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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Vehicle design considerations for active control application to subsonic transport aircraft

The state of the art in active control technology is summarized. How current design criteria and airworthiness regulations might restrict application of this emerging technology to subsonic CTOL transports of the 1980's are discussed. Facets of active control technology considered are: (1) augmentation of relaxed inherent stability; (2) center-of-gravity control; (3) ride quality control; (4) load control; (5) flutter control; (6) envelope limiting, and (7) pilot interface with the control system. A summary and appraisal of the current state of the art, design criteria, and recommended practices, as well as a projection of the risk in applying each of these facets of active control technology is given. A summary of pertinent literature and technical expansions is included.

Hofmann, L. G.↗
NASA NTRS1973

Biological activity of ionene polymers

Ionene polymers are polyammonium salts with positive nitrogens in the backbone, resulting from the polycondensation of diamines with dihalides or from the polycondensation of halo amines. The mechanism of formation of ionene polymers of different structures and their biological activity is reviewed. The antimicrobial and antifungal properties are compared with low molecular weight ammonium salts. Ionenes were found to combine with DNA by means of ionic bonds to yield similar complexes to those obtained with polyamines (spermine and spermidine). They also combine with nerve cell receptors and exercise a more powerful and longer duration ganglionic blocking action than their monomeric analogs. The antiheparin activity of ionenes and the thromboresistance of elastomeric ionene heparin coatings is described. The enhanced biological activity of ionenes as compared with low molecular weight compounds is attributed to a cooperative effect of a large number of positive charges on the polymeric chains.

Rembaum, A.↗
NASA NTRS1974

A transonic study of active flutter suppression based on an aerodymamic energy concept

The application of active control technology to the suppression of flutter has been successfully demonstrated in the Langley transonic dynamics tunnel. This study involved the implementation of an aerodynamic-energy criterion to suppress flutter of a simplified delta-wing model. Use of this technique with both leading- and trailing-edge active controls has resulted in an increase in dynamic pressure of 22% above the basic wing flutter point and with only a trailing-edge active control has resulted in an increase in dynamic pressure of 30% above the basic wing flutter point at a Mach number of 0.9. Analytical methods used to predict the open- and closed-loop behavior of the model are also discussed.

Sandford, M. C.↗
NASA NTRS1974

Nondestructive activation analysis of sample of lunar surface material returned by Luna 16 automatic station

The composition of a sample of lunar surface material returned by the Luna 16 automatic station from the Sea of Fertility was studied, using nondestructive activation analysis. The structure of the returned surface material is inhomogeneous; the surficial material is thin, quite homogeneous, and the granularity increases with depth. Based on grain size, the sample was separated into five zones. The activation analysis was conducted on a sample taken from the friable surficial layer, zone A. The content of Al, Mn, Na, Cr, Co, Fe, and Sc was determined by nondestructive activation analysis of the sample. In determining Cr, Co, Fe, and Sc, the sample was irradiated for 24 hours and cooled for 10 days. Gamma spectra of the samples were recorded with a semiconductor Ge(Li)-detector and a multichannel analyzer, and measurement data were processed with an electronic computer.

Chayko, M.↗
NASA NTRS1975

Solar activity and its relation to certain parameters of phenomena in the geophysical complex

Results of a detailed analysis of solar activity in 1957-1965 are compared with the data on solar activity with variations of cosmic ray activity, and geomagnetic, ionospheric and terrestrial currents. Cosmic ray variations are investigated with reference to the asymmetry of solar hemispheres. All storms in the IGY are classified and a symbolic diagram of the time sequence is drawn up.

Razmadze, T. S.↗
NASA NTRS1975

Flutter suppression and gust alleviation using active controls

Application of the aerodynamic energy approach to some problems of flutter suppression and gust alleviation were considered. A simple modification of the control-law is suggested for achieving the required pitch control in the use of a leading edge - trailing edge activated strip. The possible replacement of the leading edge - trailing edge activated strip by a trailing edge - tab strip is also considered as an alternate solution. Parameters affecting the performance of the activated leading edge - trailing edge strip were tested on the Arava STOL Transport and the Westwind Executive Jet Transport and include strip location, control-law gains and a variation in the control-law itself.

Nissim, E.↗
NASA NTRS1975

A study for active control research and validation using the Total In-Flight Simulator (TIFS) aircraft

The results of a feasibility study and preliminary design for active control research and validation using the Total In-Flight Simulator (TIFS) aircraft are documented. Active control functions which can be demonstrated on the TIFS aircraft and the cost of preparing, equipping, and operating the TIFS aircraft for active control technology development are determined. It is shown that the TIFS aircraft is as a suitable test bed for inflight research and validation of many ACT concepts.

Chen, R. T. N.↗
NASA NTRS1974

Active Suppression of Pogo on the Space Shuttle

The use of active pogo suppressors on the space shuttle was qualitatively investigated. Suppressor design concepts and the effectiveness of these designs in maintaining the stability of the shuttle vehicle were the primary concerns. Suppressor design concepts were developed by means of a series of parametric stability analyses. These two designs together with two designs provided by NASA were evaluated in detail for control effectiveness, performance relative to a passive suppression device, sensitivity of performance to feedback error, suppressor volume flow requirements, and suppressor development requirements. An active device at the high pressure oxidizer pump inlet was shown to provide a simple and effective design that is insensitive to error in the feedback signal. The sizing of an active suppressor was demonstrated to be dependent upon knowledge of the dynamic characteristics of the system.

Lock, M. H.↗
NASA NTRS1975

Status and trends in active control technology

The emergence of highly reliable fly-by-wire flight control systems makes it possible to consider a strong reliance on automatic control systems in the design optimization of future aircraft. This design philosophy has been referred to as the control configured vehicle approach or the application of active control technology. Several studies and flight tests sponsored by the Air Force and NASA have demonstrated the potential benefits of control configured vehicles and active control technology. The present status and trends of active control technology are reviewed and the impact it will have on aircraft designs, design techniques, and the designer is predicted.

Rediess, H. A.↗
NASA NTRS1974

Skylab extravehicular activity

The use of extravehicular activity (EVA) techniques during Skylab for accomplishing major mission objectives and major and minor repair work outside the Skylab workshop is discussed. The basic feasibility of EVA was demonstrated during the Gemini Program. Extravehicular activity was again demonstrated on Apollo, and was used during the Apollo 15 to 17 missions to retrieve film from the cameras used to map the lunar surface. The techniques developed for these earlier extravehicular activities were used to the fullest possible extent during Skylab. Premission plans for Skylab EVA included six EVA periods for a total of 29 man-hours. The objective of the EVA was to retrieve the Apollo telescope mount film and several particle sample collectors. There were actually 10 EVA periods during Skylab that lasted 82.5 man-hours. Accomplishments included those planned before the mission; but, more important, the Skylab mission was saved by EVA. The life-saving solar wing was erected during Skylab 2, and the permanent solar shield was erected during Skylab 3. In addition, 18 extra mission objectives and 13 in-flight repair tasks were accomplished through EVA during the Skylab missions.

Schultz, D. C.↗
NASA NTRS1975

Radio detection of thunderstorm activity with an earth-orbiting satellite

A study was made to determine the feasibility of using artificial earth satellites to monitor thunderstorm activity. The nighttime noise-temperature measurements made with the earth-oriented vee antenna of the Radio Astronomy Explorer (RAE 1) satellite in the frequency range 0.2-9.2 MHz were correlated with reported surface thunderstorm activity. Analysis shows that the minimum nighttime HF noise level (in the absence of surface thunderstorms) at an altitude of 5850 km over the United States is fixed by man-made noise. When thunderstorms are active below the satellite, the noise level is increased by about 6-12 dB. The highest level is associated with the most intense storms. It is concluded that thunderstorm regions can be detected by an orbiting satellite using HF radio techniques, but ionospheric effects must be taken into account.

Herman, J. R.↗
NASA NTRS1975

Comments on the course of solar activity during the declining phase of solar cycle 20 /1970-74/

Observational data on sunspots, the 2800-MHz flux, and calcium plages are interpreted which were obtained during the declining phase of solar cycle 20. It is shown that three pulses of activity occurred during this period and resulted in two conspicuous 'stillstands' in the smooth means of the sunspot, 2800-MHz, and plage data. The longitudes of centers of sunspot and flare activity are found to have clustered in identifiable zones or hemispheres for relatively long periods of time. The sun is seen to have had a relatively inactive hemisphere centered about zero deg longitude, and certain well defined coronal holes were apparently located near the middle of this hemisphere. The first sunspot groups of cycle 21 are observed to have formed in the longitude zones associated with relatively high levels of activity during cycle 20.

Dodson, H. W.↗
NASA NTRS1977

Less-costly activated carbon for sewage treatment

Lignite-aided sewage treatment is based on absorption of dissolved pollutants by activated carbon. Settling sludge is removed and dried into cakes that are pyrolyzed with lignites to yield activated carbon. Lignite is less expensive than activated carbon previously used to supplement pyrolysis yield.

Ingham, J. D.↗
NASA NTRS1975

Global exospheric temperatures and densities under active solar conditions

Temperatures measured by the OGO-6 satellite using the 6300 A airglow spectrum are compared with temperatures derived from total densities and N2 densities. It is shown that while the variation of the total densities with latitude and magnetic activity agree well with values used for CIRA (1972), the temperature behavior is very different. While the temperatures derived from the N2 density were in much better agreement there were several important differences which radically affect the pressure gradients. The variation of temperature with magnetic activity indicated a seasonal and local time effect and also a latitude and delay time variation different from previous density derived temperatures. A new magnetic index is proposed that is better correlated with the observed temperatures. The temperature variations at high latitudes were examined for three levels of magnetic activity for both solstices and equinox conditions. A temperature maximum in the pre-midnight sector and a minimum in the noon sector were noted and seasonal and geomagnetic time and latitude effects discussed. Neutral temperature, density, pressure and boundary oxygen variations for the great storm of March 8, 1970 are presented.

Wydra, B. J.↗
NASA NTRS1975

Possible relationships between solar activity and atmospheric constituents

The large body of data on solar variations and atmospheric constituents collected between 1902 and 1953 by the Astrophysical Observatory of the Smithsonian Institution (APO) was examined. Short-term variations in amounts of atmospheric aerosols and water vapor due to seasonal changes, volcanic activity, air pollution, and frontal activity are discussed. Preliminary evidence indicates that increased solar activity is at times associated with a decrease in attenuation due to airborne particulates.

Roosen, R. G.↗
NASA NTRS1975

Future monitoring of charged particle energy deposition into the upper atmosphere and comments on possible relationships between atmospheric phenomena and solar and/or geomagnetic activity

Monitoring of earth's atmosphere was conducted for several years utilizing the ITOS series of low-altitude, polar-orbiting weather satellites. A space environment monitoring package was included in these satellites to perform measurements of a portion of earth's charged particle environment. The charged particle observations proposed for the low-altitude weather satellite TIROS N, are described which will provide the capability of routine monitoring of the instantaneous total energy deposition into the upper atmosphere by the precipitation of charged particles from higher altitudes. Such observations may be of use in future studies of the relationships between geomagnetic activity and atmospheric weather pattern developments. Estimates are given to assess the potential importance of this type of energy deposition. Discussion and examples are presented illustrating the importance of distinguishing between solar and geomagnetic activity as possible causative sources. Such differentiation is necessary because of the widely different spatial and time scales involved in the atmospheric energy input resulting from these various sources of activity.

Williams, D. J.↗
NASA NTRS1975

Some problems in coupling solar activity to meteorological phenomena

The development of a theory of coupling of solar activity to meteorological phenomena is hindered by the difficulties of devising a mechanism that can modify the behavior of the troposphere while employing only a negligible amount of energy compared with the energy necessary to drive the normal meteorological system, and determining how such a mechanism can effectively couple some relevant magnetospheric process into the troposphere in such a way as to influence the weather. A clue to the nature of the interaction between the weather and solar activity might be provided by the fact that most solar activity undergoes a definite 11-yr cycle, and meteorological phenomena undergo either no closely correlated variation, an 11-yr variation, or a 22-yr variation.

Dessler, A. J.↗
NASA NTRS1975

EUV analysis of an active region

A sequence of extreme-ultraviolet (EUV) spectroheliograms of McMath region No. 10283 were obtained by OSO-6. The lines O VI (1032 A) Mg X (625 A), Si XII (499 A), and Fe XVI (335 A) were used to determine coronal temperatures and densities above the active region. A comparison of theoretical and observed line ratios yielded coronal temperatures of 2.2 to 2.3 million K above the active region and 2.0 to 2.1 million K in the surrounding area. The temperatures derived from ratios involving the O VI intensities are systematically higher than the others. This is attributed to an error in the theoretical O VI intensities. The intensities observed above the limb are compared with intensities predicted by a simple model based on cylindrical geometry. The overall agreement shows that the assumption of an isothermal corona in hydrostatic equilibrium above the active region is a resonable working hypothesis and that the adopted geometrical model for the electron density distribution is adequate.

Raghavan, N.↗