Last Words on CETI and some Space Travel Basics. HNRS 228 Spring 2008 Dr. H. Geller

Transcription

1 Last Words on CETI and some Space Travel Basics HNRS 228 Spring 2008 Dr. H. Geller

2 What I Will Cover Final words about CETI Space Travel Space Environment Spaceflight Projects Spaceflight Operations

3 A Cartoon about CETI

4 What does a telescope do? Collect electromagnetic waves Collecting ability proportional to the square of the diameter of the objective Resolve electromagnetic sources Related to the atmosphere, wavelength and curvature of the objective Magnify surfaces of planets and the Moon Magnification only of Moon, Sun and planets

5 Looking Beyond the Eyes

6 Optical Telescopes Reflector Refractor

7 Different Views of Sun Sun in Hydrogen-alpha Sun in X-ray

8 Radio Astronomy Basics

9 A Little More Detail

10 Jansky s Original Radiotelescope

11 Grote Reber s Telescope

12 170 foot Diameter Radiotelescope at Green Bank, WV

13 The 100- meter Green Bank Telescope

14 Even Bigger than you Think

15 Jupiter in Radio

16 Saturn in Radio

17 3C296 Radio/Opti cal Composite

18 Smoothing Data

19 Visualizing the Data

20 Colorizing the Data

21 Must Deal With Noise

22 Worldwide Noise Sources

23 Space Environment Solar System Reference System Gravity and Mechanics Trajectories Planetary Orbits Electromagnetics

24 Solar System Considerations Distance From Sun Energy, temperature, condensation of matter Hostile Environment Radiation (gamma ray) Radiation (x-ray) Radiation (UV)

25 Coordinate Reference Systems Geographic Celestial Precession

26 Gravity and Mechanics Orbits Kepler Newton

27 Orbital Transfers

28 Planets and Gravity

29 Flight Projects Mission Inception Experiments Spacecraft Classification Telecom Onboard Systems Science Instruments Navigation

30 Mission Inception

31 Instruments

32 Telecommunications

33 Onboard Systems

34 Operations Launch Cruise Encounter Extended Operations Deep Space Network

35 Launch

36 Cruise

37 Encounter

38 Deep Space Network

39 Interstellar Spaceflight Considerations

40 THE PHYSICS AND MATH OF SPACE TRAVEL For a spacecraft accelerating at a rate a, the velocity v reached and distance x traveled in a given interval of time t is: v(t) = x(t) = c2 a at () 1+ at 2 c () 1+ at 2 c Accelerating at 1g = 9.8 m/s 2 : 1 c = speed of light Crew Duration (yr) Earth Duration (yr) Range (pc) nearest stars ,000 5,400 - center of Galaxy

41 iclicker Question What does the letter c stand for in the equations shown? A B C Speed of sound Speed of light A constant of unknown value D A generic constant E Speed of time

42 Considerations for Interstellar Travel Three considerations for interstellar travel 1. Imagination - not a problem today 2. Technology - constantly improving 3. Laws of Nature - may provide ultimate limits Unless there is a MAJOR revolution in technology - rockets are all we have. Rocket engines most efficient when v~v exhaust. Going faster makes them less efficient. Rockets must accelerate not only the payload but also all the fuel they carry!

43 For a final velocity V f, a ratio of initial mass (payload plus fuel) to final mass (ditto) M, and exhaust velocity W, then: V f c 1 M 2W /c = 1+ M 2W /c For V f < 0.1c, then M = e = For a round trip, where 4 legs of the trip each require a factor of M: M RT = M 4 Suppose we took a round trip to a star 5 pc away: Via Chemical Rocket Via Nuclear Rocket V f / c ~ 10-5 V f / c ~ 10-1 M RT = 55 (=e 4 ) M RT = 55 t = 3 million years t = 300 years

44 iclicker Question What does the letter e represent in these equations? A B C Speed of light The natural logarithm base An irrational number D A rational number E Both B and C are correct

45 Energy Costs of Interstellar Travel Example: Controlled Nuclear Fusion (can t do this yet!) 1000 ton payload 55,000 tons fuel in the form of H, dissociated from 440,000 tons of H 2 O ice mined from one of Saturn s moons Dissociating 440,000 tons of ice requires Joules (Wattsec) = 3x10 9 kw-hours = 3000 GW-h ~ 0.1% total annual energy consumption in the USA But it won t go very fast.

46 iclicker Question When do you think the USA will develop a feasible nuclear fusion reactor? A B C Within the next 10 years Within the next 20 years Within the next 30 years D Within the next 50 years E Never

47 Matter/Antimatter Rockets W = c V f c = 1 M M 2 ( ) x ( dist.) = c 2 M + M a T ( earth) = 2 c M M 1 a ( ) t ( crew ) = c a ln(m ) Illustration - flat-out acceleration (No stopping, drifting, or return). V f /c = 0.1 V f /c = 0.98 V f /c = 0.1 V f /c = 0.98 a = 0.01 g a = 0.01 g a = 1 g a = 1 g M = 1.1 M = 9.95 M = 1.1 M = 9.95 T crew = 9.7 y T crew = 230 y T crew = 0.1 y T crew = 2.3 y t earth = 39 y t earth = 2000 y t earth = 0.4 y t earth = 20 y The fuel supply needed to reach V f / c=0.98 for a round-trip (M RT =M 4 =9,800) 10-ton payload requires 100,000 tons matter-antimatter mc 2 = E = Joules About 1 million times the annual energy consumption in the USA

48 iclicker Question What is the value of v2/c2 when v is very small compared to c? A Near zero B Near one C Effectively infinite

49 iclicker Question What is the value of (1 - v 2 /c 2 ) when v is very small compared to c? A B C Effectively zero Effectively one Effectively infinite

50 iclicker Question What is the value of (1 - v 2 /c 2 ) when v is approaching the speed of light? A B C Effectively zero Effectively one Effectively infinite

51 iclicker Question What is the value of 1 / (1 - v 2 /c 2 ) when v is approaching the speed of light? A B C Effectively zero Effectively one Effectively infinite

52 Project Orion - detonate nuclear bombs to provide thrust (motion picture Deep Impact )

53 iclicker Question Do you support the use of nuclear weapons for space travel? A B Yes No

54 Solar Sailing Solar wind only reaches 0.003c, need to use sunlight Planetary Society - Cosmos 1 June 21, 2005, launched on Volna rocket from Russian sub. Failed to reach orbit

55 Suppose we start at 1 AU from the Sun (i.e. Earth's orbit), a sail area A and a payload (plus sail mass) M. v = 2x R 1AU x = AL Sun M 2πc 10-ton payload, sail 1000 km x 1000 km in size. v is then only 0.04 c. It would take roughly 3/0.04 = 75 years to get anywhere, i.e. 3 ly away (ignoring deceleration & stopping) Oops! The SAIL ALSO has mass! A 1000 km x 1000 km. A gold leaf sail 1 atom thick (a real sail would have to be much thicker) would have a mass of 170 tons (it effectively becomes the payload), and so the top speed is c. Now it takes over 300 years to get anywhere! Science fiction story - sails from star to star in a day or two (1/300 th of a year), This is impossible by a factor of 300 x 300 = 90,000 times! Such trips are, therefore, unrealistic fantasy.

56 Yet other "Possibilities" for Interstellar Flight Ships pushed by X-ray lasers A rear reflector plays the same role to a powerful planet-based light source as the solar sail did to sunlight. Interstellar Ramjets This uses interstellar gas as fuel. You no longer need to carry it with you. Avoid low-density regions? How do you get the fuel into the engine? FTL (Faster-Than-Light) Warp drives, etc. Contrary to all known physics. Sorry.

57 Exploration by Proxy - Robotics Von Neumann Machines/Probes - self-replicating: 1. Travel to a destination 2. Mine resources 3. Make copies of itself 4. Send copies out to new destination 5. Spread though the Galaxy as exponentially growing fleet of machines that consume raw resources Is this really a good idea?

58 Commentary on Interstellar Space Travel Unless there is a major revolution in our understanding of the laws of nature, space travel is likely to be confined to the solar system, unless someone wants to launch "generation ships" where only their distant descendents will see arrive somewhere. IF interstellar travel were to become a reality, but still limited to relatively slow travel, all trips will be 1-way. For M="e", M 1way = M 2 = 7.4, while M RT = M 4 = 55. Also, why return? Everyone you know back on Earth will be dead. You will be an anachronism (how would your great-great-great-great grandparents fit into today's society?), or worse, a specimen in a zoo.

59 iclicker Question You take a spaceship to Alpha Centaurus and return to Earth. Which of the following is the case when you return to Earth? A All who knew you will be dead. B There will be no time noticed to have passed on Earth. C All who knew you will be alive. D This is not possible. D More information is needed.

60 Another Hazard of interstellar flight A 1-mm grain (mass of grams) hit by a spacecraft traveling 0.1 c - energy (E=1/2 mv 2 ) of 5.4x10 9 J. Same energy as a 1-ton object hitting at Mach 9.5 (7,000 mi/hr)!! Unless there is a way to screen out all interstellar dust, the spacecraft will be easily destroyed.

61 iclicker Question If you double the mass of a moving object, its kinetic energy will A be doubled. B be tribled. C be quadrupled. D decrease. E Cannot be determined, more information is needed.

62 iclicker Question If you double the mass of a moving object, its kinetic energy will A be doubled. B be tribled. C be quadrupled. D decrease. E Cannot be determined, more information is needed.

63 Past "Attempts" at Physical Contact The Pioneer 10 spacecraft - plaque The Voyager 1 and 2 spacecraft - gold record (and stylus for "playing") with images and sounds of Planet Earth.

64 iclicker Question Do you believe it s easy to construct a message for another civilization? A B True False

65 More Scenes of Earth

66 Voyager Trajectories Interstellar Spacecraft Neither of these are targeted at any specific star. Their trajectories were constrained by their science missions to the jovian planets.

67 Will the Pioneer & Voyager Spacecraft ever get anywhere? To come within 1 AU of a star & accidentally be found: Mean Free Path (how far to go in order to hit something) x=1/(σn) n = number of systems per pc 3 σ = "target area" to be hit. (For a circle, the target area is π times the radius (here 1 AU) squared, which we will express in pc 2 to get the units we need.) n = 2.5x10 3 stars / ly 3 = 0.1star / pc 3 σ = π 1AU ( ) 2 = π ,265 pc = π pc 2 x = 1 σn = 1 ( 0.1pc 3 )7.5x10 11 pc 2 ( ) = 1.3x1011 pc The MW is less than 10 5 pc across (and less than 10 3 pc thick) Changes of hitting are less than 10-6 or %. Using Neptune s orbit as target - goes up to a whopping 0.1%.

68 iclicker Question Can the previous calculation be applied to the likelihood of intercepting a radio signal from another civilization? A Yes B No