[Illustration: 33. _Vanguard 1_, second American satellite launched.
Information from _Vanguard_ showed that the Earth is not quite
round.]
The first artificial earth satellites were sometimes called
“long-playing rockets” because they carried the same instruments and
investigated the same problems as had the sounding rockets. The great
advantage of the satellite was its ability to provide a continuous flow
of information for long periods of time. The first science satellites
were the forerunners of later vehicles that would demonstrate the direct
benefits that satellites could offer to such varied fields as weather
observation and communication.
The advent of the earth satellite provided scientists with a new and
valuable research tool. Science satellites have been used for such tasks
as solar and astronomical observations, biology experiments, or
atmospheric investigation. Explorer 1 (launched January 31, 1958) and
Vanguard 1 (launched March 17, 1958), the first American earth
satellites, carried scientific payloads into space.
Project Vanguard’s important contributions to America’s space program
were the creation of the minitrack tracking system, the first use of
silicon solar cells for electric power in a satellite, as well as the
discovery that Earth is not quite round. The Vanguard program drew to a
close with the 1959 launch of Vanguard 3. This satellite studied
variations in solar and x-ray radiation and the earth’s magnetosphere.
It also determined air density in the upper atmosphere.
The mysteries of the near-earth space environment drew _Explorer 6_,
launched August 7, 1959. _Explorer 6_ instruments measured radiation
levels in the Van Allen radiation belts, mapped the earth’s magnetic
field, counted micrometeorites, and studied the behavior of radio waves
in space. In addition, _Explorer 6_ carried a scanning device which
returned the first complete television cloud-cover picture of the
earth’s surface.
[Illustration: 34. Artist’s concept of IMP-E. This satellite’s
primary mission is to study solar wind and the interplanetary
magnetic field at lunar distance and their interaction with the
Moon.]
_Explorer 10_, launched on board a Thor-Delta rocket on March 25, 1961,
confirmed the existence of the solar wind—the stream of particles that
carries the Sun’s magnetic field beyond the orbit of Earth. During the
satellite’s planned 52 hours in orbit, it relayed information on the
relationship between terrestrial and interplanetary magnetic fields and
the solar wind.
To continue the study of solar wind and interplanetary magnetic fields,
_Explorer 12_ was orbited by a Delta launch vehicle on August 16, 1961.
It was the first in a series of satellites to study energetic particles
in space. These electrons and protons constitute the earth’s radiation
belts and they affect weather and other phenomena on Earth.
_Atmosphere Explorer-A_ was the first of NASA’s aeronomy satellites. It
was designed to remain in operation three months, studying the
composition, density, pressure, and temperature of the upper atmosphere.
This satellite discovered a belt of neutral helium atoms around the
Earth.
Deriving its name from a spirit in Shakespeare’s play, _The Tempest_,
_Ariel 1_ explored the ionosphere, a region of electrically charged air
which begins about 40 kilometers (25 miles) above the surface of the
Earth. Launched April 26, 1962, _Ariel_ was a cooperative venture
between Great Britain and the United States. It was both the first
British satellite and NASA’s first international satellite. The Royal
Society’s British National Committee on Space Research coordinated the
experimental program; NASA scientists and technicians built the craft.
Two small scientific laboratories, called Interplanetary Monitoring
Platforms, were launched in 1967 to study the solar wind and other
phenomena. IMP-E investigated interplanetary magnetic fields in the
vicinity of the Moon. IMP-F investigated the interplanetary magnetic
field also, in addition to the earth’s magnetosphere and radiation
levels in space.
Interplanetary space between the Earth and Venus was the subject area
for _Pioneer 5_, launched March 11, 1960. The satellite tested
long-range communications systems, developed methods for measuring
astronomical distances, studied the effects of solar flares, and
performed other tasks before it went into orbit around the Sun.
With increasing interest in the earth’s space environment, a satellite
was launched on September 7, 1967, to investigate the impact of space on
biological processes. _Biosatellite 2_ was the second satellite in the
program of three such vehicles. Frog eggs, plants, micro-organisms and
insects were placed in orbit to enable scientists to study the combined
effects of weightlessness, artificially produced radiation, and the
absence of the normal day-night cycle on these organisms. Following two
days in space, the capsule containing the experimental package reentered
the atmosphere and was caught in mid-air by an Air Force recovery
aircraft.
_Vanguard 1_ is from John P. Hagan. _Vanguard 3_, _Explorer 10_,
_Explorer 12_, _AE-A_, _Ariel 1_, IMP-E & F, and _Biosatellite 2_ are
from the National Aeronautics and Space Administration. The models of
_Explorer 6_ and _Pioneer 5_ are from Space Technology Laboratories.