  The ultimate astronomical observatory would be a formation flying
interferometer in space, immune to atmospheric turbulence and absorption, free
from atmospheric and telescope thermal emission, and reconfigurable to adjust
baselines according to the required angular resolution. Imagine the
near/mid-infrared sensitivity of the JWST and the far-IR sensitivity of
Herschel but with ALMA-level angular resolution, or imagine having the
precision control to null host star light across 250m baselines and to detect
molecules from the atmospheres of nearby exo-Earths. With no practical
engineering limit to the formation's size or number of telescopes in the array,
formation flying interferometry will revolutionize astronomy and this White
Paper makes the case that it is now time to accelerate investments in this
technological area. Here we provide a brief overview of the required
technologies needed to allow light to be collected and interfered using
separate spacecrafts. We emphasize the emerging role of inexpensive smallSat
projects and the excitement for the LISA Gravitational Wave Interferometer to
push development of the required engineering building-blocks. We urge the
Astro2020 Decadal Survey Committee to highlight the need for a small-scale
formation flying space interferometer project to demonstrate end-to-end
competency with a timeline for first stellar fringes by the end of the decade.
