Hypothetically, If we wanted to travel only to Proxima Centauri, then the only aspect of that aspiration which would truly be ‘possible’, would be the fact that sheer Faster-Than-Light travel would not be required. Being able to travel at some significant fraction of the speed of light, such as 1/4 or so, should make that possible.
We do not yet know what to use for propulsion, because even though fission / ion-drive technology is within reach, fission cannot propel us to 1/4 light-speed. The reason for that is somewhat straightforward. When a Uranium atom fissions, the energy it releases does not come close, to the energy / mass equivalent of this fuel. Therefore, fission will also fail to propel a spacecraft to a velocity, that will cause its mass to exceed its rest mass significantly. But let us say for the sheer game of it, that a propulsion system could be devised.
The next problem which experts already know about, is that interstellar dust would collide with a hypothetical spacecraft, and that like the spacecraft, it would have fractional-light-speed. When Physicists create new elements, they bombard heavy nuclei with other, neutron-enriched nuclei, using approximately the same magnitudes of velocity. Therefore, the dust particles in space would have enough kinetic energy, slowly to render their target radioactive. And so an idea which has been kicked around, is that some type of energy-beam could sweep ahead of such a spacecraft, and could deflect the space-dust, thus preventing it from colliding with the spaceship.
Actually, this idea is already quite old. The first Star Trek series had such a concept: Their “navigational deflector”.
The problem with an energy-based ‘navigational deflector’, is the fact that no form of energy-beam we know, would actually propel a particle sideways. A laser would fail to do this. A very powerful laser could cause one side of a carbon-based dust-particle to vaporize, and the ablative effect of that could make the particle accelerate down the path of the spacecraft, away from it. So wow, our spacecraft might get to collide with the same particle, a few microseconds later than it would otherwise have collided with it!
And I think that a phenomenon also exists, by which a pair of particles can be subject to a wavelike phenomenon, and by which they could be subject to an attraction towards each other. Neat! Instead of being hit by uncountable smaller particles, our spacecraft could now be hit by clumps of them!
I think that when Physicist try to design a navigational deflector based purely on energy, they may be going about it the wrong way.
A question I have asked myself, has been, why a spacecraft needs to consist of one connected object. A historical reason has simply been, that compact packages are easier to lift into orbit, than distributed packages. But ultimately, I think that a spacecraft could consist of numerous objects at significant distance to each other, held in place by more-conventional Electromagnetic effects, that would be similar to how the A/C fields work in present-day electrical motors. Each of these objects would consist of matter.
And so I have also come to ask myself, whether a copper shield could be used, roughly similar to round shields used in the Bronze Age for battle, but with a diameter that gently exceeds that of our spacecraft. And I’ve wondered whether low-frequency magnetic effects could be shaped and modulated – from the real spacecraft – in such a way, as to prevent such a shield from drifting sideways out of the path of the spacecraft, and which could also push it gently forward, so that it stays approximately a kilometer ahead of the spacecraft – weightlessly in space.
We know that such an object would become radioactive. But if it was kept at a distance of a kilometer from the spacecraft, becoming radioactive would not prevent it from serving its purpose.
And while relativistic dust can pack a wallop, I don’t see it penetrating ?2 centimeters? of copper. And one reason I don’t has to do with the myth of ultra-fast collisions leading to clean, narrow holes, being a myth. After the speed with which objects collide has exceeded 5000 meters /second or so, their behavior starts to resemble either that of a fluid, or that of a powder. They form craters, not tunnels. This is because within such time-frames, tensile strength becomes negligible, and the only two forces which really govern a collision, are density, and resistance to compression. We are by then describing how a water-droplet interacts with a surface of water.
The only factor which makes the outcome different, is the fact that after a water-droplet has been deflected by the surface of a stationary pool of water, it still has the surface-tension to become a water-droplet again. Depending on how certain solids exit a collision, there may be nothing that causes the incident particle, to reform a particle. And so a fluid-motion of powder can be an outcome, if atoms once belonging to one projectile, simply continue going in different directions.
A bullet-hole forms, when a bullet has enough tensile strength to survive the collision.
(Edit : )
If I may modify my idea slightly, the hypothetical spacecraft could be assembled in space, which might alternatively mean, that a deflector-disk could be attached to it by way of a lightweight scaffolding, rather than by way of anything electromagnetic. Only, the scaffolding should not be warped after positioning the disk about a kilometer in front of the spacecraft proper.
One advantage to this approach would be, that we could make it two deflector-disks, not one. The second disk could be made out of steel, since this one is to stop lower-velocity attacks.
The main problem with a 2cm -thick copper disk would be, that eventual micro-meteor which is above-average in size, maybe not quite so microscopic, but maybe more than a micron in diameter. If that was to hit a 2cm copper disk, it would blast a hole clear through it. Yet, if there was so much as a second disk, maybe 50 meters behind the first one, then the debris from the first disk would first sprawl over 50m of empty space, before hitting that second disk, which could then stop it.
But even if some sort of very-mass-efficient boom was employed, a difficult question would form out of, what is supposed to separate the two disks. Naively, we could just put more of the same – although unknown – scaffolding. But then the risk becomes, that any perforation of the first disk, might take place by chance, exactly where this scaffolding has its members, thus compromising the scaffolding between the two disks.
In order to avoid that, it might be better to fill the 50 meters between any two disks, with a more-redundant system of many, thinner struts.
(Edit 08/03/2017 : )
At the same time, any large disk would be difficult to lift into space as such. It might be best to make each one out of of rectangular, grooved, interlocking tiles, so that only copper and steel tiles need to be lifted… And then assembled in space.