Fill 'er up! A Functional Analysis of a Cryogenic Propellant Depot at Earth-Moon L1

摘要

This paper presents a functional analysis for a remotely operated cryogenic propellant depot. Selected studies and concept papers are reviewed to synthesize a concept of operations (ConOps). Top-level functions are taken from the ConOps, decomposed, and allocated to lower levels. These are depicted in functional flow block diagrams. Functional and system/subsystem interfaces are identified using N2 diagrams. Depot operations are shown to include both routine spacecraft operations and propellant operations. Propellant operations include four broad functions: 1) Propellant Maintenance, in which the depot maintains its supply of liquid hydrogen and oxygen; 2) Propellant Receiving, in which the depot receives propellants from a supply vehicle; 3) Propellant Dispensing, in which the depot transfers propellants to a customer vehicle; and 4) Contingency Recovery, in which the depot responds to off-nominal conditions to protect itself and its propellant supply, and seeks to re-establish nominal operations. Each of these functions is further decomposed and described. The analysis provides several insights into depot operation. First, the four broad propellant functions identified appear to completely describe the spectrum of propellant operations. Second, the command & data handling system is identified as a critical system for the depot, in that all commanding of the depot and all reporting of depot and propellant status flow through that system. Third, the N2 diagrams illustrate the many fluid, mechanical, and electrical interfaces with the propellant tanks. Special precautions will be required in the design and operation of the depot to ensure safe operations. Fourth, many anomalies in propellant operations are manifested as spikes in propellant tank temperature and pressure. Therefore, the status of the propellant tanks must be carefully and continuously monitored. The paper concludes that functional analysis and the related diagrams are effective tools to gain understan