CHAPTER 24: COMMUNICATIONS SATELLITES
© John F. Graham, 1995
Photos courtesy NASA
Of all the revolutions accomplished by the space program the most impressive
is the communications capabilities established by satellites since the first
communications satellite was launched in 1958. Since that year the world has
literally shrunk. A company person in a Boston firm can order a commodity from
Tokyo, talk immediately to its representative in France, talk to the subsidiary
head in Buenos Aires, Argentina, fill an order over an 800 number from Nome,
Alaska, and talk to the new department head in Moscow, Russia in less than 15
minutes. This amazing capability is now routine and has literally changed our
lives. The reason for these changes were spearheaded by communications
satellites.
These satellites are divided into two groups: active and passive satellites.
In the beginning of the Space Age the passive communications satellites showed
the most promise, but with the advent of integrated circuits active satellites
could contain millions of circuits on small chips thus allowing thousands of
telephone calls, data transmissions, and television programs on one satellite.
Passive satellites soon disappeared from the scene after this revolution.
SCORE
On December 18, 1958 the U.S. Army launched the first communications
satellite into orbit. This was not a true communications satellite in that no
real communications were passed from one person to another, but rather it
transmitted President Eisenhower's recorded Christmas Greetings to the world and
his hope for peace.
ECHO
The world's first true communications satellite was a 100 foot mylar balloon
launched on August 12, 1960. Echo 1 was a passive communications satellite
because signals were sent from a transmitting station, bounced off Echo 1 and
reflected to a receiving station. Echo 1 remained in orbit until May 24, 1968
TELSTAR
On July 10, 1962 NASA launched the first active real-time communications
satellite, Telstar 1. Owned by the AT&T Bell Laboratories, Telstar received,
amplified, and retransmitted communications from Earth. This spacecraft was in
low Earth orbit and was the initial part of a Bell Labs plan to run a privately
owned communications system. This 77kg satellite had a perigee of 952 km and an
apogee of 5636 km and a period of 115 minutes. This allowed the spacecraft to
"hang" over the northern hemisphere in order to lengthen transmission
times. This idea was adopted by the Soviets for their Molniya Communications
Satellite System. Telstar was very reliable, but fell to the prey of the U.S.
Government going into the communications satellite business.
COMSAT
On August 31, 1962 President Kennedy signed legislation creating the
Communications Satellite Corporation (COMSAT). COMSAT's mission was to establish
a world-wide communications network to promote world peace and understanding. By
committing to this program the young president helped to establish a new
infrastructure in the geosynchronous belt.
In 1945 Arthur C. Clarke had written an scientific paper concerning the
establishment of a worldwide communications system by placing three satellites
at equidistant locations in the geosynchronous belt. He theorized that this
could work and would probably be in place by the turn of the century. Neither
Mr. Clarke nor the rest of the world anticipated how fast events changed after
Sputnik's launch. 1
On February 14, 1963 the electronics failed in Syncom 1, COMSAT's first
attempt to place a satellite into geosynchronous orbit. Mr Clarke's dream was
finally realized on July 26, 1963 when Syncom 2 became the world's first
geosynchronous communications satellite. The U.S. received television pictures
from this satellite during the 1964 Olympics in Japan. This success was followed
by Syncom 3 in 1964 and the world's first commercial communications satellite
known as Early Bird, also known as INTELSAT 1.
INTELSAT
The International Telecommunications Satellite Organization was established
on August 20, 1964. It currently has 125 nation members consisting of
governments or communication entities designated by governments to oversee
communications requirements. These organizations use 19 satellites located in
geosynchronous orbit over the Atlantic, Pacific and Indian Oceans to provide
international links to 180 nations, domestic links to 40 countries and 900
separate ground stations. These satellites and ground stations provided >
70,000 hours of television and 133,000 channels for telephone calls. A basic
tenant of the organization is non discriminatory access which means that both
member and non-member users pay the same rates for Intelsat.
The organization operates under a four-tiered structure based upon the
Intelsat Agreement that went into force on February 12, 1973. This structure
includes the Board of Governors, the managers of the organization. This Board
provides recommendations to the Assembly of Parties and the Meeting of
Signatories. The Assembly of Parties represent all the entities who have signed
an agreement with Intelsat. This group considers resolutions and recommendations
from the Board of Governors for long term plans. The Meeting of Signatories is
made of representatives from the Signatories to the Operational Agreement. This
organization meets to consider issues relating to financial, technical, and
operational aspects of the system. Both of the above organizations work on the
one nation/one vote rule. A simple majority is required for procedural matters
while a two thirds majority is required for substantial operational matters.
Ownership and investment in the system is in relationship to the amount of
use. Investment shares represent the percentage of each signatories contribution
of capital for expenditures. All revenues from the system are reinvested back
into the organization. This has been one of the most successful international
organizations in modern times.
HUGHES COMSATS
The most commonly used platform for civil satellite communications is the
Hughes HS-376 design. This spacecraft is almost ubiquitous in its use by
countries the world over for GEO comsats. A typical Hughes comsat is spin
stabilized at 50 rpm and drum shaped. It has a diameter of 2.16m and a length of
6.6m. The satellite has a stowed length of 2.8m and when the spacecraft reaches
its deployment position it deploys a 3.8m skirt which contains additional body
mounted solar cells to increase the power. The communications shelf is despun to
constantly point at the Earth station.
MOLNIYA
Most of Russia lies north of the 45th latitude parallel. Because of this the
access to GEO satellites is limited. Since Russia has over thirteen time zones,
the need for communications in this huge country is paramount. Satellite
communications is ideal for a country as large as this because it can tie the
entire country together without the need for extended ground transportation
routes or wire telegraph/telephone lines through some very inhospitable country.
Rather than attempt a GEO system the Russian communications scientists started
by Korolev in the early 1960s envisioned a communications system which suspended
over the Northern Hemisphere in order to complete communications very similar to
a GEO communications platform.
To accomplish this the Molniya series of spacecraft were developed. Molniya,
lightning in Russian, is launched into a 62.8° inclination in order to keep the
rotation of apsides at 0. The apogee of this orbit is about 44,000 km while the
perigee is 400km. Because of this, the spacecraft spends about ten of its 12
hour orbit over Russia and two hours speeding through the Southern Hemisphere.
While the spacecraft is over the Northern Hemisphere it can be used to relay
communications from one end of Russia to the other. The normal spacecraft
deployment calls for three satellites per orbit. This allows a satellite always
to be in the ground station's field of view.
First launched on April 23, 1965 the Molniya spacecraft have gone through
three models. The most common are the Molniya 1 model and the Molniya 3. Molniya
2 never worked and was subsequently never deployed. Molniya is used mostly for
military operations, but since the revolution of 1991 Molniya is being used more
for domestic communications such as telephone and television. The Molniya
spacecraft has been a great success story in the highly successful Russian Space
Program.
GORIZONT
The Russian have launched several GEO spacecraft for communications purposes.
The Gorizont television satellite made its debut on December 19, 1978. The
initial purpose of this satellite was to relay television broadcast of the 1980
Olympics being held in Moscow. The second Gorizont was launched on July 5, 1979
and seemed to support that argument.
The Gorizont has a mass of 2800 kg and two solar arrays.
The spacecraft has a large circular antenna and three smaller antennas for
communications relay in the 4 GHz band. It also contains a 40 watt repeater and
five 15 watt repeaters.
CHAPTER 25: WEATHER SATELLITES
© John F. Graham, 1995
Photos courtesy NASA
Every day we listen to the weather reports; and every day we are either
disappointed or happy that the weather is pretty much what the local television
meteorologist told us. There was a time before the first weather satellites were
launched when meteorology was almost akin to alchemy. The meteorologist would
make a prediction for snow and a 70° temperate day with lots of sunshine came
forth. There were even times when, in spite of the meteorologists' best efforts,
tragedy struck and thousands of people lost there lives due to hurricanes,
floods, and tornadoes. The space age brought forth remarkable machines which
were so effective that, in spite of horrid destruction, only a few people
perished during Hurricane Andrew in South Florida. The weather satellites have
contributed greatly to changing our lives on Earth. Before weather satellites
orbited world meteorologists could monitor about 20% of the Earth's surface for
weather conditions. Today, meteorologists monitor 100% of the Earth's surface
and obtain six hour updates concerning temperature, winds, and storms.
HISTORY
On April 4, 1960 the U.S. launched the world's first weather satellite, TIROS
(Television and InfraRed Observation Satellite). The first transmitted weather
picture was that which showed clouds over the Gulf of St Lawrence. TIROS
produced 22,500 photographs of the Earth's weather before it was declared not
operational. This small spacecraft weighed 122.5 kg and was shaped like a tiny
hat box. By 1965 nine Tiros series spacecraft had been launched with better
sensors to measure the weather patterns. To gather weather from the entire
planet, the new Tiros spacecraft were placed into polar and sun synchronous
orbits.
On August 28, 1964 the U.S. launched a second generation spacecraft known as
the NIMBUS satellite. This vehicle was placed into a sun synchronous orbit with
an inclination of 98.48°, perigee of 450 km and an apogee of 924km. The Nimbus
carried advanced TV cameras including a sophisticated cloud mapping system and
an infrared radiometer which allowed weather pictures to be taken at night.
Seven Nimbus satellites were placed into orbit by 1978. This was the direct
forerunner of the advanced weather forecasting system we have today.
NOAA
The National Oceanic and Atmospheric Administration includes the National
Weather Service (NWS). NOAA was organized in 1971 from the former Environmental
Science Services Administration and is established within the Department of
Commerce. NOAA uses satellite data to monitor weather conditions, issue severe
weather warnings, assess human impact and natural factors on the world's food
and fuel supplies, and assess the environment. Within NOAA the National
Environmental Satellite, Data and Information Service manages the polar and GEO
weather spacecraft.
GOES
The Geostationary Operational Environment Satellite takes the big picture of
the western hemisphere's weather from its high advantageous location in
geostationary orbit. Its primary mission is to locate and track large
destructive storms such as hurricanes. Working in pairs these spacecraft are
located at 75°W and 135°W and are known as GOES East and GOES West
respectively. These spacecraft provide visible and infrared imagery of the
entire hemisphere 24 hours per day. The first seven GOES spacecraft were built
by Hughes were spin stabilized with body mounted solar arrays. The two newest
spacecraft in orbit, GOES 8 and GOES 9, are built by Loral and are three axis
stabilized. This is the start of a series of spacecraft GOES 8-12.
NOAA SPACECRAFT
The NOAA spacecraft are polar orbiting satellites that can view the entire
Earth's surface twice in 24 hours. Besides returning weather imagery with a
resolution of one kilometer these spacecraft monitor atmospheric humidity and
temperature, snow and ice cover, total ozone content, atmospheric aerosol
content, and cospas/sarsat distress signals. These satellites are designed for
two year lives and have morning orbits and evening orbits. These spacecraft work
in pairs with one being six hours behind the other in the same orbit. The latest
spacecraft to be launched in the NOAA series was NOAA 14 launched in December of
1994.
Under pressure from the Government Accounting Office,
NOAA is currently undertaking a study along with the Department of Defense to
determine whether or not it would be feasible to merge the polar orbiting
satellites with the Defense Meteorological Satellite Program which performs
essentially the same mission. In this way the system will not be duplicating the
missions and money will be saved.
CHAPTER 26: NAVIGATION SATELLITES
© John F. Graham, 1995
Photos courtesy NASA
Since the 1960s the U.S. military has had on orbit a satellite or a
constellation of satellites to aid the military in determining the position of
ships, airplanes, or personnel. The U.S. Navy has particular need of extremely
accurate navigation not only to determine their location, but also to inertially
update high tech weaponry which most ships carry. For this reason the Transit,
Timation, and Nova systems were built. A more accurate system known as the
Global Positioning System or NAVSTAR has been placed in orbit. This
constellation of satellites now allows users to determine where they are located
within a few meters. Infantry soldiers can determine their location extremely
accurately making map reading far more reliable than previously. Aircraft can
fly anywhere in the world without using conventional navigation equipment and
determine their location within a hundred feet. Weapons can also be programmed
to bring the possibility of precision weapon use to even poor countries, an
ominous fact in a very useful peaceable system.
TRANSIT
The first navigation satellite the Transit was launched on April 13, 1960
into a 51° inclination orbit with an apogee of 745 and a perigee of 373 km. The
spacecraft operated for three months. By 1968 there were 23 Transit satellites
operating in circular orbits of 850km. These spacecraft far out-lived their
design some lasting as long as 11 years.
This spacecraft was developed for updating the inertial navigation systems on
board the Polaris submarines. This spacecraft operates on the principle of the
measurement of the Doppler Shift. As a single spacecraft travels overhead the
user measures the Doppler shift over a fifteen minute period by receiving
satellite timing marks and satellite orbital information on two separate
frequencies, 149.99 and 399.97MHz. These signals are corrected for ionospheric
refraction and the information is then fed into the user's navigation system.
The Transit System is run by the U.S. Navy at Point Magu, California in
conjunction with tracking stations located in Maine, Minnesota, and Hawaii.
Using this system ships can obtain accuracies of 80 - 100 m for a single
satellite. A ship can obtain fixes every 35 - 100 minutes using the current
Transit System. For stationary locations such as ocean based oil rigs 25 Transit
passes can be integrated and an accuracy of 5 m can be determined. The Transit
continues in use today, but by 1996 it will be totally replaced by the Global
Positioning System.
NOVA AND TIMATION
Two other navigation systems grew out of the Transit system, the Nova and the
Timation. Nova was an improved Transit which had a more powerful transmitter, a
greater computer capacity, a better clock, and a 7.6 meter boom for gravity
gradient stabilization. There were three satellites in this system at 109° and
90° inclinations with a circular orbit of about 1200 km. All three spacecraft
remain operational today, but no more will be orbited because of the success
with GPS. Timation was the prototype of GPS which was initially launched on May
31, 1967 into a 70° inclination circular orbit with a height of 900 km. Two
other timation satellites were launched in 1969 and 1974 after which the program
was merged with the Transit and GPS Programs
GPS NAVSTAR
The Global Positioning System (GPS) was begun in 1973 to replace the 200m
accuracy Transit system. This program is also known as Navigation Satellite
Timing And Ranging (NAVSTAR) and serves as a world wide navigation system. The
system consists of a constellation of 24 satellites in six orbital planes. Each
satellite contains two rubidium and two cesium atomic clocks with the stability
of 1 second in 300,000 years for the former and 1 second in 160,000 years for
the latter. These clocks are updated every day to promote even greater accuracy.
The spacecraft are put into 55° inclined circular orbits at an altitude of
20,900km which gives it a period of 12 hours. These six orbits allow a receiver
anywhere in the world to have four satellites constantly in view. This allows
the spacecraft to provide extremely accurate navigation: position within 16m,
velocity to 0.1 m/sec, and time to within 100 nanoseconds (a nanosecond is a
billionth of a second).
The GPS spacecraft is 820 kg and three axis stabilized. It contains two Sun
sensors, an Earth sensor, and three gyros for attitude determination along with
22 thrusters and four reaction wheels for attitude control. It relies on a
digital control electronics assembly for guidance and sends its clock
information to the users via a telemetry, tracking, and commanding receiver.
Once the spacecraft is on-orbit and checked out by its master control station
at Falcon Air Force Base, Colorado it begins to provide navigation information
to its users. A typical user will receive signals from four satellites either
simultaneously or sequentially. Each satellite transmits a precision signal over
two links which are encrypted for military operations and allows them to receive
16m accurate data. The civilians receive a degraded course acquisition on one
link which degrades the accuracy to 100m. The receiver calculates the range
information from the spacecraft by calculating the difference between the
current receiver time and the time transmitted over the link from the
spacecraft. This difference is multiplied by the speed of light. This corrected
difference to three satellites is applied to a computed algorithm which
determines a position fix in latitude and longitude. The fourth satellite's
information is used to determine altitude.
Differential GPS is currently being used to obtain unbelievable accuracies
for everything from precision landing systems for aircraft to measuring the
movement of the Earth's crust. This is accomplished by placing a receiver at a
known position and then transmitting corrections to other receivers in the local
area. Accuracies have been reported in the millimeter range. GPS will change not
only the military, but also our everyday lives. Avis Rent A Car now has a
digital map with a GPS receiver on board to keep their customers from becoming
lost as they travel the roads of America.
GLONASS
The Soviet Union/Russia/CIS also has a navigation program very similar to the
U.S. GPS. The Global Navigation Satellite System (GLONASS) will have a
constellation of 24 satellites which will orbit at 19,100km at an inclination of
64.8°. This allows the spacecraft to repeat their groundtrack every 8 days for
precision. GLONASS intends to service maritime and aviation users throughout the
world.
The Russians hope to achieve accuracies of 150m in
altitude, 100m in latitude-longitude, and 15 cm/sec in velocity. Like GPS the
spacecraft transmits two signals, 1.250 GHz and 1.6035 GHz. The latter frequency
is causing a great deal of alarm among the radio astronomy community because the
very important hydroxyl line is located at 1.612 GHz. The current lifetime of
the GLONASS spacecraft is 3 years, but hopefully improvements will change its
secondary frequency and increase its lifespan. Northwest Airlines has outfitted
some of their planes which fly polar routes with GLONASS receivers to take
advantage of both GLONASS and GPS information and perhaps fuse this data into
even more accurate position and altitude data.
CHAPTER 27: REMOTE SENSING
© John F. Graham, 1995
Photos courtesy NASA
Remote sensing has been around humanity as long as the species has been on
the planet. Whenever persons looked over the hill and saw a tree full of fruit,
a waterhole, or a saber tooth tiger, they were using remote sensing. The human
eye is a typical form of remote sensing equipment and it allowed our species to
advance, but now the visual spectra are not enough to determine the condition of
our Earth; infrared and radar are needed to determine the status of plantlife,
geology, and water.
There are two basic types of sensing - remote and direct. These are best
illustrated by noting the operation of a burner on an electric range. When we
walk into a kitchen we can see that the burner is operating by the red glow that
the burner emits. If we approach close enough we can feel the heat being
emitted. These two acts are remote sensing. If we were to be forgetful or had
never been in contact with a electric range burner we might attempt direct
sensing by touching the pretty red metal. After direct sensing of the burner we
would learn never to touch the pretty red metal again! Remote sensing is more
practical and easy to accomplish by satellites.
Remote sensing has become very important with the advent of the space program
for several reasons. When the first people went into space they could see more
than was expected of humans at that great height. Photographs from the Mercury
and Gemini missions inspired proposals for a civilian remote sensing satellites.
Human eyes soon gave way to cameras - they were a lot cheaper and didn't need
the life support. The first remote sensing missions were the spy satellites
which remotely sensed the Soviet Union and the U.S. missile fields and bomber
bases. Neither country was will to admit to the rest of the world that they were
spying on each other so remote sensing initially stayed in the realm of the dark
world. Other parts of remote sensing were improved. Weather satellites could be
used to determine vegetative indices as well as moisture content in clouds. By
1968 the Department of Interior requested that a satellite be built for Earth
resources observation. By 1969 this was agreed to after NASA established a
cooperative plan and funds were granted. On July 23, 1972 the first Earth
Resources Technology Satellite (ERTS) was launched; it was later known as
Landsat.
LANDSAT
General Electric built the first three Landsat spacecraft. These were
enlarged and improved versions of the Nimbus weather satellite. The plan
initially called for two Landsats to be launched within the first two years 1972
and 1973 as an experiment to systematically survey the Earth's surface to study
crop health and for potential use of Earth's land and oceans. Three hundred
investigators from fifty countries stood amazed as Landsat 1 began to transmit
images of the Earth from the time it was operational. The quality of the images
from this spacecraft soon provided evidence that such pictures of the Earth
could be vital for land management, energy locations, and environmental
investigations.
Before Landsat's launch NASA stated that all of the images broadcast from the
satellite and its successors would be unclassified and made available to the
public. The 9000 weekly images were sent to the EROS Data Center in Sioux Falls,
South Dakota where they were made available to the public for $1.25 per picture.
The immediate success of this project caused EROS to be swamped by requests for
data from all over the world. Countries over the entire world requested that
ground stations be established on their soil. For $4 - $7 million initial
construction costs, $1-$2 million operating costs, and a $200,000 operating fee
countries such as South Africa, Canada, Brazil, Italy, Japan, Thailand,
Australia, Zaire, Sweden, India, Iran, Argentina and China established their own
ground stations.
The Landsat spacecraft had several sensors on board which were designed to
accomplish the missions mentioned above and to provide continuity from one
spacecraft to the next. For example, Landsat 1 had a return beam vidicon (RBV)
and a multispectral scanner (MSS). Since technical problems disallowed the use
of the RBV on Landsats 1 and 2 the MSS provided most of the original data.
Landsat 1 had an 80m resolution for both instruments; its RBV had three bands :
Band 1 from 0.475 - 0.575µm; Band 2 from 0.580 - 0.680µm; and Band 3 from
0.690 - 0.830µm. The MSS had four bands numbered Band 4 from 0.50 - 0.60µm;
Band 5 from 0.60 - 0.70; Band 6 from 0.70 - 0.80; and Band 7 from 0.80 -
1.10µm. Landsat 3 had a Band 8 from 10.40 - 12.50µm. Even though the RBV was
removed on Landsats 4 and 5 they still kept the same band numbering system for
the MSS. This allowed data continuity. Since the RBV was removed on both
Landsats 4 and 5 they had a new instrument known as a Thematic Mapper (TM).
The TM had greater resolution (30m) and a greater number of spectral bands(7)
than its predecessors. The TM includes Band 1 from 0.45 - 0.52µm; Band 2 from
0.52 - 0.60µm; Band 3 from 0.63 - 0.69µm; Band 4 from 0.76 - 0.90µm; Band 5
from 1.55 - 1.75µm; Band 6 from 10.40 - 12.50µm; and Band 7 from 2.08 - 2.35.
Each of these bands measure everything from the amount of chlorophyll absorption
in plants to the amount of moisture in the soil.
Landsats 4 and 5 continue to orbit. The last TM scene from Landsat 4 came in
October of 1987 while Landsat 5 is expected to continue broadcasting direct to
ground stations until 1987. EOSAT, a company which was to be a commercial remote
sensing entity as noted by the Reagan Administration's Remote Sensing
Commercialization Act of 1984, attempted to launch Landsat 6 in 1994. A
misplaced switch caused the spacecraft to fall into the Pacific when its second
stage failed to ignite to place the craft into orbit.
The pricing policies of EOSAT continued to gain the ire of potential users
and the U.S. Government revoked the 1984 Act replacing it by the 1992 Remote
Sensing Act which stated that the U.S. Government would take over the Landsat
system starting with Landsat 7. NASA and DOD were to form a team to build
Landsat 7, but DOD pulled out of the team in 1994. The DOD sensor could not be
included in a cost effective manner so it was cancelled and with it DOD's
interest in the entire project. Landsat 7 may get into orbit during the final
days of Landsat 5. In the recent frenzy of budget cutting in Washington, D.C.,
Congress may cut Landsat without much thought of the consequences for data
continuation to monitor changes in the Earth's condition. The future of remote
sensing will probably be determined by the Earth Observation System (EOS) and
SPOT.
SPOT
On February 22, 1986 the French Space Agency launched its first Systeme
Probatoire d'Observation de la Terre (SPOT) satellite from Kourou, French Guiana
aboard an Ariane 1. The SPOT spacecraft was placed into a Sun synchronous
circular orbit at 98.7° inclination and an altitude of 820km. The spacecraft
had a design life of two years, but surpassed it by two years when it was
retired on December 31, 1990.
The spacecraft has two CCD imagers with an off-nadir viewing allowing the
spacecraft to look at its side more effectively than Landsat. The tilting mirror
permits SPOT to image a particular area on seven consecutive passes at the
equator and eleven passes at 45° latitude. SPOT has three bands of spectral
images: Band 1 from 0.05 - 0.59µm; Band 2 from 0.61 - 0.68µm; and Band 3 from
0.79 - 0.89µm. The spectral bands have a 20m resolution. Also on the spacecraft
is a panchromatic band from 0.51 - 0.73µm with a resolution of 10m. Three SPOT
spacecraft have been launched as of 1995 and all three have the same
capabilities.
The SPOT Mission Center is located in Toulouse, France. A second command
center is located at Kiruna, Sweden. At these sites ground operators collect
real-time images, within 2500km of the ground stations, and stored images from
other parts of the Earth. The two ground stations have the capacity of receiving
500,000 images per year. SPOT Image, the company which runs the SPOT marketing,
runs a number of Direct Receiving Stations which receive real-time images only.
These stations are located in Canada, India, Spain, Brazil, Thailand, Japan,
Pakistan, Saudi Arabia, South Africa, Australia, and Equador.
For the future, SPOT Image is working on constructing a SPOT satellite which
will have a 5m resolution in at least two bands along with a stereo capability
which would generate simultaneous stereo pairs. The launches of these
spacecraft, tentatively known as SPOT 5 and 6, are currently projected for 1999
- 2000 and will cost about 6 - 7 billion French Francs.
RUSSIAN REMOTE SENSING
The Russians have always had a very active and prolific remote sensing
program which has been normally used for military reconnaissance purposes. Even
though satellite programs like Almaz and Resurs have had their roots steeped
deeply in military programs, the results from these satellites have been open
for everybody to obtain.
The Almaz (Russian for diamond) Program initially came from a military
reconnaissance spacecraft intended to be launched in 1981. A disagreement
between the chief designer of the project and the Minister of Defense led to the
project being cancelled. The concept was reintroduced in 1987 as a prototype
under the name of Cosmos 1870. Its primary missions were to monitor oil
pollution and to determine the extent of ice throughout the Arctic Ocean. The
main imaging instrument was a synthetic aperture radar with a resolution of 30
meters. By the time Almaz 1 was launched in 1991, the resolution was improved to
15m and data were transmitted through satellite downlinks. 40 x 40km scenes are
available for purchase from the Almaz Corporation for $2500 per scene. Various
products from Almaz were available including mosaics, mapsheets, custom
colorization, interpretation and enhancements. This spacecraft was rather large
for imaging spacecraft. It had a mass of 18.5 tons, 15m in length, 4 m in
diameter and had two solar arrays with 86m2 area which produced 10Kw of power.
Almaz was placed into a very low circular orbit of 275km at an inclination of
72°.
Increased solar activity in 1991-1992 mandated a number of orbit raisings
until the craft's fuel was depleted. The Russians deorbited the huge craft on
October 17, 1992 into the Pacific after the sale of only 200 images. Almaz 2 has
been designed with two radars and a four band optical imager, but due to
financial problems it was not launched. The second block of Almaz has been
designed to be possibly man-tended or refueled by a Progress vehicle. The
spacecraft will be placed into a 73° inclined orbit with a 6.5 ton payload. The
payload will be placed into a 600 km circular orbit with a life expectancy of 5
years. Block 2 will have three radar bands: one band at 23 cm for vegetation and
soil moisture; one at 9.6 cm to detect storms; and one band at 5.6 cm for ice
and wave determination. Rainfall observations would be optimized in one of the
two radars. Because of the $100 - $120 million pricetag, the launch of the Block
2 Almaz is highly unlikely until the financial fortunes of Russia are reversed.
Another major civilian remote sensing spacecraft in Russia is the Resurs
series. Resurs is a 1900 kg multispectral imaging spacecraft very similar to
Landsat. The first Resurs spacecraft became operational in 1988 following a
successful retrograde launch from Tyuratam into a 98° inclination with an
altitude of 630km. This spacecraft has a resolution of 45m visible, 170m in the
infrared band, and 600m in the thermal band. The spacecraft uses CCDs similar to
Landsat and SPOT for its 5 bands of coverage. On November 4, 1994, Resurs 01 -
03 was launched into a Sun synchronous orbit by an SL-16 Zenit-2, the first time
this spacecraft has been used for such a launch. The launch and deployment was
successful and the satellite can expect a five year lifetime. A Resurs 02 is
planned which will be an entire upgrade of the Resurs 01 system. This system
will include a microwave imager, a radiometer, and a side looking radar along
with the standard Resurs 01 imagers. The resolution will be improved from 45m to
17m. Both Resurs and Almaz will play significant roles in the Russian
contribution to Mission to Planet Earth.
MISSION TO PLANET EARTH
In 1987 the NASA Administrator, Dr. James Fletcher, formed a task group
headed by astronaut Dr. Sally Ride to define potential space programs and
evaluate these in terms of opportunities for the United States to regain
leadership in space exploration. This task group formulated four different
exploration initiatives of which one was Mission to Planet Earth.
The purpose of Mission to Planet Earth is to obtain a scientific
understanding of the entire Planet Earth, how its systems work, how they
interact with one another, and how they may evolve. Currently, science does not
have the capability to determine long term effects of actions taken by humans on
the Earth's environment. There are no models upon which to base intelligent
guesses as to what will occur next in the Earth's evolution. Space affords a
unique position to observe the Earth and all its various systems. By using an
integrated system of observing the earth constantly from GEO and the same area
more closely, but intermittently, from LEO, scientists may be provided enough
data to start constructing more accurate models of the Earth's systems.
In her committee's report, Dr. Ride suggested that a series of four sun
synchronous spacecraft and five GEO platforms be used to measure the Earth's
characteristics such as cloud cover, vegetation mass, ice cover, movement of the
Earth's tectonic plates, ocean plantlife, ocean motion, and atmospheric content.
These space observations would be coordinated with ground observations to obtain
truth data which would be integrated into a permanent data base. The data
amounts which this program will produce is a prodigious, one trillion bits of
data per day. That is more data in one day than has ever been produced by all
the satellites orbiting anywhere around the solar system. Since 1987 a number of
changes to the plan have occurred.
The Earth Observing System (EOS) is the largest element in Mission to Planet
Earth. It will study the Earth's solid surfaces, oceans, atmosphere, ice, and
biological processes. EOS is particularly designed to observe relationships of
the above with the flow of energy and water around the globe. This program will
be accomplished by combining the observations made by EOS with archived
processed data from the EOS Data and Information System (EOSDIS). EOSDIS will be
used to perform EOS Science.
EOS Science defines the goal of Mission to Planet Earth. It determines the
current state of the earth's systems; develops an understanding of these
systems; and uses both of these facts to build models. The models will be used
to develop a "whole Earth" system and could point to various
interaction processes.
EOSDIS provides the computational power and the network required to
accomplish data processing, archiving, interpreting, and modeling. EOSDIS will
also achieve command and control of the spacecraft and its instruments. To
accomplish the Mission to Planet Earth EOSDIS will need eight distributed active
archive centers (DAACs) to not only process and archive the EOS data, but also
the in situ or truth data determined from ground observations. These DAACs are
Goddard Spaceflight Center, JPL, Langley, EROS Data Center, the National Snow
and Ice Data Center, the University of Alaska, Marshall Spaceflight Center, and
the national Laboratories at Oak Ridge, Tennessee.
The EOS flights as stated above are several large satellites being placed
into GEO and LEO positions. Some of these spacecraft are called AM, PM, ALT,
CHEM, and AERO.
The AM spacecraft will monitor clouds, greenhouse gases, and aerosols. These
spacecraft will be at Sun synchronous inclinations in a circular orbit of 700
km.
The PM spacecraft will monitor clouds, precipitation, snow, sea ice, and sea
surface temperature. The spacecraft will have the same characteristics as the AM
spacecraft.
The ALT spacecraft will measure ocean circulation and the ice sheet mass
balance throughout the world.
The CHEM spacecraft will measure atmosphere chemistry including all the
different gases located near the earth's surface.
The AERO spacecraft will provide aerosol and cloud data for more enhance
atmospheric models.
These spacecraft will fly at five year intervals to note
any changes in the Earth's composition. The data will be sent to EOS sites which
will use EOSDIS to accomplish the modeling required for EOS Science.
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