Kestrel was built around the same pintle architecture as the Space X Merlin engine but does not have a turbo-pump and is fed only by tank pressure.
Kestrel is ablatively cooled in the chamber and throat and radiatively cooled in the nozzle, which is 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.Helium pressurant efficiency is substantially increased via a titanium heat exchanger on the ablative/niobium boundary.
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 system is used to provide multiple restart capability on the upper stage. In a multi-manifested mission, this allows for drop off at different altitudes and inclinations.
Enhancements to the design of the original Kestrel engine were planned, called the Kestrel 2.
The engine was planned to continue to be pressure-fed design, but was to have flown on a newly designed second stage that was to use Aluminum Lithium alloy2195 rather than the 2014 Aluminum used in the Falcon 1 second stage. Engine changes were to include tighter tolerances to improve consistency, higher Isp, and lighter weight.[dated info] 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 upperstage.