Engineering topics
Publications and source records attributed to Wilson, R..
The objective of this work is the development of efficient techniques for preliminary optimization of the cost associated with transfer trajectories to libration point orbits in the Sun-Earth-Moon four body problem; such transfers may also include lunar gravity assists.
The objective of this work is the development of efficient techniques to optimize the cost associated with transfer trajectories to libration point orbits in the Sun-Earth-Moon four body problem, that may include lunar gravity assists.
The Genesis spacecraft will collect solar wind samples from a halo orbit about the Sun-Earth L1 point for two years, returning those samples to Earth in 2003 for on-Earth analysis and examination.
This paper describes the design of the JPL institutional Multi-Mission Spacecraft Analysis System (MSAS) and its initial adaptation to the Cassini mission.
The gamma ray burst detector aboard the ESA-NASA Ulysses spacecraft, in operation since Nov. 1990, has detected numerous gamma bursts in conjunction with the BATSE experiment aboard the Compton Observatory. Initial results are presented on burst locations for three events (21 April, 2 May, and 3 May, 1991) obtained by arrival time analysis, and they are compared with the BATSE locations. The arrival time analysis annuli have typical widths of 5'. The preliminary analysis indicates that both experiments are likely to have unresolved systematic errors, but that further work will improve the location accuracy substantially.
A cursory examination of cosmic gamma-ray burst time profiles indicates an inhomogeneous distribution of structure. In the first approximation, there seem to be two types of profiles; smooth ones with little structure and highly variable ones with lots of structure. To put this observation to the test, we have examined the statistical nature of the profile derivative to choose which parameter might best be called the burst 'spikiness'. We have found that a good estimator is given by a count of the number of 'spikes' (defined by a specific numerical recipe) and not by the rms deviations from either a pre-burst background or any type of moving average background. The application of this parameter to 30 burst time histories shows it to be consistent over a wide range of profile types. The analysis also reveals a preferred average time between spikes of approximately 1.5 seconds.
The Earth Radiation Budget Satellite (ERBS) and the NOAA-9 spacecraft solar monitors were used to measure the total solar irradiance during the period October 1984 to December 1989. Decreasing trends in the irradiance measurements were observed as sunspot activity decreased to minimum levels in 1986; after 1986, increasing trends were observed as sunspot activity increased. The magnitude of the irradiance variability was found to be approximately 0.1 percent between sunspot minimum and maximum (late 1989). When compared with the 1984 to 1989 indices of solar magnetic activity, the irradiance trends appear to be in phase with the 11-year sunspot cycle. Both irradiance series yielded 1,365/sq Wm as the mean value of the solar irradiance, normalized to the mean earth/sun distance. The monitors are electrical substitution, active-cavity radiometers with estimated measurement precisions and accuracies of less than 0.02 and 0.2 percent, respectively.
Atmospheric sounding of the middle atmosphere by Rayleigh scattering has been performed in France for several years, from two stations with different orographic situations: one in the Alps, the Observatoire de Haute Provence, one on the Atlantic coast at Biscarosse. The vertical profiles of density and temperature are obtained with a temporal and spatial resolution of, respectively, 15 mn and 300 m between 30 and 80 km. A statistical study of the atmospheric fluctuations due to gravity waves was performed and the main results are presented: climatology of the gravity wave activity, distribution of energy versus vertical wave number and altitude, and comparison of the observations at the two sites. Conclusions are presented on the saturation of the wave field, the filtering by the mean wind, the transfer of energy and momentum into the atmosphere.
An ultraviolet astronomy mission (Columbus) is described. It exploits the spectral region between 900 and 1200A, which is extremely rich in containing the Lyman lines of hydrogen and deuterium and the Lyman band of their molecules, together with the resonance lines of many important ions. High resolving power and high sensitivity provide a unique capability for studying the brightest members of neighboring galaxies, the HeI and HeII absorption systems in quasars out to a red shift of 2, and the halos of intervening galaxies. Complementary focal plane instruments are planned in order to allow observations to longer (2000A) and shorter (100A) wavelengths. This wide coverage embraces the resonance lines of all the cosmically abundant elements and a wide range of temperature zones up to 100 million K.
The results of a campaign of monitoring HZ Her with the IUE satellite are presented. The spectrum and light variation outside of eclipse are consistent with the Milgrom and Salpeter model for emission from the X-ray heated photosphere of the primary. Near eclipse there is UV flux in excess of the prediction of the heated photosphere model, which shows significant 35 day variations and is consistent with an origin in a precessing disk, as described by Gerend and Boynton. The spectrum shows the strong emission lines of N V and C IV, which generally vary in the sense of the continuum. The N V/C IV ratio is greater than 2 near orbital phase 0.5 and approaches unity near eclipse. It is suggested that these emission lines are optically thick and arise from both the heated photosphere and the accretion disk.
Six 128 x 128 CID imagers fabricated on bulk silicon and with thin polysilicon upper-level electrodes were tested in a star tracking mode. Noise and spectral response were measured as a function of temperature over the range of +25 C to -40 C. Noise at 0 C and below was less than 40 rms carriers/pixel for all devices at an effective noise bandwidth of 150 Hz. Quantum yield for all devices averaged 40% from 0.4 to 1.0 microns with no measurable temperature dependence. Extrapolating from these performance parameters to those of a large (400 x 400) array and accounting for design and processing improvements, indicates that the larger array would show a further improvement in noise performance -- on the order of 25 carriers. A preliminary evaluation of the projected performance of the 400 x 400 array and a representative set of star sensor requirements indicates that the CID has excellent potential as a stellar tracking device.
By means of a collaboration across the Atlantic, very long exposures (about 14 hours) have been made with IUE of two high redshift QSO's during October 1978. Target acquisition and initiation was carried out at Vilspa, and the completion of the exposure and read-out of the image was executed at Goddard. The first object Q 2204-408 is an optical QSO with m(v) = 17.5 and z = 3.18 whose spectrum had just been detected earlier with a 350 minute exposure in the short wavelength spectrograph (Wilson, et al. 1978). In this case two longer exposures were obtained in both spectrographs. The other object is the radio QSO PKS 2126-158 with m(v) = 17.3 and z = 3.27 for which a detectable spectrum was obtained in the short wavelength spectrograph.
The results of a campaign of monitoring HZ Her with the IUE satellite are presented. The spectrum and light variation outside of eclipse are fairly consistent with the Milgrom and Salpeter (1975) model for emission from the X-ray heated photosphere of the primary. Near eclipse there is UV flux in excess of the prediction of the heated photosphere model. This suggests an additional emitting component whose relative importance decreases toward shorter wavelengths. The excess flux near 1500A appears to vary with 35 day phase in a manner consistent with the model of Gerend and Boynton (1976) in which the flux contributed by the accretion disk is modulated by precession.
A 128 x 128 element CID imager was operated in a simulated stellar trackling environment and evaluated for temporal and pattern noise and spectral response over a temperature range of -40 C to +25 C. The test devices were fabricated on long-lifetime bulk silicon material and utilized very thin upper-level polysilicon electrodes for enhanced spectral response. A standard microcomputer was used to generate all control signals and to collect and process performance data. The results of this program were used to predict the performance of a 400 x 400 CID array designed specifically for stellar-tracking.
During the commissioning phase of IUE observations were made of a selection of hot stars: the white dwarf HZ43, the hot subdwarf BD +75 deg 325, the nucleus of the planetary nebula NGC 6826, the dwarf nova SS Cygni, and the peculiar object Eta Carinae. The observations were made in the low dispersion mode and the data have been reduced using a preliminary calibration. The results are presented and discussed for each object.
Results from a preliminary study of interstellar absorption lines in the spectra of the three stars HD149757, HD93521 and HD153919, observed by the IUE during its commissioning phase are presented. They demonstrate the capabilities of the IUE for interstellar research. Results from a preliminary study of the emission line spectrum of the planetary nebula NGC 7027 are outlined and used to study its interstellar reddening.
During the commissioning phase of IUE several extragalactic objects were observed spectrally at low dispersion in the UV range lambda lambda 1150-3200: the Seyfert galaxies NGC4151 and NGC1068, the QSO 3C273, the BL Lacertae object B2 1101+38, the giant elliptical galaxy M87 and the spiral galaxy M81. The results obtained are presented and a preliminary analysis given for all six objects, discussing the continuous spectrum, extinction, emission line spectrum and absorption line spectrum, where possible for each case. Several new or confirmatory astrophysical results are obtained.