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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 75W and 135W 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 - 0.575m; Band 2 from 0.580 - 0.680m; and Band 3 from 0.690 - 0.830m. The MSS had four bands numbered Band 4 from 0.50 - 0.60m; Band 5 from 0.60 - 0.70; Band 6 from 0.70 - 0.80; and Band 7 from 0.80 - 1.10m. Landsat 3 had a Band 8 from 10.40 - 12.50m. 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 - 0.52m; Band 2 from 0.52 - 0.60m; Band 3 from 0.63 - 0.69m; Band 4 from 0.76 - 0.90m; Band 5 from 1.55 - 1.75m; Band 6 from 10.40 - 12.50m; 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 - 0.59m; Band 2 from 0.61 - 0.68m; and Band 3 from 0.79 - 0.89m. The spectral bands have a 20m resolution. Also on the spacecraft is a panchromatic band from 0.51 - 0.73m 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.