Propulsion systems for a starshade rendezvous mission with the Habitable World Observatory

Abstract

We assess how propulsion and operational constraints shape the exo-Earth characterization performance of a starshade rendezvous architecture for a Habitable Worlds Observatory (HWO)–like telescope at Sun–Earth L2. Using end-to-end Monte Carlo mission simulations with EXOSIMS, we model two representative starshade point designs: a 60 m occulter optimized for visible-band (VIS) spectroscopy (500 to 1000 nm) and a 35 m occulter optimized for near-ultraviolet (NUV) characterization (250 to 550 nm). For the 60 m case, we compare three electric-propulsion options spanning Hall and gridded-ion technologies (AEPS Hall, NEXT ion, and a Starlink-class Hall system) and quantify yield sensitivity to onboard propellant capacity, retargeting trajectory “burn-portion” (accelerate and decelerate fraction of slew), and the presence or absence of on-orbit refueling. In fuel-limited scenarios (1000 to 3000 kg initial propellant), the higher-Isp NEXT system delivers the largest characterization yield, providing 9% to 13% more characterizations than AEPS and 13% to 16% more than the Starlink-class option by enabling more retargeting slews per kilogram of propellant. When refueling is allowed, cumulative yields converge across thruster choices (about 120 cumulative characterizations over a 10-year campaign), while the propulsion choice primarily trades against the number of refueling events. For the 35 m near-UV starshade (modeled with AEPS), yields are substantially less fuel-sensitive and are instead dominated by mission time and geometric accessibility; tightening the minimum solar keepout (scarf) angle from 40 deg toward ≥50 deg barely impacts yield, from 50 deg to 65 deg modestly impacts yield, and ≥65 deg reduces yield rapidly, with severe degradation near 80 deg. These results identify regimes where starshade performance is fundamentally fuel-limited versus time/keepout-limited and provide quantitative guidance for jointly optimizing propulsion selection, tank size, refueling policy, and keepout constraints in HWO starshade architectures.

The authors' abstract, as published at the source. Journal of Astronomical Telescopes Instruments and Systems, 2026 · DOI ↗