Mercury Atlas 6 (MA-6, also designated Friendship 7) was the first orbital flight of an American rocket with a human on board. The pilot was John H. Glenn, Jr. The objectives of MA-6 were to: (1) evaluate the performance of a man-spacecraft system in a three-orbit mission; (2) evaluate the effects of space flight on the astronaut; and, (3) obtain the astronaut's evaluation of the operational suitability of the spacecraft and supporting systems for manned space flight. Originally scheduled for launch in late January, the mission was twice postponed, once (27 January) for weather and once (30 January) for a fuel leak in the Atlas rocket. Even on the day it was successfully launched there were four holds placed on the countdown due to various problems. Finally all the problems were resolved and Friendship 7 was launched as an estimated 60 million people witnessed it via live television broadcast. During the flight two major problems were encountered. First, a yaw attitude control jet became clogged, forcing the pilot to abandon use of the automatic control system in favor of the manual-electrical fly-by-wire and manual-mechanical systems. Second, a signal in the heat shield circuit indicated that the clamp which held the shield in place had been prematurely released. This latter problem resulted in the retrorocket pack not being jettisoned prior to reentry, but retained as a safety measure to hold the heat shield in place in the event it had loosened. This signal was later determined to be false and attributed to a faulty switch. Prior to the flight there had been concerns regarding the physiological effects of prolonged weightlessness and exposure to radiation on the astronauts. Glenn reported that the zero g conditions were "very handy" in performing his tasks and that he felt exhilerated during his 4.5 hour weightless period. It was later ascertained by physicians that Glenn had also received less than half of the expected radiation dosage during his flight, proving that the spacecraft walls had provided excellent shielding. A curious event which occurred during Glenn's flight was his report of "fire flies" when he entered the sunrise portion of an orbit. Although this phenomenon was a mystery at the time, it was resolved during the flight of Mercury Atlas 7 when Scott Carpenter accidentally tapped the wall of the spacecraft with his hand, releasing many of the so-called "fire flies". The source was determined to be frost from the reaction control jets. During the flight, the spacecraft attained a maximum velocity in excess of 28,000 km/hour and an altitude of about 260 km. The capsule reentered after completing three orbits, coming down in the Atlantic Ocean some 1,300 km southeast of Bermuda. The duration of the flight was 4 hours 55 minutes and 23 seconds during which Glenn travelled over 121,000 km. After splashdown, the Mercury capsule with its pilot still inside were picked up after 21 minutes in the water and returned by helicopter to the destroyer USS Noa.