Bit of Administration ….

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

3. D Newton’s Law of Gravity 2 1 Fg Fg M1 = Mass of object 1 (grams) M2 = Mass of object 2 (grams) D = Distance between objects (cm) G = 6.67x10-8 cm3/sec2/gm

4. Newton’s Law of Gravity Kepler’s 3rd Law In order for planet P to travel in a circle around the Sun… Central Force = Gravitational Force A P S 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 P C

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

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 Mcentral >> Morbiting object A orb C P = Period of Orbit (years) A = Semi-Major Axis of Orbit (AU) Mc = Mass of central body (Solar Masses, Mo)

9. Newton’s Law of Gravity Kepler’s 3rd Law - Weighing the Solar System 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 A

10. Astronautics

11. Astronautics

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

13. Astronautics

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

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

18. Astronautics

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

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

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

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

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

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

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

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

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

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

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

32. ConcepTest! • 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 • B) South • C) Southwest • D) West