Survey of Mission Concepts for Exploring the Dark Ages Universe

The Dark Ages Epoch of the early Universe has not been explored for cosmological observations to date! Observations of the Dark Ages has the potential to revolutionize physics and cosmology by improving our understanding of fundamental particle physics, Dark matter and Dark energy physics, and inflation. The Dark Ages Epoch represent the period in the early evolution of the Universe, starting immediately after the decoupling of Cosmic Microwave Background (CMB) photons from matter, and ending with the formation of the first stars and galaxies. The Hi signal (with rest wavelength and frequency 21 cm and 1420 MHz, respectively) is the only available probe we can use to understand this crucial phase in the cosmological history of the Universe and answer fundamental questions about the validity of the standard cosmological model, dark matter physics, and inflation. Due to cosmological redshift, this signal is now only observable in the 5–40 MHz frequency band. The biggest challenge with these observations is separating the Dark Ages signal from the 5-orders-of-magnitude stronger Galactic Foreground noise, which is the synchrotron radiation emitted by relativistic electrons that travel on spiraling paths in our Milky Way Galaxy's magnetic field. A number of mission concepts have been proposed that could observe the Dark Ages from the lunar far-side. They are broadly classified into: (1) Single telescope concept on the lunar surface, (2) Sparse dipole array concepts on the lunar surface, (3) Satellite constellation concepts in Moon orbit, and (4) Satellite constellation concepts in Earth-Moon system. This paper presents a survey of different mission concepts that have been proposed to observe the Dark Ages Universe.