Explorer 52, also known as Hawkeye-1, Injun-F, Neutral Point Explorer, IE-D, Ionospheric Explorer-D, was a NASA satellite launched on 3 June 1974, from Vandenberg Air Force Base on a Scout E-1 launch vehicle. Mission The primary mission objective of Explorer 52 (Hawkeye-1) was to conduct particles and fields investigations of the polar magnetosphere of the Earth out to 21 Earth radii. Secondary objectives were to make magnetic field and plasma distribution measurements in the solar wind, and to study Type-3 radio emissions caused by solar electron streams in the interplanetary medium. To accomplish these objectives, the spacecraft was instrumented with following instruments: A plasma wave receivers; A fluxgate magnetometer; A low energy proton-electron differential energy analyzer. Experiments Extremely low frequency (ELF) / Very low frequency (VLF) Receivers This experiment measured electric and magnetic fields using a electric dipole (tip-to-tip) and a search coil antenna deployed from the spacecraft. The electric field spectrum measurements were made in 16 logarithmically spaced frequency channels extending from 1.78 Hz to 178 kHz, and DC electric fields were also measured. The bandwidth of these channels varied from 7.5% to 30% depending on center frequency. Channel sensitivity and dynamic range were 1E-6 V/m and 100 dB, respectively. A wideband receiver was also used, with two selectable bandwidth ranges: 0.15 to 10-kHz or 1 to 45-kHz. The magnetic field spectrum was measured in eight discrete, logarithmically spaced channels from 1.78 Hz to 5.62 kHz. The bandwidth of these channels varied from 7.5% to 30% depending on frequency. The dynamic range was 100 dB, and the sensitivity ranged from 0.1-nT at 1.78 Hz to 3.4E-4 nT at 5.62-kHz. The wideband receiver described above could be used with the magnetic antenna. Each discrete channel was sampled once every 11.52-seconds. Low-Energy Proton and Electron Differential Energy Analyzer (LEPEDEA) This particle spectrometer (LEPEDEA) employed two electrostatic analyzers to measure protrons and electrons simultaneously. A GM tube was an additional detector sensitive to protons above 600 keV and electrons above 45 keV. The sensors were mounted normal to the spacecraft spin axis. Angular distributions of particles were determined with a sector resolution of 50° for analyzer voltage steps and 10° for analyzer voltage sweeps of its whole range. The electrostatic analyzers had a field of view of 8° by 30° and measured protons and electrons from 0.05 to 40-keV. The Geiger–Müller tube had a conical field of view of 15° half-angle. Two