so here's my theory of interstellar travel. Could this work?

Question

http://uk.answers.yahoo.com/question/?qid=20060722144831AAlNdua&r=w&pa=BIFqNXbjPnbSRhDhh2.WnFD3mSIDOCvaMD9YAbriARXWrlirKpI10w-- for why it won't work. But that aside, how about this?

We're off to Alpha Proxima, 4.5 light years away I think. Let's say ten or so years is a reasonable time to get there, so half of light speed is OK. No need for multiple generations or suspended animation, though a good DVD library would help.

(1) Mass - We can't hit infinite mass or we become a black hole. How massy are we? Let's say we started at 100 tonnes. As far as I recall it's 1/(1-u^2/c^2), so our new mass is 133 tonnes. Fine!

(2) Acceleration. We can tolerate 1g, in fact that's extremely comfortable. So we accelerate at 10m/s^2. That takes us a bit less than six months to get to speed. Also fine!

(3) Energy. We need E=1/2 * mass * u^2, which comes to 415,625,000 TWh of energy, which is 30 times the world's annual electricity production.

Ah.

OK, can you fix this?

Answer 1

Using anti-matter as a fuel source would give you 100% efficiency. Let's assume technology could exist to make and store anti-hydrogen in liquid form.

Let's figure out how much mass would need to be converted to generate that much energy:

E (joules) = m (kg) c^2 (m^2/s^2)

1 TWh = 3.6x10^15 J

According to your numbers, you'd need 1.4963 x 10^24 J, so

m (kg) = 1.4963x10^24 / (299792458)^2
= 16,658,026 kg

You would need 16,648,025 kg of matter/anti-matter fuel to generate that much energy. That's more than 22 space shuttle external fuel tanks worth of liquid hydrogen/anti-hydrogen. Plus whatever mechanism you would need to contain the anti-hydrogen. It's also about 62 times the mass of your hypothetical ship.

Answer 2

alpha centauri (proxima centauri) is 4.2 light years away.

1) im not sure about how to calculate that, but sounds good... maybe 100 tonnes is a little light for a workable, standalone spacecraft though.

2) the g force wouldnt really matter all that much, as you may recall, there isnt much gravity in space besides the immediate gravity of the spaceship. Therefore you can accelerate to speed much faster than that (assuming its possible... onto next question). Astronauts would be pulling 1000's of g's if they were subjected to the full gravitational pull of earth...fortunately something we wont have to worry about.

3) That is why we cannot get to speed, because thats impossible. even the best nuclear generator wouldnt produce 1/10th the speed of light. I think you'd have to find some sort of compromise between time and speed.

The sheer fact that we cant go all that fast given our current tech (in a relative sense) is the entire reason that such community ships with multiple generations was thought up. Even if we had a powerful reactor wed run out of fuel before we got there, and all options that would last the distance are incredibly slow (like an ion sail type thing).

We wont be going anytime soon, but as you show... all we need to do is find a workable, practical power source.

Answer 3

rhsaunders is not entirely correct, there is another way to accelerate without throwing mass out your back end: radiation pressure. See http://en.wikipedia.org/wiki/Starwisp for an example of an unmanned interstellar craft that is possible with present-day technology. The energy requirement to accelerate a manned craft to relativistic speeds is indeed enormous. And don't forget, you will have to spend just as much energy to slow down at the end of your trip. I would use antimatter. If your craft's mass is 100tonnes, you could take 200tonnes of antimatter and 200tonnes of matter, and then slowly combine them and channel the resulting EM radiation, i.e. light out your backend, resulting in maximum possible specific impulse. This should get you up to a good fraction of c, and you'll still have some left over for braking. Of course, you'd have to produce 200tonnes of antimatter first, which is a pain. Maybe you could use a Dyson swarm around the Sun? And your equations are slightly wrong. Relativistic mass = 1/(1-u^2/c^2)^0.5 (though no one on board will notice a thing, so you don't have to worry about too much mass) and relativistic kinetic energy = m*(c^2/(1-u^2/c^2)^0.5-1)

Answer 4

A very very interesting Q. There are many practical ways to achieve high acceleration. You can use the gravitational fields of planets and suns to help you slingshot along the way. You could use some fancy propellant machines to speed you on the way OR you could just use the simple fact that the faster you go slower time travels for you. So you pick up some speed and then keep it up. Although when and if you decide to return to earth you will not be recognised by anyone but you may have reached your goal in as less as 15-20 years.

Answer 5

How are you planning on getting upto half light speed? You can't push against anything so the only way of accelerating is by throwing stuff out of the back of your spaceship. To achieve 1g acceleration involves throwing out ALOT of stuff (generally known as reaction mass). Your equation of E=1/2mv^2 ignores accelerating all this extra mass. For a quick and simple example look at a rocket lauch, compare the mass of what leaves the pad with what arrives in orbit after a relativly feeble acceleration of 11 Km/s/s. For your 0.5c spaceship at a wild guess 99.99999% would need to be reaction mass which needs to be accelerated so increases your energy requirements to something vast!

Just to comment on some later answers.
Photons are the most mass efficient but the least energy efficient. Even this relies on the momentum of photons.
Solar sail/reflectors are useless in interstellar space where it is effectivly dark.

Answer 6

Can't, and that's the rub. Actually, that number is MUCH bigger than the world's power production, which is on the order of 35,000 TWh per year. But it gets worse: we know of no way to accelerate a space vehicle other than kicking mass out the back end and relying on Newton's law of reaction. The momentum imparted to the spacecraft is the momentum of the ejecta: its mass times the velocity of the ejected material. But to buy momentum, you have to spend energy, which goes up as the square of the velocity. Which means that if you want to travel the solar system, you need to raise your Isp from the 250 seconds or so available with chemical rockets up to the order of a million, so you need 4,000 squared = 16,000,000 times the energy. This means nuclear. With a thermonuclear reactor (and we have no idea how to build such a thing), you could build a spacecraft that would navigate the solar system in a matter of days. But as for the stars, no way.

Answer 7

Just think you are going there. The subconscious mind does not need everything that you use in your formula to travel through space and time. Controlling the brain to travel from one space to another is about as believeable as your theory of physics. The whole thing would be possible in the future but you are here now and the only possible travel now is the method I am using. You could become a real thinker if you could figure out how to leave your body and travel through space. Just imagine the possibilities!

Answer 8

I believe the best way to get from here to any other place in space, is to stop thinking about in terms of the common means of travel ( i.e., speed of light), but rather, how on the quantum level, that two things can exist at points at the same time. My guess is that there is some way of triggering an object that exists in one space, to somehow appear in another distant place without the need of ever even having to had traveled there. Much like tuning a string to achieve a certain note, an entity can be tuned to make a replica of itself at any given point in space. To be precise, a vibration carries the object along the designated point at which it would appear, instantly. :)

Answer 9

Actually the required energy is still a bit out of reach at the time. But there would be a few sources that would definatly generate enough power for that purpose. A black hole could produce that and more.

Answer 10

These are great thoughts! And I am absolutely sure you would live and die of enjoyment reading "Entering Space" by Dr. Robert Zubrin, PhD, available on Amazon.com and in many local bookstores. It is a serious engineering discussion of these issues, intended for the intelligent layman, i.e. very few equations, almost all talk, and very easy reading for a smart person as you apparently are.