Miniature High-Let Radiation Spectrometer for Space and Avionics Applications

This paper reports on the design and characterization of a small, low power, and low weight instrument, a High-LET Radiation Spectrometer (HiLRS), that measures energy deposited by heavy ions in microelectronic devices. The HILRS operates on pulse-height analysis principles and is designed for space and avionics applications. The detector component in the instrument is based on large scale arrays of p-n junctions. In this system, the pulse amplitude from a particle hit is directly proportional to the particle LET. A prototype flight unit has been fabricated and calibrated using several heavy ions with varying LETs and protons with several energies. The unit has been delivered to the Ballistic Missile Defense Organization (BMDO) c/o the Air Force Research Laboratory in Albuquerque, NM, for integration into the military Space Technology Research Vehicle (STRV), a US-UK cooperative mission. Another version of HILRS is being prepared for delivery in April to the Hubble Space Telescope (HST) project, to fly on the HST Orbital Systems Test (HOST) Platform on a shuttle mission

Forty-Year "Drift" and Change of the SAA

A comprehensive study was conducted to evaluate the change in the location and size of the South Atlantic Anomaly (SAA) as a function of time, primarily in relation to trapped Van Allen Belt proton populations. The study was limited to one altitude only (800 km), which is still within the Earth's atmosphere but is removed from the atmospheric cut-off level located at about 100-200 km

Prediction and measurement of radiation damage to CMOS devices on board spacecraft

The CMOS Radiation Effects Measurement (CREM) experiment is presently being flown on the Explorer-55. The purpose of the experiment is to evaluate device performance in the actual space radiation environment and to correlate the respective measurements to on-the-ground laboratory irradiation results. The experiment contains an assembly of C-MOS and P-MOS devices shielded in front by flat slabs of aluminum and by a practically infinite shield in the back. Predictions of radiation damage to C-MOS devices are based on standard environment models and computational techniques. A comparison of the shifts in CMOS threshold potentials, that is, those measured in space to those obtained from the on-the-ground simulation experiment with Co-60, indicates that the measured space damage is smaller than predicted by about a factor of 2-3 for thin shields, but agrees well with predictions for thicker shields

Measurement of Cosmic Ray and Trapped Proton LET Spectra on the STS-95 HOST Mission

This paper reports on in situ measurements of the Linear-Energy-Transfer (LET) spectra of galactic cosmic rays and their progeny and of trapped Van Allen belt protons as recorded by a Pulse Height Analyzer (PHA) radiation spectrometer which flew on the STS-95 DISCOVERY mission on the Hubble Orbital Systems Test (HOST) cradle. The Shuttle was launched on 29 October 1998 and had a mission duration of 8.5 days during the minimum phase of the solar activity cycle. The orbit of the STS-95 was about 550 km altitude and 28.5deg inclination. A close correlation was seen between radiation environment model predictions and the measurements of the PHA

CRRES microelectronics package flight data analysis

A detailed in-depth analysis was performed on the data from some of the CRRES MEP (Microelectronics Package) devices. These space flight measurements covered a period of about fourteen months of mission lifetime. Several types of invalid data were identified and corrections were made. Other problems were noted and adjustments applied, as necessary. Particularly important and surprising were observations of abnormal device behavior in many parts that could neither be explained nor correlated to causative events. Also, contrary to prevailing theory, proton effects appeared to be far more significant and numerous than cosmic ray effects. Another unexpected result was the realization that only nine out of thirty-two p-MOS dosimeters on the MEP indicated a valid operation. Comments, conclusions, and recommendations are given

Beyond Hebb: Exclusive-OR and Biological Learning

A learning algorithm for multilayer neural networks based on biologically plausible mechanisms is studied. Motivated by findings in experimental neurobiology, we consider synaptic averaging in the induction of plasticity changes, which happen on a slower time scale than firing dynamics. This mechanism is shown to enable learning of the exclusive-OR (XOR) problem without the aid of error back-propagation, as well as to increase robustness of learning in the presence of noise.Comment: 4 pages RevTeX, 2 figures PostScript, revised versio

Fractal Stability Border in Plane Couette Flow

We study the dynamics of localised perturbations in plane Couette flow with periodic lateral boundary conditions. For small Reynolds number and small amplitude of the initial state the perturbation decays on a viscous time scale $t \propto Re$. For Reynolds number larger than about 200, chaotic transients appear with life times longer than the viscous one. Depending on the type of the perturbation isolated initial conditions with infinite life time appear for Reynolds numbers larger than about 270--320. In this third regime, the life time as a function of Reynolds number and amplitude is fractal. These results suggest that in the transition region the turbulent dynamics is characterised by a chaotic repeller rather than an attractor.Comment: 4 pages, Latex, 4 eps-figures, submitted to Phys. Rev. Le

Avalanche dynamics, surface roughening and self-organized criticality - experiments on a 3 dimensional pile of rice

We present a two-dimensional system which exhibits features of self-organized criticality. The avalanches which occur on the surface of a pile of rice are found to exhibit finite size scaling in their probability distribution. The critical exponents are $\tau$ = 1.21(2) for the avalanche size distribution and $D$ = 1.99(2) for the cut-off size. Furthermore the geometry of the avalanches is studied leading to a fractal dimension of the active sites of $d_B$ = 1.58(2). Using a set of scaling relations, we can calculate the roughness exponent $\alpha = D - d_B$ = 0.41(3) and the dynamic exponent $z = D(2 - \tau)$ = 1.56(8). This result is compared with that obtained from a power spectrum analysis of the surface roughness, which yields $\alpha$ = 0.42(3) and $z$ = 1.5(1) in excellent agreement with those obtained from the scaling relations.Comment: 7 pages, 8 figures, accepted for publication in PR

Single Event Effect Flight Data Analysis of Multiple NASA Spacecraft and Experiments

Abstract We present the spaceflight Single Event Effect (SEE) data for the emerging commercial technologies utilized in multiple NASA spacecraft and experiments. Analyses of device performance as well as design implications of the flight results are discussed