ramana: I don't have to be an adherent to anything to consider the implications of what people are doing (BTW, what is CT?) (or, correction, I am a Flat Earth Society adherent, based on the link I posted). I am not going to do any comparison of Agony anything with anything - those are for ppl who want to show off their detailed inside knowledge of military stuff. I am bissful onlee, as u know.
The reasoning above is based on what ppl are posting, and it is actually new to me. I was not aware of the imminent nature of these things, but like the "Paki Nook-Nood", I can speculate on what I would do, and reason that ppl who are smart and focused will do even better.
About the Megawattage needed to burn through rocket tanks in boost phase, I am sure it is quite large, and focusing it to the tight beam diameter needed, seems a very tough challenge. Making sure that there are enough optical systems close enough to hit a number of launches within seconds seemed hopeless even if it was North Korea, so I never paid much heed to BPI. My realization is based on what Gerard posted:
That the US, Russia and China are going to great lengths to counter boost-phase intercepts on their first-stage vehicles.
So if I believe that this is not disinformation, I ask why they are doing this. I ask ppl to do simple trignometry which is not ITAR yet, and calculate how high up you have to be, while staying outside the borders of these countries, to hit something rising from their typical silo sites while the vehicle is still below, say, 100,000 feet (to have any impact on the first stage fuel tank). This will immediately show with middle-school level mathematics that the perceived threat is not from ground-based, water-based or aircraft-based beam weapons. This leads to a 4th possibility. I am not an expert on any of these, so I had no idea of what the present capabilities are. But now I can see that people fear the 4th possibility. There's your answer: I don't have to waste time calculating MW or GW or atmospheric distortion or absorption spectra to the 4th decimal place. I can work backwards and see what is implied about the sort of vehicles that constitute the "4th possibility" but need not go into detail. I just have to see what people are preparing for.
IOW, if I see people putting plastic sheets over levees and dumping sandbags on top, I gather that they fear rising rivers, weakness of rain-soaked levees, etc. more than they fear drought or earthquake. I don't have to do detailed weather prediction models or seismology as your advice suggests.
Obviously these nations would not be spending money on hardening skins, putting reflective coatings, minimizing window of vulnerability with risky fast-burn propellants, etc. if they saw no danger in the next, say, 30 years.
Then I ask what that implies for the chances of Indian launch vehicles, if these big nations fear boost-phase intercept on their vehicles (which implies certain locations and technology for BPI as seen above).
If these large countries are worried about the "4th possibility" for BPI, then surely they have also concluded that mid-course intercept in orbit is entirely feasible, using kinetic kill. If they fear one of the other countries is putting up such resources, then they are also probably doing / planning to do so. So they are also seeing how to shoot down such defenses, which is what the Chinese ASAT did. That was a hit on a satellite, not a weapon trajectory. The US response was to hit a large tumbling satellite near re-entry. You can see the lessons from both of those.
The tests from the Japanese warship Kongo showed that they can now hit a missile 60 miles above sea level, 7 minutes into its flight. This is an IRBM in the upper atmosphere, or an ICBM climbing to space.
The Indian tests also show similar capabilities. Announced twice already, and with media present.
The THAAD tests by the US show hits on missiles nearer to the target (I think). Anyway, if you can hit something at 60 miles up 7 minutes into flight, you can also hit it at 60 miles, 15 or 30 minutes into flight (it may be much faster, but you just have to stand in its way or get your fingers there, as I demonstrated with the goalie analogy).
The other part is terminal-stage intercepts at fairly high altitudes. Yes, fast air-launched interceptors, probably unmanned to take the high-Gs, are what I would use as the equivalent of the racing fielder, to get close to the anticipated trajectory of the warhead. Then I would use small, very fast vehicles to do a dispersed kinetic-kill cloud using an explosion, if it is not close enough for a direct impact. This is the equivalent of the fielder's or goalkeeper's diving reach. Either way, people who do air-to-air gaming and control work can figure out the best way to do these. The ASAT and the Indian/US/Japanese tests show that the timing can be perfected and recalculated to hit something at such enormous speeds, correcting for atmospheric deflections etc. Now if you have aerodynamic maneuvering and airbreathing thrust as well, doesn't the probability go way up?
What matters is that with air-launched, you get vastly more area coverage, can wait to launch until you are quite sure, can recover MOST of the "boost vehicle", and have the two huge advantages of air-to-air intercept:
1) actual height and
2) total energy
at start of game.
In every way, the game is entirely different than with ground-launched intercepts, EXCEPT that air-launched may not be enough to deal with permanent sentry duty against a single surprise attack. You may not always have large airplanes on patrol, but in a threat situation, you will have many on patrol.
So probability of kill in every stage of the ballistic trajectory is easily over 50%, and terminal stage intercept using air-launched intercept, I believe is over 90% (the "dropped catch" or "tipped goal shot" is the exception, not the expectation). Put all those together, and you realize that the ballistic attacker is out of the game altogether, so again, the relevance to this thread is that MT-level warheads are a hopelessly flawed approach to deterrence, starting pretty soon.
I forgot about the final defence: Patriot-type things for point defence.
If anyone has detailed counters to these, I will be glad to be educated.
BTW, just as a point for anyone impressed by "fast-burn". Theoretically, the ideal way to launch a ballistic vehicle is by Impulse Launch. This is why Jules Verne imagined people being launched in cannons to the Moon. The idea is simple: you put ALL your thrust into as short a time as possible, so that you don't waste any fuel boosting other fuel to some height and speed. "Less Luggage, More Comfort. Make Travel a Pleasure" as Indian Railways used to say.
So "fast-burn" is more efficient that way. The down sides are
1) Fast burn takes you close to the stability boundary for a rocket, IOW, explosion probability is very high. This is also an easy calculation, but not one I want to post here.
2) High thrust-to-weight ratio at liftoff means that the whole vehicle must be built to take stresses of several times its weight. So the fuel tanks etc. become much heavier, so for the same total mass, the final velocity or height reached by the payload is lower. This cancels out most of the efficiency advantage for long-range vehicles.
So fast-burn missiles are highly dangerous to those launching it, and are probably less efficient overall in getting a given mass to a given speed and height. HOWEVER, they will do so in LESS TIME, and they spend much less time dilly-dallying at low acceleration right after liftoff.
When you are faced with an incoming warhead, this is probably the biggest factor, so interceptor missiles will use fast-burn regardless of the hazards. Using it on long-range missiles indicates that the missile can easily achieve the intended range and warhead mass, so they can afford to play with the vehicle total mass in order to reduce flight time, and MAYBE reduce chances of boost phase intercept.