The SpaceX Kestrel was an LOX/RP-1pressure-fedrocket engine. The Kestrel engine was developed in the 2000s by SpaceX for upper stage use on the Falcon 1 rocket. Kestrel is no longer being manufactured; the last flight of Falcon 1 was in 2009.
Kestrel was built around the same pintle architecture as the SpaceX Merlin engine but does not have a turbopump and is fed only by tank pressure.
Kestrel was ablatively cooled in the chamber and throat and radiatively cooled in the nozzle, which was fabricated from a high strength niobium alloy. As a metal, niobium is highly resistant to cracking compared to carbon-carbon. According to SpaceX, an impact from orbital debris or during stage separation might dent the metal but have no meaningful effect on engine performance.[4]Helium pressurant efficiency is substantially increased via a titanium heat exchanger on the ablative/niobium boundary.[5]
Thrust vector control is provided by electro-mechanical actuators on the engine dome for pitch and yaw. Roll control (and attitude control during coast phases) is provided by helium cold gas thrusters.
A TEA-TEB pyrophoric ignition system is used to provide restart capability on the upper stage and simplify design.[6] In a multi-manifested mission, this design would allow for drop off at different altitudes and inclinations.
Kestrel 2
Enhancements to the design of the original Kestrel engine were planned, called the Kestrel 2.[7]
The engine design was still pressure-fed, and was supposed to fly on a newly designed second stage that used Aluminium-lithium alloy2195, rather than the 2014 Aluminum used in the Falcon 1 second stage.[7]
Engine changes were to include tighter tolerances to improve consistency, higher Isp, and lighter weight.[8]
The Kestrel 2 did not remain in active development after the Falcon 1 was replaced by the much larger Falcon 9 v1.0 which used an improved Merlin 1C for its upper stage.
