StarshipsStarships

Lecture Twenty-Eight, Apr. 11, Lecture Twenty-Eight, Apr. 11, 20032003

PlutoPluto

• In 1991, the United In 1991, the United States Postal Service States Postal Service issued a series of issued a series of stamps stamps commemorating commemorating American space American space exploration. The stamp exploration. The stamp for Pluto consisted of a for Pluto consisted of a painting of a grayish painting of a grayish disk with an apology of disk with an apology of sorts underneath: "Not sorts underneath: "Not Yet Explored." Yet Explored."

• Spacecraft have visited Spacecraft have visited other planets.other planets.

Pluto’s discoveryPluto’s discovery

• Clyde W. Tombaugh spent years searching for a Clyde W. Tombaugh spent years searching for a hypothesized ninth planet to explain small hypothesized ninth planet to explain small perturbations in the orbits of Uranus and Neptune, perturbations in the orbits of Uranus and Neptune, and then on Feb. 18, 1930, he found Pluto. Note, and then on Feb. 18, 1930, he found Pluto. Note, the perturbation calculations were wrong, and Pluto, the perturbation calculations were wrong, and Pluto, turned out to be smaller than Earth's Moon — too turned out to be smaller than Earth's Moon — too small to account for the perturbations, in any case. small to account for the perturbations, in any case.

• In June 1978, James W. Christy noticed that in one In June 1978, James W. Christy noticed that in one image, Pluto's point of light seemed to have a bump image, Pluto's point of light seemed to have a bump on it. He went back and looked at other on it. He went back and looked at other photographs and Pluto seemed to have a bump in photographs and Pluto seemed to have a bump in many of those images, too, and the bump seemed many of those images, too, and the bump seemed to be moving around. This was discovery of moon to be moving around. This was discovery of moon Charon.Charon.

Is Pluto a Planet?Is Pluto a Planet?

• It is very small. Much smaller then several moons.It is very small. Much smaller then several moons.• It has an odd orbit that is tilted out of the plane by 17 It has an odd orbit that is tilted out of the plane by 17

degrees and is very eccentric. So eccentric that it degrees and is very eccentric. So eccentric that it crosses the orbit of Neptune.crosses the orbit of Neptune.

• Pluto discovered 72 years ago. In recent time we Pluto discovered 72 years ago. In recent time we have found many other minor planets even farther have found many other minor planets even farther from the sun. Some of these are quite large from the sun. Some of these are quite large (although none yet as large as Pluto).(although none yet as large as Pluto).

• Many astronomers think we will soon find an object as Many astronomers think we will soon find an object as large or larger than Pluto, far from sun in Kuiper belt.large or larger than Pluto, far from sun in Kuiper belt.

• Pluto is a planet because have called it so for 70 Pluto is a planet because have called it so for 70 years!years!

• If Pluto were to be discovered today it might be If Pluto were to be discovered today it might be classified as a minor planet, just one of many in the classified as a minor planet, just one of many in the Kuiper belt.Kuiper belt.

Pluto and its moon Charon are Pluto and its moon Charon are a “double planet”a “double planet”

PlutoPluto

• Has an atmosphere and mysterious Has an atmosphere and mysterious bright and dark marking with large bright and dark marking with large contrast.contrast.

• Charon probably formed in a large Charon probably formed in a large collision like earth’s moon.collision like earth’s moon.

• Spectra suggest nitrogen, methane Spectra suggest nitrogen, methane and carbon monoxide frost on Pluto, and carbon monoxide frost on Pluto, and water frost on Charon. and water frost on Charon.

New Horizons Mission to New Horizons Mission to PlutoPluto• Planned for 2006 Planned for 2006

launch and 10 year launch and 10 year journey to Pluto.journey to Pluto.

• Need very small Need very small spacecraft that can be spacecraft that can be accelerated to high accelerated to high speed.speed.

• Uses nuclear power Uses nuclear power and miniature and miniature instruments.instruments.

• Plan is to flyby Pluto Plan is to flyby Pluto and explore one or and explore one or more other Kuiper belt more other Kuiper belt objects.objects.

Interstellar FlightInterstellar Flight

• Can we search beyond our solar system Can we search beyond our solar system for life near other stars?for life near other stars?

• Can we go to another star?Can we go to another star?

• What can we learn about life near other What can we learn about life near other stars by using sensitive instruments stars by using sensitive instruments (without leaving the solar system).(without leaving the solar system).

• Can we leave our Milky Way galaxy and Can we leave our Milky Way galaxy and search for life in other galaxies? (Probably search for life in other galaxies? (Probably no.)no.)

A Light YearA Light Year

• Light travels 186,000 miles per second.Light travels 186,000 miles per second.

• In one year light travels 6 In one year light travels 6 ££ 10 101212 miles. miles.

• Thus a light year is 6 trillion miles!Thus a light year is 6 trillion miles!

• The nearest star is 4.3 light years away.The nearest star is 4.3 light years away.

• Interstellar journeys need to cover many Interstellar journeys need to cover many trillions of miles! trillions of miles!

Where would you like to go today?Where would you like to go today?

Andromeda Galaxy with hundreds of billions of stars

Interstellar flight is hardInterstellar flight is hard

• Need to go fast given huge distances.Need to go fast given huge distances.

• It takes a very big and efficient rocket to go It takes a very big and efficient rocket to go fast.fast.

• Suppose you have a 1 ton payload and a 9 Suppose you have a 1 ton payload and a 9 ton rocket can boost the payload to a speed ton rocket can boost the payload to a speed v. v.

• How big a rocket does it take to go 2v?How big a rocket does it take to go 2v?

• Answer 100 tons total and a 1000 ton Answer 100 tons total and a 1000 ton rocket is needed to go 3v!rocket is needed to go 3v!

2 stage rocket2 stage rocket

• A 10 ton system (9 ton A 10 ton system (9 ton rocket plus 1 ton rocket plus 1 ton payload) can go a speed payload) can go a speed v.v.

• Then a 90 ton booster Then a 90 ton booster rocket can boost this 10 rocket can boost this 10 ton payload to a speed ton payload to a speed v.v.

• After booster runs out of After booster runs out of fuel fire 9 ton 2fuel fire 9 ton 2ndnd stage stage to accelerate from v to to accelerate from v to 2v. 2v.

1 ton 1 ton payloadpayload

9 ton 29 ton 2ndnd stage rocketstage rocket

90 ton 90 ton booster booster rocketrocket

Giant Saturn Giant Saturn 5 Moon 5 Moon Rocket and Rocket and Apollo Apollo spacecraft is spacecraft is 363 feet 363 feet tall.tall.

Rockets are giganticRockets are gigantic

• Because first stage must accelerate Because first stage must accelerate both payload and all the weight of both payload and all the weight of the upper stages and their fuel.the upper stages and their fuel.

• A rocket spends most of its energy A rocket spends most of its energy accelerating the fuel rather then accelerating the fuel rather then accelerating the payload.accelerating the payload.

Options for Interstellar flightOptions for Interstellar flight

• Use a fuel with much more energy Use a fuel with much more energy per pound compared to conventional per pound compared to conventional chemical fuels such as hydrogen and chemical fuels such as hydrogen and oxygen.oxygen.

• Use some scheme where it is not Use some scheme where it is not necessary to carry the fuel.necessary to carry the fuel.

• Be prepared for a very long trip!Be prepared for a very long trip!

Slow BoatsSlow Boats

• Can a mission of 1,000 or 10,000 years Can a mission of 1,000 or 10,000 years succeed?succeed?

• Automated probes to explore another solar Automated probes to explore another solar system.system.

• Generation ships (or space colonizes). How Generation ships (or space colonizes). How large would they have to be and with how large would they have to be and with how many people? How to accelerate this large many people? How to accelerate this large mass?mass?

• Suspended animation (send people in Suspended animation (send people in hibernation).hibernation).

• Send frozen fertilized human eggs and Send frozen fertilized human eggs and specialized machines. specialized machines.

More Powerful RocketsMore Powerful Rockets

• Nuclear power such as project Orion.Nuclear power such as project Orion.

• Antimatter rockets.Antimatter rockets.

• Laser acceleration: Place a large Laser acceleration: Place a large mirror on the starship and bounce a mirror on the starship and bounce a powerful ground based laser off of it powerful ground based laser off of it to accelerate the ship. Don’t need to to accelerate the ship. Don’t need to accelerate the fuel on earth! accelerate the fuel on earth! Problem, how to stop? Problem, how to stop?

Nuclear Explosive PowerNuclear Explosive Power

• Explode a whole series of small Explode a whole series of small nuclear weapons behind a pusher nuclear weapons behind a pusher plate.plate.

• Very high temperatures reached in Very high temperatures reached in nuclear explosions accelerate debris nuclear explosions accelerate debris to very high speeds.to very high speeds.

• This makes an incredibly powerful This makes an incredibly powerful rocket if your spacecraft survives.rocket if your spacecraft survives.

Antimatter RocketsAntimatter Rockets

• Each particle has a corresponding antiparticle Each particle has a corresponding antiparticle with the same mass but opposite charge. with the same mass but opposite charge. The anti-electron is called a positron. A The anti-electron is called a positron. A hydrogen atom has an electron orbiting a hydrogen atom has an electron orbiting a proton.proton.

• An antihydrogen atom has a positron orbiting An antihydrogen atom has a positron orbiting an antiproton. This is the simplest atom of an antiproton. This is the simplest atom of antimatter.antimatter.

• When antimatter and matter meet they When antimatter and matter meet they annihilate into gamma rays releasing giant annihilate into gamma rays releasing giant amounts of energy.amounts of energy.

Making antimatterMaking antimatter

• Accelerators can make antiparticles by Accelerators can make antiparticles by colliding high energy particle beams.colliding high energy particle beams.

• We can collect these antiparticles using We can collect these antiparticles using magnetic fields and other means and magnetic fields and other means and accelerate them to produce beams of accelerate them to produce beams of antiparticles. SLAC in California collides a antiparticles. SLAC in California collides a positron beam with an electron beam.positron beam with an electron beam.

• To date we have only been able to make a To date we have only been able to make a few atoms of antihydrogen by combining few atoms of antihydrogen by combining positrons and antiprotons. positrons and antiprotons.

Antimatter rocketsAntimatter rockets

• Antimatter is perhaps the ultimate Antimatter is perhaps the ultimate fuel because it can release the most fuel because it can release the most energy per mass.energy per mass.

• However very very hard to make the However very very hard to make the antimatter, store it and annihilate it antimatter, store it and annihilate it in such a way that all the gamma in such a way that all the gamma rays go backwards so the rocket will rays go backwards so the rocket will recoil forward.recoil forward.

Relativistic Time DilationRelativistic Time Dilation

• If a rocket has enough energy to go a If a rocket has enough energy to go a significant fraction of the speed of light significant fraction of the speed of light strange things happen.strange things happen.

• Time seems to slow down on the rocket.Time seems to slow down on the rocket.• TTrocketrocket = [1-(v/c) = [1-(v/c)22]]1/2 1/2 TTearthearth

• Here v is speed of rocket and c is speed of Here v is speed of rocket and c is speed of light. light.

• Example v=0.9c: TExample v=0.9c: Trocketrocket=0.43 T=0.43 Tearthearth

• Passangers age only 4 years during a 10 year Passangers age only 4 years during a 10 year trip at 0.9 c.trip at 0.9 c.

’39by Brian May of Queen’39by Brian May of Queen

In the year of '39 assembled here the volunteersIn the year of '39 assembled here the volunteers In the days when the lands were fewIn the days when the lands were few Here the ship sailed out into the blue and sunny mornHere the ship sailed out into the blue and sunny morn Sweetest sign ever seenSweetest sign ever seen

And the night followed dayAnd the night followed day And the story tellers sayAnd the story tellers say That the score brave souls insideThat the score brave souls inside For many a lonely day sailed across the milky seasFor many a lonely day sailed across the milky seas Ne'er looked back, never feared, never criedNe'er looked back, never feared, never cried

Don't you hear my call though you're many years Don't you hear my call though you're many years awayaway

Don't you hear me calling youDon't you hear me calling you Write your letters in the sandWrite your letters in the sand For the day I take your handFor the day I take your hand In the land that our grandchildren knewIn the land that our grandchildren knew

Aah, aah, aah, aahAah, aah, aah, aah

In the year of '39 came a ship in from the blueIn the year of '39 came a ship in from the blueThe volunteers came home that dayThe volunteers came home that dayAnd they bring good news of a world so newly bornAnd they bring good news of a world so newly bornThough their hearts so heavily weighThough their hearts so heavily weighFor the earth is old and grey, little darling we'll awayFor the earth is old and grey, little darling we'll awayBut my love this cannot beBut my love this cannot beOh so many years have gone though I'm older but a yearOh so many years have gone though I'm older but a yearYour mother's eyes from your eyes cry to meYour mother's eyes from your eyes cry to me

Don't you hear my call though you're many years awayDon't you hear my call though you're many years away Don't you hear me calling youDon't you hear me calling you Write your letters in the sand for the day I take your handWrite your letters in the sand for the day I take your hand In the land that our grandchildren knewIn the land that our grandchildren knew

Don't you hear my call though you're many years awayDon't you hear my call though you're many years away Don't you hear me calling youDon't you hear me calling you All your letters in the sand cannot heal me like your handAll your letters in the sand cannot heal me like your hand

For my lifeFor my life Still aheadStill ahead Pity mePity me

StarshipsStarships

• Are very very hard to build because the Are very very hard to build because the distances are so great.distances are so great.

• It might cost 100 billion $ to send people It might cost 100 billion $ to send people to Mars. This is comparable to the space to Mars. This is comparable to the space station or the Apollo moon landings.station or the Apollo moon landings.

• A starship might cost our full gross A starship might cost our full gross national product???national product???

• Only for a far future time when worlds Only for a far future time when worlds economy is larger. economy is larger.

Justifying the CostJustifying the Cost

• Maybe starships are too expensive Maybe starships are too expensive just to explore other stars.just to explore other stars.

• Colonization of new worlds could Colonization of new worlds could justify great cost. Or avoiding justify great cost. Or avoiding disaster on earth.disaster on earth.

• For now work hard to explore other For now work hard to explore other stars with sensitive instruments from stars with sensitive instruments from within our solar system.within our solar system.