
VTVL

Vertical takeoff, vertical landing (VTVL) is a form of takeoff and landing for rockets. Multiple VTVL craft have flown. The most widely known and commercially successful VTVL rocket is SpaceX's Falcon 9 first stage.
VTVL technologies were developed substantially with small rockets after 2000, in part due to incentive prize competitions like the Lunar Lander Challenge. Successful small VTVL rockets were developed by Masten Space Systems, Armadillo Aerospace, and others.
Starting in the mid 2010s, VTVL was under intense development as a technology for reusable rockets large enough to transport people. In 2013, SpaceX demonstrated vertical landing on a Falcon 9 prototype after climbing 744 meters in the air. Later, Blue Origin (New Shepard) and SpaceX (Falcon 9), both demonstrated recovery of launch vehicles after return to the launch site (RTLS) operations, with Blue Origin's New Shepard booster rocket making the first successful vertical landing on November 23, 2015 following a flight that reached outer space, and SpaceX's Falcon 9 flight 20 marking the first landing of a commercial orbital booster roughly a month later, on December 22, 2015.
VTVL rockets are not to be confused with aircraft which take off and land vertically which use the air for support and propulsion, such as helicopters and jump jets which are VTOL aircraft.
Vertical landing technology.
The technology required to successfully achieve retropropulsive landings—the vertical landing or "VL" addition to the standard vertical takeoff (VT) technology of the early decades of human spaceflight—has several parts. First, thrust must be greater than weight, second the thrust is normally required to be vectored and requires some degree of throttling. Guidance must be capable of calculating the position and altitude of the vehicle, small deviations from the vertical can cause large deviations of the vehicles horizontal position. RCS systems are usually required to keep the vehicle at the correct angle.
SpaceX also use grid fins for attitude control during landing of their Falcon 9 boosters.
It can also be necessary to be able to ignite engines in a variety of conditions potentially including vacuum, hypersonic, supersonic, transonic, and subsonic.
The additional weight of fuel, larger tank, landing legs and their deployment mechanisms will usually reduce the performance of a soft landing system compared to expendable vehicles, all other things being equal.
The main benefit of the technology is seen in the potential for substantial reductions in space flight costs as a result of being able to reuse rockets after successful VTVL landings.
Popular culture.
Vertical landing of spaceships was the predominant mode of rocket landing envisioned in the pre-spaceflight era. Many science fiction authors as well as depictions in popular culture showed rockets landing vertically, typically resting after landing on the space vehicle's fins. This view was sufficiently ingrained in popular culture that in 1993, following a successful low-altitude test flight of a prototype rocket, a writer opined: "The DC-X launched vertically, hovered in mid-air ... The spacecraft stopped mid-air again and, as the engines throttled back, began its successful vertical landing. Just like Buck Rogers."
In the 2010s, SpaceX rockets have likewise seen the appellation to this popular culture notion of Buck Rogers in a "Quest to Create a "'Buck Rogers'" Reusable Rocket."