Educating the SLS engines – Brains for the RS-25s undergoing certification
The effort to certify the Space Launch System RS-25 engines for the first launch will soon reach a critical milestone with the delivery of the first flight model engine controller unit (ECU). NASA is planning to finish its first-flight certification program next year, culminating in the planned shipment of the four flight engines to the Core Stage assembly facility in New Orleans by next Spring.
The engine control system for the RS-25 was updated from the engine’s previous life in the Space Shuttle program to operate in the SLS environment.
Development engine 0528 remains installed in the A-1 test stand at Stennis Space Center in Mississippi, where the last hot-fire test was conducted on August 18. The engine was fired for 420 seconds, covering the remaining set of test objectives left over from two previous firings in July.
E0528 was installed on the stand in late May / early June and originally only one hot-fire was planned in July, but that test on July 14 was cutoff early due to a test facility issue.
Although the test was cut short, there were no issues with the engine hardware; two weeks later, E0528 was fired on July 29 for the originally planned 650 seconds.
The additional hot-fire allowed more test objectives to be covered than the original, single test, leaving a smaller set of objectives and therefore shortening the duration of the August test.
“When we get all the objectives that we need with this thrust profile, we just stop,” Steve Wofford, manager of the SLS Liquid Engines Office, explained in an interview just before the August test. “We don’t run just for the sake of…running.”
During the six-minute firing, E0528 was taken through a busy throttle profile, with over a dozen “excursions” throttling the engine through multiple power levels.
“It’s a weird thrust profile – 144 seconds at 109%, there’s a pretty good bit of time at 80%, and four short seconds at 111,” Mr. Wofford said at the time.
Another test objective was to get another data point on engine inlet start box conditions. “Edge of the start box today,” Mr. Wofford added, “so it’s high pressure, nominal temperature.”
Upcoming test schedule with flight controllers:
The first three hot-fire tests in this latest test series with E0528 used an Engineering Model 5 (EM5) controller, the last engineering model of the hardware built by Honeywell, and the August test was the last one in the series planned with a development controller.
The SLS program is anticipating delivery of the first flight model controller, FM1, at the end of the month; however, the first controller will not be hot-fired. FM1 will go to Marshall Space Flight Center in Alabama for certification testing in a lab environment; plans are that FM1 will always be a lab test subject.
FM2 will be the first of many flight model ECUs delivered to Stennis, currently planned for the end of October. The controller will be installed on E0528 to be “green run.”
Critical engine components that are newly built or rebuilt are typically taken through a hot-fire test for validation purposes and beginning with FM2 the plan is to “green run” each of the new controllers on the test stand prior to completion of the hot-fire part of certification testing next year.
FM2 will be installed on E0528 and its green run will be a part of the next hot-fire test at Stennis; recent schedules forecast that test for November 9. FM3 will follow FM2 to Stennis shortly thereafter and will be installed on E0528 for the following hot-fire, currently forecast on November 30. FM4 is pointed at the last hot-fire test of the year, planned for December 21.
Along with FM5, these four controllers are planned to be integrated with the four flight engines assigned to the first SLS launch, designated Exploration Mission-1 (EM-1). After they are green run on the test stand, FM2 will be installed on Engine 2045, FM3 on Engine 2056, and FM4 on Engine 2058.
Currently, FM5 will be installed on the remaining EM-1 engine, Engine 2060, without being hot-fired as a component; however, all four engines will be “green run” during the full stage Green Run test, scheduled for the end of 2017.
Almost all of the flight engines have remained in long-term storage at prime contractor Aerojet Rocketdyne’s facility in Building 9101 at Stennis since they were shipped from Kennedy Space Center in Florida after flying their last Space Shuttle flights.
The flight engines mostly remain bagged up and purged with air to keep them clean and dry.
After the controllers come off their green run hot-fire, they will be taken back to Building 9101 for installation on the flight engines.
Honeywell will continue to assemble and ship flight ECUs to Aerojet Rocketdyne at Stennis to build up a set of spares; after the EM-1 flight engines get their controllers, the next two controllers will be green run after being paired with their flight engines. Engines 2062 and 2063 have not been flown or hot-fired before, so they will both be “green run” individually at Stennis.
Currently scheduled for late Winter or early Spring next year, E2063 will go to the A-1 test stand first for its “full up” green run after receiving the FM6 controller that it should eventually fly with on the second Core Stage (CS-2). The FM7 controller will be installed on E2062 and that engine will follow E2063 for its green run hot-fire.
After E2063 and E2062 are green run with their flight controllers next year, Engine 0528 will be re-installed on the test stand to green run controllers FM8, FM9, and FM10, which will more or less complete the outfitting of more flight engines for SLS.
The four engines that are pointed at the second Core Stage are planned to be available as spares for the first flight; in addition to E2063 and E2062, Engines 2047 and 2059 are assigned to CS-2. Those two engines will be outfitted with controllers FM8 and FM9, respectively.
Pathfinder engine to be used at MAF for practicing engine installations:
By early next year, the four flight engines for EM-1 should be ready to ship to the Michoud Assembly Facility (MAF) in New Orleans, Louisiana, where the SLS Core Stage is assembled.
Once the Core Stage is in final assembly, it will be ready for the engines to be installed in the back of the engine section.
This will be the first time engine installations will be done in a Core Stage. Newly-integrated ground support equipment modified from the Shuttle program and Shuttle-heritage “Pathfinder” hardware will be used for practice before handling the flight engines.
“We’ve…taken some of the installation hardware for the engines from the same hardware that we used to load the engines into the [Space Shuttle] orbiter,” Patrick Whipps, NASA resident manager at MAF for the SLS Core Stage, explained during an interview there last year.
“We haven’t brought the big tractor…with us, but the business-end that actually touches the engines is going to be used – it worked great for all the orbiters. We’ve taken another approach to have a driveable vehicle [and] it will have…upper and…lower stages so we can load engines, two at the top, two at the bottom.”
The Pathfinder engine, with a powerhead that flew on the first Shuttle flight in 1981, is currently being stored at Stennis with the flight engines. Next year, the historical Space Shuttle Main Engine (SSME) will be shipped to MAF for those installation rehearsals.
Production restart, testing affordability changes:
NASA awarded a contract to Aerojet Rocketdyne last year to restart production of RS-25 engines with a series of affordability changes incorporated into the design and manufacturing process. Groundwork is underway to prepare for hot-fire testing of engines assembled with those affordability changes.
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Testing will start after the current design is certified for use on the first SLS launch. Development Engine 0525, which started RS-25 hot-fire testing early last year, has been partially disassembled and will be rebuilt with hardware from the newly restarted production.
“It’s going through a minor teardown and rebuild right now,” Wofford said. “The nozzle is off, so it looks kind of sad. All of the instrumentation is disconnected, but the engine is still largely intact.”
In addition to new flight engines for downstream SLS launches, Aerojet Rocketdyne will produce new hardware to outfit the existing two development engines and a new ground-test one. “We’ll have to retrofit [the development] engines,” Wofford explained.
“The core of these engines are what we’re going to be using, but we’re going to be introducing a lot of new parts that we’re going to certify on these engines, so they’ll be kind of mixed configurations.
“We’re buying about an engine and a half’s worth of the new stuff [for ground testing], [and] the final engine that we’re not going to fly in this upcoming test series is going to be a full-up, brand new certification engine with the [affordability] changes.”
After the initial certification testing for the first SLS launches is complete towards the end of next year, the re-assembled Engine 0525 will go back on the test stand to begin certification of the RS-25 design incorporating the affordability changes. The new configuration will also be certified for flight at 111% of the original, 1970s, Space Shuttle rated power level.
“Actually, we’re going to be certifying to fly at 111 [percent], so we’ll be over-testing – we’ll be testing at 113 percent on a subsequent test series,” Wofford noted.
The four seconds of run-time at 111% in the August hot-fire are a part of the same type of over-testing that will be done in this initial certification at 109% for the first SLS launches.
(Images: Via Aerojet Rocketdyne, NASA and L2 – including photos from Philip Sloss and SLS renders from L2 artist Nathan Koga – The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)
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