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Abstract The current aim of NASA's Journey to Mars is a stepwise approach towards landing humans on the Red Planet, culminating in a sustained presence. There are many recent studies on how this could be achieved in an evolvable and affordable manner. Most architectures begin with crewed missions to Phobos or Mars orbit in the mid-2030's, progress toward short-stay missions on the surface, and then culminate with regular, long-stay missions at a permanent outpost in the 2040's. A common factor of these architectures is that many robotic launches would be required in order to support the crew by prepositioning mission elements and other needed supplies. In this paper, the use of 150 kW reusable Solar Electric Propulsion (SEP) tugs as a means to deliver elements both to orbit and the surface is studied. The conceptual SEP tugs make use of continued technology developments that were initialized through the Asteroid Redirect Robotic Mission (ARRM). They would also be used to deliver food and supplies to sustain the crews similar to resupply missions for the International Space Station. These SEP tugs would cycle (with loitering) between staging orbits in cislunar space and Mars orbit. The concepts presented here focus on the use of SEP for purposes of delivering cargo, and could potentially be complimentary to many human Mars architectures presented in the literature. In order to characterize mission design parameters such as dates, masses, and durations, thousands of optimized trajectories were run using low-thrust optimization software. Solutions are found for all launch/arrival date pairs for the years 2038–2053. They can be displayed as contour plots called Bacon plots – the SEP equivalent of porkchop plots. Possible mission architecture concepts for a steady-state human presence on Mars along with the cargo missions needed to keep it functioning are described and the relevant mission parameters such as launch dates, masses, arrival dates, etc., are given. It was found that the reusable SEP tug architecture would be highly beneficial to the logistics of a sustainable Mars outpost. Highlights • Solar Electric Propulsion offers an efficient method to transfer cargo to Mars. • Reusable SEP tugs stationed at the Lunar gateway offer flexible trajectories. • ARRM project SEP technologies can be levied for use in human mission architectures. • Optimal SEP tugs would require 100–200 kW of power to provide sufficient acceleration. [ABSTRACT FROM AUTHOR]