Pioneer 4

NSSDC ID: 1959-013A

Description:
Pioneer 4 was a spin stabilized spacecraft launched on a lunar
flyby trajectory and into a heliocentric orbit making it the first US
probe to escape from the Earth's gravity. It carried a payload
similar to Pioneer 3: a lunar radiation environment experiment
using a Geiger-Mueller tube detector and a lunar photography
experiment. It passed within 60,000 km of the Moon's surface.
However, Pioneer 4 did not come close enough to trigger the
photoelectric sensor. No lunar radiation was detected. The
spacecraft was still in solar orbit as of 1969. 

Pioneer 4 was a cone-shaped probe 51 cm high and 23 cm in
diameter at its base. The cone was composed of a thin fiberglass
shell coated with a gold wash to make it electrically conducting and
painted with white stripes to maintain the temperature between 10
and 50 degrees C. At the tip of the cone was a small probe which
combined with the cone itself to act as an antenna. At the base of
the cone a ring of mercury batteries provided power. A photoelectric
sensor protruded from the center of the ring. The sensor was
designed with two photocells which would be triggered by the light
of the Moon when the probe was within about 30,000 km of the
Moon. At the center of the cone was a voltage supply tube and two
Geiger-Mueller tubes. A transmitter with a mass of 0.5 kg delivered
a phase-modulated signal of 0.1 W at a frequency of 960.05 MHz.
The modulated carrier power was 0.08 W and the total effective
radiated