Propulsion Trades for a 2035-2040 Solar Gravitational Lens Mission

TL;DR

This paper compares propulsion options like solar sailing and nuclear electric propulsion for a 2035-2040 mission to reach 650 AU for Solar Gravitational Lens science, analyzing trade-offs in speed, mass, and technology readiness.

Contribution

It provides a comparative analysis of propulsion architectures and identifies near-term feasible pathways for rapid deep-space travel to enable SGL science.

Findings

Solar sailing requires ultra-low areal density for 20-year transit.

Nuclear electric propulsion can reach 650 AU in 27-33 years with specific power and thrust.

Hybrid architectures can potentially reduce transit time to around 20 years.

Abstract

The Solar Gravitational Lens (SGL) enables resolved imaging and spectroscopy of nearby terrestrial exoplanets, but useful science begins only after a spacecraft reaches roughly 650-900 astronomical units (AU). A 20 yr lower-bound trip to 650 AU requires an average radial speed of 32.5 AU per year, or 154 km/s, before launch, targeting, steering, and operations margins. We compare close-perihelion solar sailing, fission-electric nuclear electric propulsion (NEP), and high-thrust Oberth injection followed by NEP cruise using common lower-bound outbound-leg architecture envelopes, not closed end-to-end trajectories. For an ideal sail passing 0.05 AU from the Sun, total sailcraft areal density must be about 4.9 grams per square meter to reach 105 km/s, and 2.3 grams per square meter to reach 155 km/s. Thus sub-20 yr sail-only access requires ultra-low areal density plus deep-perihelion thermal qualification. For a 20 t NEP spacecraft with 800 kg payload and Isp=9000 s, optimized constant-power transfers reach 650 AU in t_rep ~ 27-33 yr when the integrated power-plus-propulsion specific mass is 10-20 kg per electric kilowatt, requiring 0.18-0.30 megawatt-electric (MWe) and few-newton thrust. NEP-only t_rep <20 yr requires <3 kg per electric kilowatt, while hybrid architectures can approach t_rep ~ 20 yr if an upstream injection stage supplies 50-70 km/s. Thus sail-first is the nearer-term lightweight-access path; hybrid injection+NEP is higher-capability but requires prior high-energy-injection and 0.2-0.4 MWe integrated NEP demonstrations.