Multi-Echelon, Multi-Indenture Models With Periodic Supply And Redundancy

The theory in this chapter was motivated by a need to develop a stockage model for Space Station Freedom, the large multi-national effort being managed by NASA that was launched in the mid-nineties. The most important difference between this application and those considered in the previous chapters is that here the operating base cannot place a resupply order at any time. Resupply is periodic, depending on the frequency of the space shuttle flights. There will be several a year, but depending on the item and whether it needs pressurized or unpressurized storage, it may only be eligible for certain resupply flights. This periodic supply modeling is applicable to other problems such as a base in Antarctica which can only be resupplied during the summer months or ships which can be resupplied only when they return to port.

A Space Station is comprised of many different types of systems such as Electric Power, Laboratory Module, Habitation Module, etc. A given system type will usually have significant redundancy in its design. After all we are talking about systems that may be critical for life support, and which are designed to operate for thirty years.