SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Measurements made on several doped-silicon detectors are reported. Topics discussed include: Si:Sb detector, the effects of detector bias on dielectric relaxation; characterization of spontaneous noise and gamma-induced spikes and their circumvention; and the time response of two detectors to step changes in the background photon flux density. Several potential system programs are indicated.
Very high time resolution data can be obtained from the Space Telescope Imaging Spectrograph (STIS) Multi-Anode Microchannel Array (MAMA) detectors using the time-tag observing mode. In this mode, the photon events are not accumulated onboard the spacecraft. Instead, each event is recorded internally and transmitted to the ground as an X and Y location with an event time. Event times are recorded in units of 125 microseconds. Analysis of STIS Crab Pulsar data demonstrates that a time resolution of approaching 125 microseconds can be achieved. Furthermore, the time-tag observing mode has been demonstrated to be a very powerful diagnostic tool and can be used to increase the resolution of both imaging and spectral data.
Excessheat capacity in a bolometric detector has the consequence of increasing or leading to multiple device time con-stants.The Mo/Au bilayer transition edge sensor (TES) bolo-metric detectors intended for the high resolution mid-infrared spectrometer (HIRMES) have two response time, one of which is a few times longer than that estimated from materials used in the design. The relative contribution of this settling time to the overall time response of the detectors is roughly proportional with the pixel area, which ranges between ~0.3 and 2.6 mm2.Use of laser ablation to remove sections of the silicon membranes comprising the pixels results in a detector response with a smaller contribution from the secondary time constant.Additional information about the nature of this excess heat capacity is gleaned from glancing in-cidence x-ray diffraction, which reveals the presence of molyb-denum silicides near the silicon surface from the bi-layer deposi-tion.Quantitative analysis of the concentration of excess molyb-denum, estimated with secondary ion mass spectroscopy, is com-mensurate to the additional heat capacity needed to explain the anomalous time response of the detectors.
Nuclear radiation detectors with volumes of approximately 1 cu cm was fabricated from single crystals of germanium-silicon alloy containing as much as 20 weight percent germanium. The properties of these detectors were investigated and will be discussed. Tests reveal that the gamma ray photoelectric peak efficiency of an alloy detector with only 12 weight percent germanium is approximately 4 times that of a silicon detector of equal volume. The room temperature roomure appears to be a good possibility. Storage for long periods at room temperature does not seem to adversely affect these devices. The results of preliminary radiation damage experiments suggest that the alloy detectors possess a radiation damage resistance far greater than that of silicon.
A solid-state radiation detector includes a pattern of conductive metal on a zinc oxide substrate. The pattern provides an arrangement of interdigitated electrode fingers. The wide band gap substrate is sensitive to UV light, which can cause a conductivity change in the substrate. The electrode fingers are configured to sense a difference in substrate conductivity resulting from UV light. The detector has a fast response time, which enables it to detect Cherenkov light. The compact detector provides savings on size, weight, and required power. Thus, the solid-state detector can be used to replace photomultiplier tubes in Cherenkov detectors. The features of the novel detector allow for an improved system to detect and monitor UV radiation, especially during deep space missions.
The Burst and Transient Source Experiment (BATSE) for the Gamma Ray Observatory (GRO) consists of eight detector modules that provide full-sky coverage for gamma-ray bursts and other transient phenomena such as solar flares. Each detector module has a thin, large-area scintillation detector (2025 sq cm) for high time-resolution studies, and a thicker spectroscopy detector (125 sq cm) to extend the energy range and provide better spectral resolution. The total energy range of the system is 15 keV to 100 MeV. These 16 detectors and the associated onboard data system should provide unprecedented capabilities for observing rapid spectral changes and gamma-ray lines from solar flares. The presence of a solar flare can be detected in real-time by BATSE; a trigger signal is sent to two other experiments on the GRO. The launch of the GRO is scheduled for June 1990, so that BATSE can be an important component of the Max '91 campaign.
A higher than normal ratio is reported for the decrease of cosmic ray intensity on 18 December 1965. This value was attributed to the depletion of a low rigidity electron component which also contributes to the counting rate of the IMP 3 detector. Significant difference is observed in the onset times recorded by the IMP 3 detector and Alert neutron monitor.
Particulate detector which monitors emissions from solid propellant fuels can monitor air quality. High signal-to-noise ratio detector can count aerosols and particles efficiently. Detector can distinguish one particle from another with respect to both time and energy of impact. Detector consists of accelerator, capacitor sensor, and readout recording equipment.
The survival of the Galactic magnetic field almost certainly sets an astrophysical upper bound of approx. 10 to the minus 15th power cm(-2) sr(-1) s(-1) on the flux of monopoles. To improve significantly upon this Parker limit with direct, real time searches would require a detector area of approx. 10,000 square meters and a collection time of years. Several such searches are being contemplated. A novel alternative scheme using large mica crystals capable of recording and storing tracks of slow monopoles over a time scale of approx. 10 to the 9th power years was proposed.
An actively-shielded, high-energy X-ray telescope was launched onboard OSO-8 on 21 June 1975. The primary objectives of this experiment are the measurements of the energy spectrum of discrete cosmic X-ray sources in the range 20 keV to 3 MeV and of the temporal variations in the intensity of each source detected with a time resolution of 0.3 msec. This detector provides the highest duty factor and the finest time resolution of any of its kind for observations over a period of up to 10 days. The background spectrum of this detector in orbit was monitored continuously since shortly after launch. The minimum detectable source strength is estimated to be between 10,000 and 100,000 photons/sq-cm-sec keV, limited primary by the effects of induced radioactivity. From 16 July through 18 July 1975, the X-ray binary, Cen X-3, was observed with the hard X-ray telescope.
Thermal analysis of large area high temperature superconducting infrared detector operating in the equilibrium mode (bolometer) was performed. An expression for the temperature coefficient beta=1/R(dR/dT) in terms of the thermal conductance and the thermal time constant of the detector were derived. A superconducting transition edge bolometer is a thermistor consisting of a thin film superconducting YBaCuO evaporated into a suitable thermally isolated substrate. The operating temperature of the bolometer is maintained close to the midpoint of the superconducting transition region where the resistance R has a maximum dynamic range. A detector with a strip configuration was analyzed and an expression for the temperature rise (delta T) above the ambient due to a uniform illumination with a source of power density P(sub i) was calculated. An expression for the thermal responsivity of the detector was derived using the thermal diffusion analysis with appropriate boundary conditions. It was found that the thermal responsibility depends upon the spatial modulation frequency and the angular frequency of the incoming radiation. The problem of the thermal cross talk between different detector elements was addressed. In the case of monolithic HTS detector array with a row of square elements of dimensions 2a and CCD or CID readout electronics the thermal spread function was derived for different spacing between elements. This analysis can be critical for future design and applications of large area focal plane arrays as broad band optical detectors made of granular thin films HTS YBaCuO.
Thermal analysis of large area high temperature superconducting infrared detector operating in the equilibrium mode (bolometer) was performed. An expression for the temperature coefficient beta = 1/R(dR/dT) in terms of the thermal conductance and the thermal time constant of the detector were derived. A superconducting transition edge bolometer is a thermistor consisting of a thin film superconducting YBaCuO evaporated into a suitable thermally isolated substrate. The operating temperature of the bolometer is maintained close to the midpoint of the superconducting transition region where the resistance R has a maximum dynamic range. A detector with a strip configuration was analyzed and an expression for the temperature rise (delta T) above the ambient due to a uniform illumination with a source of power density was calculated. An expression for the thermal responsibility depends upon the spatial modulation frequency and the angular frequency of the incoming radiation. The problem of the thermal cross talk between different detector elements was addressed. In the case of monolithic HTS detector array with a row of square elements of dimensions 2a and CCD or CID readout electronics the thermal spread function was derived for different spacing between elements.
Input circuitry is provided for a high voltage operated radiation detector to receive pulses from the detector having a rise time in the range of from about one nanosecond to about ten nanoseconds. An integrator circuit, which utilizes current feedback, receives the incoming charge from the radiation detector and creates voltage by integrating across a small capacitor. The integrator utilizes an amplifier which closely follows the voltage across the capacitor to produce an integrator output pulse with a peak value which may be used to determine the energy which produced the pulse. The pulse width of the output is stretched to approximately 50 to 300 nanoseconds for use by subsequent circuits which may then use amplifiers with lower slew rates.
The feasibility of the design, construction, launch and retrieval of a hinged 15 ft by 110 ft the platform containing an array of interleaved CR-39 and Lexan track-recording detectors to be placed into circular orbit by space shuttle is assessed. The total weight of the detector assembly plus supporting structure and accessories is 32,000 pounds. The modular construction permits as little as one fourth of the payload to be exposed at one time. The CR-39 detector has sensitivity adequate to detect and study cosmic rays ranging from minimum ionizing iron-group nuclei to the heaviest elements. The detectors will survive a one year exposure to trapped protons without losing their high resolution. Advantages include low cost, huge collecting power (approximately 150 sq m) as well as the high resolution previously attainable only with electronic detectors.
A formal model for the study of on-line diagnosis is introduced and used to investigate the diagnosis of unrestricted faults. A fault of a system S is considered to be a transformation of S into another system S' at some time tau. The resulting faulty system is taken to be the system which looks like S up to time tau, and like S' thereafter. Notions of fault tolerance error are defined in terms of the resulting system being able to mimic some desired behavior as specified by a system similar to S. A notion of on-line diagnosis is formulated which involves an external detector and a maximum time delay within which every error caused by a fault in a prescribed set must be detected. It is shown that if a system is on-line diagnosable for the unrestricted set of faults then the detector is at least as complex, in terms of state set size, as the specification. The use of inverse systems for the diagnosis of unrestricted faults is considered. A partial characterization of those inverses which can be used for unrestricted fault diagnosis is obtained.
Explore the source record for details and available documents.
No abstract available
In 1990, NASA grounded its space shuttle fleet. The reason: leaks detected in the hydrogen fuel systems of the Space Shuttles Atlantis and Columbia. Unless the sources of the leaks could be identified and fixed, the shuttles would not be safe to fly. To help locate the existing leaks and check for others, Kennedy Space Center engineers used portable ultrasonic detectors to scan the fuel systems. As a gas or liquid escapes from a leak, the resulting turbulence creates ultrasonic noise, explains Gary Mohr, president of Elmsford, New York-based UE Systems Inc., a long-time leader in ultrasonic detector technologies. "In lay terms, the leak is like a dog whistle, and the detector is like the dog ear." Because the ultrasound emissions from a leak are highly localized, they can be used not only to identify the presence of a leak but also to help pinpoint a leak s location. The NASA engineers employed UE s detectors to examine the shuttle fuel tanks and solid rocket boosters, but encountered difficulty with the devices limited range-certain areas of the shuttle proved difficult or unsafe to scan up close. To remedy the problem, the engineers created a long-range attachment for the detectors, similar to "a zoom lens on a camera," Mohr says. "If you are on the ground, and the leak is 50 feet away, the detector would now give you the same impression as if you were only 25 feet away." The enhancement also had the effect of reducing background noise, allowing for a clearer, more precise detection of a leak s location.