of the spacecraft cylinder near the cosmic ray device. Near the bottom of the detector deck four circularly polarized turnstile stainless steel wire whip antennas protruded radially from the side of the spacecraft, equally spaced around the axis. A gap for the high powered antenna and a heat radiation shield were between the payload and the rocket motor. The micrometeorite detectors were arranged in a ring around the cylinder near the bottom of the spacecraft. Four temperature gauges were mounted a various locations in the spacecraft. Explorer 2 was equipped with a Geiger counter for the purposes of detecting cosmic rays. After Explorer 3, it was decided that the original Geiger counter had been overwhelmed by strong radiation coming from a belt of charged particles trapped in space by the Earth's magnetic field (see: Van Allen radiation belt). Explorer 2 was also equipped with a wire grid array and an acoustic detector for the purpose of micrometeorite detection. Instruments Geiger counter An Anton 314 omnidirectional Geiger tube detector was used to measure the flux of energetic charged particles (protons E>30 MeV and electrons E>3 MeV). The instrument consisted of a single Geiger-Mueller tube, a scaling circuit to reduce the number of pulses, and a telemetry system to transmit the data to ground receiving stations. The Geiger-Mueller tube was a type 314 Anton halogen quenched counter with stainless steel (approximately 75% iron, 25% chromium) wall of approximately thickness. The instrument was mounted within the spacecraft hull, which had thick stainless steel walls. The counter was long by diameter and the internal wire was in length. The tube had a very small variation in counting efficiency over the range -55° to +175° Celsius. It had approximately 85% counting efficiency for cosmic rays, and about 0.3% counting efficiency for photons of energy 660 keV. The "dead time" (time to reset to record the next count) of the counters was about 100 microseconds. The counter was connected to a current amplifier, which directly fed a scaler stage, a bistable transistor multivibrator that could operate over a wide range of voltages and a temperature range of -15° to +85°Celsius, limited primarily by the supply batteries. The scaler resolving time was 250 microseconds. For pulse counts higher than 4000 per second, the scaler indicated a count of 4000. Results were sent to the ground through the telemetry system in real time. The experiment had no onboard