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At least 199 records · Page 11

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NASA NTRS1972

The temporal characteristics of the terrestrial radiation belt

The terrestrial radiation belt effects on the detectors in the Wisconsin equipment are considered. The lowest dark count rate observed in orbit, compared with that measured in the thermal vacuum test on the ground, shows no measurable difference for the solar blind ASCOP 541-F photomultiplier tubes while the EMI-6256B tubes show an increase in minimum dark count of a factor of from 20 to 150 times that observed on the ground. All instruments are perturbed when in the South Atlantic anomaly, but the EMI tubes are by far the most sensitive to it. Indeed, the effect never goes away.

Mcnall, J. F.↗

NASA NTRS1972

Analysis of radiation and meteoroid satellite data

The data obtained in earth orbit by the Radiation and Meteoroid Satellite (RMS) were interpreted and reduced to a form which will be usable by future space experimenters. The required tasks are detailed. Computer programs were written which lifted the raw data and associated emphemeris data from the GFE magnetic tapes. The engineering data was then used to evaluate the performance of the spacecraft and the experiments. The radiation data was used to prepare flux, spectral, and dose maps of the South Atlantic magnetic anomaly where possible. The meteoroid data was used to determine a rough estimate of the meteoroid flux and in general evaluate the performance of the thin-film meteoroid sensors. The degree of success of the RMS mission was evaluated in light of the separation anomaly which occurred between RMS and OFO during launch.

Farmer, B. J.↗

NASA NTRS1973

The diffuse X-ray spectrum from 14-200 keV as measured on OSO-5

The measurement of energy spectrum of the diffuse component of cosmic X-ray flux made on the OSO-5 spacecraft is described. The contributions to the total counting rate of the actively shielded X-ray detector are considered in some detail and the techniques used to eliminate the non-cosmic components are described. Positive values for the cosmic flux are obtained in seven energy channels between 14 and 200 keV and two upper limits are obtained between 200 and 254 keV. The results can be fitted by a power law spectrum. A critical comparison is made with the OSO-3 results. Conclusions show that the reported break in the energy spectrum at 40 keV is probably produced by an erroneous correction for the radioactivity induced in the detector on each passage through the intense charged particle fluxes in the South Atlantic anomaly.

Dennis, B. R.↗

NASA NTRS1974

Analysis of the nature of excessive cosmic radiation in the area of the Brazilian magnetic anomaly at altitudes 250-500km, from Kosmos-225 satellite data

Results are presented from a study of the region of anomalous cosmic radiation in the area of the Brazilian magnetic anomaly at the altitudes 250-500 km, using data measurements taken on the Kosmos-225 satellite (14-29 June 1968). The existence of a stable intensity anomaly discovered in the experiments on the second and third Soviet spacecraft-satellites is confirmed. The total vector of the geomagnetic field at different altitudes was compared with isoline maps. An altitude profile of the South Atlantic anomaly of radiation intensity was obtained, using data from the same instrument. The nature of the anomalies in cosmic radiation intensity over the regions of negative magnetic anomalies is discussed.

Raychenko, L. V.↗

NASA NTRS1973

The diffuse X-ray spectrum from 14 to 200 keV as measured on OSO-5

Evaluation of OSO-5 measurements of the energy spectrum of the diffuse component of the cosmic X-ray flux in the energy range from 14 to 200 keV. A detailed description is given of the X-ray detector employed and of the method of selection and pulse-height analysis of X-ray events. The method employed in eliminating noncosmic X-ray contributions to the total counting rate is discussed. The final energy spectrum is found to be best fitted by a power law which is in essential agreement with that obtained from OSO-3 by Schwartz et al. (1970), in spite of what is regarded as an erroneous correction procedure used by them. In particular, it is suggested that the break in the energy spectrum at 40 keV which they reported may have been produced by an erroneous correction for the radioactivity induced in the detector during each passage through the intense charged-particle fluxes in the South Atlantic Anomaly.

Dennis, B. R.↗

NASA NTRS1974

Secular-invariant relationships among internal geomagnetic field coefficients

Some features of the secular variation of the geomagnetic field are examined. Contours encircling constant magnetic flux (third adiabatic invariant), corresponding to a shell of field lines in secular motion, reveal a general westward drift that is longitude and latitude dependent (with minima in the north Pacific and south Atlantic areas). Some invariant relationships appear among the field coefficients in the tilted, centered dipole (geomagnetic) coordinate system.

Roederer, J. G.↗

NASA NTRS1975

Light flashes observed by astronauts on Skylab 4

Two dedicated light flash observing sessions were conducted by one of the crewmen during the Skylab 4 mission. Analyses of his observations reveal a strong correlation between flash frequency and primary cosmic-ray flux, and an even stronger correlation between flash frequency and the South Atlantic Anomaly (SAA) region of the inner belt trapped radiation. Calculations indicate that an all-proton inner belt probably cannot produce the observed SAA flash rate, and they suggest that there may exist a previously unobserved inner belt flux of multiply charged nuclei.

Pinsky, L. S.↗

NASA NTRS1976

Nuclear emulsion measurements of the astronauts' radiation exposure on the Apollo-Soyuz mission

On the Apollo-Soyuz mission each astronaut carried one passive dosimeter containing nuclear photographic emulsions, plastic foils, TLD chips, and neutron-activation foils for recording radiation exposure. This report is limited to the presentation of data retrieved from nuclear emulsions. Protons, most of them trapped particles encountered in numerous passes through the South Atlantic Anomaly, contributed by far the largest share to the mission dose. Their linear energy transfer (LET) spectrum was established from track and grain counts in a G.5 emulsion which is used for medium and high energies, and from ender counts in a K.2 emulsion which is used for low energies. The total mission fluence of protons was found to be equivalent to a unidirectional beam of 448,500 square centimeters. The broad spectrum was broken down into small LET intervals, which allowed for the computation of absorbed doses and dose equivalents. The totals are 51 millirad and 74 millirem. Counts of disintegration stars in K.2 emulsion are incomplete at present. While a total of 467 stars were identified, counting their prong numbers is still in progress. It was concluded that the Apollo-Soyuz astronauts' radiation exposure as such did not contain anything out of the ordinary that would seem to require special attention.

Schaefer, H. J.↗

NASA NTRS1975

Monte Carlo simulation of astronaut light flash observations on Apollo and Skylab missions

Monte Carlo calculations are performed to study the relation between cosmic ray nuclei and visual flashes observed by astronauts, in space. A satisfactory overall fit to all available data excluding the Skylab observations in the South Atlantic Anomaly (SAA) has been achieved by varying three visual system parameters: effective retinal thickness, minimum projected track length inside retina and minimum energy loss rate. All light flash data from space excluding the SAA observations can be understood fully upon the basis of the primary cosmic ray charge and energy spectra together with the fitted values of the three visual system parameters. Monte Carlo simulations of the SAA observations suggest the existence of a previously unobserved multiply-charged component of the inner radiation belt.

Osborne, W. Z.↗

NASA NTRS1977

New features of global climatology revealed by satellite-derived oceanic rainfall maps

Quantitative rainfall maps over the oceanic areas of the globe were derived from the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR) data. Analysis of satellite derived oceanic rainfall maps reveal certain distinctive characteristics of global patterns for the years 1973-74. The main ones are (1) the forking of the Intertropical Convergence Zone in the Pacific, (2) a previously unrecognized rain area in the South Atlantic, (3) the bimodal behavior of rainbelts in the Indian Ocean and (4) the large interannual variability in oceanic rainfall. These features are discussed.

Rao, M. S. V.↗

NASA NTRS1977

Skylab 4 crew observations

Comments on food, exercise, scheduling, medical training, the effect of fluid shift, and vestibular phenomena are briefly reported. A ballistocardiographic effect of around 60 beats per minute was observed several times for the whole Skylab cluster. Also experienced were light flashes that were well correlated with the South Atlantic anomaly.

E. G. Gibson↗

NASA NTRS1976

Payload influences on technology development and utilization of the Space Shuttle extravehicular mobility unit

Historical EVA approaches are examined. The considered data emphasize the overall importance of EVA for Shuttle payload operations. Twenty requirement categories related to crew protection, crew performance, and payload protection are listed in a table. Attention is given to a preliminary assessment of payload related requirements, an evaluation of the natural thermal environment in the case of the Shuttle orbiter bay, and the ability of the extravehicular mobility unit (EMU) to protect the crewman from induced or natural radiation as found in the Van Allen radiation belt South Atlantic anomaly. On the basis of the evaluation it appears very likely that design improvements alone can make the EMU meet payload requirements without requiring significant technology advances.

Patrick, J. W.↗

NASA NTRS1977

Electrification of the proof mass of a drag-free or accelerometric satellite

The exploitation of the data provided by the Cactus accelerometer, which makes up the payload of the D5B Castor Satellite of CNES confirmed the existence of an electric current charging the proof mass under the influence of the magnetospheric protons, and revealed a periodic variation of this current, due to the passage of the apogee through the South Atlantic magnetic anomaly. Results of in-orbit measurements of this charging current are presented, as well as calculations made for determining this current and its variations from data on proton flux at the satellite altitudes. The comparison of measured and calculated values shows that the calculation method is valid and precise enough to be used for drag-free or accelerometric satellites.

Juillert, R.↗

NASA NTRS1978

Recursive estimator for OSO-8 attitude

Modifications and enhancements that have been made to the Recursive Estimation Attitude Program (REAP) are discussed. Continuous attitudes for OSO-8 to + or - 0.05 degree accuracy are determined from Sun and star slit sensors mounted on the spinning portion of the spacecraft. The bulk of the attitude production is performed by a Weighted Least Squares (WLS) batch processor, but REAP is used for problem passes such as those involving gas jet maneuvers, sparse star fields, or star sensor saturation by high energy particles in the South Atlantic Anomaly.

Headrick, R. D.↗

NASA NTRS1978

The IRAS radiation environment

Orbital flux integration for three selected mission altitudes and geographic instantaneous flux-mapping for nominal flight-path altitude were used to determine the external charged particle radiation predicted for the Infrared Astronomy Satellite. A current field model was used for magnetic field definitions for three nominal circular trajectories and for the geographic mapping positions. Innovative analysis features introduced include (1) positional fluxes as a function of time and energy for the most severe pass through the South Atlantic Anomaly; (2) total positional doses as a function of time and shield thickness; (3) comparison mapping fluxes for ratios of positional intensities to orbit integrated averages; and (4) statistical exposure-time history of a trajectory as a function of energy indicating, in percent of total mission duration, the time intervals over which the instantaneous fluxes would exceed the orbit integrated averages. Results are presented in tables and graphs.

Stassinopoulos, E. G.↗

NASA NTRS1978

Open ocean tide modelling

Two trends evident in global tidal modelling since the first GEOP conference in 1972 are described. The first centers on the incorporation of terms for ocean loading and gravitational self attraction into Laplace's tidal equations. The second centers on a better understanding of the problem of near resonant modelling and the need for realistic maps of tidal elevation for use by geodesists and geophysicists. Although new models still show significant differences, especially in the South Atlantic, there are significant similarities in many of the world's oceans. This allows suggestions to be made for future locations for bottom pressure gauge measurements. Where available, estimates of M2 tidal dissipation from the new models are significantly lower than estimates from previous models.

Parke, M. E.↗

NASA NTRS1978

Remote sensing of the boundary layer over the oceans

The paper explores the possibility of remotely sensing the boundary layer structure over the oceans by means of the Nimbus 4 IR Interferometric Spectrometer (IRIS) measurements in the water vapor bands. It is found from theoretical considerations that the moderately strong spectral lines in the 9-micron water vapor window region contain useful information about the lowest layers in the atmosphere. The difference between the observed line strength and the theoretically predicted line strength provides information about the departure in the atmospheric temperature and water vapor profiles from standard conditions. The observations of METEOR oceanographic expedition over the North and South Atlantic, and the Indian Ocean expedition make it possible to model the inversion conditions. It is concluded that significant characteristics of the temperature and water vapor profiles in the boundary layer of the atmosphere can be remotely sensed using the water vapor spectral measurements over the oceans.

Prabhakara, C.↗

NASA NTRS1980

Light flash phenomena induced by HzE particles

Astronauts and Apollo and Skylab missions have reported observing a variety of visual phenomena when their eyes are closed and adapted to darkness. These phenomena have been collectively labelled as light flashes. Visual phenomena which are similar in appearance to those observed in space have been demonstrated at the number of accelerator facilities by expressing the eyes of human subjects to beams of various types of radiation. In some laboratory experiments Cerenkov radiation was found to be the basis for the flashes observed while in other experiments Cerenkov radiation could apparently be ruled out. Experiments that differentiate between Cerenkov radiation and other possible mechanisms for inducing visual phenomena was then compared. The phenomena obtained in the presence and absence of Cerenkov radiation were designed and conducted. A new mechanism proposed to explain the visual phenomena observed by Skylab astronauts as they passed through the South Atlantic Anomaly, namely nuclear interactions in and near the sensitive layer of the retina, is covered. Also some studies to search for similar transient effects of space radiation on sensors and microcomputer memories are described.

Mcnulty, P. J.↗