Spaceplane Hangar
From Kerbal Space Program Wiki
The Space Plane Hangar is a building recently added to Kerbal Space Program which allows players to construct air and spacecraft in a horizontal environment and proceed to launch them from a conventional runway. The Space Plane Hangar made its debut with the release of KSP v.15.
The hanger either allows a single part to be placed, or two which can get closer to each other as you move them up and down.
