Propulsion
Introduction
There are many and varied forms of propulsion available. What you choose will depend upon your budget and on what yoy are trying to propel.
tiny gas jets are sufficient for maneouvers beyond the karman line, but where gravity is stronger, significantly more thrust is required.
Vertical lift from the ground is the most difficult to achieve, and requires the greatest thrust capacity. If considering a launch vehicle, consider options such as horizontal lift from a conventional runway, or hitch a ride, as demonstrated by the recent successful sub-orbital launches by White Knight / SpaceshipOne.
Fuel can be expensive - it is also potentially dangerous. Again, consider some of the recent research into hybrid fuels, which are intrinsically safe until combined. Long reach interstellar travel is really beyond the scope of this site, but research here suggests that ion drives or space 'sails' are the best option.
Air breathing designs can be effective for low / mid altitude lift, but you will need to supply all elements required for high altitude / space propulsion.
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