VTVL

Vertical takeoff, vertical landing (VTVL) is a form of takeoff and landing for rockets. Multiple VTVL craft have flown. As of 2016^[update], VTVL is under intense development as a technology for reusable rockets, with two companies, Blue Origin and SpaceX, both having 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 following a test flight that reached outer space, and SpaceX's Falcon 9 Flight 20 marking the first landing of a commercial orbital booster, both in late 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.

The technology required to successfully achieve VTVL 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 attitude 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. Landing legs and deployment mechanisms add to the weight of the vehicle compared to expendable vehicles, which can reduce performance. Aerodynamics and mass distribution are also crucial; vehicles generally have to be nose heavy during ascent, but need to be stable during landing, usually on their tail, and after touchdown, where they are susceptible to winds.

It can also be necessary to be able to ignite engines in a variety of conditions potentially including vacuum, hypersonic, supersonic, transonic, and subsonic.

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