ERS 13 was a spin-stabilized tetrahedron that weighed 2.1 kg and measured 22.86 cm along each triangular edge. The spin rate was approximately 10 rpm, and power was obtained by solar cells. The satellite carried a scintillation counter and a solid-state detector to measure electrons and protons in the radiation belts. Because of the low (100 mW) transmitter power at 136 MHz, no data were obtained beyond 6 earth radii (40,280 km). The transmission was normal from launch until October 20, 1964, when the transmitter became intermittent. A PAM/FM/PM telemetry system using IRIG (Inter-Range Instrumentation Group) channel 5 was employed.