Shields, forcefields, and screens of various kinds adorn much of science fiction that deals with interstellar travel. There's a literary reason why this is so. As per the linked New Scientist Article, while there are on average only 2 hydrogen atoms per cubic centimeter in the vacuum of space (Earth's atmosphere at sea level is 15 billion billion times as dense), a ship going near-light speed would slam into so many hydrogen atoms that the effect would be like standing directly in front of the business end of the Large Hadron Collider. At a high percentage of the speed of light, a human being would receive a lethal dose of radiation in far less than a second.
The way stories have dealt with this phenomenon for the most part is to imagine some future design using a force, unknown to today's physics that conveniently blocks all that pesky radiation. In a future post I'll talk about what I think the best candidate for such a design would be, but for now let's say that any concept of a screen or field or force that could block very high radiation or futuristic weapons fire has no basis in scientific reality. Shields and forcefields just don't work. (Note that not all writers of science fiction have employed them--there has been plenty of realistic writing about space combat, but those stories may not be as well-known to the general public.)
The problem with shields and fields doesn't mean starships could not exist. It might limit their velocity, to say, 10% the speed of light. Using wormholes or "gateways" (yes, also problematic in theoretical physics, but let's ignore that for the moment) could make traveling anything near the speed of light unnecessary anyway.
So humans, assuming the apocalypse doesn't come first, will probably sooner or later design vessels that travel between stars. And before that, in between planets. We can imagine these future humans will have no need for weapons, space fortresses, and space vessels designed for combat. But a brief examination of human history strongly suggests that wherever human beings go, warfare and instruments of war go right along with us.
So, since the standard sci-fi fare of screens and fields won't work, what will? How do you defend a space station or starship against attack? Let me suggest the following seven ways:
1. Dispersion. While space defenses are mostly totally fictional, space weapons are not. Very powerful weapons including lasers, nuclear bombs, and antimatter torpedoes are all solidly either in existence or established as something that would really work. And the best way to survive an atomic or similar blast is not be there when it goes off. Building a vast array of little outposts separated from one another by a healthy distance is the best way to defend against attack. In Star Wars terms, a million TIE fighters is much better for defense than a single Death Star. And may take around the same resources to build (note though that Star Wars blasters and other weapons as they are portrayed are not only weaker than the Hiroshima blast of 1945, they are, with the exception of the Death Star itself, much weaker--likewise with Star Trek weaponry generally--our most popular sci-fi has led the public astray from what's scientifically plausible).
2. Decoys. Related to point 1, sending out as many as possible robotic decoys that employ electronic signatures like the main ship would provide a way to draw off an enemy's devastating ability to attack. The chief difference to this approach from number one is that decoys don't necessarily have any combat power, unlike the dispersion method.
3. Disguise, a.k.a. "cloaking devices" or "invisibility cloaks." The Star Trek universe treats shields like they are standard technology that virtually everyone has, whereas cloaking devices are advanced technology only a few species have mastered. From a scientific viewpoint, they have it backwards. The Pentagon is already experimenting with an invisibility cloak. The thing works, right now, but only for a fraction of a second at a time. You can be sure when spaceships are able to hurl weapons at one another with mega- and gigaton level equivalents of TNT, starships with be protected with cloaking devices. Space warfare will be largely like submarine warfare of our age. The biggest part of the battle will simply be finding the other vessel and successfully firing first. Combat probably would amount to the first on-target torpedo strike and that's it, the battle is over.
4. Mobility. Yes, there is probably an absolute speed a space vessel can practically go, but consider that the position of a craft is known by light coming away from it to a potential attacker. If a vessel is moving at a significant fraction of the speed of light and is far enough away, an attacker can only guess where a starship might be, based on last known location. Not where it actually is. It's challenging to engage a target if you don't know where it is.
5. Natural body protection. This method is not very compatible with the four methods above, but burying a base deep within a iron-nickel asteroid provides pretty good protection. Yes, an antimatter torpedo does have the blast power to split an asteroid open, but by nature most of the blast power will radiate out into the vacuum of space. As per the movie Armageddon, you'd have to drill into the asteroid to actually crack it. Though of course you could still attack whatever weapons are on the surface of the asteroid, rendering it a worthless rock in space. But I can imagine drilling teams on the surface trying to dig a tunnel, counter-attacked by teams from below the asteroid surface. Space infantry would be the most important element of such a battle (though if it were up to me, I'd send robots to do the drilling).
6. Mass. Yes, while it's also contrary to what's probably better advice of 1-4 above, there is something to be said for making a massively huge body with a smooth outer surface, one naturally resistant to blast damage by its size, one that would be very difficult to drill into, one whose surface could be covered with so many weapons that destroying them all would only come with considerable risk. The problem of course is the bigger you make it, the harder it is for it to move. The easier it is for an enemy to simply bypass it. That means you'd probably only build such a thing in orbit of a home planet. Better build at least 2 or 3, lest an enemy swing around to the opposite side of the planet from your space fortress and attack the home world at will.
7. Composite materials. Whether a future space force adopted the strategy of a massive body that's tough to kill or a plethora of smaller craft that are hard to find, you've got to build the vessel out of something. Our knowledge of modern sailing ships might lead a science fiction writer to assume spaceships would be made out of metal. But of all known materials, carbon has the strongest bonds. It is therefore the most resistant to direct damage and has a very high meting point. It's very difficult to damage by heat alone. Certain plastics are surprisingly good at absorbing radiation and a thin film of gold is good at blocking radiation as well. Make a composite of materials like this and fill it with water in a system designed to vent superheated H2O from the heat produced by a blast and the water will go a long way to protect the surface of the composite material. A design like this may not keep a future space soldier alive for any longer than a single impact of an enemy weapon. But that's better than "one hit and you're dead"...