Explanation of Change (EoC) Study: Approach and Findings

This study investigated thirty historical NASA science missions to explain the cost change experienced. The study included investigation of historical milestone and monthly status report documentation followed by interviews with key project personnel. Based on the information collected, the reasons for cost change were binned, at the highest level, into four separate categories: NASA External, Project External, Internal Planning, and Internal Execution. The results identified that roughly a third of the change is outside of the project's control, a third is due to assumptions made in project planning, and a third is due to the inherent difficulty of building highly complex, one-of-a-kind, cutting edge, Earth and space science missions

Explanation of Change (EoC) Study: Considerations and Implementation Challenges

This paper discusses the implementation of considerations resulting from a study investigating the cost change experienced by historical NASA science missions. The study investigated historical milestone and monthly status report documentation followed by interviews with key project personnel. The reasons for cost change were binned as being external to NASA, external to the project and internal to the project relative to the project's planning and execution. Based on the results of the binning process and the synthesis of project meetings and interviews, ten considerations were made with the objective to decrease the potential for cost change in future missions. Although no one magic bullet consideration was discovered, the considerations taken as a whole should help reduce cost and schedule change in future NASA missions

X-chromosome Gene Order in Different Mus Species Crosses

The advent of molecular genetics heralds a new era in linkage analysis. It is now possible to map any locus and define its linkage relationship within the mammalian genome using a single set of informative offspring. This new mapping methodology, which has been used successfully to map both autosomal genes and sex-linked loci, utilizes naturally occurring polymorphisms at the level of the nucleotide sequence between inbred strains of mice and those derived from the wild species Mus spretus and Mus musculus. In their study of chromosome 4, Nadeau et al. suggested there was a potential rearrangement in gene order between the laboratory mouse and wild-derived M. spretus. Additional data now suggests that there may also be a difference in the arrangement of genes within the t-complex on chromosome 17. The t-complex, however, is quite unusual in that inversional rearrangements have been reported even among closely related M. musculus and M. domesticus populations in the wild. If rearrangements in gene order have occurred between the more evolutionarily divergent Mus species it may limit the usefulness of interspecific crosses for ordering genes within the mouse genome. Structural rearrangements in the genome may be an important mechanism for the maintenance of speciation, since they (i) inhibit illegitimate recombination which might otherwise lead to a loss or duplication of information, and (ii) affect normal chromosomal assortment. If there are such rearrangements among the Mus species, they are not cytogenetically detectable, since karyotypic analysis suggests that there is little, if any, difference in the physical appearance of chromosomes among diverse Mus species. In an attempt to address the issues of (i) interspecies variation in gene order, and (ii) possible differences in relative recombination frequencies within interspecific crosses, such crosses were constructed between the inbred laboratory strain C57BL/6JRos and two different wild-derived Mus species: M. musculus from Denmark and M. spretus. For reasons of historical interest, we began our study by examining markers on the mouse X chromosome. Analysis of major and minor satellite sequences and dispersed repeated elements shows no qualitative differences between these mice and laboratory strains