The cost for each spare part is computed as follows:

Cost = (k1 price) + (k2 weight) + (k3 volume) + k4

This approach makes it possible to solve spare parts optimization problems for a variety of mission applications. When the only consideration is the actual price of the spare part, and weight and volume have no cost impact, then the cost coefficients are defined as follows:

k1 =1; k2 = k3 = k4= 0

These are the module’s default settings.

If the primary restriction is weight, such as for fly-away kits, then the coefficients would be

k1 =0; k2 =1; k3 = k4= 0

In early stages of analysis, when pricing data are not available, rough calculations can be obtained by defining a fixed cost for all spare parts as follows:

k1 =k2 = k3 =0; k4 = constant

For example, it is generally supposed that the cost to send 1 kilogram into space is $10,000. A 1 kilogram reel of wire, which may normally cost $5 in a retail store, becomes extraordinarily expensive when orbiting the earth.

Take a look at the values in the Item Data - Miscellaneous tab dialog box on page 413 and the ISLE - Spare Optimization dialog box on page 415. The total cost for taking the particular item on the mission as a spare part is as follows:

Cost        =        (k1 price) + (k2 weight) + (k3 volume) + k4

 =        (1 × 100,000) + (100 × 1) + (500 × 0.3) + 1,000

 =        101,250

When computing optimal quantities, RAM Commander makes sure that the total cost does not exceed a budget you specify.