Men have attempted to fly for a very long time. From the early attempts by Daedalus and his father to fly on wings to the Wright brothers men have wished to reach higher and higher.
In the early days of rocketry men floated or rose into the air by the use of balloons particularly hot air balloons. The earliest and simplest example or model of a balloon would be perhaps the sky lantern that rose up with a candle heating the balloon in the place of a closed paper structure (pictured).
|Candle placed at the base of a balloon envelope (like an enclosed||lamp shade)|
You can see the principles upon which a rocket flies if you blow air into a balloon , then hold the air filled balloon by pinching the opening of it, then release the opening of the air filled balloon and watch it "rocket" through the air. As we see in the following diagram this is the principle that makes a balloon "rocket" through the air :
It is on this principle that rocket engines are perhaps based upon: a souped up hot air balloon.
Following are figures illustrating the general idea behind a rocket engine. It illustrates how gases trapped in a sphere when given an outlet propel the object so:
|As opposed to a balloon's envelope here the hot air pushes against the dome and exits via the nozzle propelling rocket forward|
|Above is how a rocket works - very similar to how a hot air balloon might operate|
|A simplified rocket Engine (oxidizer optional)|
If you are wondering how the ignition happens in an ignition chamber it is along the same lines as the ignition that happens in your car's internal combustion engine :
|A Car's internal combustion engine |
1) fuel comes in
3) the spark plug (of your car) ignites the fuel
4) the air expands and pushes the lever and
exhaust leaves through the other end after having
pushed the piston down
Essentially then all rockets are composed of dozens of hot air balloons at the bottom. With a hot air balloon there is only one "combustion chamber" :
|There can be dozens of engines at the bottom providing thrust|
Perhaps expenditure on space is useful because it may help us alleviate poverty, suffering and privation. However to set aside work against poverty , disease, labor, sustainability and scarcity and to work to escape earth and the solar system (particularly in anticipation of its demise) is incorrect even if a "backup colony" argument is used.