Explorer 52, also known as Hawkeye-1, Injun-F, Neutral Point Explorer, IE-D, Ionospheric Explorer-D, was a NASA satellite launched on June 3, 1974, from Vandenberg Air Force Base on a Scout E-1 launch vehicle.

To accomplish these objectives, the spacecraft was instrumented with the following instruments: This experiment measured electric and magnetic fields using a 42.7 m (140 ft) electric dipole (tip-to-tip) and a search coil antenna deployed 1.58 m (5 ft 2 in) from the spacecraft.

The magnetic field spectrum was measured in eight discrete, logarithmically spaced channels from 1.78 Hz to 5.62 kHz.

[3] This particle spectrometer (LEPEDEA) employed two electrostatic analyzers to measure protons and electrons simultaneously.

The electrostatic analyzers had a field of view of 8° by 30° and measured protons and electrons from 0.05 to 40 keV.

[5] A four-range, triaxial fluxgate magnetometer mounted on a 1.52 m (5 ft 0 in) boom, was used to measure the ambient magnetic field.

Satellite stray fields were constrained to be less than 0.1 nT, which was also the RMS instrument noise level.

After this period, the aspect had to be determined by observing the effect of optical illumination from the Sun on a plasma measurement system.

[6] In 1992, Dr. James Van Allen (Hawkeye Project Scientist) and the other Hawkeye principal investigators provided the National Space Science Data Center (NSSDC) with the high-resolution digital data (referred to as Master Science Files) from Explorer 52 (Hawkeye-1).