Yes, you’re seeing this image correctly. There are icicles forming at the rim of this rocket engine bell, and this particular engine generates a scalding 2,760 C (5,000 F) degree steam and a whopping 13,000 lbs of thrust. How can that happen? Cryogenics. NASA is developing the engines that will be used for the next generation lunar lander, the Altair. These engines are called the Common Extensible Cryogenic Engine (CECE). CECE is fueled by a mixture of -182 C (-297 F) liquid oxygen and -253 C (-423 F) liquid hydrogen. The engine components are super-cooled to similar low temperatures–and that’s where the icicles come from. As CECE burns its frigid fuels, hot steam and other gases are propelled out the nozzle. The steam is cooled by the cold nozzle, condensing and eventually freezing to form icicles around the rim. Watch the video.
More about the engine.
CECE, is a deep-throttling engine, which means it has the flexibility to reduce thrust from 100 percent down to 10 percent — allowing a spacecraft to gently land on the lunar surface. During the test, the engine was successfully throttled from a high of 104 percent of the engine’s potential down to eight percent, a record for an engine of this type. A cryogenic engine is needed to provide high performance and put more payload on the surface of the moon. The CECE demonstrator has evaluated two engine configurations during three rounds of hot-fire testing.
The tests are being done by Pratt & Whitney Rocketdyne in West Palm Beach, Florida. This was the third test for these engines. Previous tests in 2006 and 2007 showed the engines needed some fine tuning. Tony Kim, Deep Throttling Engine project manager at NASA’s Marshall Space Flight Center, Huntsville, Ala, said, “Testing in 2007 provided an in-depth examination of low-power-level throttling and engine performance characteristics. This third cycle we actively addressed and found solutions to the challenges we faced.”
The team carefully assessed test results that showed pressure oscillations in the engine at lower throttle levels called “chugging.” Chugging may not be a concern for the engine itself, but the resulting vibrations could have the potential to resonate with the structure of the rocket and cause problems for the lander or crew.
Injector and propellant feed system modifications successfully eliminated engine chugging by controlling liquid hydrogen and liquid oxygen flow to the combustion chamber. The latest engine configuration incorporates a new injector design and propellant feed system that carefully manages the pressure, temperature and flow of propellants. And it seemed to work quite well.