Last Words on CETI and some Space Travel Basics

HNRS 228Spring 2008Dr. H. Geller

What I Will Cover

Final words about CETISpace TravelSpace EnvironmentSpaceflight ProjectsSpaceflight Operations

A Cartoon about CETI

What does a telescope do?

Collect electromagnetic wavesCollecting ability proportional to the square of the diameter of the objective

Resolve electromagnetic sourcesRelated to the atmosphere, wavelength and curvature of the objective

Magnify surfaces of planets and the MoonMagnification only of Moon, Sun and planets

Looking Beyond the Eyes

Optical Telescopes

Reflector

Refractor

Different Views of Sun

Sun in Hydrogen-alpha Sun in X-ray

Radio Astronomy Basics

A Little More Detail

Jansky’s Original Radiotelescope

Grote Reber’s Telescope

170 foot Diameter Radio-telescope at Green Bank, WV

The 100-meter Green Bank Telescope

Even Bigger than you Think

Jupiter in Radio

Saturn in Radio

3C296 Radio/Optical Composite

Smoothing Data

Visualizing the Data

Colorizing the Data

Must Deal With Noise

Worldwide Noise Sources

Space Environment

Solar SystemReference SystemGravity and MechanicsTrajectoriesPlanetary OrbitsElectromagnetics

Solar System Considerations

DistanceFrom Sun⌧Energy,

temperature, condensation of matter

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

Coordinate Reference Systems

GeographicCelestialPrecession

Gravity and Mechanics

OrbitsKeplerNewton

Orbital Transfers

Planets and Gravity

Flight Projects

Mission InceptionExperimentsSpacecraft ClassificationTelecomOnboard SystemsScience InstrumentsNavigation

Mission Inception

Instruments

Telecommunications

Onboard Systems

Operations

LaunchCruiseEncounterExtended OperationsDeep Space Network

Launch

Cruise

Encounter

Deep Space Network

Interstellar Spaceflight

Considerations

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+ atc( )

2⎧⎨⎪

⎩⎪−1

⎫⎬⎪

⎭⎪

c = speed of light

Crew Duration (yr) Earth Duration (yr) Range (pc)1 1 0.02

10 24 3 - nearest stars20 270 4240 36,000 5,400 - center of Galaxy

Accelerating at 1g = 9.8 m/s2:

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

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!

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 = M4

Suppose we took a round trip to a star 5 pc away:Via Chemical Rocket Via Nuclear Rocket

Vf / c ~ 10-5 Vf / c ~ 10-1MRT = 55 (=e4) MRT = 55t = 3 million years t = 300 years

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

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.

iClicker Question

When do you think the USA will develop a feasible nuclear fusion reactor?A Within the next 10 yearsB Within the next 20 yearsC Within the next 30 yearsD Within the next 50 yearsE Never

Matter/Antimatter RocketsW = c

V fc

=1 − M − 2

1 + M − 2

x ( d i s t . ) =c 2

2 aM + M − 1 − 2( )

T ( e a r t h ) =2 ca

M − M − 1( )t ( c r e w ) =

ca

l n ( 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

iClicker Question

What is the value of v2/c2 when v is very small compared to c?A Near zeroB Near oneC Effectively infinite

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

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

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

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

iClicker Question

Do you support the use of nuclear weapons for space travel?A YesB No

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

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 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 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.

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.

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?

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.

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.

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.

iClicker Question

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

iClicker Question

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

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.

iClicker Question

Do you believe it’s easy to construct a message for another civilization?A TrueB False

More Scenes of Earth

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.

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 pc3σ = "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 pc2 to

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

σ = π 1AU( )2 = π 1206,265

pc⎛⎝⎜

⎞⎠⎟

2= π × 2.4 ×10−11 pc2

x =1σn

=1

0.1pc−3( ) 7.5x10−11 pc2( )= 1.3x1011 pc

The MW is less than 105 pc across (and less than 103 pc thick)

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

iClicker Question

Can the previous calculation be applied to the likelihood of intercepting a radio signal from another civilization?A YesB No

Last Words on CETI and some Space Travel BasicsWhat I Will CoverA Cartoon about CETIWhat does a telescope do?Looking Beyond the EyesOptical TelescopesDifferent Views of SunRadio Astronomy BasicsA Little More DetailJansky’s Original RadiotelescopeGrote Reber’s Telescope170 foot Diameter Radio-telescope at Green Bank, WVThe 100-meter Green Bank TelescopeEven Bigger than you ThinkJupiter in RadioSaturn in Radio3C296 Radio/Optical CompositeSmoothing DataVisualizing the DataColorizing the DataMust Deal With NoiseWorldwide Noise SourcesSpace EnvironmentSolar System ConsiderationsCoordinate Reference SystemsGravity and MechanicsOrbital TransfersPlanets and GravityFlight ProjectsMission InceptionInstrumentsTelecommunicationsOnboard SystemsOperationsLaunchCruiseEncounterDeep Space NetworkInterstellar Spaceflight ConsiderationsiClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker QuestioniClicker Question