From the article: > To see whether fuel resources and infrastructure in space would benefit manned missions to Mars, Ishimatsu developed a network flow model t

From the article: > To see whether fuel resources and infrastructure in space would benefit manned missions to Mars, Ishimatsu developed a network flow model to explore various routes to Mars — ranging from a direct carry-along flight to a series of refueling pit stops along the way. The objective of the model was to minimize the mass that would be launched from Earth, even when including the mass of a fuel-producing plant, and spares that would need to be pre-deployed.