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NASA NTRSDate not supplied

Experimental Methods Using Force Application of A Single Boom for A 500-M²-Class Solar Sail

Solar sailing missions rely on deployable systems for large area-to-mass ratios once in space, while still being small enough for launcher envelopes in the stowed configuration. Many of these deployable systems feature booms that are flattened and subsequently coiled onto a spool / hub. As part of a collaborative deployable space structures research effort between the National Aeronautics and Space Administration (NASA) and German Aerospace Center (DLR), a boom deployment system for a future 500 m² solar sail has been developed. To achieve the respective solar sail size goal, 16.5-m-long booms produced by NASA were integrated into a DLR-designed deployer mechanism. This considerable size, as well as the lightweight construction of the booms and respective deployable systems makes testing on the ground a significant challenge. Some systems for gravity compensation as well as vertical testing to minimize the influence of gravity have been used in the past. However, an uncertainty factor remains towards the behaviour in the space environment. The focus of this paper is the load application testing of the integrated boom-deployment mechanism system under microgravity condition, as well as a comparison to vertical testing under gravity. Testing in microgravity was performed during a parabolic flight test inside an aircraft and it included stowage and full deployment of a single boom along the longitudinal axis of the aircraft. The load application was split into two categories: static testing, which induced a linear force ramp to the static boom for either compression or compression-bending; and dynamic testing, which applied a constant force to a boom during extension provided by the deployer mechanism. Both types of tests were performed multiple times at two distinct lengths of the boom, fully deployed (12.76 m) and ~28.6 % deployed (3.65 m). More parameters that are vital to the test philosophy are the angles of attack in the force application and the highest force applied. The data acquisition used for the applied load and deflection measurements of the boom is also presented.

Martin Richter↗

NASA NTRS2009

Extravehicular Activity Testing in Analog Environments: Evaluating the Effects of Center of Gravity and Environment on Human Performance

The EVA Physiology, Systems and Performance (EPSP) Project is performing tests in different analog environments to understand human performance during Extravehicular Activity (EVA) with the aim of developing more safe and efficient systems for lunar exploration missions and the Constellation Program. The project is characterizing human EVA performance in studies using several test beds, including the underwater NASA Extreme Environment Mission Operations (NEEMO) and Neutral Buoyancy Laboratory (NBL) facilities, JSC fs Partial Gravity Simulator (POGO), and the NASA Reduced Gravity Office (RGO) parabolic flight aircraft. Using these varied testing environments, NASA can gain a more complete understanding of human performance issues related to EVA and the limitations of each testing environment. Tests are focused on identifying and understanding the EVA system factors that affect human performance such as center of gravity (CG), inertial mass, ground reaction forces (GRF), suit weight, and suit pressure. The test results will lead to the development of lunar EVA systems operations concepts and design requirements that optimize human performance and exploration capabilities. METHODS: Tests were conducted in the NBL and during NEEMO missions in the NOAA Aquarius Habitat. A reconfigurable back pack with repositionable mass was used to simulate Perfect, Low, Forward, High, Aft and NASA Baseline CG locations. Subjects performed simulated exploration tasks that included ambulation, kneel and recovery, rock pick-up, and shoveling. Testing using POGO, that simulates partial gravity via pneumatic weight offload system and a similar reconfigurable rig, is underway for a subset of the same tasks. Additionally, test trials are being performed on the RGO parabolic flight aircraft. Subject performance was assessed using a modified Cooper-Harper scale to assess operator compensation required to achieve desired performance. All CG locations are based on the assumption of a standardized 6 ft 180 lb subject. RESULTS: The modified Cooper-Harper Scale assesses desired task performance described as performance in a reduced gravity environment as compared to a 1G environment. Modified Cooper-Harper ratings of . 3 indicate no improvements are needed, ratings of 4-6 indicate improvements are desirable, and ratings . 7 indicate improvements are mandatory. DISCUSSION: Differences were noted in suited CH results based on environment at the same CG and suit pressure. Additionally, results suggest that CG location affects unsuited human performance. Subjects preferred locations near their natural CG over those that are high, aft, or a combination of high and aft. Further testing and analyses are planned to compare these unsuited results to suited performance.

Gernhardt, M.L.↗

NASA NTRS2015

Improved Band-to-Band Registration Characterization for VIIRS Reflective Solar Bands Based on Lunar Observations

Spectral bands of the Visible Infrared Imaging Radiometer Suite (VIIRS) instrumentaboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite are spatially co-registered.The accuracy of the band-to-band registration (BBR) is one of the key spatial parameters that must becharacterized. Unlike its predecessor, the Moderate Resolution Imaging Spectroradiometer (MODIS), VIIRS has no on-board calibrator specifically designed to perform on-orbit BBR characterization.To circumvent this problem, a BBR characterization method for VIIRS reflective solar bands (RSB) based on regularly-acquired lunar images has been developed. While its results can satisfactorily demonstrate that the long-term stability of the BBR is well within +/- 0.1 moderate resolution bandpixels, undesired seasonal oscillations have been observed in the trending. The oscillations are most obvious between the visiblenear-infrared bands and short-middle wave infrared bands. This paper investigates the oscillations and identifies their cause as the band spectral dependence of the centroid position and the seasonal rotation of the lunar images over calibration events. Accordingly, an improved algorithm is proposed to quantify the rotation and compensate for its impact. After the correction, the seasonal oscillation in the resulting BBR is reduced from up to 0.05 moderate resolution band pixels to around 0.01 moderate resolution band pixels. After removing this spurious seasonal oscillation, the BBR, as well as its long-term drift are well determined.

Wang, Zhipeng↗

NASA NTRS2014

A Modular Aerospike Engine Design Using Additive Manufacturing

A modular aerospike engine concept has been developed with the objective of demonstrating the viability of the aerospike design using additive manufacturing techniques. The aerospike system is a self-compensating design that allows for optimal performance over the entire flight regime and allows for the lowest possible mass vehicle designs. At low altitudes, improvements in Isp can be traded against chamber pressure, staging, and payload. In upper stage applications, expansion ratio and engine envelope can be traded against nozzle efficiency. These features provide flexibility to the System Designer optimizing a complete vehicle stage. The aerospike concept is a good example of a component that has demonstrated improved performance capability, but traditionally has manufacturing requirements that are too expensive and complex to use in a production vehicle. In recent years, additive manufacturing has emerged as a potential method for improving the speed and cost of building geometrically complex components in rocket engines. It offers a reduction in tooling overhead and significant improvements in the integration of the designer and manufacturing method. In addition, the modularity of the engine design provides the ability to perform full scale testing on the combustion devices outside of the full engine configuration. The proposed design uses a hydrocarbon based gas-generator cycle, with plans to take advantage of existing powerhead hardware while focusing DDT&E resources on manufacturing and sub-system testing of the combustion devices. The major risks for the modular aerospike concept lie in the performance of the propellant feed system, the structural integrity of the additive manufactured components, and the aerodynamic efficiency of the exhaust flow.

Peugeot, John↗

NASA NTRS1972

Ephemeris of a highly eccentric orbit - Explorer 28.

An ephemeris has been obtained for Explorer 28 (IMP 3) which agrees well with 2 years of radio observations and with SAO observations a year later. This ephemeris is generated over the 3 year lifetime by a numerical integration method utilizing a set of initial conditions at launch and without requiring further differential correction. Because highly eccentric orbits are difficult to compute with acceptable accuracy and because a long continuous arc has been obtained which compares with actual data to a known precision, this ephemeris may be used as a standard for computing highly eccentric orbits in the earth-moon system. Orbit improvement was used to obtain the initial conditions which generated the ephemeris. This improvement was based on correcting the energy by adjusting the semimajor axis to match computed times of perigee passage with the observed. This procedure may generate errors in semimajor axis to compensate for model errors in the energy; however, this compensation error is also implicit in orbit determination itself.

Lowrey, B. E.↗

NASA NTRS2009

Use of Intermittent Recompression and Nitrox Breathing Mixtures during Lunar Extravehicular Activities

INTRODUCTION: NASA's plans for lunar surface exploration include pressurized suitport rovers that are quickly ingressed and egressed with minimal consumables losses. This capability enables crewmembers to perform multiple short extravehicular activities (EVAs) at different locations in a single day versus a single 8-hr EVA. Modeling work and empirical human and animal data indicate that intermittent recompressions between EVA suit pressure and cabin pressure reduce decompression stress. Savings in crew time and gas losses may also be achieved if the N2 purge is shortened to 2 minutes, achieving 80% O2 (vs. 8 minutes, 95% O2). METHODS: A validated Tissue Bubble Dynamics Model was used to predict decompression stress using 80% and 95% O2 breathing mixtures during 3 x 2-hr EVAs (4.3 PSIA) with 1hr recompressions back to 8.0 PSIA (32% O2) versus a single 8-hr EVA. 15 minutes was spent at 6.0 PSIA before depressurizations to 4.3 PSIA; initial EVA tasks could be performed during this time. Model validation was based on significant prediction (p<0.001) and goodness of fit with 84 cases of DCS in 668 altitude exposures (McFadden s rho-squared=0.214). RESULTS: A 2.2% predicted increase in DCS risk due to the shortened purge is more than compensated for by a predicted 2.5% reduction in DCS risk due to intermittent recompression. 15 minutes at 80% O2, 6.0 PSIA prior to a 4.3 PSIA EVA prevents supersaturation in the brain and spinal cord (5-10 minute half-time compartments) and reduces tissue tensions in 40 min compartments, where most of the body s inert gas is located, to approximately the same levels (4.39 vs 4.00 PSIA) as achieved during a 40 min 95% O2 prebreathe at 10.2 PSIA. CONCLUSIONS: Intermittent recompressions between lunar EVAs may enable reductions in suit purge and prebreathe requirements, decompression stress, and/or suit operating pressures.

Gernhardt, M.L.↗

NASA NTRS1994

Acceleration recorder and playback module

The present invention is directed to methods and apparatus relating to an accelerometer electrical signal recorder and playback module. The recorder module may be manufactured in lightweight configuration and includes analog memory components to store data. Signal conditioning circuitry is incorporated into the module so that signals may be connected directly from the accelerometer to the recorder module. A battery pack may be included for powering both the module and the accelerometer. Timing circuitry is included to control the time duration within which data is recorded or played back so as to avoid overloading the analog memory components. Multiple accelerometer signal recordings may be taken simultaneously without analog to digital circuits, multiplexing circuitry or software to compensate for the effects of multiplexing the signals.

Bozeman, Richard J., Jr.↗

NASA NTRS1996

Acceleration Recorder and Playback Module

Bozeman, Richard J., Jr.↗

NASA NTRS1986

Thermal stability tests of CFRP sandwich panels for far infrared astronomy

An account is given of fabrication methods and low temperature figure tests for CFRP sandwich panels, in order to ascertain their applicability to ultralightweight 3-m aperture primary mirrors for balloon-borne sub-mm and far-IF telescopes that must maintain a 1-2 micron rms surface figure accuracy at -40 to -50 C. Optical figure measurements on the first two of a series of four 0.5-m test panels, replicated to a spherical surface, show a radius-of-curvature change and astigmatism down to -60 C; this approximately follows the composite's theoretical predictions and implies that material and process control is excellent, so that the large scale changes observed can be compensated for.

Hoffmann, W. F.↗

NASA NTRS1989

The role of topography in geodetic gravity field modelling

Masses associated with the topography, bathymetry, and its isostatic compensation are a dominant source of gravity field variations, especially at shorter wavelengths. On global scales the topographic/isostatic effects are also significant, except for the lowest harmonics. In practice, though, global effects need not be taken into account as such effects are included in the coefficients of the geopotential reference fields. On local scales, the short-wavelength gravity variations due to the topography may, in rugged terrain, be an order of magnitude larger than other effects. In such cases, explicit or implicit terrain reduction procedures are mandatory in order to obtain good prediction results. Such effects may be computed by space-domain integration or by fast Fourier transformation (FFT) methods. Numerical examples are given for areas of the Canadian Rockies. In principle, good knowledge of the topographic densities is required to produce the smoothest residual field. Densities may be determined from sample measurements or by gravimetric means, but both are somewhat troublesome methods in practice. The use of a standard density, e.g., 2.67 g/cu cm, may often yield satisfactory results and may be put within a consistent theoretical framework. The independence of density assumptions is the key point of the classical Molodensky approach to the geodetic boundary value problem. The Molodensky solutions take into account that land gravity field observations are done on a non-level surface. Molodensky's problem may be solved by integral expansions or more effective FFT methods, but the solution should not be intermixed with the use of terrain reductions. The methods are actually complimentary and may both be required in order to obtain the smoothest possible signal, least prone to aliasing and other effects coming from sparse data coverage, typical of rugged topography.

Forsberg, R.↗

NASA NTRS1978

Microwave radiometer measurement of water vapor path delay: Data reduction techniques

Data reduction techniques are developed to compensate for water vapor path delay, a limiting error source in geodetic measurements made with very long baseline interferometry and in radio ranging to spacecraft. It is shown that water vapor path delay is proportional to a linear combination of saturation-corrected sky brightness temperatures, measured on and off the water vapor line. The effects of emission from liquid water droplets in clouds as well as most of the oxygen emission are removed by the off-line channel. Sky brightness temperatures are saturation-corrected or 'linearized' using estimates of effective sky temperatures made from surface temperature. Tipping curves are used to remove instrumental error. Coefficients are found by two methods: from a regression analysis of measured brightness temperatures versus radiosonde measured delay, and from a regression analysis of theoretical brightness temperatures versus radiosonde measured delay. In each case the coefficients are adjusted for differing climatic conditions by measurements of surface temperature, pressure, and relative humidity. Regression solutions are constrained to remove liquid water contributions and to give the correct slope for radiometer versus radiosonde path delay.

Claflin, E. S.↗

NASA NTRS2017

Thermally-Conductive Metallic Coatings and Applications for Heat Removal on In-Space Cryogenic Vehicles

For large in-space cryogenic upper stages, substantial axial heat removal from a forward skirt by vapor-based heat interception may not be achieved by simple attachment methods unless sufficient thermal conductance from the skirt to the cooling fluid can be achieved. Preferable methods would allow for the addition of the cooling system to existing structure with minimal impact on the structure. Otherwise, significant modification to the basic structural design andor novel and complex attachment mechanisms with high effective thermal conductance are likely to be required. The approach being pursued by evolvable Cryogenics (eCryo) is to increase the thermal performance of a relatively simple attachment system by applying metallic or other thermally conductive material coatings to the mating surface area of the fluid channel where it is attached the skirt wall. The expectation of candidate materials is that the dramatic increase in conductivity of pure metals at temperatures close to liquid hydrogen vapor temperature will compensate for the reduced actual contact area typical of mechanical joints. Basic contact conductance data at low temperatures for candidate interface materials is required to enable the test approach. A test rig was designed at NASA Glenn Research Center to provide thermal contact resistance testing between small sample coupons coated with conductive material via electron beam evaporation, a low-temperature option that will not affect physical properties of base materials. Average coating thicknesses were 10 k. The test fixture was designed to mount directly to a cryocooler cold head within a vacuum test chamber. The purpose of this test was to determine qualitative contact conductance between various test samples. Results from this effort will be implemented in a sub-scale vapor-based heat interception test, where the applicability for increased heat removal on large structural skirts will be considered.

small scale testing↗

NASA NTRS1996

Cascade Error Projection: A Learning Algorithm for Hardware Implementation

In this paper, we workout a detailed mathematical analysis for a new learning algorithm termed Cascade Error Projection (CEP) and a general learning frame work. This frame work can be used to obtain the cascade correlation learning algorithm by choosing a particular set of parameters. Furthermore, CEP learning algorithm is operated only on one layer, whereas the other set of weights can be calculated deterministically. In association with the dynamical stepsize change concept to convert the weight update from infinite space into a finite space, the relation between the current stepsize and the previous energy level is also given and the estimation procedure for optimal stepsize is used for validation of our proposed technique. The weight values of zero are used for starting the learning for every layer, and a single hidden unit is applied instead of using a pool of candidate hidden units similar to cascade correlation scheme. Therefore, simplicity in hardware implementation is also obtained. Furthermore, this analysis allows us to select from other methods (such as the conjugate gradient descent or the Newton's second order) one of which will be a good candidate for the learning technique. The choice of learning technique depends on the constraints of the problem (e.g., speed, performance, and hardware implementation); one technique may be more suitable than others. Moreover, for a discrete weight space, the theoretical analysis presents the capability of learning with limited weight quantization. Finally, 5- to 8-bit parity and chaotic time series prediction problems are investigated; the simulation results demonstrate that 4-bit or more weight quantization is sufficient for learning neural network using CEP. In addition, it is demonstrated that this technique is able to compensate for less bit weight resolution by incorporating additional hidden units. However, generation result may suffer somewhat with lower bit weight quantization.

Duong, Tuan A.↗

NASA NTRS2002

Radiometric Characterization of IKONOS Multispectral Imagery

A radiometric characterization of Space Imaging's IKONOS 4-m multispectral imagery has been performed by a NASA funded team from the John C. Stennis Space Center (SSC), the University of Arizona Remote Sensing Group (UARSG), and South Dakota State University (SDSU). Both intrinsic radiometry and the effects of Space Imaging processing on radiometry were investigated. Relative radiometry was examined with uniform Antarctic and Saharan sites. Absolute radiometric calibration was performed using reflectance-based vicarious calibration methods on several uniform sites imaged by IKONOS, coincident with ground-based surface and atmospheric measurements. Ground-based data and the IKONOS spectral response function served as input to radiative transfer codes to generate a Top-of-Atmosphere radiance estimate. Calibration coefficients derived from each vicarious calibration were combined to generate an IKONOS radiometric gain coefficient for each multispectral band assuming a linear response over the full dynamic range of the instrument. These calibration coefficients were made available to Space Imaging, which subsequently adopted them by updating its initial set of calibration coefficients. IKONOS imagery procured through the NASA Scientific Data Purchase program is processed with or without a Modulation Transfer Function Compensation kernel. The radiometric effects of this kernel on various scene types was also investigated. All imagery characterized was procured through the NASA Scientific Data Purchase program.

Pagnutti, Mary↗

NASA NTRS1982

Reliability and performance experience with flat-plate photovoltaic modules

Statistical models developed to define the most likely sources of photovoltaic (PV) array failures and the optimum method of allowing for the defects in order to achieve a 20 yr lifetime with acceptable performance degradation are summarized. Significant parameters were the cost of energy, annual power output, initial cost, replacement cost, rate of module replacement, the discount rate, and the plant lifetime. Acceptable degradation allocations were calculated to be 0.0001 cell failures/yr, 0.005 module failures/yr, 0.05 power loss/yr, a 0.01 rate of power loss/yr, and a 25 yr module wear-out length. Circuit redundancy techniques were determined to offset cell failures using fault tolerant designs such as series/parallel and bypass diode arrangements. Screening processes have been devised to eliminate cells that will crack in operation, and multiple electrical contacts at each cell compensate for the cells which escape the screening test and then crack when installed. The 20 yr array lifetime is expected to be achieved in the near-term.

Ross, R. G., Jr.↗

NASA NTRS2023

Development of a Field-Deployable Microphone Phased Array for Airframe Noise Flyover Measurements

This technical memorandum describes in detail the construction and use of a large channel-count, field-deployable microphone phased array designed for airframe noise flyover measurements for a range of aircraft types and scales. The array incorporated 185 hardened, weather-resistant sensors suitable for outdoor use. A custom 4-mA current loop receiver circuit with temperature compensation was developed to power the sensors over extended cable lengths with minimal loss of signal-to-noise. Extensive calibrations and performance testing of the sensors were conducted to verify the design specifications. A compact data system combining sensor power, signal conditioning, and digitization was assembled for use with the array. Complementing the data system was a robust analysis system capable of near real-time presentation of beamformed and deconvolved contour plots and integrated spectra obtained from data acquired during flyover passes of the array. Additional instrumentation systems needed to process the array data were also developed, including a commercial 10-meter weather station comprised of a sonic anemometer, aspirated temperature/humidity probe and pressure sensor. Unique methods for assessing the health of the array in-situ were developed and demonstrated. A detailed mock-up of the instrumentation suite (phased array, weather station, and data processor) was performed in the NASA Langley Acoustic Development Laboratory in 2014 to vet the system performance. Issues with the sensors and electronics were identified during the mock-up and subsequently corrected. The array was then deployed for preliminary field testing at Fort A.P. Hill in Virginia in 2015 followed by the array being utilized in three separate full-scale airframe noise test campaigns at Edwards Air Force Base in California from 2016 to 2018 where the system was used to characterize the noise generated by both baseline and treated flaps and main landing gear on a commercial transport-sized vehicle.

Phased Array↗

NASA NTRS1976

Response of deep and shallow tropical maritime cumuli to large-scale processes

The bulk diagnostic method of Yanai et al. (1973) and a simplified version of the spectral diagnostic method of Nitta (1975) are used for a more quantitative evaluation of the response of various types of cumuliform clouds to large-scale processes, using the same data set in the Marshall Islands area for a 100-day period in 1956. The dependence of the cloud mass flux distribution on radiative cooling, large-scale vertical motion, and evaporation from the sea is examined. It is shown that typical radiative cooling rates in the tropics tend to produce a bimodal distribution of mass spectrum exhibiting deep and shallow clouds. The bimodal distribution is further enhanced when the large-scale vertical motion is upward, and a nearly unimodal distribution of shallow clouds prevails when the relative cooling is compensated by the heating due to the large-scale subsidence. Both deep and shallow clouds are modulated by large-scale disturbances. The primary role of surface evaporation is to maintain the moisture flux at the cloud base.

Yanai, M.↗

NASA NTRS2005

Ionizing Radiation Environment on the International Space Station: Performance vs. Expectations for Avionics and Material

The role of structural shielding mass in the design, verification, and in-flight performance of International Space Station (ISS), in both the natural and induced orbital ionizing radiation (IR) environments, is reported. Detailed consideration of the effects of both the natural and induced ionizing radiation environment during ISS design, development, and flight operations has produced a safe, efficient manned space platform that is largely immune to deleterious effects of the LEO ionizing radiation environment. The assumption of a small shielding mass for purposes of design and verification has been shown to be a valid worst-case approximation approach to design for reliability, though predicted dependences of single event effect (SEE) effects on latitude, longitude, SEP events, and spacecraft structural shielding mass are not observed. The Figure of Merit (FOM) method over predicts the rate for median shielding masses of about 10g/cm(exp 2) by only a factor of 3, while the Scott Effective Flux Approach (SEFA) method overestimated by about one order of magnitude as expected. The Integral Rectangular Parallelepiped (IRPP), SEFA, and FOM methods for estimating on-orbit (Single Event Upsets) SEU rates all utilize some version of the CREME-96 treatment of energetic particle interaction with structural shielding, which has been shown to underestimate the production of secondary particles in heavily shielded manned spacecraft. The need for more work directed to development of a practical understanding of secondary particle production in massive structural shielding for SEE design and verification is indicated. In contrast, total dose estimates using CAD based shielding mass distributions functions and the Shieldose Code provided a reasonable accurate estimate of accumulated dose in Grays internal to the ISS pressurized elements, albeit as a result of using worst-on-worst case assumptions (500 km altitude x 2) that compensate for ignoring both GCR and secondary particle production in massive structural shielding.

Koontz, Steven L.↗