Scholarship & Research

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RadPC@Scale: an approach to mitigate single event upsets in the memory of space computers
(Montana State University - Bozeman, College of Engineering, 2022) Williams, Justin Patrick; Chairperson, Graduate Committee: Brock LaMeres
This thesis presents the flight test results of a single event upset (SEU) mitigation strategy for computer data memory. This memory fault mitigation strategy is part of a larger effort to build a radiation tolerant computing system using commercial-off-the-shelf (COTS) field programmable gate arrays (FPGAs) called RadPC. While previous iterations of RadPC used FPGA block RAM (BRAM) for its data memory, the specific component of RadPC that is presented in this paper is a novel external memory scheme with accompanying systems that can detect, and correct faults that occur in the proposed data memory of the computer while allowing the computer to continue foreground operation. A prototype implementation of this memory protection scheme was flown on a Raven Aerostar Thunderhead high-altitude balloon system in July of 2021. This flight carried the experiment to an altitude of 75,000 feet for 50 hours allowing the memory in the experiment to be bombarded with ionizing radiation without being attenuated by the majority of Earth's atmosphere. This thesis discusses the details of the fault mitigation strategy, the design-of-experiments for the flight demonstration, and the results from the flight data. This thesis may be of interest to engineers that are designing flight computer systems that will be exposed to ionizing radiation and are looking for a lower cost SEU mitigation strategy compared to existing radiation- hardened solutions.
Infrared cloud imager development for atmospheric optical communication characterization, and measurements at the JPL Table Mountain Facility
(2013-02) Nugent, Paul W.; Shaw, Joseph A.; Piazzolla, S.
The continuous demand for high data return in deep space and near-Earth satellite missions has led NASA and international institutions to consider alternative technologies for high-data-rate communications. One solution is the establishment of widebandwidth Earth–space optical communication links, which require (among other things) a nearly obstruction-free atmospheric path. Considering the atmospheric channel, the most common and most apparent impairments on Earth–space optical communication paths arise from clouds. Therefore, the characterization of the statistical behavior of cloud coverage for optical communication ground station candidate sites is of vital importance. In this article, we describe the development and deployment of a ground-based, long-wavelength infrared cloud imaging system able to monitor and characterize the cloud coverage. This system is based on a commercially available camera with a 62-deg diagonal field of view. A novel internal-shutter-based calibration technique allows radiometric calibration of the camera, which operates without a thermoelectric cooler. This cloud imaging system provides continuous day–night cloud detection with constant sensitivity. The cloud imaging system also includes data-processing algorithms that calculate and remove atmospheric emission to isolate cloud signatures, and enable classification of clouds according to their optical attenuation. Measurements of long-wavelength infrared cloud radiance are used to retrieve the optical attenuation (cloud optical depth due to absorption and scattering) in the wavelength range of interest from visible to near-infrared, where the cloud attenuation is quite constant. This article addresses the specifics of the operation, calibration, and data processing of the imaging system that was deployed at the NASA/JPL Table Mountain Facility (TMF) in California. Data are reported from July 2008 to July 2010. These data describe seasonal variability in cloud cover at the TMF site, with cloud amount (percentage of cloudy pixels) peaking at just over 51 percent during February, of which more than 60 percent had optical attenuation exceeding 12 dB at wavelengths in the range from the visible to the near-infrared. The lowest cloud amount was found during August, averaging 19.6 percent, and these clouds were mostly optically thin, with low attenuation.
A fault-tolerant computer architecture for space vehicle applications
(Montana State University - Bozeman, College of Engineering, 2012) Hane, Jennifer Susan; Chairperson, Graduate Committee: Brock LaMeres
The discovery of new methods to protect electronics from harsh radiation environments outside earth's atmosphere is important to the future of space exploration. Reconfigurable, SRAM-based Field Programmable Gate Arrays (FPGAs) are especially promising candidates for future spacecraft computing platforms; however, their susceptibility to radiation-induced faults in their configuration memory makes their use a challenge. This thesis presents the design and testing of a redundant fault-tolerant architecture targeted at the Xilinx Virtex-6 FPGA. The architecture is based on a combination of triple modulo redundancy (TMR), numerous spare units, repair (scrubbing), and environmental awareness. By using the spares and the partial reconfiguration capabilities of the FPGA, the system can remain operational while repair of damaged modules proceeds in the background. The environmental awareness is supplied by a multi-pixel radiation sensor designed to rest above the FPGA chip, providing information about which areas of the chip have received radiation strikes. The system places these potentially damaged areas first in the queue for scrubbing. Four implementations of the architecture with different types of computing module and numbers of spares reveal its versatility and scalability. These four demonstration systems were modeled with theoretical Markov calculations, for the purpose of determining their reliability. They were also implemented on Xilinx hardware and tested by the injection of simulated faults, based on realistic orbital fault rate data from the Cosmic Ray Effects on Micro-Electronics Code (CREME96) tool. These results confirm that the systems will be highly reliable under typical earth orbit conditions. The results also demonstrate that the inclusion of numerous spares and the sensor both lead to substantial improvements in the Mean Time Before Failure, over a traditional TMR system with only three modules and scrubbing.

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