The Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) is a radio interferometer funded by the National Science Foundation[1] to detect 21 cm hydrogen (HI) fluctuations occurring when the first galaxies ionized intergalactic gas at around 500 million years after the Big Bang.

Given the stringent dynamic range requirements for detecting reionization in the face of foregrounds that are five orders of magnitude brighter, the PAPER project is taking a carefully staged engineering approach, optimizing each component in the array to mitigate, at the outset, any potentially debilitating problems in subsequent data calibration and analysis.

The instrument is located at the P2 site on the Square Kilometre Array South Africa (SKA-SA) in the Meerkat National Park near the small town of Carnarvon.

HERA II entails applying lessons learned during Phase I to define and build a larger array capable of detailed characterization of the statistical signal and imaging the brightest reionization structures.

The final stage of HERA, Phase III, will address the challenges of full tomographic imaging using an SKA-scale facility with capabilities informed by the earlier work.