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Missions

Transit IV-A

Transit 4A (the cylindrical spacecraft at the bottom), with its companion payloads, before launch in 1961. The Transit was a U.S. Navy satellite program to provide exact navigational positions regardless of surface weather. Credit: Johns Hopkins University Applied Physics Laboratory

Transit IV-A: The First Radioisotope Power System

  • Launched on June 29, 1961
  • First satellite to carry a radioisotope power supply into space
  • Set at record at its time for the longest operating satellite launched by the Johns Hopkins University Applied Physics Laboratory

Goals: The mission was deisgned to conduct navigation trials and demonstrations, improve the understanding of the effects of ionospheric refraction on radio waves and inncrease knowledge of the earth's shape and gravitational field.

Accomplishments: Transit 4A met all launch objectives. Doppler data from this satellite confirmed that the equator of the earth is elliptical, not circular (long and short axes differ by approximately 250 feet).

Transit 4A News Clipping
Transit 4A, with its companion payloads, was put in orbit on June 29th, 1961. The sphere at the top is Greb III, designed to measure solar X-rays. In the middle is Injun, an experiment to record the flux of charged particles responsible for the aurora and airglow. Solar cells (the rectangular elements covering most of the payloads' exteriors) extract energy from sunlight for supplementary power. The Transit series of satellites is sponsored by the U.S. Navy, its purpose being to provide exact navigational positions regardless of surface weather. Credit: Johns Hopkins University Applied Physics Laboratory

Transit 4-A and 4-B design represented the first departure from the sphere-shaped configuration of the earlier satellites; it resembled a modified drum and had an expandable outer shell covered with solar cells. Satellite 4-A was the first space vehicle to employ a radioisotope power supply (RIPS) and the first to switch power systems by command; 4-B was similarly configured.