4GREAT - a four-color receiver for high-resolution airborne terahertz spectroscopy

4GREAT is an extension of the German receiver for astronomy at terahertz frequencies (GREAT) operated aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The spectrometer comprises four different detector bands and their associated subsystems for simultaneous and fully independent science operation. All detector beams are coaligned on the sky. The frequency bands of 4GREAT cover 491–635, 890–1090, 1240—1525, and 2490–2590 GHz, respectively. This article presents the design and characterization of the instrument, and its in-flight performance. The first light of 4GREAT was on June 2018. It has been offered to the interested SOFIA communities starting with observing cycle 6.