The project successfully demonstrated that dual lock-step comparison of commercial RISC processors is a viable fault-tolerant approach to handling SEU in space environment. The fault tolerant approach on orbit error rate was 38 times less than the single processor error rate. The random nature of the upsets and appearance in critical code section show it is essential to incorporate both hardware and software in the design and operation of fault-tolerant computers.

Proton and ion single event phenomena (SEP) tests were performed on 32-b processors including R3000A's from all commercial manufacturers along with the Performance PR3400 family, Integrated Device Technology Inc. 79R3081, LSI Logic Corporation LR33000HC, and Intel i80960MX parts. The microprocessors had acceptable upset rates for operation in a low earth orbit or a lunar mission such as CLEMENTINE with a wide range in proton total dose failure. Even though R3000A devices are 60% smaller in physical area than R3000 devices, there was a 340% increase in device single event upset (SEU) cross section. Software tests of varying complexity demonstrate that registers and other functional blocks using register architecture dominate the cross section. The current approach of giving a single upset cross section can lead to erroneous upset rates depending on the application software.<>

We built a relativistic backward-wave oscillator (BWO) operating at a frequency near 8 GHz. In our experiments, the parameters of the 60-ns electron beam driving this microwave source were varied over the ranges 0.8-1.5 MV and 2-10 kA. Also, we tried several different annular cathodes for launching the electron beam, varying the outer radius and shape. The axial magnetic field guiding the beam through the BWO was varied between 0.6 and 3 T. Finally, we investigated the power transfer downstream to an output waveguide as a function of the shape of the transition from the BWO to the waveguide. We discuss the scaling of the output power and frequency with these variations. In addition, we show time-resolved measurements of 2-ns-long segments of the microwave output. In observations of the microwave signal, we found the frequency shifted as the output power envelope passed through a sharp dip; we propose that this shift corresponds to a change in the longitudinal operating mode of the BWO.

This paper presents low energy (less-than-or-equal-to 60 MeV) proton exposure test results for commercial unhardened versions of the MIPS Computer Systems R3000 and R3000A microprocessors from four different vendors, and compares these results with previously obtained data at 256 MeV. Proton SEU cross sections and total dose hardness values are presented. Two of the processors functioned to about 1 Mrad. All processors, with one exception, remained functional above 40 krad. SEU cross sections were obtained with the use of specially designed software tests which were executed dynamically during radiation exposure of the chips. Radiation hardness and SEU are investigated for LEO. Results indicate that commercial R3000 and R3000A microprocessors are suitable for multi-year operation at LEO altitudes in space.

Spacecraft processors must operate with minimal degradation of performance in the Low Earth Orbit (LEO) radiation environment, which includes the effects of total accumulated ionizing dose and Single Event Phenomena (SEP) caused by protons and cosmic rays. Commercially available microprocessors can offer a number of advantages relative to radiation-hardened devices, including lower cost, reduced development and procurement time, extensive software support, higher density and performance. However, commercially available systems are not normally designed to tolerate effects induced by the LEO environment.Lawrence Livermore National Laboratory (LLNL) and others have extensively tested the MIPS R3000 Reduced Instruction Set Computer (RISC) microprocessor family for operation in LEO environments. We have characterized total dose and SEP effects for altitudes and inclinations of interest to systems operating in LEO, and we postulate techniques for detection and alleviation of SEP effects based on experimental results.

Proton single event upset (SEU) cross sections and proton total dose hardness of commercially available MIPS R3000 microprocessors (CPU) and R3010 floating point units (FPU) were obtained by exposing these parts to 256 MeV protons from the linear accelerator (LINAC) at the Los Alamos Meson Physics Facility (LAMPF). Parts from several manufacturers were tested. The CPUs and FPUs were tested dynamically during radiation exposure with specially designed assembly language codes which exercised a subset of the available instructions. Cross sections derived from the SEU data were used to calculate expected upset rates for a 500-km, 60-degree inclination, orbit during quiet solar conditions and during the August 4, 1972, King solar flare event [12, 13] modeled by Adams et al. [14].

Computational studies are made of the diffraction of microwaves by circular apertures in a conducting plane. The fields in and behind the apertures are calculated by linking high and low frequency numerical approximations through the resonance region, using a solution of the electric field integral equation (EFIE). The transient responses of the apertures to short microwave pulses with varied rise...

The computer code MORSE was used to obtain three-dimensional (3-D) Monte Carlo solutions to the adjoint Boltzman equation for photon transport. Cable SGEMP responses (C/cal) were obtained for three cable segments in a 3-D cluttered cylinder for arbitrary source/cylinder orientation and arbitrary cable SGEMP models. The clutter consists of three right circular solid aluminum cylinders. The effects ...

An analytic solution for short circuit current is obtained for SGEMP response of a cable for the case when strong coupling occurs between voltage limiting (VL) and radiation-induced conductivity (RIC). The behavior of three experimentally measurable nonlinearity numbers is investigated as a function of a dimensionless time constant of the cable response.

A cable SGEMP model is developed for calibration against low and high fluence data. This model includes localized gaps and nonlinear effects of radiation-induced conductivity and voltage limiting. These latter two effects can be represented as separable time constants of the system. An analytic solution is obtained in terms of total gap volume and a fundamental time constant. The total gap volume is obtainable from low fluence data. Three nonlinearity numbers are defined which are potentially experimentally measurable at high fluence and determine the fundamental time constant.

A two-compartment linear systems model has been developed for predicting the transport of 131I from pasture to milk. The system transfer parameters were determined from measurements of concentration of 131I in vegetation, Kv (pCi * kg−1 dry weight), and in milk, Cm (pCi * l−1), by Weiss et al. (We75) at the Monticello and Dresden nuclear power stations. These measurements indicated that the vegatation was being pulsed in time with deposits of radioactivity as a result of the action of atmospheric wet processes. Model predictions of the ratio of equilibrium values of Cm, and Kv obtained from average model parameter values are 0.19 kg * l−1 for both Monticello and Dresden. This value is higher by factors of 1.5 and 2.8, respectively, than the time-averaged values of the ratio Cm/Kv reported by Weiss et al. Data measured under pulsed conditions may be used for assessing long-term releases of radioactivity to the environment provided the data are properly time-averaged.