA Lewis Research Center found that shock-induced vibrations would not be as great as the previously specified levels of Lockheed Martin. The EOS pyroshock separation testing, which was completed in 1997, produced a large quantity of accelerometer data to characterize the shock response levels at the launch vehicle/spacecraft interface. Thirteen pyroshock separation firings of the EOS and payload adapter configuration yielded 78 total measurements at the interface. The multiple firings were necessary to qualify the newly developed Lockheed Martin six-hardpoint separation system. Because of the unusually large amount of data acquired, Lewis developed a statistical methodology to predict the maximum expected shock levels at the interface between the EOS spacecraft and the launch vehicle. Then, this methodology, which is based on six shear plate accelerometer measurements per test firing at the spacecraft/launch vehicle interface, was used to determine the shock endurance specification for EOS. Each pyroshock separation test of the EOS spacecraft simulator produced its own set of interface accelerometer data. Probability distributions, histograms, the median, and higher order moments (skew and kurtosis) were analyzed. The data were found to be lognormally distributed, which is consistent with NASA pyroshock standards. Each set of lognormally transformed test data produced was analyzed to determine if the data should be combined statistically. Statistical testing of the data's standard deviations and means (F and t testing, respectively) determined if data sets were significantly different at a 95-percent confidence level. If two data sets were found to be significantly different, these families of data were not combined for statistical purposes. This methodology produced three separate statistical data families of shear plate data. For each population, a P99.1/50 (probability/confidence) per-separation-nut firing level was calculated. By using the binomial distribution, Lewis researchers determined that this pernut firing level was equivalent to a P95/50 per-flight confidence level. The overall envelope of the per-flight P95/50 levels led to Lewis' recommended EOS interface shock endurance specification. A similar methodology was used to develop Lewis' recommended EOS mission assurance levels. The available test data for the EOS mission are significantly larger than for a normal mission, thus increasing the confidence level in the calculated expected shock environment. Lewis significantly affected the EOS mission by properly employing statistical analysis to the data. This analysis prevented a costly requalification of the spacecraft's instruments, which otherwise would have been exposed to significantly higher test levels.

McNelis, Anne M.↗

NASA NTRS1997

Acoustic Testing of the Cassini Spacecraft and Titan IV Payload Fairing: Results - Part 2

A Cassini spacecraft simulator in a full scale 60 foot high Titan 4 payload fairing with various acoustic blanket designs and configurations was recently tested in a large reverberant acoustic chamber. A first part companion paper provides the test configuration details and other background information. This paper addresses the results obtained from this test program. Emphasis will be on the effects of the new blanket designs on reducing the payload fairing's internal acoustics and the vibration response of the spacecraft's Radioisotope Thermoelectric Generators. Other results discussed include: the effect of blankets on fairing vibration, the effect of partial blanket coverage on acoustics and vibration and the effect of tuned vibration absorbers.

Hughes, William O.↗

NASA NTRS1997

Acoustic Testing of the Cassini Spacecraft and Titan 4 Payload Fairing: Introduction and Test Configuration - Part 1

NASA Lewis Research Center recently led a multi-organizational acoustic test program. This testing consisted of acoustically exciting a Cassini spacecraft simulator in a full scale 60 foot high Titan 4 payload fairing with various acoustic blanket designs and configurations in a large reverberant acoustic chamber. The primary purpose of this test program was to measure the fairing's internal acoustics and spacecraft vibration, especially the Radioisotope Thermoelectric Generators (RTG) vibration, and to quantify the mitigation efforts in reducing these levels. Key to this reduction effort was the utilization of new acoustic blanket designs. This paper will provide the background and rationale for performing this test program, state the test program's primary and secondary objectives and describe the test matrix, hardware and instrumentation. A second part companion paper will provide the test results and data analysis.

Hughes, William O.↗

NASA NTRS1996

Cassini/Titan-4 Acoustic Blanket Development and Testing

NASA Lewis Research Center recently led a multi-organizational effort to develop and test verify new acoustic blankets. These blankets support NASA's goal in reducing the Titan-4 payload fairing internal acoustic environment to allowable levels for the Cassini spacecraft. To accomplish this goal a two phase acoustic test program was utilized. Phase One consisted of testing numerous blanket designs in a flat panel configuration. Phase Two consisted of testing the most promising designs out of Phase One in a full scale cylindrical payload fairing. This paper will summarize this highly successful test program by providing the rationale and results for each test phase, the impacts of this testing on the Cassini mission, as well as providing some general information on blanket designs.

Hughes, William O.↗