Advanced Electric Propulsion Systems with Optimal Specific Impulses for Fast Interstellar Precursor Missions

Interstellar exploration is still in its infancy, but its scientific and cultural significance is enormous. For new near- and mid-term interstellar missions, advanced propulsion systems are of interest to achieve the large delta-V requirements and to increase the allowed payload mass. The choice of the optimal propulsion system, however, depends on the specific mission profile. In this study, we use the non-dimensional Tsiolkovsky equation to optimize the combined payload and structural mass fraction as a function of specific impulse, specific power, thruster efficiency, transfer time, and delta-V. We investigate three mission scenarios, assuming an advanced power source with a specific power of 1,000 W/kg and a thruster efficiency of 97%: (1) a Jupiter round trip, (2) a Pluto rendezvous, and (3) a mission to the focal point of the solar gravitational lens. For each mission, we report the optimal specific impulse that maximizes the payload mass fraction, the corresponding transit time, the electric propulsion system that could achieve such a mission, and the absolute masses assuming a launch with the Space Launch System Block 2. The analysis demonstrates that advanced electric space propulsion systems have the potential to enable higher payload mass fractions and shorter transit times than more conservative approaches to achieve interstellar trajectories.