Solar Electric Propulsion Architecture for Mars Cargo for Affordable Exploration and Sustained Permanence

Future exploration missions throughout the Solar System will require high efficiency propulsion technologies using moderate spacecraft power that are extensible to multiple mission areas and customers. Solar Electric Propulsion (SEP) has been proven at various power levels and propulsion unit design types and should be part of such a technology portfolio. Many of the SEP thrusters used for recent missions have established the high Technology Readiness Level for this technology. SEP’s high specific impulse (ISP) has a dramatic impact on reducing the required spacecraft propellant while increasing launch window flexibility, making the propulsion technology an ideal choice for delivering large unmanned cargo payloads for sustaining human Mars exploration. The future of human Mars exploration will see substantial benefit in terms of lower mission mass when SEP systems are employed in the architecture. It must be remembered that key design parameters (e.g., power, ISP, specific mass) need to be optimized in order to effectively deliver the highest payload mass possible within a given program. Architectures that have the local planetary exploration elements pre-deployed ahead of the human crew can have a significant impact on the design of the human exploration mission in terms of total mass available at Mars, the size of the crew spacecraft, and the number of total systems employed to create low risk transportation. This paper will discuss a recent Aerojet Rocketdyne (AR) study that examines the impact of SEP power levels, ISP, and stage size required for large (20+mt) cargo prepositioning missions to Mars orbit. The study also examines the impact on the crew vehicle size when different combinations of architecture elements are pre-positioned. The AR analysis has focused on finding the combination of right size launch capability and SEP vehicle power level that delivers large cargo but maintains reasonable trip times for pre-positioning. For near-term missions, we show that 50kWe SEP modules can be used either singly or in combination, enabling a path to lower cost human exploration missions. An approach that uses 40-50kWe SEP modules creates mission extensibility where these modules can also be used for cis-lunar missions and large science missions such as the Asteroid Redirect mission and geosynchronous Earth orbit commercial and military satellite delivery missions launched on existing expendable launch vehicles ensuring that the SEP modules have multiple applications. We show that this modular approach enables a dramatic reduction in total development and production costs for high power SEP and provides for a more gradual phasing of system development to fit within available budgets. 1 Fellow, Space Systems and Mission Analysis, PO Box 109680, M/S 712-67, AIAA Associate Fellow. 2 Executive Director, Space, 1300 Wilson Blvd., AIAA Associate Fellow. 3 Sr. Engineer, Mission Architecture, 555 Discovery Dr., AIAA Member. 4 Sr. Manager, Advanced Space and Launch, P.O. Box 7922 / MS RFB19, AIAA Member. 5 Executive Director, Advanced Space and Launch, 11411 139 Place, AIAA Fellow.