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 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.