Explorer 24 & 25 (AD-B & Injun4)

Injun 4 (Explorer 25) was a magnetically aligned satellite launched simultaneously with Explorer 24 (AD-B) (Air Density experiment) using a Scout-X4 rocket. The satellite's primary mission was to make measurements of the influx of energetic particles into the earth's atmosphere and to study atmospheric heating and the increase in scale height which have been correlated with geomagnetic activity. Studies of the natural and artificial trapped radiation belts were also conducted.

Explorer 24 was placed in orbit together with Explorer 25 from a single launch vehicle. Explorer 24 was identical in configuration to the previously launched balloon satellites Explorer 9 and 19. The spacecraft was 3.6 m in diameter, was built of alternating layers of aluminum foil and plastic film, and was covered uniformly with 5.1-cm white dots for thermal control. It was designed to yield atmospheric density near perigee as a function of space and time from sequential observations of the sphere's position in orbit. To facilitate ground tracking, the satellite carried a 136 MHz tracking beacon. The satellite reentered the earth's atmosphere on 18 October 1968.