[Mongoose]

"There is such a thing as a tesseract."

[eliex]

The only real kind of shield capable of absorbing damage as shown in FreeSpace that is actually plausible is a "plasma shield."

Plasma shields postulate using cold plasmas in conjunction with powerful electromagnetic fields to protect spaceships from hazards, (given that a criteria for plasma is to be ionized.) With the properties of plasma, it can protect a given ship against the hazards of space radiation but if in high concentration, will be able to protect against micrometeoroids, shrapnel, beam weapons, and other types of physical damage.

It is important to note that the plasma used is cold, and is actually easier to generate this in a vacuum.
Cold plasma is ejected around a given ship, say a Myrmidon and is held in place by electromagnetic fields generated by that ship. As the plasma itself is electrically charged, it adds to the field's strength allowing it to obtain much greater endurance at lower power levels than magnetic fields alone.

This is can partially apply to FreeSpace as upon the shield taking damage it slowly depletes as the plasma reacts. A ship might be able to eject more cold plasma to replace the reacted one although there is a limit and danger of how much plasma a ship can carry.

[redsniper]

Herra and I talked about this in #hard-light once. If we assume all FS weapons are plasma blobs (which they appear to be, but aren't in the tech descriptions) then a strong enough magnetic field could deflect the charged particles. Of course this doesn't explain how we can stop lasers, xasers, mass drivers, and missiles, but it's a start.

[Mongoose]

Missiles are made of metal, and there's nothing in either game that resembles a true laser.  There, problem solved.

[Androgeos Exeunt]

What about beam cannons?

[Snail]

The only real kind of shield capable of absorbing damage as shown in FreeSpace that is actually plausible is a "plasma shield."

Plasma shields postulate using cold plasmas in conjunction with powerful electromagnetic fields to protect spaceships from hazards, (given that a criteria for plasma is to be ionized.) With the properties of plasma, it can protect a given ship against the hazards of space radiation but if in high concentration, will be able to protect against micrometeoroids, shrapnel, beam weapons, and other types of physical damage.

It is important to note that the plasma used is cold, and is actually easier to generate this in a vacuum.
Cold plasma is ejected around a given ship, say a Myrmidon and is held in place by electromagnetic fields generated by that ship. As the plasma itself is electrically charged, it adds to the field's strength allowing it to obtain much greater endurance at lower power levels than magnetic fields alone.

This is can partially apply to FreeSpace as upon the shield taking damage it slowly depletes as the plasma reacts. A ship might be able to eject more cold plasma to replace the reacted one although there is a limit and danger of how much plasma a ship can carry.

Uh, wasn't that stealth technology?

[BengalTiger]

That's a point defense system, not a shield.

Well a better name would be "active armor", point defense systems are weapons, not devices that take hits to protect stuff behind them.

One of the definitions of "shield" (found here: http://www.merriam-webster.com/dictionary/shield) is- 
"a device or part that serves as a protective cover or barrier"

Which means a device which discharges some form of energy as a protective cover to counter an incoming projectile fits within the definition of "shield".

[General Battuta]

If it shoots down incoming attacks, it's probably a point defense weapon. Reactive armor just kind of blows itself up to destroy incoming rounds, whereas this fires a directed energy pulse to take things out.

[NGTM-1R]

Missiles are made of metal, and there's nothing in either game that resembles a true laser.  There, problem solved.

Or they're made of advanced ceramics because that's lighter and stronger than your metal.

Oh snap.

[BengalTiger]

Or they're made of advanced plastic because that's cheaper and lighter than your ceramics 

[Mobius]

They're made using advanced Nanotechlogies, which are far better than most conventional materials.

No, wait, that's INF's EA...

[General Battuta]

Oh, god, nanotechnology. The number one excuse for not writing '****ing magic' in the last thirty years of science fiction.

[NGTM-1R]

I'm pretty sure the Seventies still liked "Radiation" instead, but...

[General Battuta]

Dude, check the date. 

[NGTM-1R]

Dude, check the date. 

I did.

I also know that the 80s was Genetic Engineering.

[Killer Whale]

That's a point defense system, not a shield.

Well a better name would be "active armor", point defense systems are weapons, not devices that take hits to protect stuff behind them.

One of the definitions of "shield" (found here: http://www.merriam-webster.com/dictionary/shield) is- 
"a device or part that serves as a protective cover or barrier"

Which means a device which discharges some form of energy as a protective cover to counter an incoming projectile fits within the definition of "shield".

But then the hull of a ship is technically a shield, so it's not really what we're talking about.

[redsniper]

Oh, your hull armor is a shield in a sense, come on.

[ShadowGorrath]

What about antimatter? "Held" slightly above the surface of the ship's hull by magnetism and all that ( like antimatter atoms are held nowadays ), and it'd be much easier to keep antimatter "under control" cause it's space and all. Maybe subspace as well is included in the process of making shields work? Like getting antimatter atoms from some container ( probably from inside the ship ) to the place near the hull where the weapons are about to impact? That'd explain why shields don't work in subspace. And how you can fire with shields still on.

And since antimatter, when in contact with matter, annihilates, it can be a perfect protection against everything, except for photons ( photons don't really affect antimatter, right? ), so only beams can bypass shields.

I dunno, antimatter makes the most sense to me in the how-shields-work case. I'd explain more if I was on a PC and not a phone.

[General Battuta]

You realize you just set a massive antimatter bomb up right outside your hull, right? One that's going to be constantly abraded by interstellar debris?

Definitely not how shields would work.

[Killer Whale]

And when you collide with another ship, or missile or laser hits your shield, there would be a massive explosion. Antimatter = most powerfull explosive known to man at this time. The annihalation of even a tiny amount of anti-matter causes a gigantic explosion.

One proton-antiproton annihilation releases 300 times more energy than a fission or fusion reaction
the theoretical maximum yield-to-weight ratio for fusion weapons is 6 megatons of TNT per metric ton (25 TJ/kg)
1 kg uranium = 6 kilotons
1 kg antimatter = 1.8 megatons
Missile or laser bolt > 1 kg
yield of the harbinger = 1 megaton

In conclusion, if a piece of debris 5/9 kg (0.5555... kg) hit your shield, that would release as much energy, as a harbinger bomb.