A rough model of the Raptor rocket engine developed by Space-X for the BFR/Starship system simplified and optimized for printing the model is true scale meaning the lower engine bell diameter is about 1.3 meters but it's designed to be printed at about 1/10 scale with a regular nozzle diameter, thus details have been thickened or left out if htey are too small for this The Raptor is a conceptually optimized rocket engine combining thrust to weight ratio and efficiency with relatively easy to store fuels (compared to hydrogen) which can be acquired on mars since it is powered by liquid methane and liquid oxygen - in order to increase efficiency compared to other designs it also uses two turbopumps burning oppositely saturated mixtures allowing it to use the full energetic potential of the fuel without overheating the turbopump