The U.S. Air Force (USAF) and its rocket engine contractor Aerojet Rocketdyne (AJRD) have achieved a major milestone toward a new U.S. state-of-the-art capability to develop powerful next generation hydrocarbon rocket engines. The achievement involves completion of the first in a series of hot-fire tests on a sub-scale oxygen-rich pre-burner, built by ARJD for the USAF’s Hydrocarbon Boost Technology Demonstrator (HBTD) program.
While America once led the world in kerosene and RP-fueled rocket engine technology, the U.S. has lost such hydrocarbon rocket infrastructure and lags behind Russia, specifically with the Energomash RP-1/liquid oxygen RD-180 that powers the proven and reliable United Launch Alliance (ULA) Atlas-V.
There are two major rocket engine cycles. One is called a “gas generator cycle,” where gases used to drive an engine’s turbopump are exhausted by the pump, giving a somewhat ragged looking rocket plume due to this flaming exhaust vented beside more distinct rocket nozzle plumes.
The other cycle is the “staged combustion cycle,” where a share of the propellant—be it kerosene or oxygen or both—is first burned in a pre-burner. The resulting hot gas is first used to power the engine’s turbines and pumps, then, instead of being dumped as with the gas generator cycle, that exhausted gas is injected into the main combustion chamber, along with the rest of the propellant to generate powerful thrust. The two stages that make up the staged cycle propulsion are from the pre-burner stage, then combustion chamber stage.