After more than 12 years in earth orbit, Explorer I, the first U.S. satellite, will reenter the atmosphere and burn sometime next Spring, a Harvard astronomer has estimated.
Luigi G. Jacchia, lecturer on Astronomy, has predicted that the 31-pound satellite will fall from orbit in April 1970, much later than Wernher von Braun and other rocketry experts predicted when the satellite was launched in 1958.
Explorer I originally achieved an orbit that ranged from 219 to 1587 miles above the earth's surface. But as a result of friction with the atmosphere--extremely thin at those heights--the spacecraft's altitude slowly dropped. When a satellite's speed decreases from orbit to orbit, it cannot counterbalance the earth's gravitational field and slowly loses altitude.
By April 1970, the friction of the earth's atmosphere at high speeds and low altitudes will heat Explorer I until it burns up, much like a meteor.