The SIGNE II M P-9 experiment was designed to study cosmic and solar gamma-ray bursts. The experiment included 2 identical 15 cm diameter by 2 cm thick NaI (Tl) scintillators. One faced in the solar direction, and the other faced the anti-solar direction. Thus, 4-pi steradians were under simultaneous observation. These detectors were some 3 times larger than the previously flown SIGNE detectors.

The output pulses from each photomultiplier were analyzed simultaneously in 11 energy channels. Background counts were accumulated over 64 s intervals. A trigger signal was generated for the solar-pointed detector when the count rate exceeded the background by 8-sigma over a 0.5 s interval. For the anti-solar detector, a trigger signal was generated when the count rate in either a 0.5 s or a 2 s interval exceeded the background by 8-sigma. This led to a trigger threshold of ∼3 × 10^-7 erg/cm²/s for a gamma-ray burst spectrum of E^-2. Typically, data were integrated in 164 s bins, 11 energy channels when not triggered. Once a burst trigger occurred, data could be taken in 1/64 s bins, 4–7 energy channels. The total allocated bit rate was 6 b/s.