起落架
Landing gear has traditionally not been used on the vast majority of launch vehicles, which take off vertically and are destroyed on falling back to earth. With some exceptions for suborbital vertical-landing vehicles (e.g., Masten Xoie or the Armadillo Aerospace' Lunar Lander Challenge vehicle), or for spaceplanes that use the "vertical takeoff, horizontal landing" (VTHL) approach (e.g., the Space Shuttle orbiter, or the USAF X-37), landing gear have been largely absent from orbital vehicles during the early decades since the advent of spaceflight technology, when orbital space transport has been the exclusive preserve of national-monopoly governmental space programs. Each spaceflight system through 2015 had relied on expendable boosters to begin each ascent to orbital velocity.