This was one of the most heroic
space missions in history. For a start, the Atlas booster was not very
reliable, and blew up on the first unmanned Mercury orbital flight attempt in
March 1961. The next two unmanned orbital missions, who actually reached orbit,
were only partially successful. Mercury Atlas 6 was originally another unmanned
test before the decision was made to man it with Glenn.
The mission was originally
scheduled for December 1961, before being rescheduled first for 13 January
1962, then 16 January. On 27 January, Glenn lay in the capsule for almost six
hours before the launch attempt was scrubbed. The launch was rescheduled for 1
February, then 15 February, and finally 20 February when, after a further 3
hours 44 min in the capsule and six launch holds, Glenn was at last committed
to launch. The Atlas thundered away on the pad, reached full thrust and, at
09:27 hours local time, finally became airborne. Glenn, his heart beating at a
reasonable 110 beats per minute, announced the start of the mission in the now
customary style, confirming that the spacecraft clock had started. Observers
watched nervously as the Atlas 109D reached the point at which MA3 had exploded
in March 1961.
The vehicle went through Max Q -
the point of maximum dynamic pressure on the vehicle-at T + 100 seconds and the
two outboard engines cut off at T + 2 minutes 14 seconds. Glenn was subjected
to 7.7 G acceleration during the five minute ascent, which ended at orbital
velocity of 17,544 mph. Orbital inclination was 32.5° and maximum altitude was 165
miles. The capsule, Friendship 7, turned around and Glenn saw his Atlas
tumbling about 30 m (98 ft) away. The view took his breath away as he looked
back at the Cape, travelling backwards towards Africa on the first of his three
planned orbits. Because his orbital status gave him "go for at least seven
orbits", according to flight controllers, this has sometimes been
misinterpreted to mean that this was the plan.
Glenn experienced problems with
the automatic orientation system and continually had to manually correct a yaw
motion. He also saw strange "fireflies" on the outside of the
spacecraft, the source of which could not be explained at the time. The mission
was proceeding tolerably well, until mission controllers received a signal with
the disastrous news that the heat shield on Friendship 7 might be loose. If
this was so, then Glenn would be killed during re-entry.
After the three retro’s had fired
as Glenn was completing his third orbit, mid-way between Hawaii and Los Angeles
(giving him the impression that he was heading back to the former rather than
towards the latter), he was recommended to keep the retro-pack attached through
the re-entry, although he was not told why. His heart rate peaked at 132. The
change to the flight plan resulted in a more spectacular re-entry than envisaged,
as first the straps holding the retro-pack and then the retro-pack itself were
burnt away during the 1,650°C peak re-entry temperatures, at a speed of about 14,912mph
and an altitude of 25 miles.
After a nerve-tingling wait during
which communications were cut off by incandescent gases surrounding the craft,
Glenn's hale and hearty voice was at last heard. The heat shield had not been
loose after all. The main chute came out at 3,291 km (10,800 ft) altitude and
Friendship 7 descended into the Atlantic Ocean, 6 miles from the recovery ship,
the USS Noa, northwest of San Juan,
Puerto Rico, but 40 miles away from the prime ship, USS Randolph. The capsule
with the astronaut inside was picked up, and Glenn injured his hand slightly
when he blew the hatch. The flight time of 4 hours 55 minutes 23 seconds made
this the shortest US manned orbital flight.
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