Interstellar Travel

Problems and Challenges Huge distances Speed limit (speed of light) Speed limitations Energy issues If humans are aboard, keeping them alive.

Rockets! Popular thought! Conservation of momentum to make the craft go even in empty space! First built in late 20s. Expanded in the 30s (due to the war). Made into a race in the 50s. (Sputnik I, Oct 1957)

Chemical Rockets First were chemical (burned a chemical fuel). This makes a hot gas to expel through a narrow nozzle. Largest = Saturn V (3 separate rocket “stages”) Problem = weight of fuel (38 x weight of craft) Use multiple stages that drop off to reduce weight and fuel necessary. Not practical for interstellar. Saturn V could manage 0.1% speed of light. (4,400 years to the closest star!)

Conventional Technology Nuclear rockets Ion engines Solar Sails Laser powered rocket Interstellar arks (use a slower speed engine) Means that they are CONCEIVABLY within our reach. Nuclear Rocket: mass conversion – fission and fusion. (quick acceleration and cruise mostly) (at best, fusion converts 0.7% of mass of fusing Hydrogen) PRO: fuel available, efficient, low weight (less problem for spacecraft carrying it), possibly go faster we CON: we can’t do it yet, safety TYPES: throw bombs out the back, fire fusing pellets out the back, use nuclear reactions to heat gas BEST SPEED (theoretically): 10% speed of light Ion engine: low power engine that fires continuously, accelerates ions out the back PRO: can fire for long periods b/c the mass expelled per unit time is small, exhaust is fast (higher speed) CON: can’t lift off Earth (start in space), TYPES: tested-low power ion drive on Deep Space 1 BEST SPEED (theoretically): 1% speed of light Solar Sails: use sunlight pressure to push the sail and craft forward (accelerate and cruise) PRO: no bulky fuel, could get higher speeds with large sails CON: huge sail required, push goes down as you get further from the sun (limits speed) TYPES: large sail, laser-powered (rather than sun) for continuous push (then you could use the laser for other things. BEST SPEED (theoretically): a few % speed of light Laser Powered: use on a sail or to vaporize pellets to make propellant gas PRO: potentially higher speed CON: if Earth based laser further is harder, large power requirement, dependant on Earthlings to keep it going (hard for passengers if the crew was out to lunch), no slowing BEST SPEED (theoretically): almost 10% speed of light Interstellar Ark: Forget fast rockets and use slow speeds and a colony ship (ark) (either several generations or figure out cryosleep/hibernation, genetically engineer the crew to live a LOT longer) PRO: We know how to build slow ships CON: No one knows cryosleep/hibernation, long journey, can’t (at present) genetically alter the crew like that, deterioration of society on-board (splintering, loss of expertise)

Unconventional Rocketry Relativistic rocketry Matter-Antimatter conversions Interstellar Ramjets Hyperspace Wormholes Unconventional – may have roots in science but we can’t do them and can’t figure out how to do them. Maybe our descendents will figure it out.

Relativistic Rocketry If you travel near the speed of light, time slows down! TIME DILATION At 99.99% the speed of light, a 25 ly trip would take 4 months. Of course, the people back home would age about 25 years. If the speeds get high enough, we could go anywhere in a human lifetime. According to relativity: as you get close to the speed of light- LENGTH shorter in direction of motion MASS greater TIME slower (well, it’ll seem normal to the passengers) If you could do a steady acceleration, so much the better. You give the crew “gravity” and you cut the voyage time. You could go 500 ly in 12 years. (Again, your family has been dead for about 500 years. And then there’s the trip back.) So, if you are going to do this, take your family with you or say goodbye to them. ENERGY COSTS WOULD BE PROHIBITIVE. The faster you go, the more massive you are, the harder to move and more fuel you need.

Matter – Antimatter Rocketry More efficient conversion of matter into energy. All matter converted (not 0.7%). Could get up to 90% the speed of light! Positron-electron: burst of gamma rays Protons-antiprotons: particles that decay into neutrinos and gamma rays Could use the particles by tossing them out the back BEST SPEED (theoretically): 90% speed of light PRO: high speed, efficient CON: getting and storing antimatter, high energy requirements for making antimatter

Interstellar Ramjets Collect fuel as you go! Scoop it up, fuse it, and shoot it out the back. No heavy fuel to carry, plenty of fusible material, could achieve high speeds Could accelerate continually by continuing to scoop! Problems: not much stuff between stars, the faster you go the more likely that particle is to rip through you

Hyperspace Other (hypothetical) dimensions caused by the warping of space-time In an embedding diagram, we curve into hyperspace. This could give us short cuts to distant destinations. You could use naturally occurring high mass objects (stars) for curvature… Or you could hang a high mass object in front of the ship and have space ALWAYS curved in front of your ship. Don’t know how you’d manage to hang something that massive there, though. (this is the closest to Warp Drive)

Black Holes Infinitely curved space time. A shortcut? (wormhole) Doubt we’d survive it. How would we keep it stable and open? Infinitely curved space-time. A singularity.

Aliens Among Us Do we need to go anywhere? Are aliens HERE? Maybe THEY have interstellar travel and we don’t have to worry about it. UFOs – lots of people believe! Most UFOs are easily explained. What about the others? Either not so easily explained, or you can jump on the alien bandwagon.

Roswell Alien artifacts at Roswell 1947? No evidence Came right after the nationwide coverage of supposed “flying saucers” Do you believe the witness? Interviews were held more than 30 years after the event! Stories changed drastically over the years. Of course, something did crash. The military says it was a weather balloon. Lots of accusations, no evidence

Other Alien Antics Crop Circles Abductions Livestock killings and mutilations Visitations in ancient times Crop Circles – pranks Abductions – sleep paralysis? Livestock killings and mutilations – predators and humans kill, too Visitations in ancient times – no definitive evidence (ambiguous old drawings and such) IS THERE A CASE FOR ALIEN VISITS? Is there a government cover-up? It’s possible. Don’t know why, but it could happen. Not likely to remain secret for any length of time. Are scientists just ignoring the relevant phenomena? Since scientists compete to be first with a discovery, it’s not likely one this juicy would be overlooked. The problem is lack of physical evidence. Science goes nowhere without it.