UNIT
5: LESSON 3
SATELLITE SCIENCE
SUBJECT: Science
OBJECTIVE: Students will construct a model of a Global
Positioning System (GPS) satellite, and be introduced to GPS application
in agriculture.
MEASUREMENT: Students will have a working knowledge of the components
of a satellite, and will know that a GPS satellite sends signals to
earth for pinpointing location, and that GPS is used by farmers to make
maps of their fields.
BACKGROUND FOR TEACHERS:
A satellite is any object that orbits or revolves around another object.
For example, the moon is a satellite of the Earth, and Earth is a satellite
of the Sun.
Man-made satellites are increasingly important in our world. Their
uses range from media and communications, to weather, scientific research,
navigation and more. This unit is emphasizing the navigational uses
of satellites, primarily GPS.
GPS, which stands for Global Positioning System, is the only system
able to show you your exact location on the Earth anytime, in any weather,
anywhere. 24 GPS satellites, the first launched in 1978, orbit at 11,000
nautical miles above the earth. They continuously transmit signals that
are monitored by ground stations located worldwide. These signals can
be detected by anyone with a GPS receiver!
Each satellite takes 12 hours to complete one orbit around the earth.
They are equipped with very precise clocks that keep accurate time to
within three nanoseconds-that's 0.000000003, or three billionths, of
a second. This precision timing is important because the receiver on
the ground must determine exactly how long it takes for signals to travel
from each GPS satellite. The receiver uses this information to calculate
its exact position.
The GPS receiver (in your hand, on your car, on the farmer's combine,
etc.) calculates the difference between the time the signal is sent
and the time it is received, and multiplies that by the speed of light.
This allows it to calculate the distance to the satellite. It takes
these readings simultaneously from three to four separate satellites,
each one identifying a region on the earth. The intersection of these
regions pinpoints the exact latitude, longitude and altitude of the
receiver.
Global Positioning Systems have revolutionized the ability of people
to find or document their location on the face of the earth. As GPS
receivers are made smaller and at lower cost, they will begin to appear
everywhere in our daily lives!
STUDENT ACTIVITIES:
1. Ask students to read the story David Explores
New Worlds. Ask if any of them have ever seen a satellite moving
across the night sky as David did. Ask if they have ever seen a picture
of a satellite (David had seen one in his Weekly Reader). Talk to them
about the "satellite receiver" that Kevin attached to the backpack he
put on David. (A "receiver" receives the signals sent through space
by the satellites.) Reread the paragraph in which Kevin says ".there
are 24 GPS satellites that circle the earth.and the receiver needed
to get a signal from at least three of them to pinpoint any location
on earth."
2. Explain that there are two basic parts of all satellites-the "payload"
and the "bus." The payload is all the equipment a satellite needs to
do its job. This can include antennas, cameras, radar, and electronics.
The payload is different for every satellite. For example, the payload
for a weather satellite includes cameras to take pictures of cloud formations,
while the payload for a communications satellite includes large antennas
to transmit TV or telephone signals to Earth.
The bus is the part of the satellite that carries the payload and all
its equipment. It holds all the parts of the satellite together, and
provides the power and propulsion to the spacecraft. The bus also contains
the equipment used by the satellite to communicate with Earth.
See http://www.thetech.org/exhibits_events/online/satellite/
for illustrations of many types of satellites, as well as an interactive
satellite "construction set!"
3. Tell students they will be creating a model of a satellite, preferably
a GPS satellite. Encourage them to be creative with their choice of
materials. Tinker Toys will work, as will toothpicks and marshmallows,
wood and paper, straws and clay, etc.
Pictures of GPS satellites can be found at
http://www.thetech.org/exhibits_events/online/satellite/3/3d/3d.1.html
http://www.aero.org/publications/GPSPRIMER/Satellites.html
4. Ask students to use their models to explain how GPS works.
For younger grades: 24 students with their satellites can "orbit" a
central object (the earth), each satellite giving off a unique "signal."
If the person on the earth has a receiver that knows the location of
each satellite in relation to the earth, they can use that unique "signal"
to figure out where they are on the earth.
Older students might enjoy a Sherlock Holmes story that illustrates
the principles used in calculating location using signals that travel
through space at http://www.wowinfo.com/gps/chapter1.htm
or another story about two brothers traveling through time at http://www.wowinfo.com/gps/chapter4.htm.
Both illustrate the principles by which GPS satellites aid in pinpointing
geographic locations.
5. This NASA web site has more pictures and interactive lesson plans
about satellites: http://www.octopus.gma.surfing.satellites/.
This Trimble site is a tutorial about GPS for older students: http://www.trimble.com/gps.
6. See Lesson 2 to learn about GPS applications in agriculture.
