NASA-funded STARI mission plans first in-space transfer of starlight between free-flying spacecraft

A paper by John Monnier and colleagues at University of Michigan and other institutions introduces STARI, a NASA-funded two-spacecraft demonstrator targeting launch in 2029. The mission would fly two 8U CubeSats in low Earth orbit, separated by up to 200 m, and attempt the first in-space transfer of a narrow beam of starlight from one spacecraft to another, recoupling it into a single-mode fiber for interferometry.

The design relies on differential GNSS, visible LED beacons and fast-steering mirrors in closed-loop control to keep the relay beam aligned well enough for diffraction-limited, high-throughput fiber coupling. The key metric is sustained coupling efficiency and phase stability during formation flight. The paper is a mission-design preprint, not flight data, so the evidence is engineering validation and requirements rather than a completed measurement.

Long-baseline interferometry combines light collected far apart, creating resolution that a single mirror cannot match. STARI's 200 m relay is small by astronomy standards but could prove the hardest part: moving starlight through space without losing phase and throughput. If it works, it supports concepts such as LIFE, which aims to search nearby Earth-like exoplanets for atmospheric biosignatures, and future stellar imaging missions.

Next steps include building flight hardware, completing environmental tests and securing mission operations for the 2029 target. The mission's value will be judged by whether it can sustain fiber coupling through orbital disturbances, thermal changes and pointing errors. A successful demo would shift space interferometry from paper architecture to operational technology, giving astronomers a clearer path to direct imaging of exoplanet surfaces and atmospheres.