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Lesson 5.2: How Does a Satellite Stay in Orbit? Objectives: - Students will learn about placing a satellite into an orbit.
- Students will learn about the forces needed to keep an object in orbit.
- Students will learn that satellites orbit in paths that are elliptical and will learn about properties of ellipses.
- Students will learn Kepler's 3
^{rd}Law of Planetary Motion
Estimated Lesson Time: Four classes (4 hours) Classroom strategies: Have students add more "firsts" to timeline. Focus on the ability of man to put men and women in orbit by noting the first people to go into space orbit: Yuri Gagarin (April 12, 1961) circled Earth in Vostok-1, Alan Shepard (May 6, 1961) went suborbital to space in Frienship-1, John Glenn (Feb. 20, 1962) orbited Earth three times in five hours on Friendship-7 and was the first American in orbit; Valentina Tereshkova was first woman to orbit on Vostok-6 (June 16, 1963); Sally Ride (June 1983) was first American woman in space on Space Shuttle. Use timeline as motivation for discussion of how things stay in orbit. Use activities to reinforce elliptical orbits and orbital motions. Science Background Information: Johannes Kepler was the first to accurately describe the mathematical shape of the orbits of planets. Our Moon and the planets travel in orbits that are very close to being circular. A circle is a special kind of ellipse. By definition, an ellipse is a geometrical figure that has two foci. In a circle, both foci of the ellipse are at the same point. Orbits of artificial satellites can be elliptical or circular. A satellite that stays in orbit with just the right speed will retrace its path, just like the Moon continues to orbit the Earth. Artificial satellites also need just the right speed to stay in orbit around the Earth. Those with a smaller speed will return to the Earth as gravity pulls it down, those with a large enough speed can actually leave the Earth's gravitational tug and travel into deep space. To make this point, imagine a baseball pitcher standing on a 100-mile-high mound above the Earth. If the pitcher throws the ball horizontally at 100 miles/hour, the speed is not great enough to stay in orbit so the ball will travel outward some distance but then fall back to Earth. Now, if the pitcher throws the ball at approximately 18,000 miles/hour straight out, then the ball will have just the right speed to orbit the Earth. In this case, the ball will circle the Earth and hit the pitcher in the back of the head one orbital period later (about 90 minutes later)! You can imagine it as continuously falling around the Earth in a circle. Vocabulary: - Orbit -
- Ellipse -
- Focus (Foci) -
- Period - the time needed for a satellite to complete one orbit
- Elliptical -
Materials and Equipment: String, push pins, pens, paper, corkboard, ball (object to throw), whiffle ball Advance Preparation: Gather appropriate materials. Activities:
Homework Assignment: Have students research and determine what objects the following satellites (both artificial and natural) orbit around: the Moon (the Earth), the Earth (the Sun), Halley's Comet (the Sun), Io (Jupiter), Mimas (Saturn), Galileo (an artificial satellite orbiting Jupiter), Phobos (Mars), Charon (Pluto), GPS (Earth), Vesta (an asteroid in orbit around the Sun), Triton (Neptune). (Use a worksheet for this exercise)
References: Blueprint For Space, (Smithsonian Institute Press) Spaceflight (Smithsonian Guides) StarDate, Guide to the Solar System (University of Texas, Austin) Need references for Ptolemy and Kepler Connections: Math enrichment: Kepler's 3 Answer: First, solve for the constant k = (1.5
7 April 1999
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