The 21cm line of neutral hydrogen provides unique access to the state of the
intergalactic medium throughout our Cosmic Dawn, making it an essential tool
for understanding the history of structure formation in our universe.
Experiments are nearing a first detection of this cosmological signal and
will
begin characterizing its power spectrum. So far, the most progress has been
made with dedicated experiments like PAPER, tailored to this single science
application. The partially funded Hydrogen Epoch of Reionization Array
(HERA)
continues in this vein, competing scientifically with the Square Kilometre
Array (SKA) for a small fraction of the cost. The logical next step beyond
this involves directly imaging reionization, but unlike for power-spectral
measurements, key challenges remain unsolved for building an imaging
instrument. Given an uncertain path and timescale for solving these
challenges, the US community is faced with a tough decision. Do we join
with
SKA-low --- a leveraged instrument being designed too soon, with many
competing science applications --- or plan a separate, tailored effort once
HERA has delivered more insight?