Why to develop S-500 and A-235 is both have similar characteristics?
Not an expert in what each one does.. but by looking at the design alone you can
notice major differences just with pure observation.
A-135 and A-235 are purely fixed silo position , looks like a giant kinetic bullet.
and its designed for speed and interception ,many say is a hit to kill missile and its looks like
that. If you look at the head of the missile is like a spear with no sensors or guidance.
So it pretty much looks like an unguided kinetic missile and apparently have a nuclear warhead too.. according to wiki. This means that they are not like missiles but more like Anti ICBM artillery. To intercept nukes in the final phase 30km away of the target. So A-135 and A-235
can be said to be final phase anti ICBM artillery. Something like Active defense Arena for nukes.
It sacrifice range and maneuverability for speed and with the nuclear warhead it will defeat any missile and its decoys that comes close to it.
S-500 in the other hand are anti air +anti space missile. and can be used against anything that fly and is big. Does not use nukes but conventional warhead.. and it have sensors ,to chase things.
That said it looks the S-500 is a mid course ,any altitude air+space interceptor.
can be used against anything ,and the A-135 and A-235 is a final course anti ICBM artillery interceptor and can only target things withing 30km of distance of its deployment.
So S-500 target first nukes on its mid course before it deploy its decoys and if they fail.. the A-235 will intercept any ICBM that deploys its decoy defenses using a nuclear warhead. Both have its uses and its place and i don't think neither one replace the other.
S-400s in the other hand can probably do similar to the S-500 but with a more limited altitude range of interception. Apparently is 180km altitude ,which is not enough to intercept high altitude ICBM in space .
In theory if Russia had enough A-135 and A-235 it will handle any Trident mas attack without problems. because a nuclear warhead will wipe completely any missile and its defenses.. since target a wide area the nuclear warhead.
In real practice any system of defense in the world can be overwhelmed.. including Americans ones. So to fully defend against a mass nuclear attack of a thousand of missiles from Russia and USA is looks like wishful thinking with the weapons they have today.
Russia however is doing something very interesting with Electronic Jamming , KRET is developing a system to neutralize satellites and ICBMs in space, This means that its guidance will be dead and it will be impossible to have any accuracy. So a missile aiming Moscow could end in SIberia.. etc. Or if they take things to a new level it could destroy all the electronics of any American ICBM so it doesn't explode. So is not clear what kind of level of protection Kret company in Russia is aiming with its space counter electronic warfare. If they are successful if neutralizing ICBM electronics it will be like the invention of Powder and the plane. Truly game changing and tip the balance enourmously in Russia favor in a nuclear war. All said. Electromagnetic radioelectric weapons have a lot of future.. same can be said about lazer guns.
But radioelectric space weapons seems much more elegant ,stealthy and powerful since it target big areas at same time While lazers you need to aim directly at individual targets and require insane levels of Energy.