The landing gear of a F-104 Starfighter (shadowed)
Landing strut or landing gear was a component of some spacecraft which were capable of entering a planet's atmosphere and landing on the surface. Before the introduction of spacecraft, landing gear was used for aircraft. Normally inside the ship, the landing struts were exposed by moving panels when needed. The landing gear served to steady and support the starship upon landing. It was possible for a starship's landing gear to become stuck on a planet's surface. (VOY: "Demon")
The landing gear of an Apollo spacecraft
The lunar module of the Apollo spacecraft was equipped with landing gear. (TOS-R: "The Cage")
"Chapter 18: Bride of Chaotica", from The Adventures of Captain Proton, started with the crash landing of Captain Proton's rocket ship after the landing gear jammed. (VOY: "Bride of Chaotica!")
Klingon Bird-of-Prey landing struts
Klingon Birds-of-Prey were equipped with landing struts, and the Bird-of-Prey rechristened as the HMS Bounty by the senior staff of the late USS Enterprise used its two struts to land on Vulcan in the mid 2280s. (Star Trek III: The Search for Spock; Star Trek IV: The Voyage Home)
Intrepid-class landing struts
Starfleet's Intrepid-class was equipped with landing struts, and the USS Voyager used these several times while stranded in the Delta Quadrant in the 2370s. These occasions included an attempt to investigate the origin of an SOS on a planet with a turbulent atmosphere that would prevent shuttles and transporters arriving safely, when the Kazon temporarily stole the ship and abandoned the crew on a barren planet, when attempting to mine fuel supplies with limited power reserves available, to escape an attack by entering the hostile atmosphere of an abandoned world, and when performing vital maintenance on the ship's warp core. (VOY: "The 37's", "Basics, Part I", "Demon", "Dragon's Teeth", "Nightingale")
Protostar-class landing struts
Starfleet's Protostar-class was also equipped with a single, large landing strut located beneath the ship's center of gravity. It was wide and sturdy enough to withstand skidding across surfaces. (PRO: "Dream Catcher", "All the World's a Stage")
In 2384, the landing gear of the USS Dauntless was listed with other rooms, technologies, and systems for engineering in an operations panel on the main bridge. (PRO: "Mindwalk")
The Lamarr-class science vessel possessed landing struts. The USS Voyager-A used them to land on Solum for first contact with the Vau N'Akat. (PRO: "Ouroboros, Part II")