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Last Words on SETI & CETI and some Space Travel Basics

HNRT 228SPRING 2015Dr. H. Geller

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What I Will Cover Today

Final words about CETISpace TravelSpace EnvironmentSpaceflight ProjectsSpaceflight Operations

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iClicker Question

About how many extrasolar planets have officially been detected to date? A between 10 and 100 B between 100 and 1000 C more than 1000

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iClicker Question

How have we detected most extrasolar planets discovered to date (before Kepler mission)? A Transits B Hubble Space Telescope images C the Doppler related technique

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iClicker Question

Which technique does the Kepler mission use to search for Earth size planets around other stars? A Transits. B The astrometric technique. C The Doppler related technique. D Gravitational lensing.

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iClicker Question

Nearly all the extrasolar planets discovered to date are A terrestrial-like planets. B jovian-like planets. C large, icy worlds.

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iClicker Question

The end result of a calculation with Drake equation is intended to be an estimate of A the number of worlds in the galaxy

on which life has arisen. B the number of worlds in the galaxy

on which intelligence has arisen. C the number of worlds in the galaxy

on which civilizations are transmitting signals now.

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iClicker Question

Which of the following statements is true about the terms in the Drake equation? A Astronomical research will soon give us

firm values for all of the terms. B Some of the terms depend on

sociology, and cannot be determined by astronomers alone.

C We already know the terms of the equation to an accuracy within a factor of 2.

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iClicker Question

The fact that marine predators like dolphins and sharks have similar shapes despite different ancestry is an example of A convergent evolution. B narrow bandwidth. C spontaneous creation.

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iClicker Question

Which of the following would lead an animal to a higher encephalization quotient (EQ) as it evolved? A Growth in both body size and brain size. B Growth in body size but not in brain size. C Growth in brain size but not in body size.

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iClicker Question

Two-way conversation with other societies is probably unlikely, even if we make contact. This is mainly because A aliens won’t speak our language. B it might be dangerous to get in touch. C the time it takes for signals to cross

the distance to them could be centuries or more.

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iClicker Question

One reason the scientists doubt that crop circles have alien origin is A they are always beautiful. B they can be easily made by

humans. C their appearance is not correlated

with sightings of bright lights.

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A Cartoon about CETI

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What does a telescope do?

Collect electromagnetic waves Collecting ability proportional to the

square of the diameter of the objectiveResolve 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

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Looking Beyond the Eyes

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Optical Telescopes

Reflector

Refractor

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Different Views of Sun

                                                 

Sun in Hydrogen-alpha Sun in X-ray

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Radio Astronomy Basics

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A Little More Detail

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Jansky’s Original Radiotelescope

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Grote Reber’s Telescope

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170 foot Diameter Radio-telescope at Green Bank, WV

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The 100-meter Green Bank Telescope

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Even Bigger than you Think

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Jupiter in Radio

Saturn in Radio

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3C296 Radio/Optical Composite

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Smoothing Data

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Visualizing the Data

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Colorizing the Data

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Dealing With Noise

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Worldwide Noise Sources

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The Space Environment

Solar SystemReference SystemGravity and MechanicsTrajectoriesPlanetary OrbitsElectromagnetics

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Solar System Considerations

Distance From Sun

Energy, temperature, condensation of matter

Hostile Environment Radiation

(gamma ray) Radiation (x-ray) Radiation (UV)

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Coordinate Reference Systems

GeographicCelestialPrecession

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Gravity and Mechanics

Orbits Kepler Newton

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Orbital Transfers

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Planets and Gravity

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Flight Project Considerations

Mission InceptionExperimentsSpacecraft ClassificationTelecomOnboard SystemsScience InstrumentsNavigation

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Mission Inception

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Instruments

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Telecommunications

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Onboard Systems

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Operations Considerations

LaunchCruiseEncounterExtended OperationsDeep Space Network

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Launch Vehicles

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Cruise Portion of Mission

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Encounter Portion of Mission

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Need for Deep Space Network

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Interstellar Spaceflight

Considerations

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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) at

1 atc 2

x(t) c2

a1 at

c 2

1

c = speed of light

Crew Duration (yr) Earth Duration (yr) Range (pc) 1 1 0.0210 24 3 - nearest stars20 270 4240 36,000 5,400 - center of Galaxy

Accelerating at 1g = 9.8 m/s2:

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iClicker Question

What does the letter “c” stand for in the equations shown?

A Speed of soundB Speed of lightC A constant of unknown valueD A generic constantE Speed of time

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Considerations for Interstellar Travel

Unless there is a MAJOR revolution in technology - rockets are all we have.

Three considerations for interstellar travel

1. Imagination - not a problem today

2. Technology - constantly improving

3. Laws of Nature - may provide ultimate limits

Rocket engines most efficient when v~vexhaust. Going faster makes them less efficient.Rockets must accelerate not only the payload but also all the fuel they carry!

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For a final velocity Vf, a ratio of initial mass (payload plus fuel) to final mass (ditto) M, and exhaust velocity W, then:

Vfc

1 M 2W /c

1 M 2W /c

For Vf < 0.1c, then M = “e” = 2.7182…..

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 Vf / c ~ 10-5 Vf / c ~ 10-1

MRT = 55 (=e4) MRT = 55 t = 3 million years t = 300 years

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iClicker Question

What does the letter “e” represent in these equations?

A Speed of lightB The natural logarithm baseC An irrational numberD A rational numberE Both B and C are correct

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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 H2O ice mined from one of Saturn’s moons

Dissociating 440,000 tons of ice requires 1016 Joules (Watt-sec) = 3x109 kW-hours = 3000 GW-h ~ 0.1% total annual energy consumption in the USA

But it won’t go very fast.

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iClicker Question

When do you think the USA will develop a nuclear fusion reactor that produces more electricity than it consumes?

A Within the next 10 yearsB Within the next 20 yearsC Within the next 30 yearsD Within the next 50 yearsE Never

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Matter/Antimatter RocketsW = c

Vfc

1 M 2

1 M 2

x(dist.) c2

2aM M 1 2

T (earth) 2c

aM M 1

t(crew) c

aln(M )

Illustration - flat-out acceleration (No stopping, drifting, or return).

Vf/c = 0.1 Vf/c = 0.98 Vf/c = 0.1 Vf/c = 0.98a = 0.01 g a = 0.01 g a = 1 g a = 1 gM = 1.1 M = 9.95 M = 1.1 M = 9.95Tcrew = 9.7 y Tcrew = 230 y Tcrew = 0.1 y Tcrew = 2.3 ytearth = 39 y tearth = 2000 y tearth = 0.4 y tearth = 20 y

The fuel supply needed to reach Vf / c=0.98 for a round-trip (MRT=M4=9,800)10-ton payload requires 100,000 tons matter-antimatter

mc2 E 1025 Joules

About 1 million times the annual energy consumption in the USA

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iClicker Question

What is the value of v2/c2 when v is very small compared to c?

A Near zeroB Near oneC Effectively infinite

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iClicker Question

What is the value of (1 - v2/c2) when v is very small compared to c?

A Effectively zeroB Effectively oneC Effectively infinite

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iClicker Question

What is the value of (1 - v2/c2) when v is approaching the speed of light?

A Effectively zeroB Effectively oneC Effectively infinite

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iClicker Question

What is the value of 1 / (1 - v2/c2) when v is approaching the speed of light?

A Effectively zeroB Effectively oneC Effectively infinite

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

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iClicker Question

Do you support the use of nuclear weapons for space travel?

A YesB No

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Solar Sailing

Planetary Society - Cosmos 1

June 21, 2005, launched on Volna rocket from Russian sub. Failed to reach orbit

Solar wind only reaches 0.003c, need to use sunlight

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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

R1AU

x ALSunM 2c

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 0.009 c. Now it takes over 300 years to get anywhere!

Science fiction story - sails from star to star in a day or two (1/300th of a year), This is impossible by a factor of 300 x 300 = 90,000 times! Such trips are, therefore, unrealistic fantasy.

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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.

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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?

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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", M1way = M2 = 7.4, while MRT = M4 = 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.

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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.

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Another Hazard of interstellar flight

A 1-mm grain (mass of 0.012 grams) hit by a spacecraft traveling 0.1 c - energy (E=1/2 mv2) of 5.4x109 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.

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iClicker Question

If you double the mass of a moving object, the force needed to accelerate it would

A be doubled.B be tripled.C be quadrupled.D decrease.E Cannot be determined, more

information is needed.

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iClicker Question

If you double the mass of a moving object, its kinetic energy will

A be doubled.B be tripled.C be quadrupled.D decrease.E Cannot be determined, more

information is needed.

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iClicker Question

If you double the velocity of a moving object, its kinetic energy will

A be doubled.B be tripled.C be quadrupled.D decrease.E Cannot be determined, more

information is needed.

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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.

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iClicker Question

Do you believe it is easy to construct a message for another civilization?

A TrueB False

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More Scenes of Earth from Voyager Catalog

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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.

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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/(n)n = number of systems per pc3

= "target area" to be hit. (For a circle, the target area is times the radius (here 1 AU) squared, which we will express in pc2 to get

the units we need.) n 2.5x10 3stars / ly3 0.1star / pc3

1AU 2 1

206,265pc

2 2.4 10 11 pc2

x 1

n

1

0.1pc 3 7.5x10 11 pc2 1.3x1011 pc

The MW is about 105 pc across (and about 103 pc thick)

Chances of “hitting” are less than 10-6 or 0.0001%. Using Neptune’s orbit as target - goes up to a whopping 0.1%.

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iClicker Question

Can the previous calculation be applied to the likelihood of intercepting a radio signal from another civilization?

A YesB No

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19 November 2014New Horizons just beyond orbit of Neptune20.94 AU from Sun; 1.89 AU from Pluto