Impact of instrument schedule growth on mission cost and schedule growth for recent NASA missions
This study explores instrument schedule delays and their impacts on mission development schedule and cost growth for recent NASA missions. This study examines 86 instruments across 32 NASA missions. First, the relationship between instrument schedule growth and mission development cost growth is examined. It is found that instrument development delays have a prominent role in contributing to mission development schedule and cost growth. Second, instrument developments are analyzed in order to explore specific trends related to schedule growth and to determine potential contributing factors. Instrument schedule growth is examined as a function of mass, power, instrument type, and spacecraft destination. The results are then used to establish schedule rules-of-thumb that can be used for planning purposes by project and program managers in charge of future NASA development efforts.
Characterizing uncertainty to manage risk in spacecraft development with application to structures and mass
Most space programs experience significant cost and schedule growth over the course of program development. Poor uncertainty management has been identified as one of the leading causes of program cost and schedule overruns. Traditional methods of uncertainty management are deterministic, using industry standards to predict worst-case inputs and designing systems accordingly. However, this method can lead to inefficient use of resources due to excessive need for redesign of subsystems when other subsystems evolve. Improvements in computational power now allow more sophisticated uncertainty analysis methods using probabilistic techniques. We propose a spacecraft design methodology that uses Monte Carlo and Gradientbased Sensitivity Analysis of system models to reduce program cost and schedule overruns by identifying design issues early when redesign is less expensive. We cover applications to mass budgets and finite element analysis to illustrate this methodology. The META complexity metric is a measure of uncertainty of a quantity of interest based on exponential entropy from information theory. The Trapped Energetic Radiation Satellite (TERSat) structural design process is used as a test case to evaluate the methodology, with a focus on the mass budget and finite element analysis. While traditionally mass budget uncertainty is treated with margins and contingencies, we present a way to model the mass of a system and its components as probability distributions using studies of historical data to model the means and standard deviations. We propagate the uncertainties in the mass budget analysis through the TERSat finite element model to determine the effects of the uncertainty on structural analysis outputs. We show that uncertainty analysis and sensitivity analysis can help to identify design issues early and guide the redesign and refine processes for spacecraft development. Thesis Supervisor: Kerri Cahoy Title: Assistant Professor
The effect of schedule constraints on the success of planetary missions
Abstract Previous studies have shown that planetary missions have a significantly higher failure rate than earth-orbiting missions. One contributor to this higher failure rate appears to be schedule restrictions imposed on planetary missions by their fixed launch dates as opposed to the more relaxed launch schedules enjoyed in many cases by Earth-orbiting missions. Data will be presented showing the failure rates, planned vs. actual schedules, and other factors of planetary vs. Earth-orbiting missions that will test this hypothesis. Specific examples of this relationship will also be shown to further illustrate the correlation between fixed launch windows and an increased chance of mission failure.