The RL-10 Rocket Engine RL-10 rocket used for Centaur upper stage. Manufactured by Pratt and Whitney. Development started in 1957. First launch unsuccessful in 1962. First successful launch 1963. LeRC got the vehicle program from Marshall. Operating configurations of the RL-10: Model Thrust Ch. Pressure Specific Imp RL10A-1 15,000 300 422 RL10A-3 15,000 300 427 RL10A-3-1 15,000 300 431 RL10A-3-3 15,000 395 442 RL10A-3-3A 16,500 475 444 RL10A-4 20,800 578 449 RL10A-4-1 22,300 610 451 Engine items 1. EMAS - Electrical/mechanical actuators for engine valves. Replace gaseous helium valves with EMAs 2. Engine Electronic Controller 3. Improve ignition system. Ignition system Current problem - freezing backflow of combustion products. After the first firing, the LOLH engine forces steam back through a line. The steam condenses and freezes causing a valve not to open. The engine fails to start for the second firing. The spark plug sparks but the engine doesn't light. The freezing prevents O2 flow around the plug. Fast data acquisition allowed better understanding of the backflow problem. The engine was developed in the 1960s and is still essentially the same. Sparkplug, LOX, LH2. Water freeze on plug and plug shorts. Torch Igniter - instead of spark plug, torch at head end of combustion chamber. This idea looked good but was never developed. This is the only alternative currently being considered. Five years ago - Centaur integrated with Titan GEO mission - long coast time between firings. Centaur to inject payload into orbit. Problem with restart after first firing. Prestart - must cool fuel pump to start This is done by flowing propellants (unlit oxidizer) to cool, then start engine. Stage Separation - 3 1/2 seconds to separate, 8 seconds to start engine A spring loaded poppett valve acting as a check valve in the propellant line freezes closed in nostart condition. The first firing produces water vapor which freezes. Backflow freezes valve - this was determined with ground test data. This had been going on for years - usually got ignition by O2 from elsewhere. The torch igniter doesn't need the shutoff valve - eliminates freezing of valve shut. Nothing to freeze shut with torch igniter. Last tests - engine fails to light again 1. No valve to freeze 2. Pressure differential - 5000 samples of various pressures in start transient - chamber pressure > upstream pressure Backburn - heats valve, creates water, causes freezing. Solution - 1. no shutoff valve in oxygen supply 2. Continuously flow oxygen in lines 3. Find pressure to prevent backflow.