What are Some Unusual Forms of Space Propulsion?
Typical forms of space propulsion today are solid rocket boosters, liquid rockets, and hybrid rockets. All carry their fuel on board and use chemical energy to produce thrust. Unfortunately, they can be very expensive: it may take 25-200 kilograms of rocket to deliver a 1-kg payload to low Earth orbit. Lifting a kg to low Earth orbit costs a minimum of $4,000 US Dollars (USD), as of 2008. $10,000 USD may be more typical. The chemical rocket approach to space launch and travel is fundamentally limited. Because a rocket must propel its own fuel upwards through the densest part of the atmosphere, it isn’t very cost effective. A more recent invention is the private spacecraft SpaceShipOne, which used a carrier craft (White Knight) to carry it to 14 km (8.7 mi) altitude before launch. At this height, greater in altitude than Mt. Everest, SpaceShipOne is already above 90% of the atmosphere, and is able to use its small hybrid engine to travel the rest of the way to the edge of space (100 km
