Lesson: Keep in Touch: Communications and SatellitesContributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Educational Standards :
Learning Objectives (Return to Contents)
After this lesson, students should be able to:
Introduction/Motivation (Return to Contents)
Spacewoman Tess and Spaceman Rohan's daughter Maya is heading off on a six-month solo canoe trip through northern Canada to previously unexplored waters. Spacewoman Tess and Spaceman Robert are very excited, though very worried about their daughter. If you were Maya's parents, what would you be worried about? If you were Maya herself, what would you be worried about?
They are all worried about being able to communicate with their daughter — to know where Maya is and that she is safe. Communicating is how we are able to get ideas or messages across to another person. Let's brainstorm a list of different ways of communicating. (Possible answers include: speaking, sign language, telephone, letters, body gestures, television, radio, email, websites, etc.) Which ways work well for people who are standing close together? (Possible answers: speaking, body gestures, sign language, newspaper, etc.) Which ways work well for people that are far apart, as in a different country? (Possible answers: telephone, email, television, radio, newspaper, etc. If types of mass communication don't come up, ask students how news is communicated, or what kind of television service they have at home?) Leave this list on the board.
What about knowing where you are located or where other people are located? Let's brainstorm ways that people can know where they are or where other people are located. (Possible answers: Maps, calling people to ask them, identification markers, satellite navigation. To get the answers going, ask how pilots know where they are in the huge open sky?) How do vehicles such as aircraft or ships, or even some cars know where they are at any time? (Possible answers: maps, global positioning satellite systems, identification markers, etc.) Leave this list on the board as well.
Demonstration: Before class begins, attach a string to a ping pong or tennis ball. Hold the string/ball out in front of you, letting the ball drop towards the ground. Holding the string between your fingers, begin twirling the ball in a circle using your wrist to obtain a smooth, consistent motion. When you have the ball turning in a constant motion, cut the string.
Let's think about what has happened with the ball. Have you ever looked up into the sky at night and seen something moving really slowly across the night sky? Chances are you were seeing a man-made object that was put into the Earth's atmosphere by engineers and is now orbiting the Earth. What is an orbit? Well, an orbit is when an object moves around another object in a complete path, like a circle or an oval. What about the moon, what is it doing as it moves across the sky at night? (Answer: It is orbiting the Earth.) What about all of the nine planets in the solar system? Do they orbit? (Answer: Yes, they are all orbiting the sun.) In the demonstration, what was the ball orbiting before the string was cut? (Answer: It was orbiting the teacher's wrist; also okay to accept finger(s) as an answer.) Show the students the figure below (orbit schematic) and point out how the pull of a planet's gravity is always "down". But what does down mean? Does down mean the same thing for a person in Australia as it does for someone in the United States? (Answer: Yes and no. Yes because down is always towards the center of the earth (center of mass), no because this "down" would actually be in two very different directions...almost opposite.) The important thing to remember is: GRAVITY ALWAYS PULLS DOWN, TOWARDS THE CENTER OF MASS OF THE PLANET. If a something is in orbit (a satellite), it means that it is actually falling AROUND earth...and not just to it's surface.
The common theme we have discussed so far is satellites. Engineers design and build satellites for different types of communication. Some satellites are used for communication between people, while other satellites send data to be processed to a computer back on Earth. There are hundreds of satellites orbiting the Earth right now for various purposes, including scientific research, weather research and prediction, navigation and observation of the Earth. Actually, the Earth even has a natural satellite. Do you know what it is? (Answer: The moon!) People can communicate via satellites and even know exactly where satellites are being utilized. So, how can Spaceman Rohan, Spacewoman Tess and Maya use a satellite for their benefit? (Give time for students to answer. Possible answers may include: to find/confirm their location and to talk to each other.)
Man-made — or artificial — satellites orbit the Earth, receiving and transmitting signals. Basically, a signal is sent from a computer or a person in one location on Earth up to a satellite that is orbiting the Earth, and then back down to another person or computer somewhere else. By using orbiting satellites in space, Spaceman Rohan and Spacewoman Tess will be able to communicate with Maya by using something called a satellite phone. Can you guess how this special phone works? A satellite phone is a mobile phone that transmits (sends) signals to an orbiting satellite that receives the signal, and then transmits them to another phone. Maya's parents can definitely use a satellite phone to communicate with her. Maya can even use satellites to help her figure out exactly where she is during her trip using something called GPS (Global Positioning System). GPS is a special type of satellite that records locations of signals and sends the coordinates of that location back to another transmitter or computer. Today, we are going to learn some more about satellites and how engineers have designed them for different forms of communication.
Lesson Background & Concepts for Teachers (Return to Contents)
Figure 2 illustrates how an artificial satellite can orbit the Earth. The pull of Earth's gravity is always towards it's center, and therefore a satellite in space is always pulled "down" towards the ground. This falling, combined with a fast enough forward speed, allows the satellite to fall "around" the Earth. In theory, if a cannon is fired fairly weakly, the path of the cannonball will be that of a parabolic arc and will land perhaps a few hundred yards away. The numbered frame 1 shows a cannon using a little more gunpowder, which causes the cannonball to shoot a little bit farther. In this situation, the ball lands perhaps a few hundred miles away. We can see just a little of the Earth's curvature, but it does not really affect anything. In the second numbered frame, using a super-shooter, the cannonball is shot hard enough that it travels several thousand miles. This frame illustrates that the curvature of the Earth has had an effect. The ball travels much farther than it would have had the Earth been flat. Finally, in the third numbered frame, a mega-super-big cannon fires the cannonball at the unbelievable velocity of 5 miles/second (nearly 17,000 miles/hour; the fastest jet planes can fly 2 or 3 thousand miles/hour). The result of this shot is that the ball misses the Earth as it falls.
However, the Earth's gravitational pull causes it to both continuously change direction and continuously fall. The result is a "cannonball" which is orbiting the earth. In the absence of gravity, however, the original throw (even the shortest, slow one) would have continued in a straight line, leaving the Earth far behind.
An artificial satellite is a manufactured object that orbits Earth or something else in space on a continual basis. Satellites are used to study the universe, to help forecast the weather, to transfer telephone calls and to assist in ship and aircraft navigation. Specifically, communications satellites serve as relay stations, receiving radio signals from one location and transmitting them to another. A communications satellite can relay several television programs or many thousands of telephone calls at once. They are used to bounce messages from one part of the world to another.
Every communications satellite involves the transmission of information from an originating ground station to the satellite, followed by a retransmission of the information from the satellite back to the ground (see Figure 3). The retransmission may either be to a select number of ground stations or it may be broadcast to everyone in a large area.
Space shuttles carry some satellites into space, but most satellites are launched by rockets that fall into the ocean after the fuel is used up.
Cellular Phones and Satellite Phones
A cellular phone can be described as a very sophisticated radio. They are a type of wireless communication device that uses many small cells with a base station and a cell phone tower at the center of each cell. These cells have extensive frequencies that allow many thousands of people to use cell phones at the same time. In this process, cellular calls are transferred from base station to base station as a user travels from cell to cell. A cellular network is composed of cellular towers. In essence, when a call is placed from your cell phone, it travels by radio waves to a cellular tower that picks up the specific signal from your phone. These cellular towers are thought of as cells, with each cell able to typically pick up a signal within 10 square miles. The signal is then sent to a Mobile Telephone Switching Office (MTSO) which handles calls from several towers — called a cluster. The MTSO transfers the signal to a local phone line that sends the signal to the final destination via landline, microwave signals or satellite. The MTSO senses when the signal is becoming weak and hands your call off to the next tower — or the MTSO in the next cluster. It controls the quality of your link by keeping you connected to the best possible signal as you move from cell to cell. When you have traveled beyond the range of the towers, the signal is lost and you cannot make or receive calls.
Satellite phones do not use cells or cell towers for sending/receiving calls. Most satellite phones use Low Earth Orbiting (LEO) communication satellites. When a satellite phone is turned on, the signal goes up to any number of satellites in a compatible constellation (group of satellites) where it is then registered with the constellation. When a call is made through the satellite phone, the signal goes to the satellites and then is directed down to a ground station and then further directed to the call destination. The call can be directed to a land-line as well as a cellular network and the reverse is also true. This process allows the satellite phone to be used in the middle of no where — great distances from any cellular phone tower — and thus providing an essential form of communication for those who travel to the beyond!
Vocabulary/Definitions (Return to Contents)
Associated Activities (Return to Contents)
Lesson Closure (Return to Contents)
In this lesson, we learned that engineers design satellites for a variety of purposes, including communication. Many of these satellites are in orbit around the Earth. The satellite stays in orbit using the Earth's natural gravitational force. Rockets and other spacecraft are used to get the satellites into orbit. Satellites receive signals from one person or computer and transmit them to somewhere else. These satellites help people receive information from around the world in regards to news, weather, location, research and just the latest word from a friend. Can you remember some examples of specific satellite technologies designed by engineers? (Answers: satellite phones, global positioning satellites)
Now that we better understand some methods of communication, Spacewoman Tess, Spaceman Rohan and Maya have options available to them so they can stay in touch with Maya, even in the middle of nowhere.
Attachments (Return to Contents)
Assessment (Return to Contents)
Discussion Question: Solicit, integrate and summarize student responses.
Diagramming: Break students into groups of 2 or 3, and ask them to draw a picture of a communications satellite orbiting the Earth. Tell them to include as much detail as possible in their diagram; they should label components. The must also sketch the orbit of their satellite, and draw an arrow representing the pull of gravity down towards the center of Earth, as well as an arrow point in the direction of travel.
Post-Lesson/Lesson Summary Assessment
Diagramming/Reiteration: In their groups, have students look again at their pictures of a communications satellite orbiting the Earth. Have them discuss if there anything they need to add to the picture or take away to improve it.
Communication and Satellite Jeopardy: Break students into groups of 3 or 4. Using the chart below, ask students to pick a category and dollar amount. (Note: a copy of the chart without the questions is included in the attachments section to use an overhead or to be copied.) The answer corresponding to the dollar amount and category is read out loud. The student groups have to come up with the question (i.e., Student says: "I'll take Communication for four hundred please." The answer is read by the teacher: "This form of communication uses the computer to type and send messages that are read by their recipient on another computer via the internet." The students would have to come up with the question: "What is E-mail?")
Lesson Extension Activities (Return to Contents)
Have students investigate other methods of communication that use and do not use technology. Ask them to answer questions, such as: what types of communication did people in Asia use in the 19th century? What types of communication do specific animals use? What types of communication might people without communication technology — who are in distress — use?
Have students research what other types of satellites do and why they also might be useful. Challenge students to find pictures or other information that was generated via an Earth orbiting satellite.
Have students make models of satellites including the power-generating devices, the receiver and transmitting antenna and devices, etc.
References (Return to Contents)
Abby, Mary Kay and Reda, Ellena. "I've got Your Number: Mathematics for Telecommunications," Lab 10, The Math Works Project, Montgomery Community College, Maryland, and Dutchess Community College, New York, www.ccc.commnet.edu.
NASA's Observatorium, "Satellite Orbits," www.nasa.gov.
Oberright, John E. "Satellite, Artificial." World Book Online Reference Center, 2004, World Book, Inc., www.worldbookonline.com.
Gobalcom Satellite Communication, Decatur, IL, www.globalcomsatphone.com.
ContributorsJay Shah, Malinda Schaefer Zarske, Janet Yowell
Copyright© 2006 by Regents of the University of Colorado.
Supporting Program (Return to Contents)Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Acknowledgements (Return to Contents)
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.