Researchers submit starshade propulsion study for Habitable Worlds Observatory mission

On October 26, 2026, researchers submitted a propulsion study to the arXiv preprint server that examines how propulsion limits and operational boundaries shape exo-Earth observations for a starshade rendezvous mission with a Habitable Worlds Observatory–class telescope at Sun–Earth L2. A starshade is a large screen flown in formation with a telescope to block starlight from a target star.

The paper lists Mario Damiano, Rhonda Morgan, Michael Turmon, Dmitry Savransky, and Armen Tokadjian as its authors. It runs 39 pages with 11 figures and 4 tables and has been accepted for publication in JATIS. The work carries the arXiv identifier 2610.36200 in the astro-ph.IM category.

The team used end-to-end Monte Carlo simulations with the EXOSIMS modeling toolkit to explore how propulsion limits and operational boundaries shape exo-Earth observations. Monte Carlo simulations use repeated random sampling to model a range of possible outcomes. Those simulations underpin the paper’s conclusions about thruster performance, propellant capacity, slew scheduling, and refueling for the starshade mission.

For visible-band spectroscopy from 500 to 1000 nanometers, the study models a 60-meter starshade paired with the telescope. The visible-light design is one of two starshade sizes examined in the paper.

For near-ultraviolet characterization from 250 to 550 nanometers, the authors instead model a 35-meter starshade, covering a different spectral band in the same simulation set. The study treats the 60-meter and 35-meter designs as separate simulation cases matched to different spectral bands.

The comparison pits AEPS Hall thrusters, NEXT ion thrusters, and Starlink-class Hall thrusters against one another for the 60-meter design. The analysis also varies propellant capacity, the acceleration-deceleration split during each retargeting slew, and the possibility of on-orbit refueling.

With 1000 to 3000 kilograms of initial propellant and no refueling, the NEXT ion thruster produces the highest characterization yield. It achieves 9 to 13 percent more characterizations than AEPS and 13 to 16 percent more than the Starlink-class option under those conditions.

The NEXT thruster’s higher specific impulse lets it perform more retargeting slews per kilogram of propellant. Specific impulse measures how much thrust a thruster produces per unit of propellant over time. That efficiency advantage explains its lead when the mission cannot refuel in orbit.

When on-orbit refueling is available, characterization yields converge across thruster choices to roughly 120 cumulative characterizations over ten years. Under refueling, the propulsion choice mainly changes how many refueling events are required rather than the total science return.

For the smaller 35-meter starshade using AEPS, yield is less sensitive to fuel supply. Instead, mission duration and geometric accessibility dominate the results, pointing to a time- or keepout-limited regime distinct from the fuel-limited behavior seen with the larger design.

The solar keepout angle is the minimum separation between a target star and the Sun as viewed from the telescope. Raising the minimum solar keepout angle from 40 to 50 degrees has little effect on characterization yield. That insensitivity at lower angles defines the boundary before keepout constraints begin to erode science return.

Increasing the minimum solar keepout angle from 50 to 65 degrees has a modest effect on yield. Yield begins to decline more noticeably once the keepout angle passes 50 degrees.

Keepout angles above 65 degrees rapidly reduce characterization yield, with severe degradation near 80 degrees. Steep losses at high keepout angles mark the transition into a strongly keepout-limited operational regime.

The results separate fuel-limited and time- or keepout-limited regimes to inform thruster choice, tank size, refueling plans, and keepout limits for Habitable Worlds Observatory starshade missions. Mission designers can use these regimes to match hardware choices to expected operational bottlenecks.

The Habitable Worlds Observatory carries a projected price tag of at least $11 billion, according to the Astro2020 Decadal Survey. NASA is designing the observatory with a six-meter mirror that must remain stable within ten picometers, with work expected to continue into the early 2040s.

HWO is designed to achieve a starlight suppression contrast of ten billion to one. That ratio matches what the HOEE starshade concept requires and far exceeds the roughly one hundred million to one contrast of the Roman Space Telescope‘s coronagraph.

NASA’s Nancy Grace Roman Space Telescope is scheduled to launch on August 30, 2026, aboard a SpaceX Falcon Heavy from Kennedy Space Center. Its coronagraph instrument will be the most capable starlight-suppression system ever flown in space, though unable to directly image a rocky Earth-like planet in a Sun-like star’s habitable zone.

A separate starshade concept, the Hybrid Observatory for Earth-like Exoplanets, is led by John C. Mather, a Nobel laureate in physics and senior astrophysicist at NASA’s Goddard Space Flight Center. The concept pairs a 100-meter orbital starshade with ground-based telescopes to directly image Earth-like exoplanets. Mather serves as principal investigator.

The team published the concept on the cover of Nature Astronomy in March 2026 and estimates it could operate roughly a decade before HWO at around one-tenth the cost. The hybrid approach leverages ground-based light-collecting area.

The HOEE starshade would fly approximately 175,000 kilometers from Earth in a long elliptical orbit, hovering on the line of sight between a ground telescope and a target star to create an artificial eclipse.

Its design includes 48 petals extending 24 meters from a 50-meter central disk, for a total diameter of 100 meters. The starshade must be repositionable to within six meters of accuracy. The team proposes hot hydrogen microthruster propulsion because it produces no visible emissions that could contaminate the planet-light signal.

HOEE would rely on ground-based adaptive optics to correct atmospheric distortion while collecting light with extremely large telescopes. The ELT’s 39-meter mirror is about six times larger in diameter than HWO’s planned six-meter mirror and collects light roughly 42 times faster.

HOEE researchers project that the observatory could record planet-reflected light from an Earth-sized world in under one minute of viewing time. That detection means confirming the planet’s presence and beginning spectral analysis, not producing a resolved image.

The HOEE team completed its initial NASA NIAC Phase I study and has submitted a Phase II proposal, according to Tech Times. The team also received funding through Caltech’s Keck Institute for Space Studies, and members have applied for Phase B NIAC funding with hopes of a decision by 2027, Phys.org reported. “This is an exciting project that provides the faster, and cheaper, and more efficient way,” said Vladimir Airapetian.

NASA’s 2022 NIAC awards included 12 Phase I studies at $175,000 for nine months and five Phase II awards at $600,000 over two years, totaling $5.1 million across 17 researchers. HOEE was among the early-stage concepts supported through this program.

Mather’s team seeks to reduce the 100-meter starshade’s mass tenfold to accommodate roughly 400 kilograms of thin membrane material. The ultra-lightweight design could be assembled or built entirely in space so it need not survive launch in its final rigid form.

No starshade has ever flown, and formation-flying and fine-positioning at 175,000 kilometers have never been validated in orbit. Those capabilities have never been demonstrated in orbit for any 100-meter class starshade mission. “HOEE can observe about many times faster because it uses a ground telescope roughly six times larger than the HWO,” said Ahmed Soliman.

The propulsion results separate fuel-limited and keepout-limited regimes for HWO starshade missions, while HOEE proposes a ground-based alternative that could operate earlier and at lower cost but has never flown in formation at 175,000 kilometers. The HWO study focuses on a telescope at Sun-Earth L2, while HOEE pairs an orbital starshade with ground-based telescopes.