Orbiting solar telescope "Salyut-4" station.

The orbiting solar telescope on Salyut-4 (F = 2.5 m, d = 250 mm) produces images of the sun on the entrance slit of a stigmatic two-grating spectrograph (R₁ = 1 m, N₁ = 1200 lines/mm; R₂ = 0.5 m, N₂ = 2400 lines/mm, dispersion 16 A/mm, spectral resolution 0.3 A). The automatic system keeps the observed solar features on the slit of the spectrograph with an accuracy of 3-4 arc sec. The far UV-spectra (970-1400 A) of solar flares, brightenings, flocculi and prominences were photographed and fresh coatings of mirrors were made during the flight.