Now, let's see what science & technologies have up the sleeve...
If I tell you that :
. an isotop of the Californium element has a critical mass of 1.5g
. this element is one of the very rarest and most expensive one and available to the labs on a mg basis
. yet it can be produced on much larger quantities on nuclear explosion sites ( start for the change : Radium )
. concerning nuclear explosions, since the late 50s, the US has searched for cones of explosion
. we know how to produce incredible accelerations ( typical bullet from a rifle : 20,000G ) but surviving 'em is another matter
. special materials can be produced by small automatized mini-factories plunged into great depths in our oceans
. VERY special materials may have been produced in great quantities on the sites of the thousands of nuclear explosions test sites
My conclusion is this one : we can create uninhabited space ships for VERY large distances since the early 60s'.
But there are other things to consider...
Shade and sweet water !
I'm quite sure that when someone comes up with a solution to the oxygen problem and cold fusion finally is rationally possible, we shall conquer the space. (Until we hit the Klingons. :roll:)
Another trouble is what I would call the "relativity wall".
Let's see :
. we had the sound wall : no plane could get faster than the sound
. then the heat wall : in any atmosphere, at some speed ( round Mach 15, if I remember well ) any material melts
. then the c absolute limits AND the relativity effects which means that 'round 10% ( or even a bit less ) of c ( 299,792,458 m/s ) the relativity begins to operate...
Let's make it clear : you can push a particle or even an atom to approach c, but the electrons around atoms, all those small little links that assure the coherence of molecules and complex matter ( moreso with living beings and their gigantic organic molecules ) DO move at great speed too in order to insure these links and the c limit will make the complex matter disorganize near only 7% of c !
But space travel may prove to be a VERY dangerous activity...
I've been ready for space travel since I was a kid. Now in my early fifties I wonder if we will ever get there.
Let's suppose we have a spaceship able of travelling at the tremendous average speed of 5% of c.
Getting to the nearest star ( ~ 4.5 light years away ) would ask for ~ 90 years.
I knew the was a catch.