[Illustration: 7. Artist’s conception of _Mariner 2_ as it flew by
Venus.]
The first successful interplanetary spacecraft probed the environment of
Venus, Earth’s closest neighbor. _Mariner 2_, working flawlessly, swept
by the hot and cloudy planet at a closest approach of 34,834 kilometers
(21,645 miles) on December 14, 1962.
The journey began with lift-off on August 27 from Cape Canaveral atop an
Atlas Agena-B launch vehicle. During the 109-day trip to the planet,
_Mariner_’s on-board instruments sampled the environment of
interplanetary space and telemetered information to Earth stations.
Ground-based measurements of the Venerian surface temperature were
confirmed by the probe to be around 425° C (800° F).
_Mariner 2_ detected no measurable magnetic field or radiation belts,
indicating that Venus may have a very different history than has Earth.
_Mariner 2_ passed out of tracking range on January 4, 1963, when the
spacecraft was about 87 million kilometers (54 million miles) from
Earth. The probe is presently in orbit around the Sun.
The back-up craft on display would have been launched toward Venus if
_Mariner 2_ had failed to reach the planet.
Prime contractor for _Mariner 2_ was the Jet Propulsion Laboratory,
California Institute of Technology.
_Mariner 2_ is from the National Aeronautics and Space Administration.
[Illustration: 8. Enlarged facsimile of coded _Mariner 2_ tape
transmitted December 14, 1962, from the vicinity of Venus. Encircled
portions show microwave and infrared coding.]