Starships without energy shields.

Who are the Demarchist?

No, it really wouldn't. It isn't like artificial gravity isn't a completely different common inclusion into sci-fi. And such a defense would suffer major advantages and drawbacks.

One of the polities in the Revelation Space universe. They're mostly background antagonists in the earlier (chronologically later) books, but are the protagonists in The Prefect. Basically they're Democratic Anarchists (Demarchists, get it?) who operate via an endless series of almost-subconscious polls, plebiscites and votes coordinated through neural implants.

I dunno, a gravity field strong enough to deflect most of these things would be . . . extremely powerful. And would probably fall squarely under the 'no magic forcefield' rule. You'd need an incredible number of gravities to seriously defend against most space-based weapons since they're either travelling very fast or are some form of directed energy (which is very fast squared)

Does anyone consider Honorverse sidewalls 'not a forcefield' because they simply deflect lasers as opposed to absorbing them? I think wrapping your ship in a rolled out flattened singularity is rather against the spirit of the OP.

A gravity based defense has a number of advantages and disadvantages that are pretty unique. First of all, the energy draw is enormous. Very disproportionate with offensive systems. Unless you have a stupid amount of tech that translates to Honorverse space magic, it isn't cost effective to use it against anything your other countermeasures can deal with. But you can't chip them to death like you see with most shielding systems various properties use. You either have enough power to get through, or you wait for them them to run out of juice.

Cannon God Exxaxion is an example that uses this tech very well.

If your ship is made out of normal matter, then unless it is the size of the Death Star, you can't stop a 2 terrawatt Xray laser with a 20 meter diameter mirror at 1 light second. It will cut through your ship like it is made out of paper. Your best defense is extreme range, speed, and acceleration. Stay in a position where light speed lag makes targeting impossible and use high speed missiles to engage the enemy at range. If you have to get within a light second to finish the enemy off, do it only after you run out of missiles.

As for gravity deflection, all the other guy has to do is aim at an angle that will cause the deflected beam to hit your ship. The only true defense is not getting hit in the first place.

Gravity deflection really is just shields by another name since that's precisely how Brakiri Gravitic Shielding works in Babylon 5. Hell, Trek shields are graviton-based.

My best suggestion is to simply accept that without magic energy shields space-going warships will have to rely on speed and ECM for survival and not try to tank hits from various weapons at all. Make your warships obscenely fast, hilariously over-gunned, ridiculously sensor-studded, and hideously intelligent. Space-going bolos without the armor.

Your ship should be made of a carefully crafted asteroid, say 300-400 kilometers in diameter. There are several promising candidates in the Belt. Say, Vesta?

What about Ceres?

Also how much energy would a Demarchist railgun impart into its target, since the railgun is 1000 miles long and fires "tank sized rounds"?

I think for dealing with the energy weapon ones, I'm actually favoring putting a few layers of an extremely good conductor of heat sandwiched between plates that are connected to heat sinks. Say, make a system of NaK, which has excellent thermal conductivity and a relatively high boiling point to distribute the heat along your entire outer hull and bleed it off. Reinforce it underneath with a framework to absorb and distribute the shock of localized explosions. Over top of each NaK layer, put something that is as reflective as possible over as wide a spectrum as possible. NaK also has virtually no vapor pressure, so even if your hull is damaged, you won't hemorrhage it when exposed to vacuum. Just, uh, keep it away from air and water, but that's not such a problem in space.

Barring that, just use tons of water or stick your star drive on a decent asteroid and hollow out the inside.

unless you embrace all that that kind of gravity manipulation entails.... which is a lot. I've seen it done thoroughly once, and that setting can knock the socks off anyone short of the culture (or people using ridiculous magic).

Are you talking about Schlock Mercenary?

correct

With 70%c exit velocity, lowballing the density of metallic hydrogen to .6g/cm^3, and extrapolating from an Abrams; about 360 gigatons, IIRC.

If your civilisation has good nanoscale mass manufacturing, building a planetary phased array will probably be just as easy as building starships. With a 10,000km baseline, it's easy to detect incoming threats and put out enough light to be a reliable point-defense. Probably more effective than deca-km size asteroids.

Do these Demarchists use this type of railgun on their spacecraft as well? Is this railgun a planetary weapon or something?

I believe the Demarchist railgun is actually a thousand kilometers long, rather than a thousand miles long.

Very unclear. They're deployed in space, but it's never stated if they're dropped from ships and self-deploy or what. There is literally a single sentence describing them.

It doesn't need to be gravity per se, or even a form-fitting field. You could use focused tractor beams\repulsors for much the same purpose, and you just need to nudge projectiles ever so slightly off course while they're several thousand kilometers away, not stop them dead in their tracks. Of course, it'll be largely useless for energy weaponry, but it'll solve your projectile difficulties nicely, and possibly your particle beam troubles as well depending on how quickly your defense system can detect and redirect the beam. (FTL sensors, ultra-fast computers and reaction time, clouds of observation drones with FTL comms, or some combination of the three would be needed in that case)

In fact, that's pretty much what the ships in my sci-fi setting rely on since they don't have traditional energy shields. (along with using some other tech like cloaking, high mobility, thermal superconductors, etc to try and deal with energy weapons)

So... basically point defense with technobabble energy beams instead of non-technobabble energy beams?

Basically, although they also use beams\projectiles\missiles for PD as well. Main advantage in-universe is that gravitics are a hyperspace effect that propagates at FTL and can reach the target far faster than any other method available, although it has the downside of being easily disruptable. (gravitics being an in-universe misnomer/layman's term for configurable volumetric force fields, since whenever people hear that they think of generic energy shields rather than an area where everything inside a certain volume has a force exerted on it in a specific direction, and 'gravitics' gives a good intuitive feel for what their effects are despite having nothing at all to do with actual gravity. It fits the technology better than tractor beam or repulsor in my opinion at least. )

Curse you semantics!

And if you're going to do this, why not work something like a thermal couple into the hull to use some of that heat to run your own weapons. The heat will have to be bled off eventually, and this would help some in that respect.

You could get power from it that way, but really not that much. It would be simpler to use the NaK to heat water and have the steam spin turbines if you are going to try to get power this way (which is one of the current uses for for the stuff) and you'd probably get more power back. The main purpose of it though should be as a coolant that distributes heat over a large area of the ship that can be readily dissapated... any power you get out of it is a side benefit.

I'm inviting you all to participate in the Low Tech vs SciFi challenge.
http://forums.spacebattles.com/threads/lets-break-it-part-2-reap-the-reaper.229933/

It seems to be something up your alley.

maybe layer your ship in inches of cold neutrino star diamond?