The first two manned space missions launched by the United States were suborbital lobs. On 5 May 1961, NASA astronaut Alan B. Shepard rode a Redstone rocket (Fig. 5.1) inside his tiny Mercury spacecraft from the coast of Florida out into the Atlantic Ocean, to a distance of some 302 miles. The flight lasted only 15 min 22 s.
Let us now take a look at exactly what Shepard experienced and compare it to some other suborbital flights. Although the Redstone carried insufficient propellant to reach an orbital speed of 5 miles/s, its engines had enough thrust - some 78,000 lb - to accelerate the Mercury spacecraft to a speed of 5,180 mph, or 1/ miles per second. This was just under one third of the velocity needed to maintain orbit. As the rocket lost more and more mass with the burning of its propellant, the vehicle
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