An analysis of the effect of production quantity and inventory selection policy on the probability of meeting a specified launch schedule

摘要

An analysis of the effect of two alternative inventory selection rules is performed to determine their effect on both cost per flight and schedule reliability for the planned Space Shuttle Program.

The major objective of the Space Shuttle Program is to achieve a low cost per flight while providing a capability to support a variety of scientific, defense, commercial and international space applications. Cost per flight is the average recurring cost for operating the shuttle. One aspect of cost per flight is related to the number of new motors required to complete the mission flight schedule.

The Logistics Simulation Model (LSM) of Schlagbeck and Giglieri (1) was employed to simulate the mission flight schedule. The two inventory selection policies considered were:

(1) When a motor is needed to make a flight select the available motor with the least number of previous flights (new logic).

(2) When a motor is needed to make a flight select the available motor with the most previous flights (old logic).

The study was performed using baseline parameters as supplied by the NASA program office. The number of new motors to be produced and the production schedule was varied over the range (80-90).

The study shows that the probability of meeting a specified launch schedule is greater and the refurbishment costs lower using the new logic over the entire feasible range of production quantities.