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Shinn, Stephen

Publications and source records attributed to Shinn, Stephen.

5 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Space Chicken: A Historical Look at How the Critical Path Changes over a Mission’s Development

The critical path in schedule analysis defines the series of tasks that have no schedule slack leading to the delivery of a system. The critical path for NASA science missions, which typically runs through a spacecraft subsystem or a scientific instrument, is dynamic and changes over the development lifetime of a project. Often the critical path at the start of preliminary design will be through a specific spacecraft subsystem while the final, delivered critical path item is often a scientific instrument that is delivered late. The research for this paper looks at the postulated critical path at different milestones, and the actual critical path item at final delivery, for a variety of NASA science missions to understand what elements are impacting the delivery schedule the most. Recommendations are made based on these quantitative results relative to what elements should potentially be considered more often in early development schedules to more robustly plan for development issues.

Bitten, Robert↗
NASA NTRS2018

EoC Study Update to Examine the Cost, Schedule and Technical Changes to NASA Projects

The original National Aeronautics and Space Administration (NASA) Explanation of Change (EoC) study was conducted in 2010 to understand the underlying causes of cost and schedule growth. The first study consisted of 25 missions launched from 2000 to 2010 and looked at the events that led to growth. These events were categorized into different bins that were rolled up to quantify whether the growth was due to internal planning, or internal execution, or from external forces and found that the growth was evenly distributed among those three categories. The result of the study presented nine considerations focused at reducing growth due to project external events and internal planning events. Although no one 'magic bullet' consideration was discovered in the previous work, the nine considerations taken as a whole were postulated to help reduce cost and schedule change in future NASA missions. A recent update was conducted that included investigating 8 missions developed since the previous study to determine if the results were different. Cost, schedule, and mass increases were analyzed from the start of Phase B through Preliminary Design Review and Critical Design Review to Launch. As shown in this paper, the results are better with overall cost and schedule growth being reduced. The paper will show a comparison of the previous results to the updated results to show specific reductions and provide an explanation of which recommendations were followed.

growth↗
NASA NTRS2012

The Economics of NASA Mission Cost Reserves

Increases in NASA mission costs have led to analysis of the causes and magnitude of historical mission overruns as well as mitigation and prevention attempts. This paper hypothesizes that one cause is that the availability of reserves may reduce incentives to control costs. We draw a comparison to the insurance concept of moral hazard, and we use actuarial techniques to better understand the increase in mission costs due to the availability of reserves. NASA's CADRe database provided the data against which we tested our hypothesis and discovered that there is correlation between the amount of available reserves and project overruns, particularly for mission hardware cost increases. We address the question of how to prevent reserves from increasing mission spending without increasing cost risk to projects.

Whitley, Sally↗
NASA NTRS2012

The Economics of NASA Mission Cost Reserves

Increases in NASA mission costs are well-noted but not well-understood, and there is little evidence that they are decreasing in frequency or amount over time. The need to control spending has led to analysis of the causes and magnitude of historical mission overruns, and many program control efforts are being implemented to attempt to prevent or mitigate the problem (NPR 7120). However, cost overruns have not abated, and while some direct causes of increased spending may be obvious (requirements creep, launch delays, directed changes, etc.), the underlying impetus to spend past the original budget may be more subtle. Gaining better insight into the causes of cost overruns will help NASA and its contracting organizations to avoid .them. This paper hypothesizes that one cause of NASA mission cost overruns is that the availability of reserves gives project team members an incentive to make decisions and behave in ways that increase costs. We theorize that the presence of reserves is a contributing factor to cost overruns because it causes organizations to use their funds less efficiently or to control spending less effectively. We draw a comparison to the insurance industry concept of moral hazard, the phenomenon that the presence of insurance causes insureds to have more frequent and higher insurance losses, and we attempt to apply actuarial techniques to quantifY the increase in the expected cost of a mission due to the availability of reserves. We create a theoretical model of reserve spending motivation by defining a variable ReserveSpending as a function of total reserves. This function has a positive slope; for every dollar of reserves available, there is a positive probability of spending it. Finally, the function should be concave down; the probability of spending each incremental dollar of reserves decreases progressively. We test the model against available NASA CADRe data by examining missions with reserve dollars initially available and testing whether they are more likely to spend those dollars, and whether larger levels of reserves lead to higher cost overruns. Finally, we address the question of how to prevent reserves from increasing mission spending without increasing cost risk to projects budgeted without any reserves. Is there a "sweet spot"? How can we derive the maximum benefit associated with risk reduction from reserves while minimizing the effects of reserve spending motivation?

Whitley, Sally↗