Modeling Demand for Human Exploration

The demand for supply items is generated by a module that models the demand of the various classes of supply for a given mission (based on number of crew, mission duration and other characteristics). This ‘demand generator’ outputs the mass, volume and other relevant information of the supply items that will be transported in the mission. The demand is separately modeled for each supply class. In its current first version, supply classes 2 (crew provisions), 4 (maintenance and upkeep), and 6 (exploration and research) are addressed in detail, while relatively simple models for supply classes 3 (crew operations), 5 (stowage and restraint), and 7 (waste disposal) are used. The demand for supply classes 8 (habitation and infrastructure) and 9 (transportation and carriers) is defined explicitly by the user who defines the items (such as power plants, ISRU plants etc) that are part of the manifest and the available transportation elements.

Propellants and Fuels (1)

The demand for propellants to be used on the surface is not calculated at this time.

Crew Provisions (2)

The demand for crew provisions is based upon the crew size, mission duration, contingency mission duration and number of EVAs. Calculations are based upon historical data for human spaceflight, including ISS usage rates.

Crew Operations (3)

The demand for crew operations is based upon the crew size, mission duration and number of EVAs. Demand calculations are based upon calculations given in the textbook Human Spaceflight Mission Analysis and Design (W. Larson, L. Pranke) and actual usage rate data from ISS.

Maintenance and Upkeep (4)

The demand for this class is currently estimated by modeling the per-day mass and volume requirement of spares. The spares model depends upon several factors including duty cycle. A spare will have a different duty cycle (active or dormant) dependent upon whether it is used on an element during a specific arc. At this time, Specific spares are not ‘picked’ out for the manifest but rather a gross mass and volume estimate is computed.

Stowage and Restraint (5)

The demand for stowage and restraint is calculated based upon the mission duration and the volume of pressurized dry cargo that the mission is delivering.

Exploration and Research (6)

The exploration items include scientific and research and field exploration equipment. The demand for these items is generated through the specification of the type of exploration and science that would be carried out in the mission. The science for each mission is described by specifying weights of four categories: Life, Climate, Geology and Resources. Depending on the weights (that sum up to one), relevant scientific and field exploration items are selected for the manifest.

Waste Disposal (7)

The demand for waste management equipment is calculated based upon the crew size and mission duration. Calculations are based upon data given in Human Spaceflight Mission Analysis and Design (W. Larson, L. Pranke). The amount of waste that will be generated during the mission is calculated based upon the simple assumption that all crew provisions used will become waste.

Habitation and Infrastructure (8)

The demand for habitation and infrastructure is defined by the user.

Transportation and Carriers (9)

The set of available carriers and propulsion modules is defined by the user. The network optimization then selects the optimal set of carriers and propulsion modules to complete the mission.

Miscellaneous (10)

The demand for miscellaneous items to be used on the surface is not calculated at this time.

The detailed demand models for each COS are contained in Appendix C of the following report:

de Weck O.L., Simchi-Levi D., Shishko R., Ahn J., Gralla E., Klabjan D., Mellein J., Shull A., Siddiqi A., Bairstow B, Lee G., "SpaceNet v1.3 User's Guide", NASA/TP-2007-214725, January 2007.

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