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ABM Treaty (cont’d) Arguments for Withdrawal

ABM Treaty (cont’d) Arguments for Withdrawal. Allow U.S. to develop a ballistic missile-defense system to protect against rogue nations developing weapons. ABM Treaty (cont’d) Arguments against Withdrawal. “Fatal blow” to the Nuclear Non-Proliferation Treaty.

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ABM Treaty (cont’d) Arguments for Withdrawal

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  1. ABM Treaty (cont’d)Arguments for Withdrawal • Allow U.S. to develop a ballistic missile-defense system to protect against rogue nations developing weapons. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  2. ABM Treaty (cont’d)Arguments against Withdrawal • “Fatal blow” to the Nuclear Non-Proliferation Treaty. • Would lead to a world without effective legal limits on nuclear growth. • Reaction from Russia and China would hinder other arms negotiations (but offsetting pluses have made that reaction milder than expected). Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  3. Launch Windows and Times Above: September 1997—The Shuttle Endeavour waits for launch time. Left: April 1998—The Columbia Shuttle propels off the launch pad and accelerates into orbit. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit SECTION 7.2

  4. Getting into Orbit • To meet the conditions of a space mission, launch-team members need to: • Launch the spacecraft from a specific place. • Launch the spacecraft at a specific time. • Launch the spacecraft in a specific direction. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  5. Launch WindowsDefinition • An opportunity to launch a satellite from Earth directly into the desired orbit from a given launch site. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  6. Launch WindowsConcept • A launch window is an opportunity to launch a satellite from Earth directly into the desired orbit from a given launch site. • We can always launch into parking orbit and then perform a Hohmann Transfer to put a spacecraft in the desired orbit, but this is complicated and requires more fuel. • A launch window means getting directly into the desired orbit without having to maneuver. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  7. Launch WindowsConcept (cont’d) • Launch windows are like bus schedules. • Launch windows normally cover a period of time. • Launch vehicles must follow trajectory rules by Newton’s Laws of Motion. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  8. Launch Windows and Launch Time Columbia accelerates into orbit on STS-87 Endeavour clears the tower on STS-47 Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  9. Launch Time • To determine what time a launch site passes into a launch window, we need a new definition of how to tell time. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  10. Orbital Racetrack • If the car is one mile past the starting line, and the pit is one-half mile past the starting line, then the car must be one-half mile from the pit. • Given the car’s speed, we can figure out how long before the car reaches the pit. • Knowing this rate allows us to determine the best time to launch a spacecraft directly into orbit, or the launch window. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  11. Launch TimeSolar Time • The spacecraft must launch in a specific direction: • The vernal equinox direction is the main direction we use to describe the motion of spacecraft that orbit the Earth. • Because the Earth and the launch site rotate, it’s an easy reference from which to measure the angular distance between the orbital plane and our launch site. • Knowing this angular distance and Earth’s rotation rate, we can figure out the best times to launch. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  12. Launch TimeSolar Time (cont’d) • Greenwich Mean Time (GMT)— is the basis for the time kept on watches to handle daily business. • GMT is the mean solar time for the Prime Meridian (Greenwich, UK). • All other time zones are GMT plus or minus a certain number of hours. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  13. Launch TimeSolar Time (cont’d) The Royal Observatory in Greenwich, England Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  14. Launch TimeSolar Time • Apparent Solar Day • An Apparent Solar Day is the time between successive passages of the Sun overhead, which is from noon one day to noon the next day. • Apparent solar day’s length varies throughout the year (Earth’s orbit around the Sun is elliptical). • Average of the lengths for one year gives us a mean solar day. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  15. Launch TimeSidereal Time • Because there is a problem using solar time, the reference point for GMT rotates with the Earth, we seek an inertial (fixed) reference point: • We use the same reference point as the geocentric-equatorial coordinate frame—vernal equinox direction. • A sidereal day is the time between the subsequent passings of the vernal equinox direction overhead a particular longitude line. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  16. Launch TimeSidereal Time (cont’d) • Because the inertial reference vernal equinox is so far away, the length of a sidereal day corresponds to exactly 360° of Earth rotation. • A sidereal day is slightly shorter than an apparent solar day: 23 hours, 56 minutes, 4 seconds in solar time. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  17. Launch TimeSidereal Time (cont’d) • We can tell sidereal time in degrees. • Earth rotates 360° in 24 hours. • So, 3 a.m. (0300) is 45° of Earth’s full rotation. • Similarly, noon (1200) is 180° and 6 p.m. (1800) is 270°. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  18. Launch TimeLocal Sidereal Time (LST) • Time since the first point of constellation Aries was last overhead. • Can be expressed in time or angle • If Earth has rotated 90° since the local longitude line was aligned with the vernal equinox direction, LST is: • 90° • 0600 hrs • Mission planners mathematically convert LST back to GMT for launch timing. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  19. Launch TimeLocal Sidereal Time (LST) Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  20. Launch TimeSolar Time versus Sidereal Time Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  21. Summary • Intercontinental Ballistic Missiles (ICBMs) • Understanding Ballistic Missiles and Trajectories • Conic Sections • ICBM Trajectories • ICBM Development • The Anti-Ballistic Missile Treaty • Launch Windows and Times • Getting into Orbit • Launch Windows • Launch Time Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

  22. Next • For some payloads, the mission requires us to get a payload into orbit and get it back to Earth from space. • On the next lesson we’ll tackle the last part of a space journey: atmospheric re-entry. Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit

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