International Space Station Traffic Model Development

The NASA Space Station Program Office is responsible for integrated traffic planning for the International Space Station (ISS). Traffic planning involves the scheduling of earth-to-orbit vehicles arriving at and departing from the ISS. The main objective of ISS traffic planning is the development of sound ISS long-term traffic plans that optimize utilization of ISS transportation assets within program constraints. The development of a traffic model tool to support this objective began in late 1993. The original traffic model (TM1) was developed in the Excel spreadsheet environment and has been a powerful and effective tool, mainly used in design analysis to assess station design characteristics, such as resupply vehicle capacity. However, TM1 has some limitations. The main limitation is that only the developer clearly understands how the model works and is the only one who can use the model to generate any meaningful results. This restricts the Space Station program's ability to utilize multiple analysts to arrive at the "best" traffic plan. Another TM1 drawback is the lack of configuration control To alleviate these problems, ISS Traffic Model Version 2 (TM2) was developed. Development of TM2 began with a nation-wide search of on-going traffic modeling activity in the private and public sectors. This search answered several critical questions important to the development of a comprehensive traffic model. The TM2 development effort has emphasized structure and consistency to support a multi-user environment. The model structure promotes data control, while allowing a high degree of flexibility to support multiple traffic planning analyses. The model structure was also built to be conducive to model enhancements, such as functions that are planned to include schedule/loading optimization and launch schedule uncertainty management.