Engineering topics

Culpepper, William X.

Publications and source records attributed to Culpepper, William X..

6 records

NASA NTRS2003

A Monte Carlo Model for LET Spectra of 200 MeV Protons Used for Microelectronic Testing

The direct ionization Linear Energy Transfer (LET) for 200 MeV protons in silicon is much smaller than that for higher charged particles since LET increases as the square of the ion charge. However, occasionally the proton interacts with the silicon nuclei and produces a shower of fragments and a recoiling nucleus. When this happens, the LET produced is much greater than the direct ionization LET. Testing the single event effect susceptibility of components using energetic (200 MeV) protons is often the only viable option for system level testing commercial-off-the-shelf (COTS) avionics that have not been designed for space environments. However, the question of how a system tested with protons will perform in a heavy ion environment arises. Here the concern is not only with prediction of on-orbit upset rate, but also about possibility of on-orbit failures that were not observed during proton testing.

O'Neill, Patrick M.↗

NASA NTRS2002

On Using Commercial Off-the-Shelf (COTS) Electronic Products in Space

NASA's Johnson Space Center (JSC) has utilized COTS products in its programs since the early 1990's. Recently it has become evident that, of all failure modes possible, radiation will probably dominate; sometimes to the point of driving system architecture. It is now imperative that radiation susceptibility be addressed when writing the system requirements. Susceptibility assessment, e.g. testing, must begin early in the design phase to establish performance and continue through the hardware qualification program to prove satisfaction of the original requirements(s). Examples of requirements, testing, and architecture versus failure rate will be given.

Culpepper, William X.↗

NASA NTRS2000

Radiation Susceptibility Assessment of Off the Shelf (OTS) Hardware

The reduction in budgets, shortening of schedules and necessity of flying near state of the art technology have forced projects and designers to utilize not only modern, non-space rated EEE parts but also OTS boards, subassemblies and systems. New instrumentation, communications, portable computers and navigation systems for the International Space Station, Space Shuttle, and Crew Return Vehicle are examples of the realization of this paradigm change at the Johnson Space Center. Because of this change, there has been a shift in the radiation assessment methodology from individual part testing using low energy heavy ions to board and box level testing using high-energy particle beams. Highlights of several years of board and system level testing are presented along with lessons learned, present areas of concern, insights into test costs, and future challenges.

Culpepper, William X.↗

NASA NTRS2000

A Nuclear Interaction Model for Understanding Results of Single Event Testing with High Energy Protons

An internuclear cascade and evaporation model has been adapted to estimate the LET spectrum generated during testing with 200 MeV protons. The model-generated heavy ion LET spectrum is compared to the heavy ion LET spectrum seen on orbit. This comparison is the basis for predicting single event failure rates from heavy ions using results from a single proton test. Of equal importance, this spectra comparison also establishes an estimate of the risk of encountering a failure mode on orbit that was not detected during proton testing. Verification of the general results of the model is presented based on experiments, individual part test results, and flight data. Acceptance of this model and its estimate of remaining risk opens the hardware verification philosophy to the consideration of radiation testing with high energy protons at the board and box level instead of the more standard method of individual part testing with low energy heavy ions.

Culpepper, William X.↗

NASA NTRS1991

Tracking Systems to Support the Common Lunar Lander (CLL)

A discussion of the tracking system for Artemis (the Common Lunar Lander) is presented. Among the topics presented are the following: major drivers for system definition, results of vendor survey, baseline system properties, program considerations, and mission phases requiring tracking.

Culpepper, William X.↗

NASA NTRS1991

Initial Hardware Development Schedule

The hardware development schedule for the Common Lunar Lander's (CLLs) tracking system is presented. Among the topics covered are the following: historical perspective, solution options, industry contacts, and the rationale for selection.

Culpepper, William X.↗