Interstellar TravelInterstellar Travel
By: David RodriguezBy: David Rodriguez
Astro 5: Life in the UniverseAstro 5: Life in the Universe
Winter 2008Winter 2008
Motivation: Fermi’s ParadoxMotivation: Fermi’s Paradox
If the chances of developing a If the chances of developing a technological civilization are 1 in a technological civilization are 1 in a million:million: 100,000100,000 civilizationscivilizations in the galaxyin the galaxy This is an application of the This is an application of the Drake Drake
EquationEquation, but , but ignoringignoring the the Lifetime Lifetime of civilizationsof civilizations
If these are spread over the lifetime of the If these are spread over the lifetime of the Galaxy, the time between civilizations is about Galaxy, the time between civilizations is about 50,000 years50,000 years
Fermi’s ParadoxFermi’s ParadoxWith such a long time, a civilization might With such a long time, a civilization might
be able to colonize the Galaxy or at least be able to colonize the Galaxy or at least make its presence knownmake its presence known
They could at least send self-replicating They could at least send self-replicating machinesmachines
Solutions to Fermi’s ParadoxSolutions to Fermi’s Paradox
There are three solutions to Fermi’s There are three solutions to Fermi’s Paradox:Paradox:
1.1. We are aloneWe are alone2.2. A galactic civilization exists, but it remains A galactic civilization exists, but it remains
hidden from ushidden from us3.3. Other civilizations exist, but none have Other civilizations exist, but none have
colonized the galaxy. Why?colonized the galaxy. Why?1.1. No interest in doing soNo interest in doing so2.2. Self-annihilationSelf-annihilation3.3. Technological difficultiesTechnological difficulties
IntroductionIntroduction In order to travel to In order to travel to
the stars, colonize the stars, colonize other worlds, and other worlds, and establish an establish an Everlasting Galactic Everlasting Galactic Empire, we will need Empire, we will need interstellar travelinterstellar travel
Rocket ScienceRocket Science
Current rockets use Current rockets use chemicalchemical fuels fuels
These can be solids, These can be solids, liquids, or gasesliquids, or gases
Efficiency of a rocket Efficiency of a rocket measured with the measured with the mass ratiomass ratio = = Mass with fuel / Mass Mass with fuel / Mass
without fuelwithout fuel
Rocket ScienceRocket Science To escape the gravity To escape the gravity
of the Earth need a of the Earth need a mass ratio of ~39mass ratio of ~39
Single stage rockets Single stage rockets have mass ratios of have mass ratios of ~15 or less~15 or less
This is not enough, so This is not enough, so we can’t leave the we can’t leave the EarthEarth
Or can we?Or can we?
Multistage RocketsMultistage Rockets
Distances to StarsDistances to Stars
The nearest star system (Alpha Centauri) The nearest star system (Alpha Centauri) is 4 light-years away (40 trillion km)is 4 light-years away (40 trillion km)
At 60mph, this would take… 44 million At 60mph, this would take… 44 million yearsyears
At 17,000mph, this would take just 160,000 At 17,000mph, this would take just 160,000 yearsyears
At this speed, it would take a At this speed, it would take a billion years to reach the center billion years to reach the center of our Galaxyof our Galaxy
What can we do?What can we do?
We need to go faster!We need to go faster! It’s all a mater of getting higher efficiency It’s all a mater of getting higher efficiency
from our fuelfrom our fuel
I can make 0.5 past light speed!
Nuclear RocketsNuclear Rockets
Use fission to heat Use fission to heat hydrogen gas, which hydrogen gas, which provides the thrustprovides the thrust
Fuse small pellets of Fuse small pellets of hydrogen, the energy hydrogen, the energy released moves it released moves it forwardforward
Set off a nuclear Set off a nuclear bomb behind youbomb behind you
Ion DrivesIon Drives
Shoot out ions from light-weight gasesShoot out ions from light-weight gases Little thrust, but can work for longer times and Little thrust, but can work for longer times and
therefore get large velocitiestherefore get large velocities
Solar SailsSolar Sails
Use the pressure Use the pressure from photons of light from photons of light to push the craft to push the craft forward- like wind on forward- like wind on a sail.a sail.
Can also use lasersCan also use lasers
Antimatter is like regular matter but with opposite Antimatter is like regular matter but with opposite chargecharge
When antimatter and matter meet, they When antimatter and matter meet, they completely annihilate each other producing completely annihilate each other producing energyenergy
Antimatter EnginesAntimatter Engines
Like the solar sail, an Like the solar sail, an interstellar ramjet interstellar ramjet carries no fuelcarries no fuel
Take hydrogen from Take hydrogen from space and fuse itspace and fuse it
RamjetsRamjets
To Infinity, and Beyond!To Infinity, and Beyond!
These new These new technologies allow technologies allow light-weight space light-weight space craft to reach very craft to reach very high speeds with very high speeds with very little fuel.little fuel.
In order to go faster In order to go faster we just need to run we just need to run the engine for a the engine for a longer timelonger time
But then this guy came along…But then this guy came along…
Image credit: Kevin Hainline
A Maximum SpeedA Maximum Speed
The speed of light in a The speed of light in a vacuum is always a vacuum is always a constantconstant with respect to with respect to anyany observer. observer.
This speed, c, isThis speed, c, is 300,000 km/s300,000 km/s 186,000 miles/s186,000 miles/s 1.8 terra furlongs/fortnight1.8 terra furlongs/fortnight
Nothing can travel faster Nothing can travel faster than lightthan light
Special RelativitySpecial Relativity
All motion is relativeAll motion is relativeMany weird effects will happen when Many weird effects will happen when
special relativity is applied, but I’ll only special relativity is applied, but I’ll only mention a few:mention a few:Moving clocks run slower as seen by a Moving clocks run slower as seen by a
stationary observer stationary observer time dilationtime dilationDistances are contracted along the direction Distances are contracted along the direction
of motion of a moving object of motion of a moving object length length contractioncontraction
Special RelativitySpecial Relativity
At 99.99% of c, to go to Vega (25 At 99.99% of c, to go to Vega (25 light-years away) and back:light-years away) and back: Space ship frame: 8 monthsSpace ship frame: 8 months Earth (stationary) frame: 50 yearsEarth (stationary) frame: 50 years
But light takes 50 years to travel But light takes 50 years to travel 50 light-years, yet you do this in 8 50 light-years, yet you do this in 8 months:months: Length contraction: you travel 0.4 Length contraction: you travel 0.4
light-year rather than 25 light-yearlight-year rather than 25 light-year
General Relativity to the Rescue?General Relativity to the Rescue?
WormholesWormholes
A highly curved A highly curved region of space could region of space could intersect another intersect another region of space and region of space and form a hole between form a hole between themthem
These wormholes are These wormholes are unstable and collapseunstable and collapse if anything goes if anything goes through themthrough them
The Alternative: Interstellar ArksThe Alternative: Interstellar Arks
Use conventional technology, but be prepared Use conventional technology, but be prepared to wait a very long timeto wait a very long time
The original travelers will die and new ones will The original travelers will die and new ones will be born before reaching the destinationbe born before reaching the destination
Or you could place Or you could place everyone in suspended everyone in suspended animation for thousands animation for thousands of yearsof years
QuestionsQuestions
?