Shields are not so bad at all, not even at low tech levels, and sometimes even in small quantities. The advantage is that
shields constantly increase the ability to absorb damage, while many other methods have diminishing returns for extra investments.
That is particularly true when you compare the three only methods that allow sutained damage absorption: Beam PD defences, shields and speed. (Armour, internal hitpoints and AMM only allow temporary damage absorption/prevention, i.e. they run out eventually).
A shield will continuously recharge (if any damage has been done), i.e. it allows absorbing a given amount of damage per second. For instance a shield might be recharging 1 point per 100s. The important bit is that this scales perfectly with the number of shields, i.e. 2 shields will recharge 2 points per 100s, 20 shields will recharge 20 points per 100s etc. So the addition of a single shield (at this tech) adds 0.01 D/s (damage absorption per second) –regardless of whether it’s the first or the fifties shield on the ship.
This is not true for speed or beam PDs. As a simple (and unrealistic) example: An enemy launches a single missile every 20s. The missile is 10 agility, travels 20,000km/s and has a warhead of 4.
- Assume we don’t have any engines: speed is 0, the enemy missile has a 100% chance of hitting, causing 4 damage every 20s.
- The addition of single engine might change our speed to say 4,000 km/s. The enemy missile is now only 50% likely to hit, causing 2 damage every 20s. Thus the first engine might reduce the damage by 4D/40s =0.10 D/s (ten times better than the shield!)
- A second engine will increase the speed further, lets say to 8,000 km/s (of course the speed will not increase linearly to the number of engines, as those must propel themselves as well, but lets keep it simple). Now the enemy missile is 25% likely to hit, causing 4 damage every 80s. Thus the second engine has reduced damage by only 4D/80s=0.05D/s. So the second engine prevent much less damage than the first – and the third will prevent even less and so on. Moreover, the second engine is already equal to the shield in this crude example (you could use 5 shields a 50t instead of 1 engine a 250t).
The point is that the more engines we add, the less they add to our protection. And in particular, because they become less and less valuable, at some point adding more engines will be less valuable than shields.
The same holds for (most) beam PD weapons. Assume the example from above: enemy missile approaching at 20,000 km/s. Lets use a turreted PD laser at a tracking speed of 10,000km/s to combat that.
- The first laser has roughly a chance of 50% to kill the missile in final fire. Thus it will destroy 4 damage points from reaching the ship every second salvo (40s). Assuming the ship travels at 4,000km/s, it will thus prevent 2 damage points from hitting the ship every 40s (missile is 50% likely to hit if it reaches. In other words the beam might destroy a missile that would have missed anyway). So the “value” in terms of prevented damage is 2D/40s=0.05 D/s.
- If we add a second laser, it can only operate against the single enemy missile if the first laser has missed (otherwise there would not be a target left). Thus the chance of the second PD firing is 50%. The chance of it hitting when it fires is also 50%, thus it can stop 1 missile (4D) from reaching the ship every four salvos. Taking into account that these missiles might miss anyway, the second laser prevents 0.025D.
Again, beam weapons exhibit a decreasing return: The more you add, the less valuable the next one becomes.
Thus inevitable at some point shields will become the best investment for prolonged protection. The exact point at which that happens depends on a lot of factors- technology, warhead and speed of the enemy missiles and size of their salvos. But regardless of these factors there will be such a point.
Interestingly: that point where shields become superior to other methods will be relevant for beamwarships in open space actions (i.e. away from jumpgates)
regardless of the techlevel! If you need to cross the distance to an enemy missile ship, you will invariably be exposed to a huge amount of damage that needs to be absorbed. Thus you cant rely on armour or PD missiles alone – try fielding enough armour to sustain 2 hours or so of unopposed bombardment, or carrying enough PD missiles to last that long. But you do not only want to rely on the sustainable methods of protection, you also want to be very certain that very few enemy missiles get to cause real damage. As we saw above you need increasing amounts of say beam PDs to be more and more sure to kill the enemy missile. A single mount allowed 50% kill likelihood, but that meant half of the missiles of the enemy still got through, which would not help much. Two mounts meant 75% likelihood, still to little. To get a 90% likelihood of killing the enemy missile we would need 4 Pd weapons, in order to get 99% we would need 7 (against a single missile!). 100% can never be reached... So pretty much by default we would get to the point where shields start to look interesting. Consider say a strategy where 90% of incoming missiles get shot down, and shields are sufficient to absorb the remaining 10% of damage…
And we have not talked about beam weapons and how shields are more effective than armour at countering the “narrow, deep” damage profile of say lasers.
