TR-106

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TR-106, also known as the Low-Cost Pintle Engine (LCPE), was a United States–made rocket engine developed by TRW under the Space Launch Initiative. It used liquid oxygen and liquid hydrogen to deliver about 2,892 kN (650,000 lbf) of thrust at sea level, making it one of the most powerful engines of its kind. The design centered on a single coaxial pintle injector and ablative cooling to keep costs down, with the pintle injector allowing the engine to be throttled over a wide range, similar to the lunar module descent engine. Lead engineer Tom Mueller helped guide the project. In 2000, the LCPE was hot-fired at NASA’s Stennis Space Center at 100% thrust and at 65% thrust, and TRW adjusted the injector several times and replaced the ablative chamber to demonstrate ease of operation and stable performance across various thrusts and propellant mixes.

Development slowed after the Space Launch Initiative was canceled. In 2002, TRW was acquired by Northrop Grumman, and development continued briefly on a LOX/RP-1 version called the TR-107. Mueller later joined SpaceX as head of propulsion, applying lessons from the LCPE to the Merlin engine. The turbopump for the LCPE was built by Barber-Nichols. A trade-secrets dispute between SpaceX and Northrop Grumman related to the project was settled in 2005.