Senior Science Fellow Phil Coyle was quoted in LiveScience explaining the science behind ICBMs:
At takeoff, the ICBM enters the boost phase. During this phase, the rockets send the ICBM into the air, pushing it upward for about 2 to 5 minutes, until it reaches space, Coyle said. ICBMs can have up to three rocket stages. Each one is discarded (or ejected) after it burns out. In other words, after the first stage stops burning, rocket No. 2 takes over, and so on.
Moreover, these rockets can have liquid or solid propellant. Liquid propellants “generally burn longer in the boost phase than solid-propellant rockets [do],” Coyle said. In contrast, solid propellants “provide their energy in a shorter amount of time and burn faster.”
Liquid and solid propellants can send rockets equally far, “but most countries start out with liquid propellant technology because it’s well understood,” Coyle said. “[As] they graduate, they move to solid propellant to get the faster burn times. It also avoids the hazards of dealing with dangerous liquids that are both flammable and toxic.” Read more