Combustion tap-off cycle


Diagram of the open-cycle combustion tap-off rocket cycle. A small portion of exhaust from the combustion chamber is tapped off to power the turbine(s).

The combustion tap-off cycle is a power cycle of a bipropellant rocket engine. The cycle routes hot gases from the main combustion chamber of the rocket engine and routes them through engine turbopump turbines to pump fuel, then is exhausted. Since not all fuel flows through the throat into the nozzle, the tap-off cycle is considered an open-cycle engine. The cycle is comparable to a gas-generator cycle engine with turbines driven by main combustion chamber exhaust rather than a separate gas generator or preburner.[1]

The J-2S rocket engine, a cancelled engine developed by NASA, used the combustion tap-off cycle and was first successfully tested in 1969.[2]

By 2013, Blue Origin, with their New Shepard launch vehicle, had successfully flight-tested the BE-3 engine using a tap-off cycle. According to Blue Origin, the cycle is particularly suited to human spaceflight due to its simplicity, with only one combustion chamber and a less stressful engine shutdown process. However, engine startup is more complicated, and due to its nature of feeding gases from the main combustion chamber into the turbopumps, the turbine must be built to withstand higher-than-normal temperatures.[3] In contrast, the upper-stage variant of the BE-3, the BE-3U, uses an expander cycle to power the turbopump, and will be used on the upper stage of the New Glenn launch vehicle.[4]

See also


  1. ^ Sutton, George (November 2005). History of Liquid Propellant Rocket Engines. American Institute of Aeronautics & Astronautics. ISBN 978-1563476495.
  2. ^ "Altitude Developmental Testing of the J-2S Rocket Engine" (PDF). Defense Technical Information Center. Defense Technical Information Center.
  3. ^ Norris, Guy (9 December 2013). "Blue Origin Tests New Engine". Aviation Week & Space Technology. Penton. Retrieved 3 February 2016.
  4. ^ BE-3 test update, Blue Origin, 10 August 2018, accessed 15 August 2018].