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OCR for page 10
Appleton
Sales
In November 1982, a U.S.
weather satellite spotted a
The 1 25-mile-per-hour winds
of Hurricane Hugo begin
to lash the coast of the
southeastern United States
under the constant gage of a
U.S. weather satellite.
Satellite images warned
residents of Charleston (upper
left, of the approaching Hugo,
still 210 miles away in this
picture, giving them several
days to prepare for the storm
and evacuate the city.
0
:~\~\f~t Q1 ~dWdll ~1IU W~11~U it
start moving north. SucIdenly
the storm turned east and
raked across the islands less
than 24 hours later, leaving
nearly a quarter billion dollars
of damage in its wake. But
only one life was lost. Hurri-
cane warnings, based largely
on satellite pictures, had
alerted most people in time to
take sheller.
Twenty-five years ago, there were no
operational satellites for weather forecasting
or for any other routine application. Today,
however, satellite systems girdle the earth
watching for storms, relaying communica-
tions, mapping uncharted terrain, and
helping ships and airplanes navigate any-
where on the globe.
I Satellites started to become routine in
April 1965, when the first nonexperimental
commercial satellite flew into space and
parked in orbit over the Atlantic. Early Bird
carried circuits for 240 telephone calls or
television service between Europe and North
America. Today, several generations of
satellites later, Early Bird's descendants
handle up to 120,000 calls at once or share the
capacity with TV broadcasts, computer data,
and electronic mail. They are part of a
worldwide communications network
launched by the International Telecommuni-
cations Satellite Organization, or Intelsat,
which now has more than 100 member
nations.
Communications satellites have dramat
ically altered the nature of our global com- I
munity. Twenty-five years ago, reliable
communications existed only between
countries in the developed world. But
communications satellites and the develop
ment of small, portable television cameras
have linked people together around the
globe. In 1969, for example, communications
satellites brought TV coverage of the first
manned lunar landing live from space
to nearly a fifth of the world's population.
Today they bring instant coverage of news
and events to every corner of the earth.
Scores of civilian and military communi-
cations satellites sit in a ring around the earth
22,300 miles above the equator. At that
altitude they complete one revolution every
24 hours and therefore remain stationary
relative to the surface of the earth below.
Satellites in this geostationary orbit provide
high sky platforms for relaying signals to
and from ground stations, vehicles, boats,
and planes scattered over the surface below.
The idea for a system of radio-relay
satellites in geostationary orbit maintained
by astronauts was described by science
fiction writer and futurist Arthur C. Clarke
E N G I N E E R I N G A N D T H E A D VA N C E M E N T O F H U M A N W E L F A R E
OCR for page 11
In 1945. Astronaut custodians, however, were
impractical and, when Early Bird went up In
the 1960s, shown to be us necessary. Transis-
tors and other solid-state components of the
satellite's Innards were far more reliable than
the vacuum tubes of 1945-v~ntage radios and
small enough to fit into a tiny satellite. Early
Bird lasted more than three years without
maintenance, and todays communications
satellites frequently last until their fuel runs
out, about a decade.
A country divided by mountains,
jungles, water, or distance is now often
united by a domestic satellite commun~ca-
tions system. In 1965 the Soviet Union
established the Molniya system using
satellites In oblong orbits looping over the
northern latitudes. These satellites were not
geostationary. However, one always rose
above the country just as another set. Now
more than 40 countries have established their
own satellite communications systems, often
by constructing ground stations and renting
circuits on commercial satellites.
Before the era of routine satellite use,
weather observations were available for less
than 20 percent of the globe. Much of the
unobserved region covered the vast oceans
of the Southern Hemisphere and the tropics,
where a storm could churn into a hurricane
with no one knowing until it sank a ship or
washed away a town. But since 1966, when
the first fully operational weather satellite
A P P L I C A T I O N S A ~ E L ~ I T E S I
An astronaut retrieves a
communications satellite,
Westar ill, that failed to go
into high geostationary orbit
after being launched into low
earth orbit. The space shuttle
brought the satellite back to
earth, where it was
refurbished. Pending U.S.
government approval, the
satellite will be launched
aboard a Chinese rocket and
will provide # communications
link for East Asia.
Communications satellites
relayed live television
coverage of moon missions to
millions of people around the
world. Here, Apollo ~ 5
astronauts collect rock
I samples.
1 1
OCR for page 12
logo dish antennas near
Bogota, Colombia, aim at a
communications satellite in
geostationary orbit above the
equator.
2
system was launched, no major tropical
storm has gone undetected anywhere in the
world.
Two U.S. weather satellites circling from
pole to pole scan the earth from low orbit
twice a day. Soviet satellites also routinely
survey global weather from polar orbit.
High-flying satellites in geostationary orbit
monitor wide reaches of the planet and
generate the weather pictures seen on
television. The United States launched the
first such operational satellite, GOES
(Geostationary Operational Environmental
Satellite), in 1974 and now maintains one
above the western Atlantic and another over
the eastern Pacific. A European satellite
hovers over Africa, an Indian satellite over
the Indian Ocean, and a Japanese satellite
over the western Pacific. These five provide
continuous coverage of weather throughout
the equatorial and midlatitude regions of the
earth.
Radiometers carried by weather satel-
lites measure reflected solar energy and
infrared energy radiating from the earth and
atmosphere. Computers then turn the data
into images of clouds and weather patterns.
Radiometers also measure radiation at
precise wavelength intervals, generating
information that allows scientists to deter-
mine atmospheric temperature, water vapor,
and ozone levels. Today's radiometers are
sensitive enough to sound the atmosphere
from geostationary satellites more than
22,000 miles up in space.
Weather satellites frequently carry
equipment to relay data collected by thou-
sands of remote automatic ground stations
from instruments such as rain or river-flow
gauges. And, since 1982, increasing numbers
of U.S. weather satellites, as well as Soviet
navigation satellites, have also been carrying
search-and-rescue radio equipment, some of
it supplied by Canada and France. The
devices pick up distress calls from ships and
planes in trouble, leading to the rescue so far
of more than 1,200 persons.
Images generated by weather satellites
have been used to study snow cover, geolog-
ic faults, and other large ground features. But
the need for more detailed information
gathered in a systematic, repetitive way led
to the development of specialized terrain-
observation satellites. These orbiters create
high-quality images that can be used to help
study worldwide crop production, search for
minerals and petroleum, monitor environ-
mental problems such as desert creep and
deforestation, and measure snowmelt to
predict water resources and control flooding.
In 1972 the United States launched the first in
a series of Landsat satellites, which scrutinize
the entire earth from near-polar orbit,
observing each spot at the same local time
every 18 days.
All Landsats have carried multispectral
sensors that measure solar energy and
infrared radiation at four or more wave-
lengths. Every type of terrain reflects and
absorbs sunlight and emits infrared radiation
in ways that reveal its identity and condition.
Objects often show up better at one wave-
length than another, which gives this
technique an advantage over conventional
photography. The data are transmitted back
to one of several ground stations, processed
into images, and made available to the
public. France and the Soviet Union have
launched similar satellites and make their
images available commercially. The French
I SPOT system produces particularly high
quality images.
Infrared satellite images do not show as I
much detail as visible images, but they yield
thermal information that the others cannot
provide. Water, for example, that collects in
faults usually holds more heat than sur-
rounding rock. Infrared sensors detect this
heat differential, revealing an otherwise
hidden geologic formation. Infrared imaging
is also useful for monitoring pollution,
observing volcanic activity, and leading
I E N G I N E E R I N G A N D T H E a D VA N C E M E N T O F H U M A N W E L FA ~ E
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~ fishing boats to warm waters where fish
I might be gathered.
More recently, experimental terrain-
observation satellites have been carrying
microwave radar, which penetrates all types
of weather, day or night. Microwave radar
i can, to a certain extent, penetrate leaves and
is used to map jungle terrain. It can also
penetrate dry sand and has been used to
trace buried watercourses in the desert.
Radar return signals also tell much about the
land that is useful for mineral and petroleum
exploration.
The military forces of the United States,
the Soviet Union, and other countries use
their own terrain-observation satellites to
keep track of foreign troop movements,
electronic communications, military installa-
tions, and rocket launchings. The satellites
are hardier than their civilian counterparts,
as well as more sophisticated, capable, and
flexible. These "eyes in the sky" have greatly
reduced the possibility for surprise attack
and have thus helped maintain peace among
world powers for the past quarter century.
In the future, satellites may be used to
monitor the health of the entire earth bio-
sphere. A major step in that direction will be
taken as part of the International Space Year
I in 1992. A "Mission to Planet Earth" is being
organized using earth-observation satellites
and other means to study such problem
i areas as polar ozone holes, deforestation,
ocean productivity, landcover change, and
global warming caused by the "greenhouse
effect."
The precision of their orbits makes
satellites ideal instruments for navigation.
They have all but replaced the sextant since
about 1968, when the Navy completed a
system of navigation satellites, called Transit,
for ballistic missiles fired from submarines.
Transit employs satellites in near-polar orbits
that are spaced to provide global coverage.
I Using data encoded on satellite signals, a
computer-aided receiver on a ship or plane
can determine its location to within less than
I a quarter mile.
Several satellites have already been
launched for a new navigation system
the Global Positioning System (GPS), or
Navstar that will have 18 satellites plus
3 spares when completed. Using GPS,
receivers in ships, planes, ground vehicles,
and portable packs will be able to determine
their locations to within 10 meters. The heart
of the system is an atomic clock in each
satellite that loses or gains just one second
every 33,000 years. A plane, for example,
receives signals from four satellites, each
signal telling the time it was emitted and the
position of the satellite. The plane's comput-
erized receiver calculates how far each signal
has traveled, then uses this data to pinpoint
its position in space.
In 1988 a satellite was launched to track
long-haul trucks in the United States. A
freight company using the system immedi-
ately found one of its trucks 300 miles off
course. More advanced systems used by
some military aircraft show pilots a map of
the local area. Cars may someday be
equipped to receive satellite signals that
provide drivers with a street map of the city
being traveled. Indeed, satellites may
become our standard means of navigation,
whether on land, in the air, or at sea.
A P P ~ ~ ~ AT g O N 5 AT E ~ ~ ~ ~ E 5 I
Satellite image reveals
extensive clear cutting in
Tongass National Forest on
the northern tip of Prince of
Wales Island, Alaska. Recently
cleared areas appear pink,
cleared areas that have
started to recover are light
green, and undisturbed
forests are dark green.
Technicians prepare a
Nawstar navigation satellite
for launch. The 12 spike
antennas will form the
satellite's signal into a
cone covering the entire
hemisphere below.
13
Representative terms from entire chapter:
geostationary orbit
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