The purpose of this project is to advance the technologies required to build a subcritical regeneratively cooled liquid oxygen/methane rocket combustion chamber for an exploration-class vehicle that is deep throttling and operated on pressure-fed propellants. This project will involve building and testing low-cost combustion chambers, developing and validating an analytical tool to predict engine cooling circuit performance, and finally designing and building a full scale regen combustion chamber which will be tested for thermal steady state performance. Design, build, and test a 5,000 lbf thrust regeneratively cooled combustion chamber at JSC for a low pressure liquid oxygen/methane engine. The engine demonstrates its effectiveness by continuous steady state operation without catastrophic damage to the combustion chamber. This project will advance in three phases: 1) The addition of a regeneratively cooled test section to an existing pressure fed LOX/Methane engine. This "partial regen" engine will be hot fire tested and thereby used to validate a multiphase regen cooling model. 2) The development of a tube forming technique to construct a low cost full-size regeneratively cooled combustion chamber. 3) Using the results of #1 and 2, create a full scale regeneratively cooled combustion chamber (open loop cooling) for an existing 5,000 lbf subcritical liquid oxygen/methane rocket engine with variable chamber heat load capability. This full scale engine will be hot fire tested to demonstrate performance.