Satellites

Application Satellites

Any smaller object traveling around a larger object is called a satellite. In the context of this report, a satellite is a man-made spacecraft which has been placed in orbit. These spacecraft can be manned, such as the Space Shuttle, or unmanned, such as the Tracking and Data Relay Satellite (TDRS). They can be sent into space with the intention that they will not be recovered, or they can be designed to be recovered or repaired by Space Shuttle and Space Station crews.

Satellites also may be either active or passive. Passive satellites contain no radio transmitter or other energy signals, but rather only reflect signals beamed at them from Earth. The active satellites collect data and emit radio signals that transmit the scientific information to Earth.

Satellites are designed to serve one of two general purposes: space science and applications. The space science satellites carry instruments to measure magnetic fields, space radiation, solar characteristics, gamma-ray, X-ray and ultraviolet emissions, to name a few. The application satellites survey Earth resources, extend communications and supply weather photographs and other information to forecasters.

Meteorology/Weather Satellites

A large number of satellites have been used in the testing and development of ways to improve weather forecasting globally.

The TIROS, or Television Infrared Observation Satellite, was the first generation of meteorological satellites to carry TV cameras to photograph the Earth's cloud cover. The system was operable only during the daylight hours. However, it was highly successful and proved the value of using spacecraft for meteorological research and weather forecasting.

Nimbus, a second-generation meteorological satellite which got its name from a cloud formation, is larger and more complex than TIROS. The Nimbus program was initiated to test a global meteorological satellite system. Using a near-polar orbit, Nimbus provided full Earth coverage of weather conditions on a daily basis. The system was powered variously by solar cells and by batteries. The spacecraft could be controlled from a command and data acquisition station on Earth. The satellite provided 24-hour coverage, with a high-resolution infrared radiometer being used during darkness. The Nimbus satellites have returned a wealth of new data applicable to meteorology, climatology, oceanography, geology, geography and hydrology. Nimbus-7, launched in 1978, has played a major role in the study of both global ozone and the "ozone hole" over the Antarctic.

The TOS, TIROS Operational Satellite system, also was an operational weather satellite system providing both day and night coverage of the entire Earth from space. The system utilized television cameras for daylight images of the sunlit portion of the Earth, and infrared radiometers -- tested on the Nimbus spacecraft -- provided surface temperature information and cloud top heights continuously. TOS was operated by the Environmental Science Service Administration (ESSA), now the National Oceanic and Atmospheric Administration or NOAA.

The TOS system consisted of two satellites. One transmitted pictures immediately in real-time, and the other stored the images for transmission to large data-acquisition stations on the ground.

ITOS, Improved TIROS Operational Satellite, was the original designation of developmental spacecraft testing continuous worldwide weather observations.

The SMS, Synchronous Meteorological Satellite, series included the first operational satellite in the NOAA system. The purpose of the SMS was to provide improved meteorological data on worldwide weather phenomena for improved forecasting.

The GOES, Geostationary Operational Environmental Satellite, series provided data for severe storm evaluation, information on cloud cover, winds, ocean currents, fog distribution, storm circulation and snow melt, using visual and infrared imagery. The satellites also received transmissions from free-floating balloons, buoys and remote automatic data collection stations around the world.

Another series of meteorological satellites is known as NOAA, for National Oceanic and Atmospheric Administration. The most recent NOAA spacecraft -- NOAA-8, -9, -10, and -11* -- not only provide weather information, but also monitor search and rescue frequencies, fulfilling a U.S. commitment to an international search and rescue program known as COSPAS/SARSAT. Since its inception in 1982, the program -- as of February 1988 -- had helped save more than 1000 lives.

Multi-Purpose Satellites

ATS, Applications Technology Satellite, was a multi-purpose engineering satellite series, testing technology in communications and meteorology from geosynchronous orbit. The major objective of the early ATS satellites was to test whether gravity would anchor the satellite in a synchronous orbit (22,300 statute miles above the Earth), allowing it to move at the same rate the Earth is turning, thus seeming to remain stationary. Another program of ATS was to test the satellite system as a means of controlling traffic in the air and sea lanes.

Earth Resources Satellites Several Earth Resources Satellites have been launched, including Seasat, Landsat and the Heat Capacity Mapping Mission (HCMM).

The purpose of Seasat was to determine if microwave instruments scanning the oceans from space could provide useful scientific data for oceanographers, meteorologists and commercial users of the seas. Information was gathered on surface winds and temperatures, currents, wave heights, ice conditions, ocean topography and coastal storm activity. The satellite tested the feasibility of a Seasat network to monitor the world's oceans and to provide ships at sea with detailed, updated charts showing the latest weather conditions. Only one Seasat was launched (1978), and it functioned only for three months.

Landsat, formerly known as ERTS (Earth Resources Technology Satellite), transmitted pictures of the Earth recorded in a number of wavelengths. The more wavelengths or spectral bands used, the easier it is to identify the object. The first data received from this system were used to identify known objects which then were used as models for a computer system. Once objects could be identified reliably, Landsat images were made available to scientists working to improve life on Earth. The Landsat images are used to locate sources of sea life, minerals and even fresh water. Images provide accurate maps and charts of areas previously too remote for conventional map makers. These maps provide data to aid in urban planning and rural land use so that the most effective use can be made of the Earth's resources. Five Landsats have been launched -- the last in March 1984.

The Heat Capacity Mapping Mission (HCMM) satellite flew from April 1977 to December 1981. The satellite's primary objective was to test the feasibility of measuring the Earth's temperature from space. The spacecraft was to measure the same areas of the Earth's surface, both for maximum and minimum temperatures on a given day. This information then was used to identify different rock types which could be used to locate mineral resources.

HCMM also monitored moisture levels in soil and gave indications of the amount of water being given off by plants. Another function was measuring the heat given off in urban areas. This information was used to study the effects cities have on climate. The information taken by HCMM was correlated with Landsat data and ground observations to get better data of temperatures on the Earth's surface.

Communication Satellites

Echo I and Echo II tested the theory that voices, pictures and music could be transmitted by bouncing them off a satellite. Aluminum coated, inflated balloons, or passive satellites, carried no transmitting equipment at all. Shortly after Echo I achieved orbit (1960), a message from President Dwight Eisenhower was beamed via the satellite -- the first ever from outer space. Relay I (1962) and Relay II (1964) were low altitude active repeater satellites. They carried electronic equipment which enabled them to send signals back to Earth. They also relayed data or radiation levels in their orbital path. The satellites conducted thousands of tests and demonstrations of transoceanic and intercontinental telecasts, including the first between Japan and the U.S.

NASA has launched many communications satellites for private industry. The Telstar series was launched for the American Telephone and Telegraph Co. (AT&T). Intelsat satellites for international communications were launched for Comsat; Comsat satellites were sent aloft for domestic communications, and Marisat for maritime communications. RCA had a series of communication satellites launched. For Hughes Communications, two series of satellites were launched, one named Galaxy and the other, Syncom.