Towards an extension of equivalent system mass for human exploration missions on Mars

NASA mission systems proposals are often compared using an equivalent system mass (ESM) framework, wherein all elements of a technology to deliver an effect—its components, operations, and logistics of delivery—are converted to effective masses, which has a known cost scale in space operations. To date, ESM methods and the tools for system comparison largely fail to consider complexities stemming from multiple transit and operations stages, such as would be required to support a crewed mission to Mars, and thus do not account for different mass equivalency factors during each period and the inter-dependencies of the costs across the mission segments. Further, ESM does not account well for the differential reliabilities of the underlying technologies. The uncertainty in the performance of technology should incur an equivalent mass penalty for technology options that might otherwise provide a mass advantage. Here we draw attention to the importance of addressing these limitations and formulate the basis of an extension of ESM that allows for a direct method for analyzing, optimizing, and comparing different mission systems. We outline a preliminary example of applying extended ESM (xESM) through a techno-economic calculation of crop-production technologies as an illustrative case for developing offworld biomanufacturing systems.