Stennis conducts SLS engine firing marking RS-25 return

by Chris Bergin

NASA’s Stennis Space Center has test fired the first RS-25 (unit E0525) of the Space Launch System (SLS) era on Friday, marking the beginning of a new career for the famous engine. Four of the former Space Shuttle Main Engines (SSME) are set to power each SLS during the ride to orbit, opening with Exploration Mission -1 (EM-1) in mid-2018.

RS-25 Testing:

Preparations for the testing milestone have been ongoing ever since the decision was made to utilize the engines on the next generation launch vehicle.

For Shuttle, the RS-25D was capable of achieving 400,000 lbs of thrust with an ISP of 453 seconds in a vacuum, or 363 seconds at sea level. The engines consist of over 50,000 parts and could be reused up to 20 times during their role with Shuttle.

Their career was near-flawless during the three decades of flight, with only one major malfunction during its flight history, namely STS-51F (ME-1), resulting in a safe Abort To Orbit (ATO).

The engines were set to end their days during the final Shuttle missions, with efforts to retire the supply line already taking place well before Atlantis launched on her STS-135 mission.

In fact, NASA’s Transition Control Board (TCB) – a body that was tasked with redirection of agency assets to the CxP – directed the shutdown of engine production capabilities back in 2007, claimed only four more engines would be required throughout the remainder of the Space Shuttle Program (SSP), pre-empting the shutdown process.

Politics soon came into play, a NASA Authorization Act in 2008 placed a temporary hold on the complete shutdown of RS-25 fabrication assets – mainly from the standpoint of spare hardware availability – but also in relation to continued evaluations into short-term and long-term Shuttle extension possibilities.

There were at least two high level attempts to stop the Shuttle from entering retirement, both of which failed – however, the RS-25 continued to find fans within the space program, both as a potential engine for the since-defunct Ares V, and its eventual Heavy Lift Launch Vehicle (HLV) successor.

SLS Option in the RAC study, via L2The latter option was evaluated via the RAC (Requirements Analysis Cycle) effort, tasked with finding the best baseline for the new Space Launch System (SLS) rocket – the RS-25s were confirmed as the preferred option for all derivatives of the evolvable HLV.

The engine was confirmed as living on with the SLS when the vehicle was officially announced in September, 2011.

In preparation for this new milestone for the famous engines, Stennis engineers built and installed a new 7,755-pound thrust frame adapter for the A-1 Test Stand, in order to enable testing of the RS-25s ahead of their role on SLS’ core.

TRS-25 with the adaptorhe reason for the new adaptor relates to the requirement of different types of engines.

On the test stand, the adapter is attached to the thrust measurement system, with the engine then attached to the adapter, which must hold the engine in place and absorb the thrust produced during a test, while allowing accurate measurement of the engine performance.

The adaptor that was previous installed on the A-1 Test Stand was specific for the J-2X – an engine capable producing 294,000 pounds of thrust. The J-2X was specific to the Ares vehicles of the cancelled Constellation Program (CxP).

In its J-2X configuration, the stand couldn’t be utilized for the RS-25, given that engine is much more powerful, with the ability to produce approximately 530,000 pounds of thrust.

Z27And that thrust once again gracef the test stand on Friday – per NASA Stennis, in response to – beginning with a test fire of Engine 0525. Ignition was scheduled for between 2pm and 6pm local time.

Sources noted the firing took place around 5:42pm local time, with a full duration firing observed.

The engine tested has never flown in space, given it was one of two development engines used for component testing on Stand A-2 to support shuttle flights – 0528 was the second development engine.

In response to questions from, Aerojet Rocketdyne noted 0525 will be used to test the first couple of new engine controllers, which have progressed from the Critical Design Review (CDR) phase through to integrated testing.

The RS-25 controller provides complete and continuous monitoring and control of engine operation. In addition, it performs maintenance and start preparation checks, and collects data for historical and maintenance purposes.

The controller is an electronic package that contains five major sections; power supply section, input electronics section, output electronics sections, computer interface section, and digital computer unit.

Pressure, temperature, pump speed, flowrate, and position sensors supply the input signals. Output signals operate spark igniters, solenoid valves, and hydraulic actuators. The controller is dual redundant, which provide normal, fail-operate, and fail-safe operational mode capability.

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Once E0525 has completed all test requirements, the stand will undergo a couple of months of work on the related water system, prior to testing the engines that will launch SLS into space in mid-2018.

Z3For the debut flight – known as Exploration Mission-1 (EM-1) – NASA’ss Liquid Engine Office selected the first four engines that will loft the monster rocket uphill.

The four engines – ME-2045, ME-2056, ME-2058, and ME-2060 – are all established Shuttle veterans with numerous successful missions under their belts.

A total of 15 RS-25Ds left the Kennedy Space Center (KSC) for their new role, arriving at the Stennis Space Center in 2012.

FRR Slide for STS-133, via L2All nine of the last SSMEs to fly with the Space Shuttle performed admirably, with Discovery flying Main Engine 1 (ME-1) – serial number 2044, ME-2 – 2048 and ME-3 – 2058 during her final mission, STS-133.

For Endeavour’s swansong, ME-1 – 2059, ME-2 – 2061, and ME-3 – 2057 helped begin the flight phase of the successful STS-134 mission, while Atlantis closed out the Space Shuttle Program, flying with engines ME-1 – 2047, ME-2 – 2060 and ME-3 – 2045 during STS-135.

All of these engines will now get to fly one more time, on the core stage of the SLS.

The test path was recently revealed to by SLS manager Todd May.

Several additional engines have also been ordered from Aerojet Rocketdyne by NASA, known solely as the RS-25 (as opposed being called the RS-25E), which are cheaper, expendable versions of the engine. Further information on those engines will be revealed at the conclusion of the procurement process.

(Images: Via NASA and L2 content from L2’s SLS specific L2 section.)

(L2 is – as it has been for the past several years – providing full exclusive SLS and Exploration Planning coverage. To join L2, click here:

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