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(4) Manifest Changes Due to External Factors

External factors resulting from the change itself and its side effects have been the cause of a number of manifest changes. For example, Congressman Nelson was added to STS 61-C only 2 months before the scheduled launch. He operated the phase partitioning experiment (PPE), which also was added to that flight at L-2 months. Since seven crewmembers already had been assigned to the flight (five NASA astronauts, a Radio Corporation of America (RCA) payload specialist, and a Hughes payload specialist), one of the crewmembers had to be deleted. Headquarters decided that the Hughes payload specialist should be switched to STS 51-L in January 1986. In addition, the payload specialist's fluid dynamics experiment (FDE) was also moved from 61-C to 51-L. Finally, several middeck experiments already assigned to STS 51-L (ACES, MLR, and three student experiments) were removed to make room for the extra crewman. 

d. Manifest Change Impacts

Having discussed the area of changes and their impact on the schedules and other flights, it is appropriate to consider the manner in which NASA copes with such impacts. Emphasis will be given to two major ways of coping that reflect the two major types of efforts involved in the response to the changes. Areas affected by changes are characterized by many "parallel" efforts or by several "serial" efforts.

(1) Parallel Effects

In the area characterized by parallel efforts, any impacts can generally be managed by increasing the budget. Additionally, the amount of budget increase required to respond to any remanifests or changes depends heavily on the response time left in the 15-month template (fig. 5(a)). For early changes, those before the CIR, an impact will require a nominal increase in the budget. The effect of later changes, however, requires many more of the parallel efforts and, hence, a larger budget increase in order to achieve the same end result in the reduce response time prior to launch.

Logic dictates that if a change occurs, it will impact the budget. This conclusion leads to the question of whether such a probability is sufficiently high to require budgeting for anticipated changes. To aid in this consideration, a history of the changes that occur each month over a period of 2.5 years is shown in figure 5(b). There is a strong correlation between flight rate and change rate; i.e., more hardware does mean more hardware failures. Therefore, changes are certain, predictable, and can be scoped within a budget.

Further examination of the workload impact (fig. 6) reveals that process delays caused by these changes tend to stack several reviews on top of each other. Reviews, such as CIR's from several flights,