Editing Spaceflight (section)

=== Reaching space ===
The most commonly used definition of [[outer space]] is everything beyond the [[Kármán line]], which is {{convert|100|km|mi|sp=us}} above the Earth's surface. (The United States defines outer space as everything beyond {{convert|50|mi|km|sp=us}} in altitude.)

[[Rocket engines]] remain the only currently practical means of reaching space, with planes and [[high-altitude balloons]] failing due to lack of atmosphere and alternatives such as space elevators not yet being built. Chemical propulsion, or the acceleration of gases at high velocities, is effective mainly because of its ability to sustain thrust even as the atmosphere thins.

==== Alternatives ====
{{Main|Non-rocket spacelaunch}}

Many ways to reach space other than rocket engines have been proposed. Ideas such as the [[space elevator]], and [[momentum exchange tether]]s like [[Rotovator (tether propulsion)|rotovators]] or [[Skyhook (structure)|skyhooks]] require new materials much stronger than any currently known. Electromagnetic launchers such as [[launch loop]]s might be feasible with current technology. Other ideas include rocket-assisted aircraft/spaceplanes such as [[Reaction Engines Skylon]] (currently in early stage development), [[scramjet]] powered spaceplanes, and [[Rocket-based combined cycle|RBCC]] powered spaceplanes. Gun launch has been proposed for cargo.