Pioneer 4 launched 1959

With pressure mounting for the U.S. to keep up with the Soviets, Pioneer 4, lunar probe, was launched March 3, 1959.   Luna 1, the first Soviet probe to successfully pass by the moon, had been launched in January 1959.  Pioneer 4 was the first U.S. probe to escape Earth's gravity.  It passed within 58,983 km of the lunar surface, but it did not come close enough to trigger its photelectric sensor, which should have been activated by the moon's light.

It did send back radiation data for about 82.5 hours before contact was lost March 6.  It remains in a heliocentric orbit.  Pioneer 4 was the only successful launch by the U.S. in twelve attempts between 1959 - 1963.  In 1964, Ranger 7 would finally surpass Pioneer 4's success by accomplishing all of its mission objectives.