The TR-107 was a developmental rocket engine designed in 2002 by Northrop Grumman for the NASA and DoD-funded Space Launch Initiative. Operating on LOX/RP-1, the engine was throttleable and had a thrust of 4,900 kN (1,100,000 lbf) at a chamber pressure of 17.7 megapascals (177 bar), making it one of the most powerful engines ever constructed.^{[1] [2]}

The TR-107 was developed by TRW following the successful conclusion of the development program for the TR-106 engine, a similar throttleable engine of about half the thrust burning LOX/LH2 instead of LOX / RP-1. Tom Mueller, then VP of Propulsion Development at Northrop, was project manager for both the TR-106 and TR-107 engines.

In 2002, Mueller co-founded SpaceX with Elon Musk and became the VP of propulsion^[3] after cancellation of the SLI program.^{[citation needed]}

Northrop Grumman development of the TR-107 engine permitted consideration for potential use on next-generation launch and space transportation systems.^[1]

As of 2023^[update], no flight models are known to exist.

• Merlin 1D
• Raptor