A Historical Review of Logistics Mass and Crew Time Demands for ISS Operations

Following over 23 years of continuously crewed operations on the International Space Station (ISS), NASA is planning to return humans to the Moon and eventually send humans to Mars. ISS operations provide vital data to inform mission analysts as NASA prepares for longer and more complex missions with increased mission endurance. Endurance, defined as crewed operating time between cargo deliveries (or crew launch and return to Earth, if no cargo deliveries), is an important metric when analyzing mission needs. NASA is developing architectures to support sustained deep-space habitats in cislunar space, on the lunar surface, in Mars transit, and on the surface of Mars. Unlike the ISS, these systems will not be continuously crewed. Similar to the ISS however, these systems will not return to Earth for regular refurbishment between missions. Lunar systems will routinely go through long uncrewed periods between crewed missions. The systems on board will need to survive these dormancy periods with no crew present to provide maintenance. Mars systems will experience significantly longer endurance than past experience. Additionally, the inability to have quick aborts to return to Earth increases the need for system reliability, redundancy, and maintainability, as well as plans for contingency operations. However, ISS experience is still useful for planning future missions and remains the best test bed available to predict the requirements of future human missions. This paper analyzes the operational history of the ISS from October 2017 through December 2023, including the mass and items delivered as well as crew time allocations. During this time period, crew on board the ISS logged over 50,000 hours and the station received over 130 metric tons of logistics. Understanding logistics and crew time demands for the ISS will support NASA mission analysts and operation planners as the agency sends humans further out into space.