A jetavator is a device used to redirect the thrust of a rocket engine or motor. It differs from an aerodynamic control surface in that it operates by modifying the rocket exhaust rather than the surrounding airflow, and it differs from a jet vane in its shape and position. In general, a jetavator is a ring which, when in its neutral position, surrounds the active rocket exhaust jet. By tilting the vane in two dimensions, it can be induced to impinge on the edges of the thrust path in the form of an arc centered at the desired point. This will deflect some of the exhaust laterally, and as a result, change the sum vector of the rocket's thrust. This will impart a turning force on the rocket - or rather, on the body containing both the rocket and the jetavator mechanism. The name likely is a portmanteau of jet and elevator - as in the control surface. Jetavators are generally used with solid-fuel rockets, since unlike liquid-fuel rockets they do not have a discrete combustion chamber which can be swiveled to redirect the thrust.
The jetavator is an improvement on the earlier jet vane. A jet vane is a surface or shape which usually lies within the thrust jet, and in its neutral position lies parallel to the direction of thrust. For instance, a flat surface with its edges pointed fore and aft. However, unlike the jet vane, the jetavator does not lie in the thrust path except when it is actuated and moved to direct thrust, resulting in less stress and loss of effective thrust when not steering. Mounting and actuating a jetavator, however, is slightly more complex than mounting a jet vane. This is partially offset by the fact that its control mechanisms and structure need not withstand constant heat and battering from the exhaust.
The idea of the jetavator was first developed by a German engineer named Willy Fiedler. A test pilot in Germany when young, he worked as an engineer on the V-1 Fieseler Fi-103 or buzz-bomb. After the war, he came to the United States in 1948 along with his family under the auspices of Project Paperclip. While working at Point Mugu Naval Air Station for an organization that would eventually become part of Lockheed Aerospace, he came up with the jetavator as an evolution of the jet vanes that were used to control the V-2 rocket. The jetavator was first used in large scale in the U.S. Polaris missile, which, being launched from a conformal launch tube aboard a submarine was unable to rely on external aerodynamic control surfaces.
- Buchheim, Robert W. The Space Handbook: Astronautics and its Applications. Ch. 9 - Flight Path and Orientation Control. (RAND, Santa Monica, 1958).
- Launius, Roger D. and Jenkins, Dennis R.. To Reach The High Frontier: A History of U.S. Launch Vehicles. (University Press of Kentucky; Louisville, 2002) p. 246.