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Mariner 4 (together with Mariner 3 known as Mariner–Mars 1964) was the fourth in a series of spacecraft intended for planetary exploration in a flyby mode. It was designed to conduct closeup scientific observations of Mars and to transmit these observations to Earth. Launched on November 28, 1964, Mariner 4 performed the first successful flyby of the planet Mars returning the first pictures of the Martian surface. It captured the first images of another planet ever returned from deep space; their depiction of a cratered, seemingly dead world largely changed the view of the scientific community on life on Mars. Other mission objectives were to perform field and particle measurements in interplanetary space in the vicinity of Mars and to provide experience in and knowledge of the engineering capabilities for interplanetary flights of long duration. On December 21, 1967 communications with Mariner 4 were terminated.


Mars flyby

The spacecraft flew by Mars on July 14 and July 15, 1965. Planetary science mode was turned on at 15:41:49 UT on July 14. The camera sequence started at 00:18:36 UT on July 15 (7:18:49 p.m. EST on July 14) and 21 pictures using alternate red and green filters, plus 21 lines of a 22nd picture were taken. The images covered a discontinuous swath of Mars starting near 40° N, 170° E, down to about 35° S, 200° E, and then across to the terminator at 50° S, 255° E, representing about 1% of the planet's surface. The closest approach was 9,846 km from the Martian surface at 01:00:57 UT July 15, 1965 (8:00:57 p.m. EST July 14). The images taken during the flyby were stored in the on-board tape recorder. At 02:19:11 UT Mariner 4 passed behind Mars as seen from Earth and the radio signal ceased. The signal was reacquired at 03:13:04 UT when the spacecraft reappeared. Cruise mode was then re-established. Transmission of the taped images to Earth began about 8.5 hours after signal reacquisition and continued until August 3. All images were transmitted twice to ensure no data was missing or corrupt.

The spacecraft performed all programmed activities successfully and returned useful data from launch until 22:05:07 UT on October 1, 1965, when the long distance to Earth (309.2 million km) and the imprecise antenna orientation led to a temporary loss of communication with the spacecraft until 1967.