Design and architecture of planning and sequence system for Mars Exploration Rover (MER) Operations
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planning and sequence system Mars Exploration Rove↗
Engineering topics
Bixler, J.
Publications and source records attributed to Bixler, J..
High efficiency photon counting detectors for the FAUST Spacelab far ultraviolet astronomy payload
The performances of sealed tube microchannel-plate position sensitive detectors having transmission CsI photocathodes or opaque CsI photocathodes are compared. These devices were developed for the FAUST Spacelab payload to accomplish imaging surveys in the band between 1300 A and 1800 A. It is demonstrated that photocathode quantum efficiencies in excess of 40 percent at 1216 A have been achieved with the transmission and the opaque CsI photocathodes. The effect of the photoelectron trajectory on the spatial resolution is assessed. Spatial resolution of less than 70 microns FWHM has been obtained and is maintained up to event rates of 50,000/sec. Background rates of 0.55 events sq cm per sec have been achieved and low distortion (less than 1 percent) imaging has been demonstrated.
Siegmund, O. H. W.↗
Wedge and strip image readout systems for photon-counting detectors in space astronomy
EUV and far UV applications of wedge and strip anodes in photon-counting microchannel plate detector systems are discussed in light of performance data obtained as a result of EUV Explorer spacecraft open face detector and FAUST-Spacelab far UV sealed tube sensor calibrations. CsI quantum detection efficiencies of about 80 percent at 114 A and about 40 percent at 600 and 1300 A have been achieved; a position sensitivity of less than 10 microns is demonstrated, and the position resolution, image linearity, background rate, and flat-field characteristics are discussed.
Siegmund, O. H. W.↗
Operational characteristics of Wedge and Strip image readout systems
Application of the Wedge and Strip readout system in microchannel plate detectors for the Extreme Ultraviolet Explorer and FAUST space astronomy programs is discussed. Anode designs with high resolution (greater than 600 x 600 pixels) in imaging and spectroscopy applications have been developed. Extension of these designs to larger formats (100 mm) with higher resolution (3000 x 3000 pixels) are considered. It is shown that the resolution and imaging are highly stable, and that the flat field performance is essentially limited by photon statistics. Very high speed event response has also been achieved with output pulses having durations of less than 10 nanoseconds.
Siegmund, O. H. W.↗
Search for ultraviolet emission lines from a hot gaseous halo in the edge-on galaxy NGC 4244
Short and long wavelength IUE spectra of the halo region in the edge-on galaxy NGC 4244 are analyzed in order to identify evidence of line emission at the level of 0.000001 ergs per cu cm sr/s. Features are found at 1245 A and 1402 A, having peaks four times greater than the rms intensity fluctuations of nearby spectra. The spectral features are identified with semi-forbidden N V, semi-forbidden S IV at 1240 A, and Si IV and semi-forbidden O IV multiplets at 1400 A, respectively. The appearance of high-peak features and the lack of astrophysically important lines in the sample are evidence of a gas near T = 10 exp 5.2 and emission measure (EM) equal to about 0.000001 pc. However, the case for the existence of such a gas is weakened due to the existence of two other similarly sized features with no identifiable astrophysical origin and the extremely faint nature of the candidate features. The assumed upper limit for the line intensities in NGC 4244 leads to the conclusion that at T less than 100,000 K any emitting gas is either highly clumped or has a p/k value of less than 1000 per cu cm K. It is suggested that if the observed low level features in the short wavelength spectrum are real, the temperature and emission measures allow for a single component gas in the halo of NGC 4244, and are in agreement with those derived by Paresce et al. (1983).
Deharveng, J.-M.↗
A position sensitive microchannel photomultiplier for ultraviolet space astronomy
The 25-mm microchannel-plate, position-sensitive UV astronomy photomultiplier tube presented is intended for the EOM-1 Spacelab Mission's FAUST payload and conducts wide-field imaging surveys in the VUV over the 1400-1800-A range. The sealed detector encompasses a CsI photocathode deposited on the inner surface of a MgF2 window, a stack of microchannel plates, and a wedge-and-strip two-dimensional position-sensing anode. Since the wedge-and-strip principle requires only three anode signals, flight electronics can be reduced to three charge amplifiers and three analog-to-digital converters.
Lampton, M.↗
Counting efficiency of systems having both paralyzable and nonparalyzable elements
Electronics for processing random event trains may contain some elements which are paralyzable in combination with others which are nonparalyzable. An expression is derived which gives the counting efficiency or live time of such a system when its input is a Poisson random arrival process.
Lampton, M.↗
Observations of the high latitude far ultraviolet background in the 1040-1080 A band
Observations of the far ultraviolet background at high galactic latitudes in a band from 1040-1080 A were carried out with a rocket-borne 1 meter telescope and a 0.23 square degree field of view photometer. The photometer had a sharp cutoff shortward of 1040 A and a sensitivity at hydrogen Lyman alpha of a factor of 0.0001 below its sensitivity at 1060 A. A second photometer monitored geocoronal hydrogen Lyman alpha emission enabling an accurate evaluation of counts due to this background. The hydrogen Lyman alpha flux contributed only 17 percent of the total counts detected in the cosmic background detector. An upper limit to the emission in the 1040-1080 A band of 9700 photons per sq cm-s-sr-A is obtained. This upper limit is compared with previous measurements and theoretical predictions.
Bixler, J.↗
Search for emission lines in the gaseous halo of edge-on galaxies
Careful reductions of the short wave prime camera (SWP) spectrum was carried out. A line by line inspection of the spectrum was used to eliminate spurious spikes and a median filter applied to eliminate high frequency noise. Upper limits were obtained for far ultraviolet emission from a hot galactic halo.
Bixler, J.↗
Astronomical observations with the FAUST telescope
The far-ultraviolet space telescope (FAUST) was flown on Spacelab 1 to provide wide-field imaging in the wavelength range 1300 to 1800 angstroms.Most of the developed film showed high levels of background exposure. Frames with a lower background included exposures of the Cygnus Loop supernova remnant and an exposure in the direction of the galaxy cluster Abell 2634. Several exposures will be used in a search for hot white dwarf stars.
Bixler, J.↗
Experimental limits of the extreme ultraviolet background
Photometric observations of the diffuse extreme ultraviolet background with two photometers having bandpasses of 750-940 A and 1040-1080 A are reported. The payload, which was flown aboard an ARIES sounding rocket in June 1982, is described, including the electron detectors, filters, and calibration. The operation of the probe during the experiment, including its motions, are described. The primary experiment involved spectroscopic observation of the hot white dwarf HZ43. The photometer count rate is shown and the measurements of the diffuse background are compared with theoretical predictions. Despite the lower limits obtained using a narrowband detector, the measurements are not sensitive enough to draw any relevant astrophysical conclusions.
Wulf-Mathies, C.↗