2. Bit of Administration …. 6-Week Test6-Week Test –TONIGHT! 7:15-8:30, 3425 Sterling –55 multiple choice questions 2/3 conceptual use of the material2/3 conceptual use of the material 1/3 recall1/3 recall –All material in lecture, discussion, homeworks through Wednesday; readings on that material through Wednesday; readings on that material Reading Reading –Download NASA article from www.astro.wisc.edu/astro104

3. Newton’s Law of Gravity 1 2 FgFg FgFg M 1 = Mass of object 1 (grams) M 2 = Mass of object 2 (grams) D = Distance between objects (cm) G = 6.67x10 -8 cm 3 /sec 2 /gm D

4. Newton’s Law of Gravity Kepler’s 3rd Law A S P In order for planet P to travel in a circle around the Sun… Central Force = Gravitational Force Velocity depends only on distance, not on mass of planet Velocity decreases w. greater distance

5. Newton’s Law of Gravity Kepler’s 3rd Law A C P

6. Newton’s Law of Gravity Kepler’s 3rd Law In general, in units of cm, sec, gms For the Earth In general, in units of AU, years, solar masses For objects orbiting the Sun (M c = 1 M o ) A C P 1 Solar Mass

7. Nature and nature’s laws Lay hid in the night God said, “Let Newton be!” And all was light! - Alexander Pope

8. Newton’s Law of Gravity Kepler’s 3rd Law - General Form for M central >> M orbiting object P = Period of Orbit (years) A = Semi-Major Axis of Orbit (AU) M c = Mass of central body (Solar Masses, M o ) A C orb

9. Newton’s Law of Gravity Kepler’s 3rd Law - Weighing the Solar System A Suppose a satellite is in orbit 8600 km above the Earth’s surface. Its period is 0.2 days. What is the mass of the Earth? A = 15,000 km = 10 -4 AU (Earth radius is 6400 km) P = 0.2 days = 6 x 10 -4 yr

10. Astronautics

11. Astronautics

12. Astronautics What makes rockets go? What makes rockets go? Newton’s 3rd Law Newton’s 3rd Law

13. Astronautics

14. Astronautics Burn fuel to create hot gas Burn fuel to create hot gas Allow gas to escape Allow gas to escape Action of escaping gas => reaction of rocket motion Action of escaping gas => reaction of rocket motion Important! The rocket does not push against anything - Important! The rocket does not push against anything - this physics equally valid in the vacuum of space this physics equally valid in the vacuum of space What makes rockets go? What makes rockets go? Newton’s 3rd Law Newton’s 3rd Law

16. Astronautics Before launch, the vast majority of mass to lifted is fuel! Before launch, the vast majority of mass to lifted is fuel!

18. Astronautics

20. Astronautics Launch Trajectory Earth Atmosphere (not to scale)

21. Astronautics Launch Trajectory Earth Earth Rotation 10,800 km/hr

22. Astronautics Launch Trajectory into Orbit Earth Earth Rotation 10,800 km/hr 28,800 km/hr for orbit at Earth’s surface

24. In you were going to point in the direction that the Earth is rotating*, you would point A) To the East A) To the East B) To the West B) To the West * Or put another way, the direction that you are moving right now because of the rotation of the Earth. ConcepTest!

25. Cape Canaveral Earth Rotation 10,800 km/hr

26. Astronautics Special Orbits Special Orbits Geosynchronous Geosynchronous 36,000 km Mid-Earth Orbit Mid-Earth Orbit 20,000 km Low-Earth Orbit Low-Earth Orbit 200 km NP

27. In which orbit does a satellite have the longest period? A) Low-Earth orbit A) Low-Earth orbit B) Mid-Earth orbit B) Mid-Earth orbit C) Geo-synchronous orbit C) Geo-synchronous orbit D) Depends on the mass of the satellite D) Depends on the mass of the satelliteConcepTest!

28. Astronautics Special Orbits Special Orbits Geosynchronous Geosynchronous 36,000 km 24 hrs Weather, Surveillance Mid-Earth Orbit Mid-Earth Orbit 20,000 km 12 hrs GPS, Communications Low-Earth Orbit Low-Earth Orbit 200 km 90 min Space Shuttle, Hubble Space Telescope NP

29. In which orbit is a satellite moving faster? A) Low-Earth orbit (Space Shuttle) A) Low-Earth orbit (Space Shuttle) B) Mid-Earth orbit (GPS satellites) B) Mid-Earth orbit (GPS satellites) C) Geo-synchronous orbit (Weather satellites) C) Geo-synchronous orbit (Weather satellites) D) Depends on the mass of the satellite D) Depends on the mass of the satelliteConcepTest!

30. Astronautics Special Orbits Special Orbits Mid-Earth Polar Orbit Mid-Earth Polar Orbit 20,000 km 12 hrs Spy Satellites, GPS

31. Cape Canaveral Earth Rotation 10,800 km/hr Vandenberg AFB

32. If you are going to launch a satellite into a polar orbit from Vandenberg AFB, in which of these directions would you launch? A) Southeast A) Southeast B) South B) South C) Southwest C) Southwest D) West D) WestConcepTest!