The spacecraft, named Faith 7, completed 22 Earth orbits before splashing down in the Pacific Ocean, piloted by astronaut Gordon Cooper, then a United States Air Force major.
The Mercury-Atlas 8 flight of Walter Schirra on October 3, 1962, had been so nearly perfect that some at NASA thought that the United States should quit while it was ahead and make MA-8 the last Mercury mission rather than risk a future disaster.
Manned Spacecraft Center officials, however, believed that the Mercury team should be given the chance to test a human in space for a full day.
In September 1962, NASA concluded negotiations with McDonnell to modify four Mercury spacecraft (#12, #15, #17 and #20) to a configuration that supported a one-day mission.
Such changes to the spacecraft included the removal of the periscope and a redundant set of thrusters, and the addition of extra batteries and oxygen tanks.
The Atlas booster used for MA-9 sported several technical improvements, most notably an enhanced propulsion system with a hypergolic igniter that would eliminate the need for hold-down time at launch to prevent rough combustion.
At the first meeting of senior MSFC officials for the year (January 11), Walter Williams noted that the Air Force had yet to provide an explanation for two Atlas F failures during the second half of 1962.
Until the investigation committees released their findings and cleared the Atlas D of guilt by association, Cooper's flight could be delayed.
During the seven months between Schirra's and Cooper's flights, there were five failures of Atlas D vehicles (one of them an Atlas-Agena, the rest operational ICBM tests).
At his first press conference on February 8, Gordon Cooper admitted to not knowing much about the booster problems and focused instead on the enhancements made to his Mercury capsule.
The numerous added equipment and consumables for the day-long mission boosted the weight of Faith 7 considerably; it now weighed over 3,000 pounds (1,400 kg).
On March 15, the Atlas was rolled out of the factory a second time and passed tests with flying colors; Convair engineers expressed confidence that this "was their best bird yet."
The booster actuators were offset slightly to prevent a recurrence of the liftoff roll transient that occurred on Mercury-Atlas 8.
Several minor modifications were made to 130D as a result of postflight findings from failed Atlas launches over the previous year.
The upgraded MA-2 engines featured baffled injector heads and a hypergolic igniter, eliminating any concerns of rough combustion or the need for hold-down time prior to liftoff.
Various problems with radar in Bermuda and the diesel engine that rolled back the gantry caused the launch to be cancelled until May 15.
After the spacecraft separated and turned around to orbit attitude, Cooper watched the spent Atlas lag behind and tumble for about eight minutes.
His first task was to eject a six-inch (152 mm) diameter sphere, equipped with xenon strobe lights, from the nose of the spacecraft.
It was a 30-inch (762 mm) PET film balloon painted fluorescent orange, inflated with nitrogen and attached to a 100-foot (30 m) nylon line from the antenna canister.
During the flight Cooper reported that he could see roads, rivers, small villages, and even individual houses if the lighting and background conditions were right.
Cooper obtained photographs of North Africa, the Arabian peninsula, and eastern India, Burma, and the Himalaya region, as well as a few images of the Pacific and Indian Ocean.
Nonetheless, haze and air pollution impeded visibility for Cooper--despite passing over Los Angeles and Calcutta, he could see neither city due to smog.
At the start of the 17th orbit while crossing Cape Canaveral, Florida, Cooper transmitted slow scan black and white television pictures to Mercury Control.
On the 21st orbit, John Glenn on board the tracking ship Coastal Sentry Quebec near Kyushu, Japan, helped Cooper prepare a revised checklist for retrofire.
An hour and 20 minutes before retrofire, Cooper took a dextroamphetamine tablet to ensure his alertness; he reported not feeling any sleepiness for the remainder of the flight.
[4] Fifteen minutes later Faith 7 landed just four miles (6 km) from the prime recovery ship, the carrier USS Kearsarge.
Helicopters dropped rescue swimmers and relayed Cooper's request of an Air Force officer for permission to be hoisted aboard the Navy's carrier.
Postflight medical examination of Cooper found that he was slightly dehydrated and experienced a degree of orthostatic hypotension from being seated in the capsule an entire day, but other than that no significant effects from the flight were noted.