how ICBM works , and is solid state rocket is better for long range target instead of liquid propulsion
Answers
Actually, not all ICBMs have all-solid stages and not all Satellite Launch Vehicles have all-liquid stages.
Let’s take the example of the world’s first ICBM - The R7 Semyorka. It had It had 4 jettisonable RD-107 boosters and an RD-108 core stage. Both RD-107 and RD-108 were four combustion chamber clustered liquid rocket engines which used Liquid Oxygen and Kerosene.
One of the most powerful ICBMs ever built, the R-36M - known by its NATO name SS-18 Satan, has two stage liquid rocket engine.
But some ICBMs, such as SS-20 Saber, have two stage solid rocket motors.
The choice completely depends upon the design philosophy and operational requirements. In a general case, the Liquid Rocket Engines can be throttled. They also have a start stop mechanism, such that a more precise control over the the trajectory can be exerted. To put it simply, the flow control is achieved by adjusting the pump speeds and the valve mechanism. However, there are many other ways to control the flow.
Solid Rocket Motors do not have an active throttle control. The variation in thrust can be controlled by the precisely controlling the grain composition and geometry. That is, the composition of the mixture of solid fuel, oxidiser, binder resin, retarding agent etc.