  We present the upGREAT THz heterodyne arrays for far-infrared astronomy. The
Low Frequency Array (LFA) is designed to cover the 1.9-2.5 THz range using
2x7-pixel waveguide-based HEB mixer arrays in a dual polarization
configuration. The High Frequency Array (HFA) will perform observations of the
[OI] line at ~4.745 THz using a 7-pixel waveguide-based HEB mixer array. This
paper describes the common design for both arrays, cooled to 4.5 K using
closed- cycle pulse tube technology. We then show the laboratory and telescope
characterization of the first array with its 14 pixels (LFA), which culminated
in the successful commissioning in May 2015 aboard the SOFIA airborne
observatory observing the [CII] fine structure transition at 1.905 THz. This is
the first successful demonstration of astronomical observations with a
heterodyne focal plane array above 1 THz and is also the first time high- power
closed-cycle coolers for temperatures below 4.5 K are operated on an airborne
platform.
