The Stennis Space Center conducted the latest in a series of tests with RS-25 Engine 0525 on Friday, pushing the engine to its 109 percent limit during the 535-second firing on the A-1 Test Stand. The fifth test out of a series of seven firings is paving the way for the future milestone of Static Firing four RS-25s together on the B-2 Test Stand ahead of their role with the Space Launch System.
The return of the RS-25s to active test status began in January, focusing on a test series utilizing an engine that had never flown in space.
E0525 was built as one of two development engines used for component testing on the A-2 Test Stand to support shuttle flights.
Its role as a development unit is proving its worth, allowing the Stennis team to push the engine through rigorous test regime requirements while sporting new improvements designed for SLS.
Friday’s test was the fifth in the series for 0525. A second development engine (E0528) is set to undergo 10 tests, totaling 4,500 seconds. The test series includes testing new flight controllers and software, known as “green running”.
Both engines have been outfitted with the new engine controller – which is a vital element that allows for the engine and the vehicle to communicate with each other, relaying commands to the engine and transmitting data back to the vehicle – providing closed-loop management of the engine by regulating the thrust and fuel mixture ratio while monitoring the engine’s health and status.
Pushing E0525 to the limit, Friday’s firing tested the engine through a series of power levels, including a period of firing at 109 percent of the engine’s rated thrust.
This additional thrust rating relates to when the RS-25s were originally developed in the 1970s, as the Space Shuttle Main Engine (SSME). They were designed to produce a specific amount of thrust – up to 100 percent.
As the Shuttle Program progressed, engineers were able to improve the operational limits, increasing reliability and performance. This allowed for the engine to perform above its original power levels, with 104.5 percent the optimal full power level during Shuttle ascents.
The improvements acutally allowed for up to 109 percent of rated thrust, which was once again proven during E0525’s Static Fire on Friday.
Two more tests of E0525 are scheduled for August, again tasked with collecting data on the performance of the engine at the various power levels.
These tests are being conducted on the A-1 Test Stand at Stennis, with the goal of eventually making the switch to the modified B-2 Test Stand for the milestone test of simultaneously firing four RS-25 engines together.
These four engines will undergo their own “Green Run” testing, firing for a full mission duration of approximately 500 seconds.
For the debut launch, NASA’s Liquid Engine Office selected engines E2045, E2056, E2058, and E2060 to push the Exploration Mission-1 (EM-1) SLS uphill.
The path to the B-2 test firing also requires the validation of the Core Stage structure.
Production of that hardware is taking place at the Michoud Assembly Facility (MAF) in Louisiana, ahead of the structural test article (STA) elements being sent to Marshall Space Flight Center in Alabama for testing.
“The five structural test articles are the engine section, the forward section (forward skirt), the intertank, the hydrogen tank and the LOX tank; we’ll have a test article for each one of those things,” noted SLS manager Todd May to NASASpaceFlight.com in January.
“The test articles will come off the machines first, and then they go up to Marshall.
“We’re actually building a large strongback for the hydrogen tank and then another for the LOX tank, and then we have an existing structure for the other pieces.”
Testing of both the STAs – and the first flight unit – will run in parallel, up to a point.
“We’ll actually move forward with building the structures for the flight units, but we will stop short of firing on the B-2 stand until we’ve completed all the appropriate sequencing of the structural tests that we think we need to do before that,” added Mr. May, referring to the “Green Run” testing of the first flight unit Core Stage at Stennis.
The rocket is so tall that the sections then have to be translated to the horizontal, allowing for the application of the foam Thermal Protection System (TPS).
As previously reported, the Core won’t be painted, despite current NASA materials continuing to show an all-white rocket. (Image left – Nathan Koga L2 Rendering, based on image right showing official – yet internal – NASA documented SLS render).
“So you lay those sections on their side, and then you put the TPS on and you outfit the avionics and in the engine section you outfit it with the engines,” Mr. May continued.
“Then it’s too tall to stack, so you have to take the two halves and the final thing you do is put the two halves together horizontally. And then from that point on, you put it on the (Self Propelled Module Transporter (SPMT)) and on to the barge – (for the trip to) Stennis and it stands up on the B-2 stand for full testing.”
For the key B-2 Test Stand test ahead of the first flight, Mr. May noted the Program is discussing the potential to conduct two Static Firings, but the priority is to conduct a full mission sequence.
“The idea is to put it through its paces, make it like a flight test.”
(Images: Via NASA and L2 content from L2’s SLS specific L2 section. SLS Render by L2 artist Nathan Koga)
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