How are satellites used to transmit TV shows? What are satellites used for? How do satellites get into space and how do they stay there? What will future satellite technology bring?

Insights

The post-World War II era ushered in the development of satellites and their launch systems, and with it, the communications revolution. In 1958, the "space race" began when the Soviets launched Sputnik. The first American communications satellite, Telstar 1, was launched in 1962. It could handle 600 telephone conversations simultaneously. Today, over 200 international communications satellites, similar to the Intelstat VI family, can carry 33,000 telephone calls at once. This capability will again be exceeded with the development of future satellites.

Isaac Newton first discovered how gravity keeps satellites in orbit when he observed how the moon orbits the earth. Any object, be it the moon or a communications satellite, is pulled toward the earth by the force of gravity. But, if it is moving fast enough and is moving perpendicular to the pull of gravity, it falls in a curved path and circles the earth. Although it's always falling, it stays in orbit. (It's similar to a ball on a string: if you swing it fast enough, it will travel in a circle around your hand.) If a satellite does not move fast enough, it eventually spirals closer and closer to the earth and burns up in the earth's atmosphere.

Satellites are sent into space and placed in orbit in one of two ways. The first way is with an expendable rocket that launches the satellite out of the earth's atmosphere. A smaller rocket attached to the satellite then places the satellite into the proper orbit. The second way of getting a satellite into space is on board a space shuttle. After the shuttle reaches a low earth orbit, astronauts release the satellite. The shuttle backs away and a transfer engine on the satellite places it in its proper orbit.

Satellites orbit the earth primarily in four ways: polar orbits, geosynchronous orbits, low earth orbits, and molniya orbits. In a polar orbit, a satellite orbits the earth from pole to pole. It covers different parts of the earth as the earth turns beneath it. This orbit is used for observing the weather and mapping earth resources. Most communications satellites are put into a geosynchronous orbit. This kind of orbit positions a satellite over the equator; the satellite orbits the earth at the same speed as the earth is turning, giving the satellite the appearance of being stationary. Low earth orbits vary with the type of satellites and their primary purposes. The uses of satellites in low earth orbit may range from scientific research to surveillance. Molniya orbits are highly elliptical and are used primarily by Soviet communications satellites.

Satellites will continue to grow in popularity, complexity, and uses, limited only by the imaginations of those involved in the technology.

Connections

1. What do satellites allow you to see "live" on TV that you would not see otherwise? What are some current events that you have seen on TV either as they happened or shortly after?
2. Why do communications-satellite orbits need to be so far from the earth?

Vocabulary

digital describes a system or device in which information is transferred by
electrical "on-off," "high-low," or "1/0" pulses
elliptical having the form of a closed oval-shaped curve
gravity the force that tends to pull any two objects together
orbit a closed path followed by a satellite

Resources

Baylin, F. (1986) Satellites today: The complete guide to satellite television. Indianapolis, IN: Howard W. Sams.

Damon, T. (1989) Introduction to space: The science of space flight. Malabar, FL: Orbit Books.

Additional sources of information:

Estes Industries
1295 H Street
Penrose, CO 81240
(educational materials, including computer software for Apple IIe systems)

NASA
Education Division
Mail Code F
Washington, DC 20546

U.S. Printing Office
Superintendent of Documents
Washington, DC 20402
(request Subject Bibliography Index #297: Space, Rockets, and Satellites)

Smithsonian Museum's Air & Space
P.O. Box 53261
Boulder, CO 80301
(periodical)

Main Activity

You will learn how digital images are made, and how signals are sent and received.

Materials

• graph paper, 5 squares to the inch OR plain paper on which you have drawn lines vertically and horizontally, creating 5 squares to the inch
  
• pencils

1. Pair your students; one will be the "sender," the other the "receiver."
2. Distribute graph paper to each student, and have each student draw a 10" x 10" square on the paper.
3. Within this 10" square, have the sender draw a simple picture. The receiver should not be able to see what the sender has drawn.
4. Direct the sender to "read" her picture to the receiver, using a digital code: If a square is blank, the sender says, "Zero"; if the square is filled in, the sender says, "One." Using this code, start with the top row and read from left to right.
5. The receiver, upon hearing this code, transfers the information to his 10" square on his graph paper.
6. At the end of the first row, the sender says, "End row 1," and repeats this at the end of each row.
7. At the end of the 10th row, look at the picture on the receiver's paper. Check the results to see how accurate the transfer was.
8. Change roles and repeat steps 1 through 7. Try this activity using larger or more complex drawings.

Questions

1. What was the most difficult part of the activity to do?

2. Can you think of a better way to transmit and receive information?

3. Describe how a digital image is formed based on your experiment.

4. Can you figure out how the information is coded electronically? (Hint: Using a light switch on the wall, assign a number to the switch when it is on. Assign a different number when the switch is off.)

5. What are some other devices or systems that communicate this way using 1s and 0s?

Find out about space laws, specifically those governing geosynchronous orbits. (This kind of orbit is highly preferred, and for that reason, a branch of the United Nations governs the placement of satellites in this area of space.) How is geosynchronous space divided up? How is it determined who gets what? What if two sponsors wanted the same area in space? How could a conflict be resolved?

Find out about the parts of an electromagnetic wave: wavelength, height/amplitude, frequency, cycle, nodes, etc. Use a piece of rope (15- to 20-feet long) to demonstrate how electromagnetic waves are generated. Lay the rope out on the floor and have two people hold each end. Have one person move the rope side to side in quick motions; you have generated "waves," specifically, transverse waves. Stop the motion and the waves will stop in their form along the floor. Measure the wavelength, amplitude, and frequency. Sketch what you see.

Take a tour of a local TV station. Find out from the broadcast engineers how they receive television programs and transfer them to cable. This field trip will help you understand how Newton's Apple gets to your local PBS station, and ultimately, to your television at home or school.

Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.