  The low-frequency sky below $\sim$15 MHz (20 m) is obscured by the Earth's
ionosphere, the layer of charged particles above the neutral atmosphere. Single
spacecraft have made measurements in this band, but cannot achieve high or even
moderate angular resolution because a telescope's resolution ($\theta$) is set
by $\theta = \lambda/D$, where $\lambda$ is the wavelength and $D$ is the
telescope diameter. For wavelengths that range from tens of meters to
kilometers, a telescope must be hundreds of meters to many kilometers in
diameter for even moderate resolution.
  The Great Observatory for Long Wavelengths (GO-LoW) is an interferometric
mega-constellation space telescope operating between 300 kHz and 15 MHz. In a
departure from the traditional approach of a single, large, expensive
spacecraft (e.g., HST, Chandra, JWST), GO-LoW is an interferometric Great
Observatory comprising thousands of small, inexpensive, and reconfigurable
nodes.
  A distributed constellation of sensing elements provides (1) reliability and
robustness to failures, (2) longevity by allowing for growth over time and
infusion of new technology via staged replacement of nodes, (3) reduced costs
through leveraging mass production, and (4) formation reconfigurability to
optimize the observatory for diverse science cases.
  A low-frequency mega-constellation revolutionizes a number of compelling
science cases: high-resolution all-sky mapping, Dark Ages/Epoch of Reionization
cosmology, interstellar medium mapping, solar/planetary magnetic activity, and
exoplanetary magnetospheric radio emission.
  This report summarizes GO-LoW's concept development under NASA's NIAC Phase I
program. We discuss antenna design and sensitivity, constellation architecture,
including communication and launch infrastructure, interferometric correlation
and a technology roadmap.
