120,571 research outputs found
Spacecraft utility and the development of confidence intervals for criticality of anomalies
The concept of spacecraft utility, a measure of its performance in orbit, is discussed and its formulation is described. Performance is defined in terms of the malfunctions that occur and the criticality to the mission of these malfunctions. Different approaches to establishing average or expected values of criticality are discussed and confidence intervals are developed for parameters used in the computation of utility
Estimation procedures to measure and monitor failure rates of components during thermal-vacuum testing
Estimation procedures are described for measuring component failure rates, for comparing the failure rates of two different groups of components, and for formulating confidence intervals for testing hypotheses (based on failure rates) that the two groups perform similarly or differently. Appendix A contains an example of an analysis in which these methods are applied to investigate the characteristics of two groups of spacecraft components. The estimation procedures are adaptable to system level testing and to monitoring failure characteristics in orbit
Atomic final-state interactions in tritium decay
We calculate the effect of the Coulomb interaction of the ejected β ray with the bound atomic electron in the β decay of a tritium atom. The excited state probabilities of the residual helium ion are changed by at most 0.17% from the usual sudden approximation
The extension of the thermal-vacuum test optimization program to multiple flights
The thermal vacuum test optimization model developed to provide an approach to the optimization of a test program based on prediction of flight performance with a single flight option in mind is extended to consider reflight as in space shuttle missions. The concept of 'utility', developed under the name of 'availability', is used to follow performance through the various options encountered when the capabilities of reflight and retrievability of space shuttle are available. Also, a 'lost value' model is modified to produce a measure of the probability of a mission's success, achieving a desired utility using a minimal cost test strategy. The resulting matrix of probabilities and their associated costs provides a means for project management to evaluate various test and reflight strategies
Magnetic ionization fronts II: Jump conditions for oblique magnetization
We present the jump conditions for ionization fronts with oblique magnetic
fields. The standard nomenclature of R- and D-type fronts can still be applied,
but in the case of oblique magnetization there are fronts of each type about
each of the fast- and slow-mode speeds. As an ionization front slows, it will
drive first a fast- and then a slow-mode shock into the surrounding medium.
Even for rather weak upstream magnetic fields, the effect of magnetization on
ionization front evolution can be important. [Includes numerical MHD models and
an application to observations of S106.]Comment: 9 pages, 10 figures, Latex, to be published in MNRA
Clumpy Ultracompact HII Regions I: Fully Supersonic Wind-blown Models
We propose that a significant fraction of the ultracompact HII regions found
in massive star-forming clouds are the result of the interaction of the wind
and ionizing radiation from a young massive star with the clumpy molecular
cloud gas in its neighbourhood. Distributed mass loading in the flow allows the
compact nebulae to be long-lived. In this paper, we discuss a particularly
simple case, in which the flow in the HII region is everywhere supersonic. The
line profiles predicted for this model are highly characteristic, for the case
of uniform mass loading. We discuss briefly other observational diagnostics of
these models.Comment: To appear in Monthly Notices of the Royal Astronomical Society. 5
pages LaTeX (uses mn.sty and epsf.sty macros) + 4 PS figures. Also available
via http://axp2.ast.man.ac.uk:8000/Preprints.htm
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