1st, well if its launched a reasonable distance inside Russia, I cant see how its likely to be intercepted in the boost phase, if solid fuel rockets cant be intercepted.
What they are talking about is the early period of the Rockets flight when it is most vulnerable.
During the boost phase even the cheapest crappiest IR sensor can detect that enormous plume of fire coming out the rear of the missile... all the warheads are together and the decoys have not been deployed so for 500 warheads... lets assume about 80 rockets where some have three warheads and some have 10. This means an ABM system in Alaska has to intercept 500 real warheads and thousands and thousands of decoys. A system in Europe however has to intercept about 80 rockets.
Solid fuelled rockets burn out quicker so they are not blinding targets for as long as a liquid fuelled rocket.
They are also less powerful than liquid rockets.
(BTW yes, I know liquid fuel rockets have a longer boost stage, but on current technology, I still cant see the US hitting a missile 1200 km inside Russia in boost phase).
Due to the rotation of the earth the Russian rockets don't go over the north pole, for targets on the US east coast their trajectory would actually take them over northern europe.
The George Bush jnr plan was enormous interceptors that would have intercepted ICBMs well above Europe.
The current plan is ship based so a group of AEGIS class cruisers in the North Sea and Arctic ocean could be positioned to stop Russian ICBMs easily... the positioning of them will be easy... not the interception itself.
The point is that the radars in Europe should give them the early warning and precise trajectory information they would need for the interception attempts...
2nd, does it have to be silo launched and not vehicle launched?
Silos are already built and are actually much cheaper to use than mobile systems that require far more security.
The only real threat to a silo is an ICBM/SLBM or B-2 and there should be enough warning for the silo to be empty by the time the silo is taken out.
3rd could it be a hybrid missile eg some stages liquid, others solid fuel?
Solid fuel is expensive, modern liquid fuels are storable for the operational life of the missile and more powerful than current Russian solid fuels. They also offer the flexibility in being shut down and restarted so depressed trajectories can be implemented.
Finally, once again I wonder, why the hell does Russia spend billions on negotiating the US nonsense. Wouldnt it make sense to base shorter range missiles in Cuba, Venezuela and friendly West Indian states too?
Being an @$$hole to an @$$hole is self defeating... let them play their stupid games and let them think it makes them safer. The secret is to work out counters that will render their expensive white elephants useless without costing Russia too much.
Having a heavy weight ICBM with a 5 ton throw weight means it can be loaded with heavier warheads now but in the future if START changes or is ripped up they can load lighter smaller warheads in much larger numbers so they can rapidly increase warhead numbers without having to spend money on more missiles. In the mean time the extra space can be used for decoys and penetration aides.