Rau 2026 Review Charts Staged Architectures for Lunar and Free-Flying Interferometers Targeting Exoplanet Spectra and Microarcsecond Astrometry

The paper synthesizes mission concepts across free-flying, surface, and hybrid platforms. Science requirements dictate baseline length and wavelength first: mid-infrared nulling for temperate exoplanet thermal spectroscopy needs 100 m baselines with 10 nm metrology, while lunar far-side radio arrays target 1-30 MHz cosmic dawn signals unavailable from Earth orbit. Enabling technologies such as formation flying and cryogenic beam combiners mature mainly through flagship spillovers rather than dedicated lines.

Context from prior studies shows repeated underestimation of deployment autonomy costs; the review notes that lunar concepts benefit from Artemis logistics yet face regolith thermal cycling risks absent in free-flyers. SPIRIT far-IR and BHEX space-VLBI extensions illustrate how the same metrology stack supports planet-formation disks and black-hole photon rings once formation flying reaches TRL 6.

Decisions in the 2030s will sequence pathfinders before full arrays. Funding models must bridge laboratory demonstrations to flight hardware, a gap that has delayed prior interferometry proposals. A lunar laser interferometer for mid-band gravitational waves adds strain measurement orthogonal to LISA.

Next steps hinge on 2026-2029 technology tall poles in absolute metrology and autonomous deployment validated on ISS or CLPS landers.