Planetary Exploration Missions 871
FIGURE 1 Saturn V and N-1: The
two largest rockets ever built.the policy called for continuous contact, meaning that sta-
tions would have to be located worldwide, with of course
a worldwide ground and space communications system for
command, control and data acquisition. That led to the cre-
ation of the Deep Space Network (DSN) whose stations
today are in California, Spain, and Australia. ForApollo,a
dedicated network was built, and it was backed up by the
DSN plus a few specially equipped radio astronomy sites.
Meanwhile the Soviet system evolved. At first located
only in the Crimea, the Soviet network expanded to include
sites in the Far East and in the central USSR, plus a fleet
of tracking ships offshore. As additional nations joined in
exploring the solar system and the cosmos beyond, many
more stations were built for both tracking and radio science.
Figure 2 shows three examples of the modern deep space
stations that now exist in several countries.
2.3 Spacecraft
Sputnik 1was little more than a ball of batteries plus a
beeping transmitter radiating at a frequency that most ra-
dio amateurs could tune in. ButSputnik 2carried the dog
Laika.Sputnik 3was, for its time, a large scientific obser-
vatory outfitted to investigate the environment just outside
Earth’s atmosphere. The AmericanExplorers, though much
smaller, also carried scientific instruments, including the
radiation counters that confirmed the existence of trapped
charged particles in the Van Allen belts. From that mod-
est beginning, robotic spacecraft in LEO and GEO have
evolved into the thousands of diverse science and applica-
tions machines that have been sent into orbit. Among these
are large, multifunction craft devoted to observing Earth as
a planet, such as the EuropeanEnvisatand the American
TerraandAqua.
Meanwhile, spacecraft designed to explore the solar sys-
tem beyond Earth underwent a similar evolution. The most
important early mission was that ofLuna 3in 1959, ending
centuries of speculation by returning the first images of the
Moon’s far side. Soon after that, spacecraft design began to
elaborate on the features that are essential in interplane-
tary space: attitude stabilization for pointing cameras and
high-gain antennas, capable onboard data handling systems,
long-duration power supplies, and long-surviving electronic
equipment.