Why does missiles and satellite launch vehicles have 2-3 stages?

Question

In some missiles and satellite launch vehicles,different fuels are used in different stages.For eg in a launch vehicle used to launch heavy satellites use cryogenic engines in their upper stage.those stages use fuels different from the 1st stage.why cant there be a single stage launch vehicle?how does these stages separate from each other in flight.

Answer 1

Simply put, 2-stage or 3-stage rockets are currently the most efficient way to get payloads into the required orbits (or trajectories for deep-space). Why carry the 'dead weight' of an empty 1st stage when you can 'dump' it the moment its fuel/oxygen tanks becomes empty?

A single-stage-to-orbit (SSTO) rocket would be any space agency's 'dream', but it is just not feasible with current technology.

Stages separate from one another by using explosive bolts. When it's time to separate, squibs are electronically activated and set-off the bolts holding the stages together. When the bolts explode, there is no longer anything to hold the stages together and the lower stage 'falls' away.

More manufacturers of upper stages are designing them for cryogenic fuels because they are more efficient (weight and volume-wise), and because the technology now exists (carbon fiber, newer materials) to make these engines robust and practical.

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Answer 2

Initial reports on FOX say that South Korea (unconfirmed) says that North Korea did indeed launch a satellite, just as they said. The problem is that if they have successfully launched a 3-stage rocket that successfully put a satellite in space, that same rocket could be armed with a warhead and travel 4,000 miles or more. The White House response so far is that the act was 'provocative'. I really don't know what Obama will do about it - maybe some type of pre-emptive strike against the launch site, such as what Israel did to Syria last year. Remains to be seen.