The dedicated gamma-ray burst detector, i.e. the upper detector, faced in the direction of the Sun. It was a 4.5 cm radius by 3.7 cm thick NaI(Tl) crystal, surrounded by an 8 mm thick plastic anti-coincidence jacket. The crystal and the plastic were viewed from the side by photomultipliers. The gamma-ray burst detector operated in low time resolution “waiting” modes in the absence of a burst; low energy resolution spectra and higher energy resolution calibration spectra were transmitted in this mode. Typically, the data were accumulated into 163.8 s time bins, 1–31 energy channels. Detection of a burst triggered the storage of high time resolution count rates and spectral data. The trigger criterion was an excess count rate 8 sigma above normal in a 250 ms interval. The maximum time resolution was 1/512 s. The energy ranges examined for burst detection ranged from 20–280 keV to 80–3000 keV, depending on the detector mode. During a burst, there were 1–6 energy channels used, and, for Prognoz 7 and a “typical” burst, the nominal energy range was 80–1000 keV. The total data rate for the Prognoz 7 experiment package was 6 b/s.

Two collimated, lateral detectors were used primarily for the observation of discrete sources, while the upper, omnidirectional detector was used for bursts. The axis of the upper detector is parallel to the satellite spin axis. The axis of the lateral detectors was 9.5 degrees away from the spin axis, in order to create a roll modulation for discrete source observations. Data were collected in 9 energy bins.