As part of the wider Mariner program, in 1969 Mariner 6 and Mariner 7 ( Mariner Mars 69A / 69B) completed the first dual mission to Mars, flying over the equator and south polar regions and analysing atmosphere and surface with remote sensors as well as recording and relaying hundreds of pictures. The mission's goals were to study the surface and atmosphere of Mars during close flybys to establish the basis for future investigations, particularly those relevant to the search for extraterrestrial life, and to demonstrate and develop technologies required for future Mars missions and other long-duration missions far from the Sun. Mariner 6 also had the objective of providing experience and data which would be useful in programming the Mariner 7 encounter 5 days later.
Mariner 6 was launched from Launch Complex 36B at Cape Kennedy and Mariner 7 from Launch Complex 36A at Cape Kennedy.
On July 29, 1969, less than a week before closest approach, JPL lost contact with Mariner 7. They regained the signal via the backup low-gain antenna and were able to start using the high gain antenna again shortly after Mariner 6's close encounter. It was later determined a battery onboard Mariner 7 had exploded. Based on the observations made by Mariner 6, Mariner 7 was reprogrammed in flight to take further observations of areas of interest and actually returned more pictures than Mariner 6, despite the explosion.
By chance, both flew over cratered regions and missed both the giant northern volcanoes and the equatorial grand canyon discovered later. Their approach pictures did, however, photograph about 20% of the planet's surface, showing the dark features long seen from Earth, but none of the canals mistakenly observed by ground-based astronomers. In total 198 photos were taken and transmitted back to earth, adding more detail than the earlier mission, Mariner 4. Both craft also studied the atmosphere of Mars.
The twin Mariner craft made their closest fly-by of Mars at a distance of 2130 miles (3,430 kilometers) on August 5, 1969.
The ultraviolet spectrometer onboard Mariners 6 and 7 was constructed by the Laboratory for Atmospheric and Space Physics.
The engineering model of Mariners 6 and 7 still exists, and is owned by the Jet Propulsion Laboratory. It is currently on loan to the Laboratory for Atmospheric and Space Physics, and is on display in the lab's lobby.
The craft are now defunct in heliocentric orbits.

Spacecraft and subsystems
The Mariner 6 and 7 spacecraft were identical, consisting of an octagonal magnesium frame base, 138.4 cm diagonally and 45.7 cm deep. A conical superstructure mounted on top of the frame held the high-gain 1 meter diameter parabolic antenna and four solar panels, each measuring 215 x 90 cm, were affixed to the top corners of the frame. The tip-to-tip span of the deployed solar panels was 5.79 m. A low-gain omnidirectional antenna was mounted on a 2.23 m high mast next to the high-gain antenna. Underneath the octagonal frame was a two-axis scan platform which held scientific instruments. Overall science instrument mass was 57.6 kg. The total height of the spacecraft was 3.35 m.
The spacecraft was attitude stabilized in three axes (referenced to the sun and the star, Canopus) through the use of 3 gyros, 2 sets of 6 nitrogen jets mounted on the ends of the solar panels, a Canopus tracker, and two primary and four secondary sun sensors. Propulsion was provided by a 223 N rocket motor mounted within the frame which used monopropellant hydrazine. The nozzle with 4-jet vane vector control protruded from one wall of the octagonal structure. Power was supplied by 17,472 photovoltaic cells covering an area of 7.7 square meters on the four solar panels. These could provide 800 W of power near Earth and 449 W at Mars. The maximum power requirement was 380 W at Mars encounter. A 1200 W·h rechargeable silver-zinc battery was used to provide backup power. Thermal control was achieved through the use of adjustable louvers on the sides of the main compartment.
Three telemetry channels were available for telecommunications. Channel A carried engineering data at 8⅓ or 33⅓ bit/s, channel B carried scientific data at 66⅔ or 270 bit/s and channel C carried science data at 16,200 bit/s. Communications were accomplished via the high- and low-gain antennas via dual S-band travelling wave tube 10/20 W amplifiers for transmission and a single receiver. An analog tape recorder with a capacity of 195 million bits could store television images for subsequent transmission. Other science data was stored on a digital recorder. The command system, consisting of a central computer and sequencer (CC&S), was designed to actuate specific events at precise times. The CC&S was programmed with a standard mission and a conservative backup mission before launch, but could be commanded and reprogrammed in flight. It could perform 53 direct commands, 5 control commands, and 4 quantitative commands.
Instrumentation:

IR Spectrometer
Two-Channel IR Radiometer Mars Surface Temperature
UV Spectrometer
S-Band Occultation
Thermal Control Flux Monitor (Conical Radiometer)
Mars TV Camera
Celestial Mechanics
General Relativity