The Recent Advances of Satellites
Nicole B. / Physics 336 / 20 April
1997
Satellites are used in many fields today. Scientists use satellites
to observe and determine many different features of the earth. Scientists
use satellites to observe different types of radiation and celestial objects.
Weather satellites are used to determine many different weather conditions
and locations of weather. Satellite navigation systems help pilots and
ship navigators to also locate things. Communication satellites are used
to transmit data to different places of the world, while military satellites
are also used to transmit data but for the purpose of protecting our country.
Scientific Satellites
Scientists use satellites to observe different features of the earth
including different kinds of radiation. "Satellites provide colonized
images of the outgoing-long-wave radiation, a quantity that can aid in
detection of long-term warming or cooling" (McGinley 10). Satellites
are also used to monitor the atmospheric ozone, which is a gas that protects
the earth from harmful solar radiation. Modern satellites are sent up with
multi-channel high-resolution radiometers that cover a wide range of infrared
and microwave wavelengths. Radiometers sense cloudy and clear air, atmospheric
temperatures, and ocean winds and provide visual imagery as well. Sensors
that measure radiation are used to get a more complete picture of the atmosphere
by measuring in an area beyond visual red, where ground surface or cloud
top temperature can be determined.
Today earth-orbiting satellite observatories can observe celestial
objects without the interference caused by the earth's atmosphere. "The
orbiting astronomical observatories, and the International Ultraviolet
Explorer, for example studied faint astronomical objects in the ultraviolet
region of the electromagnetic spectrum" (15).
The National Reconnaissance Office (NRO), one of America's space agencies
was able to observe a celestial object without interference caused by the
earth's atmosphere. The NRO demonstrated the motion and survivability of
tethers in low earth orbit, littered with micro-meteoroids as well as space
stuff. "The tether is about two and one half miles long and is made
of white yarn that is wrapped in braided Spectra 1000, a tough white fiber
used in bullet proof vests and fish lines, that is one tenth of an inch
thick" (Miles 2). On both ends of the tips of the tether is an aluminum
hexagonal box covered with 18 laser reflectors. The box containing the
NASA-donated unreeling device and long-dead electronics has a mass of 83
pounds. The other box is 23 pounds. The names of the boxes are Ralph and
Norton, after Ralph Kramden, and Ed Norton of the Honeymooners.
This is the longest-lasting space tether yet, which has a great cost
of 4 million dollars. It is also the first unclassified, ongoing space
project in the 36-year history of the National Reconnaissance Office. The
NRO usually flies spy satellites. The NRO is not willing to say much about
the experiment, but it did say that on June 20, 1996, the Tether Physics
and Survivability experiment called tips was ejected from a classified
military satellite, into a 635-mile-high orbit that swings as far north
as Alaska and as far south as Chile's Cape Horn. A few hours later the
yarn (all 2 1/2 miles ) was unreeled from a spool, weighing 12 pounds,
and was swung like a jump rope and eventually straightened out. It has
been orbiting the earth for 9 months, and is observed by the NRO by ground-based
laser, radar and telescope observations. NRO officials say if the tether
isn't broken by a micrometeroid or other debris it could orbit as long
as 27 years before plunging through the atmosphere and burning up. The
NRO hopes that some day they could use tethers to connect clusters of small
satellites so they could communicate much like a computer network. Tethers
could also be used to power space craft by generating electricity as the
conductive cords sweep through earth's magnetic field to propel spacecraft's
into different orbits and to drop experiments from a space station.
Weather Satellites
Satellites are used by scientists to determine many different weather
conditions and the various locations of weather. The meteorologist, by
noting past locations, apparent qualitative strength, jet streams and storms,
and by using the satellite-improved model generated forecast, is able to
make more accurate weather predictions for a particular location. Through
the use of sensors, the satellites data provides details of individual
thunderstorms and maintains coverage over a specific location on earth
at time intervals from 5 minutes to 12 hours. "Heavy snows or rains
associated with large cyclones are often produced by mesoscale, sized thunderstorm
systems that can be easily seen and traced by visual and infrared satellite
imagery" (McGinley 20).
Polar orbiting satellites globally monitor temperature, moisture and
cloud patterns associated with these systems. The satellite measurements
are combined with other weather data to initialize computer-run mathematical
models which routinely provide forecasts for these major cyclones. Satellite
monitoring of polar ice caps helps identify important seasonal variations.
Ice caps in areas where vegetation is decreasing because of drought or
human exploitation, modify fractions of incident radiation reflected and
influence the effective solar radiation reaching the earth. Meteorological
satellites can measure radiation in a wide spectrum of electromagnetic
wavelengths. This provides the meteorologist with a supplemental source
of data including cloud imagery from visual sensors, ground surface, cloud,
and atmospheric layer temperatures, and water vapor concentration from
infrared sensors.
Navigation Satellites
Satellite navigation systems are used to help many pilots and ship
navigators locate different things in various places. By knowing the position
of several satellites from their signals, it is possible to determine the
exact location of a ship on earth. A modern system uses laser-beam signals
and can determine the position to within less than one inch. Omega, a navigation
system developed originally for ships, uses very low frequency radio beams
sent out by eight ground-based stations across the globe, and is picked
up by global positioning satellites to provide two or three dimensional
fixes on military planes. These systems permit the pilot to do his or her
own navigation, so navigation officers are not needed for commercial flights.
The techniques used by navigation satellites are also used to make
accurate maps of remote areas of earth. The US Lands System provides data
to ground stations around the world. Geologists and other specialists use
this data for mineral exploration, crop forecasting, flood control, and
land management.
Communication
Satellite
Many different communication sources such as telephone companies, television
companies, newspapers and magazines use communication satellites to transmit
data to various parts of the globe. A group of satellites used in communication
among earth stations forms a satellite communications system. Such systems
provide international communication like The International Telecommunications
Satellite Organization (INTELSAT), or provide domestic communication like
Canada's Telesat System. Intelsat is in 400 earth stations in 150 countries.
The constellation of Intelsat satellites over the Atlantic, Pacific and
Indian Oceans relays telegraph and TV transmissions and over two thirds
of all international phone calls.
Communications satellites are responsible for instantaneous television
coverage of events all over the globe, for the speed of international banking
and finance, for the almost-immediate delivery of vast amounts of information,
and for international "E" mail and telephone service to all parts
of the earth. Almost any transfer of information that depends on cables,
lines, or antennas can not be communicated through satellite. One large
communications satellite can carry at the same time over 100,000 phone
calls and several television signals.
Military Satellites
The military uses satellites for many purposed including protecting
the country. Countries use military surveillance and reconnaissance, or
spy satellites to monitor the activity of other nations. The US Big Bird
and the Soviet Cosmos satellites were used to take photos of military activity.
The Ferret satellite also reported radio and radar transmissions.
Long distance communications satellites for the military were introduced
in the late 1060's by the US and the Soviet Union and in the 1070's by
the North Atlantic Treaty Organization (NATO) and the United Kingdom. Capabilities
of these satellites have greatly improved. For example, the US Navy's FltSatCom
(Fleet Satellite Communication) system provides for world-wide high-priority
communications between naval aircraft, ships, submarines, and ground stations.
The purpose of military navigation satellites is to determine the position
of ground troops, aircraft, missiles, ships and submarines accurately.
Conclusion
Satellites are used to observe and determine things in many different
fields today. Satellites are used to observe radiation and different features
of earth. Weather satellites are used to determine many weather conditions
and location of weather. Satellites are also used for communication purposes
so information can be transmitted throughout the globe in a very short
amount of time. Navigation satellites help pilots and ship navigators determine
the exact location of things on earth. Military satellites are used to
protect the country by using military surveillance and spy satellites to
monitor activity of other nations. As stated above, satellites are what
make this world united and without them we would face many difficulties.
References
Demis Richard. "Artificial Satellites." Compton's Encyclopedia
and Fact Index. vol. 21 pg. 72-73 Chicago: Compton's Learning Company,
1996.
Jobanek, Michael. "Aircraft." The New Grolier Multimedia
Encyclopedia. CD-ROM. Danbury, CT: Groiler Electronic Publishing, Inc.,
1993.
McGinley, John A. "Satellite Meteorology." McGraw-Hill
Encyclopedia of Science and Technology. New York: McGraw, 1992.
"Miles of Yarn are an Experiment in Orbit." NewsDay
25 Mar. 1997: B 27.