Editing Mariner 6 and 7 (section)

==Launch==
[[File:Mariner 7 lift-off.jpg|thumb|Mariner 7 lift-off on March 27, 1969]]
Three Mariner probes were constructed for the mission, with two intended to fly and one as a spare in the event of a mission failure. The spacecraft were shipped to Cape Canaveral with their Atlas-Centaur boosters in December 1968 – January 1969 to begin pre-launch checkouts and testing. On February 14, Mariner 6 was undergoing a simulated countdown on LC-36A, electrical power running, but no propellant loaded in the booster. During the test run, an electrical relay in the Atlas malfunctioned and opened two valves in the pneumatic system which allowed helium pressure gas to escape from the booster's balloon skin. The Atlas began to crumple over, however two pad technicians quickly activated a manual override switch to close the valves and pump helium back in. Although Mariner 6 and its Centaur stage had been saved, the Atlas had sustained structural damage and could not be reused, so they were removed from the booster and placed atop Mariner 7's launch vehicle on the adjacent LC-36B, while a different Atlas was used for Mariner 7.

[[NASA]] awarded the quick-thinking technicians, Bill McClure and Charles (Jack) Beverlin, [[NASA Exceptional Bravery Medal|Exceptional Bravery Medal]]s for their courage in risking being crushed underneath the {{convert|124|ft|adj=on}} rocket. In 2014, an escarpment on Mars which NASA'S ''Opportunity'' rover had recently visited was named the McClure-Beverlin Ridge in honor of the pair, who had since died.{{r|nasa3|508pir|memorial}}

Mariner 6 lifted off from LC-36B at Cape Canaveral on February 25, 1969, using the Atlas-Centaur AC-20 rocket, while Mariner 7 lifted off from LC-36A on March 27, using the Atlas-Centaur AC-19 rocket. The boost phase for both spacecraft went according to plan and no serious anomalies occurred with either launch vehicle. A minor [[Liquid oxygen|LOX]] leak froze some telemetry probes in AC-20 which registered as a drop in [[sustainer engine]] fuel pressure; however, the engine performed normally through powered flight. In addition, {{Abbr|BECO|Booster Engine Cut-Off, the event during launch of a rocket with boosters where they stop firing}} occurred a few seconds early due to a faulty cutoff switch, resulting in longer than intended burn time of the sustainer engine, but this had no serious effect on vehicle performance or the flight path. AC-20 was launched at a 108-degree azimuth.<ref name=nasa4/>

The Centaur stage on both flights was set up to perform a retrorocket maneuver after capsule separation. This served two purposes, firstly to prevent venting propellant from the spent Centaur from contacting the probe, secondly to put the vehicle on a trajectory that would send it into solar orbit and not impact the Martian surface, potentially contaminating the planet with [[Earth]] microbes.