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  • 1
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    An Alternative Lunar Ephemeris Model for On-Board Flight Software Use (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: In calculating the position vector of the Moon in on-board flight software, one often begins by using a series expansion to calculate the ecliptic latitude and longitude of the Moon, referred to the mean ecliptic and equinox of date. One then performs a reduction for precession, followed by a rotation of the position vector from the ecliptic plane to the equator, and a transformation from spherical to Cartesian coordinates before finally arriving at the desired result: equatorial J2000 Cartesian components of the lunar position vector. An alternative method is developed here in which the equatorial J2000 Cartesian components of the lunar position vector are calculated directly by a series expansion, saving valuable onboard computer resources.
    Keywords: Astronomy
    Type: 1999 Flight Mechanics Symposium; 175-184; NASA/CP-1999-209235
    Format: text
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  • 2
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    An Astronomical Test of CCD Photometric Precision (2001)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Ground-based differential photometry is limited to a precision of order 10(exp -3) because of atmospheric effects. A space-based photometer should be limited only by the inherent instrument precision and shot noise. Laboratory tests have shown that a precision of order 10-5 is achievable with commercially available charged coupled devices (CCDs). We have proposed to take this one step further by performing measurements at a telescope using a Wollaston prism as a beam splitter First-order atmospheric effects (e.g., extinction) will appear to be identical in the two images of each star formed by the prism and will be removed in the data analysis. This arrangement can determine the precision that is achievable under the influence of second-order atmospheric effects (e.g., variable point-spread function (PSF) from seeing). These telescopic observations will thus provide a lower limit to the precision that can be realized by a space-based differential photometer.
    Keywords: Astronomy
    Type: Third Workshop on Photometry; 95-102; NASA/CP-2000-209614
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  • 3
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    An Alternative Lunar Ephemeris Model for On-Board Flight Software Use (1998)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: In calculating the position vector of the Moon in on-board flight software, one often begins by using a series expansion to calculate the ecliptic latitude and longitude of the Moon, referred to the mean ecliptic and equinox of date. One then performs a reduction for precession, followed by a rotation of the position vector from the ecliptic plane to the equator, and a transformation from spherical to Cartesian coordinates before finally arriving at the desired result: equatorial J2000 Cartesian components of the lunar position vector. An alternative method is developed here in which the equatorial J2000 Cartesian components of the lunar position vector are calculated directly by a series expansion, saving valuable on-board computer resources.
    Keywords: Astronomy
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  • 4
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    Ground operation of robotics on Space Station Freedom (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: This paper reflects work carried out on Ground Operated Telerobotics (GOT) in 1992 to refine further the ideas, procedures, and technologies needed to test the procedures in a high latency environment, and to integrate GOT into Space Station Freedom operations. Space Station Freedom (SSF) will be in operation for 30 years, and will depend on robots to carry out a significant part of the assembly, maintenance, and utilization workload. Current plans call for on-orbit robotics to be operated by on-board crew members. This approach implies that on-orbit robotics operations use up considerable crew time, and that these operations cannot be carried out when SSF is unmanned. GOT will allow robotic operations to be operated from the ground, with on-orbit crew interventions only when absolutely required. The paper reviews how GOT would be implemented, how GOT operations would be planned and supported, and reviews GOT issues, critical success factors, and benefits.
    Keywords: MECHANICAL ENGINEERING
    Type: JPL, SpaceOps 1992: Proceedings of the Second International Symposium on Ground Data Systems for Space Mission Operations; p 51-55
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  • 5
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    From Top to Bottom - the Multiwavelength Campaign of V824 Ara (HD 155555) (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A great deal of progress has been made in recent years in decomposing the 2-D structure in the atmospheres of late-type stars. Doppler images of many photospheres single stars, T Tauri stars, Algols, RS CV(sub n) binaries to name a few - are regularly published (Strassmeier 1996; Richards and Albright 1996; Rice and Strassmeier 1996; Kuerster et al. 1994). Ultraviolet spectral images of chromospheres appear in the literature (e.g., Walter et al. 1987; Neff et al. 1989) but are less common owing to the difficult nature of obtaining complete phase coverage. Zeeman doppler images of magnetic fields are now feasible (e.g., Donati et al. 1992). Performing Doppler imaging of the same targets over many seasons has also been accomplished (e.g, Vogt et al. 1997). Even when a true image reconstruction is not possible due to poor spectral resolution, we can still infer a great deal about spatial structure if enough phases are observed. However, it is increasingly apparent that to make sense of recent results, many different spectral features spanning a range of formation temperature and density must be observed simultaneously for a coherent picture to emerge. Here we report on one such campaign. In 1996, we observed the southern hemisphere RS CV(sub n) binary V824 Ara (P=1(sup d).68, G5IV+K0V-IV-IV) over one complete stellar rotation with the Hubble Space Telescope and EUVE. In conjunction, radio and optical photometry and spectroscopy were obtained from the ground. Unique to this campaign is the complete phase coverage of a number of activity proxy indicators that cover source temperatures ranging from the photosphere to the corona.
    Keywords: Astronomy
    Type: NASA/CR-97-207189 , NAS 1.26:207189
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  • 6
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    Development of a full-scale transmission testing procedure to evaluate advanced lubricants (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Experimental tests were performed on the OH-58A helicopter main rotor transmission in the NASA Lewis 500-hp Helicopter Transmission Test Stand. The testing was part of a joint Navy/NASA/Army lubrication program. The objective of the program was to develop a separate lubricant for gearboxes and demonstrate an improved performance in life and load-carrying capacity. The goal of the experiments was to develop a testing procedure to fail certain transmission components using a MIL-L-23699 base reference oil, then run identical tests with improved lubricants and demonstrate performance. The tests were directed at failing components that the Navy has had problems with due to marginal lubrication. These failures included mast shaft bearing micropitting, sun gear and planet bearing fatigue, and spiral bevel gear scoring. A variety of tests were performed and over 900 hours of total run time accumulated for these tests. Some success was achieved in developing a testing procedure to produce sun gear and planet bearing fatigue failures. Only marginal success was achieved in producing mast shaft bearing micropitting and spiral bevel gear scoring.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TP-3265 , E-6531 , NAS 1.60:3265 , AVSCOM-TR-91-C-026 , AD-A257204
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  • 7
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    Vibration characteristics of OH-58A helicopter main rotor transmission (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Experimental vibration tests covering a range of torque and speed conditions were performed on the OH-58A helicopter main rotor transmission at the NASA Lewis Research Center. Signals from accelerometers located on the transmission housing were analyzed by using Fourier spectra, power spectral density functions, and averaging techniques. Most peaks of the Fourier spectra occurred at the spiral bevel and planetary gear mesh harmonics. The highest level of vibration occurred at the spiral bevel meshing frequency. Transmission speed and vibration measurement location had a significant effect on measured vibration; transmission torque and measurement direction had a small effect.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TP-2705 , E-3368 , NAS 1.60:2705 , AVSCOM-TR-86-C-42 , AD-A180364
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  • 8
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    Helicopter transmission testing at NASA Lewis Research Center (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The helicopter has evolved into a highly valuable air mobile vehicle for both military and civilian needs. The helicopter transmission requires advanced studies to develop a technology base for future rotorcraft advances. A joint helicopter transmission research program between the NASA Lewis Research Center and the U.S. Army Aviation Systems Command has existed since 1970. Program goals are to reduce weight and noise and to increase life and reliability. The current experimental activities at Lewis consist of full-scale helicopter transmission testing, a base effort in gearing technology, and a future effort in noise reduction technology. The experimental facilities at Lewis for helicopter transmission testing are described. A description of each of the rigs is presented along with some significant results and near-term plans.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-89912 , E-3603 , NAS 1.15:89912 , AVSCOM-TR-87-C-10
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  • 9
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    Predicted effect of dynamic load on pitting fatigue life for low-contact-ratio spur gears (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: How dynamic load affects the surface pitting fatigue life of external spur gears was predicted by using the NASA computer program TELSGE. Parametric studies were performed over a range of various gear parameters modeling low-contact-ratio involute spur gears. In general, gear life predictions based on dynamic loads differed significantly from those based on static loads, with the predictions being strongly influenced by the maximum dynamic load during contact. Gear mesh operating speed strongly affected predicted dynamic load and life. Meshes operating at a resonant speed or one-half the resonant speed had significantly shorter lives. Dynamic life factors for gear surface pitting fatigue were developed on the basis of the parametric studies. In general, meshes with higher contact ratios had higher dynamic life factors than meshes with lower contact ratios. A design chart was developed for hand calculations of dynamic life factors.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TP-2610 , E-2989 , NAS 1.60:2610 , AD-A170906 , AVSCOM-TR-86-C-21
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  • 10
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    Suppression of Subsynchronous Vibration in the SSME HPFTP (1991)
    In:  CASI
    Details
    Publication Date: 2014-09-24
    Description: Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump (HPFTP) hot-fire dynamic data evaluation and rotordynamic analysis both confirm that two of the most significant turbopump attributes in determining susceptibility to subsynchronous vibration are impeller interstage seal configuration and rotor sideload resulting from turbine turnaround duct configuration and hot gas manifold. Recent hot-fire testing has provided promising indications that the incorporation of roughened damping seals at the impeller interstages may further increase the stability margin of this machine. A summary of the analysis which led to the conclusion that roughened seals would enhance the stability margin is presented along with a correlation of the analysis with recent test data.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center, Rotordynamic Instability Problems in High-Performance Turbomachinery, 1990; p 191-202
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