Space Shuttle Main Engine (SSME) Options for the Future Shuttle

SPACE SHUTTLE MMN ENGINE (SSME) OPTIONS FOR THE FUTURE SHUTTLEFred Jue and Fritz KuckThe Boeing CompanyCanoga Park, CaliforniaAbstractThe main engines for the Future Shuttle will focus onimproved safety and operability. Performanceenhancements may also be required for vehicle safetypurposes to achieve more desirable abort scenarios.This paper discusses the potential improvements thatwill be considered for implementation into the FutureShuttle. Integrated engine and vehicle healthmanagement systems will achieve additional system-level reliability improvements over those currently indevelopment. Advanced instrumentation for detectingleaks, analyzing component wear and degradation, andproviding sophisticated operational data will be usedfor reliable engine control and scheduling maintenanceoperations. A new nozzle and main combustionchamber (MCC) will reduce failure probability by 50%and allow for higher thrust capability without requiringthe entire engine to be redesigned. Turbopumpimprovements may range |rom minor componentimprovements to using 3rd-generation pumps built onthe advanced concepts demonstrated by the IntegratedPowerhead Development (IPD) program and the SpaceLaunch Initiative (SLI) prototype engines.Introduct ionThe Space Shuttle is expected to be operational for twoto three decades into the 21 st century. So the question isnot whether there will be a space shuttle, but ratherwhat will it be like. From a propulsion perspective, itwill likely continue as a two-stage-to-orbit vehicle. Theboosters could be liquid or solid propulsion, but themain engines will remain liquid oxygen (LOX)/liquidhydrogen engines. This paper examines some potentialrequirements for the Future Shuttle main engines, andpresents some options for achieving those goals.Future Shuttle En_ RequirementsThe primary goals of the Space Shuttle Program havebeen to:• Fly safely• Meet the manifest• Improve mission supportability• Improve the systemThese worthy goals are expected to be the cornerstonesfor Future Shuttle vehicle and propulsion requirements.SSME safety goals for a future shuttle are likely toinclude a factor of 3 or more for risk reduction forcatastrophic failure and possibly abort-to-orbit (ATO)or abort-to-TAL (Trans-Atlantic Landing) off thelaunch pad with a single engine out. Meet-the-manifestrequirements translate into having a full complement ofengines installed and ready on each vehicle. Improve-mission-supportability requirements translate intoreduced maintenance and repair work and capability tokeep the engines on the vehicle between flights withengine overhaul occurring simultaneously with vehicleoverhaul. Improve-the-system requirements can be farreaching and include methods of improving theinfrastructure and systems that NASA and thecontractors use to execute the Space Shuttle. Skill andknowledge retention and infrastructure capability playan important role in this area as the program continuesto mature and obsolescence becomes a greater threat.Privatization of certain parts or aspects of the programis one consideration, and the engine for the FutureShuttle must be developed to be compatible with a widerange of potential systems and infrastructures.History of SSME UpgradesTo envision where the SSME can go, it is beneficial toexamine the current SSME requirements andconfiguration of the engine and its history of upgrades.Figure 1 shows an SSME and its major requirements;Figure 2 is a summary of the major upgrades since theinitial Shuttle flight in 1981 through the first flight ofthe Block II SSME in 2001. The most significantimprovements in the Phase II engine for return to flightafter the Challenger incident were safety/reliability/lifeimprovements in turbopump components and new andimproved sensors. Major changes in the Block I/IAconfigurations were the two-duct powerhead with anintegral single tube heat exchanger, and a new high-pressure oxidizer turbopump (HPOTP) made by Pratt &1American Institute of Aeronautics and Astronautics