Based on what I know (I did a module on phased array radars, lasers and military technology during my studies), there are a few issues that militaries haven't really addressed in their statements about laser weapon developments as well as defending ship's against ballistic missiles.
1. Radar tracking of ballistic missiles. This is an issue for current ship-borne radars, which are designed and mounted in optimum positions for sea-skimming missiles. They are also optimised to track aircraft at high altitudes at a distance (for threats such as those posed by bombers carrying ASCMs).
Unfortunately, there is currently no radar that I'm aware of on a ship that looks directly upwards. And this is where a ballistic missile is likely to come from.
Whilst Phased Array Radars may be able to provide some tracking at such elevated angles, their tracking performance is likely to be sub-optimal since it is likely to be at or near the extremities of the electronic steering capabilities of the radar.
To illustrate this, let's look at the Aegic cruiser, which mounts 4 PARs to provide all-round horizontal coverage. Thus, it can be deduced that the optimal coverage of each PAR is ~90 deg (or +/- 45 either side of its facing). Factoring in an arbitrary overlap (since the actual overlap is classified and not in public domains) of +/- 15 deg provides a good coverage of +/- 60 deg coverage either side of its facing. Applying this to the vertical plane (assuming the performance horizontally and vertically is similar), than a ballistic missile coming in at 80deg on top of its target will make tracking difficult for an Aegis ship.
Personally, I believe this is 1 of the factors that drove PLAN thinking in development of the ASBM.
2. Conventional CIWS. These weapons are traditionally optimised for sea-skimming missiles. Typically, these systems have their own tracker, but needs to be cued to the target by surveillance radars so that their trackers can lock on to the target. Thus, pt 1 above needs to be solved for these guys to be useful.
In addition, there is a upper limit to their elevation. The latest Phalanx CIWS can be elevated up to 85 deg.
Thus, a ballistic missile coming in at more than 85 deg renders this weapon useless since it is beyond its firing arc.
Even if the ballistic missile is coming in at high elevations such as 80 deg, and the CIWS is able to hit the ASBM, the resulting debris travelling at hypersonic speeds will still hit the target ship. Not a happy prospect.
3. Laser Weapons. 1 of the most interesting aspects I find about Pentagon reports on their laser weapon developments is that they omit important information that relates to the effectiveness of the laser weapon itself.
a. How long does it take the laser (such as the ABL) to do damage to its target? The recent ABL test failure alluded to this aspect whilst previous statements did not mention how long it takes for the laser to cause damage at all.
Personally, I think the laser will take some time to shine at the same spot before it causes any damage (based on my experience doing experiments with lasers in my physics lab during my student days). The duration is likely to be more than a few seconds. And the greater the range, the longer the duration required (tyranny of inverse square root). If the duration required is in the order of 0.5 mins or more, than laser as a CIWS defence against a ASBM is practically useless.
b. What is the recharge time for lasers weapons before they can fire again? This was never mentioned anywhere at all in reports. While the mobile THEL was mentioned as:
The report did not mention whether the multiple mortar rounds were shot down within a few minutes, or the shooting down took place over an hour (or longer duration).
c. What is the effective range of laser weapons? For the ABL, the test range was never revealed, although the recent failed test was mentioned to be at a range of more than 50 miles. Since it was also mentioned that this is double the range of the previous successful test, the logical deduction is that the ABL was successfully tested at less than 50 miles previously.
Assuming that the ABL has an effective range of 100 miles (double what was revealed), let's look at what this means for laser weapons (taking into consideration pt 2 above).
i. At current tech levels, a laser the size of a 747 aircraft is effective out to 100 miles. Scaling it down means that vehicle mounted lasers will be effective at much shorter ranges. On the other hand, ship mounted lasers can conceivably be effective at more than 10 miles (if mounted on a large enough ship, such as a cruiser). This makes the laser more effective than a CIWS, if it can have a high rate of fire and is lethal in short time durations (seconds, not mins).
ii. The ABL takes advantage of the rarefied atmosphere at high altitudes, which translates into reduced atmospheric dispersion for the laser beam, thus increasing its effective range.
There is no such luxury at sea level.
The salt content at sea level, and higher levels of moisture (dust in land environments) in the air will result in higher levels of atmospheric dispersion for the laser beam. Which translates into reduced effective range for the laser.
While all the points above sound like serious constrains to laser weapons, it does not mean that they are not viable. However, it does mean that a lot of developmental effort will be required to overcome all these challenges to make laser weapons viable in an operational environment.
Furthermore, the advantages of a speed of light weapon is not to be dismissed lightly. If successful, laser weapons will probably revolutionise warfare the same way guided weapons did in the past.
Thank you for the indepth analysis! What is your opinion on pulse lasers, which deal damage through ablation and not through direct heating?