Checking Computations of Formal Method Tools - A Secondary Toolchain for ProB

We present the implementation of pyB, a predicate - and expression - checker for the B language. The tool is to be used for a secondary tool chain for data validation and data generation, with ProB being used in the primary tool chain. Indeed, pyB is an independent cleanroom-implementation which is used to double-check solutions generated by ProB, an animator and model-checker for B specifications. One of the major goals is to use ProB together with pyB to generate reliable outputs for high-integrity safety critical applications. Although pyB is still work in progress, the ProB/pyB toolchain has already been successfully tested on various industrial B machines and data validation tasks.Comment: In Proceedings F-IDE 2014, arXiv:1404.578

Goal Structured Notation in a Radiation Hardening Safety Case for COTS-Based Spacecraft

A systematic approach is presented to constructing a radiation assurance case using Goal Structured Notation (GSN) for spacecraft containing COTS parts. The GSN paradigm is applied to an SRAM single-event upset experiment board designed to fly on a CubeSat November 2016. Construction of a radiation assurance case without use of hardened parts or extensive radiation testing is discussed

Model Based Systems Engineering for CubeSat Mission Reliability

Model Based Systems Engineering (MBSE) is moving to the forefront of small spacecraft development. The benefits of SysML as a language for the elucidation of the system architecture for CubeSats is well understood and is implemented in standard model formats. Concurrently, the benefits of the evolving development of MBSE for assurance has been recognized and is emerging as Model Based Mission Assurance (MBMA), which promises the development of integral assurance stakeholder views into the model as well as the production of useful products from the model. In this regard, the assurance organizations of NASA, ESA, and JAXA are exploring jointly the potential benefits of MBSE and MBMA in anticipation of future joint projects in which an architecture for a flight mission will be shared in a SysML model. Traditionally, only mission-critical aspects of large systems have been able to justify the time and expense of creating reliability analyses. This work aims to make these analyses practical for a wide range of missions, from small to large to support architectural design decisions, rapidly and cost effectively, across organizations. In additions to exploring basic modeling concepts and communicating over the model, the partners have shown that reliability analysis can be generated from the model. These include early Failure Modes, Effects, and Critically Analysis (FMECA) and Fault Tree Analysis (FTA) based on the simulated mission. The intent is to test basic meta-model frameworks and compare these results across the agencies. One such basic framework employs SysML state machines as the basis for developing FMEAs and FTAs. When failures are modeled using this framework, plugins (developed by NASA under a Small Business Innovation Research project) for the SysML tool are able to automatically to generate a FMECA table and Fault Trees. The expected outcome of this project is a compilation of lessons learned across the 3 agencies (NASA-ESA-JAXA) to be shared with their assurance communities. In addition, comparisons and utility of SysML derived products from the model are planned. Finally, a framework for standardization to the extent possible will be proposed to facilitate model sharing in the future for more complex scenarios, as a result of lessons learned herein

A Framework for Reliability and Safety Analysis of Complex Space Missions

Long duration and complex mission scenarios are characteristics of NASA's human exploration of Mars, and will provide unprecedented challenges. Systems reliability and safety will become increasingly demanding and management of uncertainty will be increasingly important. NASA's current pioneering strategy recognizes and relies upon assurance of crew and asset safety. In this regard, flexibility to develop and innovate in the emergence of new design environments and methodologies, encompassing modeling of complex systems, is essential to meet the challenges

SYSTEMS ENGINEERING AND ASSURANCE MODELING (SEAM): A WEB-BASED SOLUTION FOR INTEGRATED MISSION ASSURANCE

We present an overview of the Systems Engineering and Assurance Modeling (SEAM) platform, a web-browser-based tool which is designed to help engineers evaluate the radiation vulnerabilities and develop an assurance approach for electronic parts in space systems. The SEAM framework consists of three interconnected modeling tools, a SysML compatible system description tool, a Goal Structuring Notation (GSN) visual argument tool, and Bayesian Net and Fault Tree extraction and export tools. The SysML and GSN sections also have a coverage check application that ensures that every radiation fault identified on the SysML side is also addressed in the assurance case in GSN. The SEAM platform works on space systems of any degree of radiation hardness but is especially helpful for assessing radiation performance in systems with commercial-off-the-shelf (COTS) electronic components

Enhanced Charge Collection in SiC Power MOSFETs Demonstrated by Pulse-Laser Two-Photon Absorption SEE Experiments

A two-photon absorption technique is used to understand the mechanisms of single-event effects in silicon carbide power MOSFETs and power junction barrier Schottky diodes. The MOSFETs and diodes have similar structures enabling identification of effects associated specifically with the parasitic bipolar structure that is present in the MOSFETs, but not the diodes. The collected charge in the diodes varies only with laser depth, whereas it varies with depth and lateral position in the MOSFETs. Optical simulations demonstrate that the variations in collected charge observed are from the semiconductor device structure, and not from metal/passivationinduced reflection. The difference in the spatial dependence of collected charge between the MOSFET and diode is explained by bipolar amplification of the charge carriers in the MOSFETs. TCAD device simulations extend this analysis to heavy ioninduced charge collection. In addition, there is discussion comparing this analysis with experimental results from prior works that show enhanced charge collection resulting from heavy ion irradiation.peerReviewe