SPACE TODAY ONLINE FACTOID:

What is an Amateur Radio Satellite?

One of the oldest and most important uses for space satellites has been relaying human communications around the globe by radio. The first radio relays in the sky were launched by the United States government between 1958 and 1963. Known as Score, Echo, Telstar, Relay and Syncom, they blazed a path for today's sophisticated communications satellites which relay many telephone, data and television signals simultaneously.

• 1945 -- author Arthur C. Clarke described a global communication system using satellites in stationary orbit.
  
  
• 1957 -- the USSR launched Sputnik-1, the first artificial satellite in Earth orbit.
  
  
• 1958 -- the U.S. launched Explorer-1, America's first satellite in orbit. Later that year,the U.S. Score spacecraft became the first communication satellite in Earth orbit. It was a one-way communication system with a transmitter to broadcast from space to Earth a pre-recorded message, taped on the ground before launch by President Dwight D. Eisenhower.
  
  
• 1961 -- the first ham-designed-and-built, amateur radio satellite, OSCAR-1, was launched to a low orbit.

Private groups of amateur radio operators -- radio hams -- around the globe have built and sent dozens of amateur radio communications and science satellites to orbit since OSCAR-1 was launched on December 12, 1961.

The high-tech spacecraft have been financed through donations of time, hardware and cash from hams in the United States, Canada, Great Britain, Australia, Russia, Germany, France, Italy, Japan, Brazil, Argentina, Belgium, South Korea, Finland, Israel, Mexico, South Africa and other nations.

OSCAR. A California group of amateur radio operators, calling itself Project OSCAR for Orbital Satellite Carrying Amateur Radio, built the first amateur radio satellite in 1961. Since then, most "hamsats" have been called OSCAR. Amateur radio OSCARs are not the same as the U.S. Navy series of Oscar navigation satellites.

Radiosputnik, or RS for short, has been the name of most USSR and Russian amateur radio satellites. Three USSR hamsats were called Iskra which is Russian for "spark."British amateur radio satellites, built at the University of Surrey, have been called UoSAT. Japanese hamsats have been called Fuji which is Japanese for "wisteria."

Flourishing. The number of amateur radio satellites has been mushrooming. Only four were orbited in all of the 1960s. Six went to space in the 1970s. Seventeen amateur radio and amateur-related satellites were launched in the 1980s. So far in the 1990s, two dozen amateur radio and amateur-related satellites have launched with several more planned for launch by the end of the 1990s.

Record launch years were 1981 and 1990, with eight hamsats each. Close behind was 1991 with four hamsats and eight amateur-related satellites launched. Most hamsats remain in orbit today and many still are in use.

Launches. Hamsats often receive free rides to space as ballast on U.S., Russian, European and Japanese government rockets which happen to be carrying other commercial or government satellites to orbit. However, with available space over-booked, paid tickets sometimes are required today.

Orbits. The orbit is the path of an artificial satellite as it revolves around Earth:

• Low orbit -- Many amateur-radio, commercial and government communications satellites are in low Earth orbits (LEO) at altitudes of only 100 to 1,000 miles above the surface of our planet.
  
  
• Elliptical orbit -- Larger communications satellites, such as Russia's Molniya series, are in long elliptical orbits which repeatedly take them out beyond 22,000 miles before they swing back to within 1,000 miles of Earth's surface.
  
  
• Stationary orbit -- Major satellites are in high orbits from where they seem to hang stationary in the sky. Actually, they whirl around the globe at the same speed as Earth rotates, girdling the equator at 22,300 miles altitude. They can spritz radio signals over an entire hemisphere. (Learn more about stationary satellites.)

Amateur radio operators who have built the hamsat communication satellites refer to them by the types of orbits in which they fly:

• Phase-1 and Phase-2. Most hamsats have been what radio amateurs refer to as Phase-1 and Phase-2. They fly in north-south polar orbits or low east-west equatorial orbits from 200-1,000 miles altitude. That's just a bit higher than a space shuttle usually flies.
  
  A low-flying hamsat circles the globe, coming within range of a ham station on the ground every hour or so. It stays overhead only 15 to 30 minutes. Polar-orbit satellites come within range of a ground station about the same time every day.
  
  
• Phase-3. A few amateur satellites are in long elliptical orbits which keep them in view of ground stations for hours at a time. Radio amateurs refer to such hamsats as Phase-3.
  
  They range out 20,000-30,000 miles from Earth, but loop back around the planet, within 1,500-2,500 miles, every ten to twelve hours. Their long elliptical tracks are known as Molniya orbits after a class of Russian communications satellites which follow similar paths through space.
  
  
• Phase-4. A Phase-4 hamsat would be an OSCAR in stationary orbit. There probably won't be one until after the year 2000. (Learn more about stationary satellites.)

Sky-High Repeaters. What's inside? Communications satellites are outfitted with radio receivers, amplifiers, transmitters and multiplexing computers to relay many telephone, data and television signals simultaneously.

Like all kinds of satellites, communications satellites have internal sensors measuring voltages, currents and temperatures. That data is encoded into telemetry signals transmitted to ground controllers.

Many communications satellites have attitude-control equipment to maintain desired orbits, to point radio antennas at ground stations, and to keep solar-power generators pointing at the Sun. Most are powered by electricity converted from sunlight.

Communications satellites must stay in touch so their work can be directed by human operators in ground control stations. For instance, the radio frequency used by a broadcast satellite to beam down a TV movie can be changed.

Controllers talk with their birds by sending coded radio signals to them and receiving similar signals from them. For instance, NASA's constellation of TDRS communication satellites are controlled from a ground station in White Sands, New Mexico.

Signals transmitted from the ground to a satellite are uplinks. Signals transmitted from a satellite to the ground are downlinks.

Hamsats. Early amateur satellites carried only one-way radio beacons which sent down telemetry information about conditions of satellite equipment and the space environment to anybody interested in receiving the data. Hamsats of the 1990s still transmit beacons, but they also have transponders for two-way communications.

For the most part, hamsats are communications repeaters in the sky. Their transponders relay voice, Morse code and digital-computer signals. Most amateur satellites carry gear for digital computer-to-computer communication and store-and-forward message bulletin-board systems (bbs). Sometimes they have transmitters for radio propagation tests, ionospheric research, radioteletype and meteor sounding; receivers for radioastronomy, radiolocation and other original science research; and television cameras for photos of Earth.

Hamsats are open for use by all appropriately-licensed amateur radio operators around the world. The satellites serve the public, as well, by training satellite trackers, relaying medical data, teaching school science groups and providing emergency communications for disaster relief.

A hamsat monitors its solar cells and battery. Its telemetry beacon reports the amount of current being generated by the solar cells, the voltage available from the battery, the temperature of the battery, transmitter power, temperatures of other parts of the satellite, and other useful information. Such telemetry data is easily read by amateurs.

• Along with building their spacecraft, hamsat users enjoy an old-fashioned "rag chew" (conversation) via OSCAR. Contests and achievement awards add spice to their time on the air.
  
  
• Citations include Worked All States for contacting a station in each of the United States via satellite, Satellite DXCC for contacting hams in 100 countries via satellite, and a series of technical achievement awards.
  
  
• Radio amateurs love to track down hidden transmitters in "fox hunts." In a SatFox Test, amateurs at home simulate a hidden transmitter hunt using a hamsat to find a hidden "fox."
  
  
• ZRO Technical Achievement Award is earned for superior station performance in a sensitivity test of receiving weak satellite signals.
  
  
• Weekly amateur radio meetings on the air, known as "nets," spread the latest news of the amateur space program.

The Radio Amateur Satellite Corporation (AMSAT) was founded in 1969 as a group of ham operators around the globe who want to communicate by satellite. AMSAT groups have constructed and operated numerous OSCARs. Information is available from AMSAT, P.O. Box 27, Washington, D.C. 20044.

Information on amateur radio satellites is available from the American Radio Relay League (ARRL), the national amateur radio fraternity at 225 Main Street, Newington, Connecticut 06111.

Tucson Amateur Packet Radio (TAPR) was founded by members of an Arizona chapter of the IEEE Computer Society to develop amateur packet radio, including hamsat systems. Information is available from TAPR at P.O. Box 12925, Tucson, Arizona 85732.

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