Page 289 - NS-2 Textbook

284 NAUTICAL SCIENCES

artificial satellites and other spacecraft sent into space on
scientific astronomical missions.
Explorer I was fitted with a device designed to map
Earth's magnetic field by measuring the energies of in-
coming charged particles at different levels of the outer
ahnosphere. Although it failed at this, it succeeded in
providing a COtillt of charged particles trapped in previ-
ously unknown bands around Earth far above the upper
ahnosphere-the now familiar Van Allen radiation belts.
Since that time, many astronomical spacecraft have
been launched into space by NASA, by the former Soviet
Union, and by several other nations. Some of these, in-
cluding the Apollo missions of the late 1960s, the Ameri-
can Skylab orbited in 1973, the Russian MIR space station
that orbited between 1986 and 2001, and most recently
the Illtemational Space Station, have been marmed. The as-
tronomical data and new knowledge gained by these
Scientists of the Office of Naval Research launch a plastic high- spacecraft during the last forty years has greatly ex-
altitude balloon from a Coast Guard ship. The balloon's apparatus
will measure cosmic radiations near the northern magnetic pole. ceeded the total knowledge acquired by all previous
earthbound observations since the dawn of history.
The study of our solar system by manned and un-
manned spacecraft has been done in three distinct phases
since 1957:
BALLOON OBSERVATORIES
• The reconnaissance phase consists of flybys, photog-
The ahnospheric shield that protects Earth from radiation
raphy, and, more recently, TV imaging.
also distorts the light that gets through to our telescopes
• The exploration phase involves the use of orbiter
on Earth. In order to gain more accurate knowledge of
and probe (exploratory) spacecraft to do detailed
the universe, we have to go beyond our ahnosphere. For
mapping and measurement.
this purpose, astronomers use high-altitude balloon ob-
• The intensive study phase uses marmed and un-
servatories that can go up to about 20 miles above the sur-
marmed landers and space probes for closeup ex-
face. In these balloons, they are above 99 percent of the
amination and experimentation.
ahnosphere.
Although relatively new, balloon astronomy is play- A summary of the more significant of these efforts to date
ing a great part in the study of the universe. Balloons are follows.
much cheaper than spacecraft and can easily carry peo-
ple aloft in their gondolas. They also can carry up to two
THE EXPLORATION OF THE SOLAR SYSTEM
tons of telescopes, spectrographs, and other instruments.
The pictures and other findings can be brought directly The Explorer I satellite was followed by about fifty addi-
down to Earth, rather than sent by radio transmission, as tional Explorer reconnaissance spacecraft, which collec-
from satellites. tively provided a wealth of information about Earth and
1110ugh balloons have their advantages, they also its region of the solar system, including the following:
have several disadvantages. They are difficult to stabilize,
• The nahlre and effect of the solar wind
they are not self-propelled, and the upper ahnosphere
• 111e nature, extent, and behavior of Earth's mag-
causes observational distortions. Consequently, astro-
netosphere (Earth's magnetic field)
physicists and astronomers in recent years have found
• A detailed survey of the space between Earth and
the space-based platforms discussed in the following sec-
the Moon
tion far more useful.
• The nahtre and density of Earth's upper ahno-
sphere
SATELLITES AND EXPLORATORY SPACECRAFT
Between 1962 and 1975 a total of eight orbiting solar ob-
The true beginning of the space age was 4 October 1957, servatories (OSOs) were launched into orbit around
when the first artificial satellite, Sputllik I, was success- Earth to study the Still. Their insh'uments returned much
fully launched by the Soviet Union. Sputnik I was fol- data on solar flares, the Sun's corona (outer ahnosphere),
lowed four months later by the first U.S. satellite, Ex- and solar activity in the gamma ray, x-ray, and ultraviolet
plorer 1. Since then there has been a steady procession of bands of the electromagnetic spectrum.