  A concept for a new space-based cosmology mission called the Dark Ages Radio
Explore (DARE) is presented in this paper. DARE's science objectives include
(1) When did the first stars form? (2) When did the first accreting black holes
form? (3) When did Reionization begin? (4) What surprises does the end of the
Dark Ages hold (e.g., Dark Matter decay)? DARE will use the highly-redshifted
hyperfine 21-cm transition from neutral hydrogen to track the formation of the
first luminous objects by their impact on the intergalactic medium during the
end of the Dark Ages and during Cosmic Dawn (redshifts z=11-35). It will
measure the sky-averaged spin temperature of neutral hydrogen at the unexplored
epoch 80-420 million years after the Big Bang, providing the first evidence of
the earliest stars and galaxies to illuminate the cosmos and testing our models
of galaxy formation. DARE's approach is to measure the expected spectral
features in the sky-averaged, redshifted 21-cm signal over a radio bandpass of
40-120 MHz. DARE orbits the Moon for a mission lifetime of 3 years and takes
data above the lunar farside, the only location in the inner solar system
proven to be free of human-generated radio frequency interference and any
significant ionosphere. The science instrument is composed of a three-element
radiometer, including electrically-short, tapered, bi-conical dipole antennas,
a receiver, and a digital spectrometer. The smooth frequency response of the
antennas and the differential spectral calibration approach using a Markov
Chain Monte Carlo technique will be applied to detect the weak cosmic 21-cm
signal in the presence of the intense solar system and Galactic foreground
emissions.
