Abstract— <p>The “Sun–Terahertz” space experiment is planned to be performed on board of the Russian segment of the International Space Station beginning with 2026. The objectives of the experiment are to obtain data on the terahertz radiation from the Sun, as well as to study solar active regions and solar flares. The “Sun–Terahertz” scientific equipment consists of eight detectors, whose target frequencies are in the range of 0.4–12.0 THz. A heat source is required for the primary calibration of the detectors of the scientific equipment. For this purpose, a blackbody simulator was developed, which allows directing flows from the radiating element at different temperatures to the telescopes of the scientific equipment. Based on the results of the experimental verification, conclusions were made about the accuracy of setting the temperatures by the measuring controller and about the temperature gradient from the center to the edge of the radiator mirror. This article may be useful for experimenters involved in thermophysical measurements, spectrometric scientific instruments based on opto-acoustic detector (Golay cell), and other sensitive elements.</p>