There's a trade off between how efficient a thruster is, and how much power it produces over a fixed amount of time. (Good reading is the specific impulse arti

There's a trade off between how efficient a thruster is, and how much power it produces over a fixed amount of time. (Good reading is the specific impulse article on Wikipedia: http://en.wikipedia.org/wiki/Specific_Impulse http://en.wikipedia.org/wiki/Specific_Impulse ) At any given point, our technology allows us to create highly efficient but relatively "weak" engines (e.g. ion thrusters), or "powerful" but inefficient ones (e.g. rockets). Actually, both use Newton's second law to generate thrust, i.e. some kind of material has to exit the engine in the opposite direction, in order to get things moving. So, even ion drives and similar designs carry some material for the purpose of being ejected, it's usually just on a completely different scale to rockets. Energy also needs to come from somewhere to facilitate this, with rockets, it's the chemical energy from the fuel itself. With ion drives, it is usually some form of electricity, generated with a solar panel or nuclear power plant, etc. So in reality, even the efficient drives also have to carry some way to power themselves. To get more thrust, they need to have more power. If you run the maths, by the time they have enough power to overcome Earth's gravity, they need to have an entire solar farm worth of panels (which are heavy), or a rather large nuclear power station on board (which is also quite heavy). So, unless we find ways to make more powerful sources of energy, or even more ridiculously efficient drives, the thrust coming from these will not be able to overcome near-Earth gravity.