When it comes to the future of aerospace power fear that people will first think of nuclear power, our current chemical fuel rocket thrust was too small, so each shot must find the right launch window in order to use the planet's gravity to accelerate, so that they can really fly to deep space, up to now, all deep space probe launched by the humans do not have a do not use the planet's gravity. This is a clever idea, but, after all, only reluctantly alternative means is time consuming, and the route is too restrictive. Installed nuclear-powered spaceships and probes because thrust is powerful, you don't need to use the planet's gravity, not to worry too much on the restrictions on the routes.
But development of nuclear-powered engine is not as easy as expected, rocket engines now rely on jet fuel after combustion gases, according to conservation of momentum, the rocket itself would be the thrust. Nuclear-powered engine problem here, however, that there was no material available for Jet. Even nuclear-powered engine can generate enormous amounts of energy, nor itself provided the momentum for the rocket bodies, energy is wasted as heat radiation only.