Instrumentation for Measurement of Cosmic Noise at 2.0 and 2.5 MHz from a Polar Orbiting Geophysical Observatory

This paper describes the radio astronomy instrument flown on both Polar Orbiting Geophysical Observatories II and IV (OGO-II and OGO-IV). The instrument was designed to map the brightness distribution of cosmic noise over the sky at 2.0 and 2.5 MHz by using the theoretically predicted ionospheric focusing of an electrically short antenna. An antenna impedance bridge was included as a necessary part of the system. The system is unusual because the impedance bridge and the 2.5-MHz radiometer operate simultaneously at the same frequency. OGO-II was launched on October 14, 1965, and the instrument operated normally until the spacecraft was turned off November 1, 1967. During this period the instrument was operated for 4495 hours with many on-off cycles. OGO-IV was launched July 28, 1967, and the instrument operated properly for 18 330 hours prior to termination of spacecraft operations on October 23, 1969. Results of these experiments are published separately [5], [6].