ASTR/GEOL 3300: ET Life

1. ASTR/GEOL 3300: ET Life • Announcements: • ELECTRONIC COPIES OF YOUR PEER REVIEWS ARE DUE TODAY! • You must email your document to me before 5pm TODAY at: mojzsis@colorado.edu • Plan for Today: • Getting there.

3. Interstellar Travel“Getting there”

4. Interstellar Travel • Is it possible? Why is it so difficult? • Technology needed? What won’t work? • What would it be like if it is possible? • Can we tell if other civilizations are capable of it? http://www.daviddarling.info/encyclopedia/ETEmain.html

5. Is it possible? Why is it so difficult? • Interstellar travel might be possible, but it would be very difficult because stars are so very far away and space is quite empty. The difference between going to the Moon and the nearest star is like the difference between walking across town and walking to the Sun! Walking across town at 1.3 m/s for 10 km takes about 2 hours. To get to the Sun (149.6 x 106 km) at this rate would take: 3,646 years It would be something like 100,000,000 times farther than we’ve ever traveled.

7. Is it possible? Why is it so difficult? • Conventional rockets will not work, a new kind of propulsion is needed if we want to go fast. The easiest way to travel between the stars may be to just go slowly and live a long time. There might be ways to get around this (e.g. “wormholes”), but all indications are that this kind of technology (to manipulate space-time) is unimaginably advanced.

8. Is it possible? Why is it so difficult? • Contrasting various kinds of propulsion Why do cars, ships, planes and balloons move forward? How do they stop? Why doesn’t this principle work in space? Stuff has to be taken to push against. How does a rocket work? What determines the speed of a rocket?

9. What determines a rocket’s speed? • How much propellant is used • The velocity of the propellant • In space, you can reach the same top speed by taking either a lot of propellant and throwing it slowly, or by taking a little bit of propellant and throwing it fast.

10. Maximum speed is different from maximum acceleration • With a Yugo (or GEO Metro), can still reach 120 kph on the freeway (at your own risk!), a Porsche can just get to that speed faster. • Quick acceleration or uphill travel takes power • Rocket: power = amount of propellant can be expelled per unit time (more in a shorter time = more power • Escaping a planetary surface is like going uphill • Once in space, power’s less of a big deal – it’s like driving on a long, flat straight road. • The engine to get off a planet is probably different from the engine used to get to another star

11. Houston, do we have a problem? • The faster we want to go, the more propellant we have to carry • More propellant = more weight = heavier spaceship • Heavier ship means harder to accelerate! Better get as much propellant out as we possibly can to get there faster!

13. This turns out to be a huge problem • Different propellant-based propulsion systems • Specific impulse (Isp): a measure of how much thrust you get out of each unit of propellant • How much propellant would it take to get to the nearest star in 1000 years? Of course, the mass of the propellant needed can’t be larger than the mass of the ship!

14. Chemical • Isp ~500 • Massp = 10137 kg… more than all the mass in the Universe • All ‘traditional’ rockets: V2, Saturn V, Space Shuttle, ICBMs, etc.

15. Saturn V Jules Verne W. v. Braun LEM and jeep

16. ASTR/GEOL 3300: ET Life • Announcements: • Pick up your reviews today! • THE FINAL PAPER IS DUE AT THE FINAL EXAM • Plan for Today: • More about Getting there. • FCQs

17. Pick up your packets now EUR: GARCIA HEIDENREICH IVES KRAVITZ MCCONNELL STAUTER HZO: JACOBSEN ROSENSTEIN VENTURELLA DAMPHOUSE GARY TRATTLER IMP: ADAMS GRAY MENDT RUDENKO TICE PRE: LEWIS MELVILLE RASMUSSEN SILVER TRIOLO ZIMMERMAN ESP: BURGMAN FAIRBANKS GALLAGHER HAZLITT HECHT HENKE KAZPRZYK MCCOLLUM MCNEILL RYNNING TEFFELTOR THOMAS WATSON OTH: COLLETTE FIELD TROHMAN ELY UHLE WALLS MAR: BUCZEK DYKAN IVANITSKI KATZ KELLY OKONOWSKY TOWNSEND WORDWORTH SET: BRANDT BRENKERT GRUDZINSKI HALLOCK HINES ISAAK KOHEN RACHKO SALVATORI

18. Nuclear Thermal • Isp ~1000 • still more than all the mass in the Universe • Tested in the 1960s for a post-Apollo Mars mission (scrapped; ATT). Great for interplanetary travel

20. Fission and Fusion • Isp ~5000 – 10,000 • Massp = 109 fission or 103 fusion supertankers • Basic designs

22. Ion Drive • Isp ~5000 – 50,000 • Massp = 10 equivalent railroad tanker cars of Xe propellant • Actually built and flown! DS1 xenon ion drive in 1999, exhaust velocities ~100,000 km/s but need another source of power (nuclear, solar) to run engine

24. Matter/Antimatter • Isp ~105 - 107 • Might work at ~100% efficiency, mass required is reasonable • No real designs, many enormous hurdles (containment, production, radiation, efficiency) • 100 billion dollars for 1 mg!

25. RECALL • This is for a 1000 year, one-way voyage to the nearest star. • Are there ways to do this without carrying the propellant with you? • Space is not quite empty

27. Relativity and other weirdness • No matter who you are or where you are, how fast you’re moving and in what direction, the speed of light in vacuum always appears the same to you. • Whoa, but this has been verified many times • You can’t go more than 3 x 108 m/s • The faster you move, the slower time passes • The faster you move, the more massive you get

28. 4 ly 10 ly 50 ly 150 ly 20,000 ly 2,000,000 ly 106 ly Perceived travel times To where? How long (to traveler) ? How far? • Alpha Centauri • Epsilon Eridani • Deneb • Pleides • Center of Milky Way • Andromeda galaxy • Virgo cluster • 2.5 y • 5 y • 10 y • 15 y • 21 y • 28 y • 30 y