The RS-25 team at the Stennis Space Center in Mississippi began the next development test series on Tuesday afternoon. Development Engine 0525 (E5025) was back in the A-1 test stand at Stennis for the first of nine tests to certify affordability changes and operational upgrades for newly-built engines that will start being delivered by prime contractor Aerojet Rocketdyne to NASA’s Space Launch System (SLS) Program in the early 2020s. However, the test aborted early due to what is understood to be a “facility issue”, although all the test objectives were achieved.



NASA Administrator Jim Bridenstine was in attendance at Stennis for what was supposed to be a 500-second long engine test, which focused on profiling the performance of a new main combustion chamber (MCC).

Another engine controller unit (ECU) was being “acceptance tested” during this firing, set for the existing inventory of adaptation engines inherited from the Space Shuttle Program.

However, despite congratulating the teams on the 500 second test – likely via prepared remarks – the test actually aborted after 319 seconds.

Today’s RS-25 Engine Test @ NASA's John C. Stennis Space Center has concluded with a duration of 319 seconds. #SLSFiredUp pic.twitter.com/oMY5GZ26NZ — Stennis Space Center (@NASAStennis) August 14, 2018

“Early cut issued at 319 seconds by test conductor due to LH transfer initiation issue,” noted L2 information into the abort. Further inquiries pointed to this being related to a facility issue – as was the case with a previous test abort in 2016 – meaning the engine was not at fault.

First Retrofit 1b series test

The Stennis test team of personnel from NASA, Aerojet Rocketdyne, and facilities contractor Syncom Space Services (S3) once again took the engine through an event-driven countdown beginning on Tuesday morning.

The test started when all of the prerequisite steps prior to ignition were complete and the hardware and the people were ready. Ignition was at 3:41 PM Eastern.

“[There are] Two primary objectives: Greenrun of ECU FM13 [and] evaluate HIP-bonded Main Combustion Chamber (MCC),” Philip Benefield, Systems and Requirements Team Lead for the SLS Liquid Engines Office, told NASASpaceflight.com in an email ahead of the test.

The MCCs for production restart engines use a method called “hot-isostatic press” (HIP) bonding to form the jacket around the liner. “You’ve got the liner and you’ve got the jacket separately, you put that into the furnace and that hot, high-pressure allows you to make that bond between the liner and jacket and that’s what we’re utilizing now on the MCC,” Dan Adamski, RS-25 Program Director for Aerojet Rocketdyne said in a recent interview.

“[It] is exactly the same process that’s used on the RS-68 engine and exactly the same process that we used on the J-2X engine and ultimately what that does, we were able to reduce the cost and the cycle time on the MCC by over 50 percent of what it was for heritage SSME.”

Manufacturing of MCC 8001 was completed at Aerojet Rocketdyne’s Canoga Park facility in the Los Angeles area in the Spring and shipped to Stennis where it was integrated with E0525.

For the new MCC’s first integrated test, E0525 was to go through a nominal test profile similar to full engine “green runs” or acceptance tests. The test was to run for a flight-duration like 500 seconds and was started under nominal conditions.

“We’re targeting nominal LOX and fuel propellant conditions at start,” Benefield said. “The engine will operate from 80% RPL up to 111% RPL. A majority of the test, 342 seconds, will be spent at 111% RPL, and 79 seconds at 80% RPL.”

Information acquired later in the day noted they did get to 111% RPL before the abort and that the objectives were achieved.

Designed in the 1970s as the Space Shuttle Main Engine (SSME) for the Shuttle Program, the engine’s original rated power level (RPL) of 100 percent was 375,000 pounds of thrust at sea-level, 470,000 pounds in a vacuum. At the end of the Shuttle program, the engines were normally operated at 104.5 percent RPL; for SLS, the adaptation engines will run at 109 percent RPL and then 111 percent RPL for the production restart units.

The engines are throttleable, and in SLS as with Shuttle they will be throttled depending on in-flight conditions and performance.

The additive-manufactured pogo accumulator assembly that was test fired four times between December and February on Engine 0528 as a part of the Retrofit 1a test series has also moved over to E0525. Aerojet Rocketdyne is using modern manufacturing techniques and the pogo accumulator was fabricated using an additive manufacturing / 3-D printing method called selective laser melting (SLM).

Aerojet Rocketdyne was awarded a contract by NASA in late 2015 to restart production of the RS-25, formerly known as the Space Shuttle Main Engine (SSME). The SLS Program has sixteen engines left over from the Space Shuttle era, which will be expended on the first four launches.

The goals of the contract are to re-establish the RS-25 production line and supply chain in a more cost-effective manner than for SSME units. By using modern techniques already developed in other engine programs, it is hoped to reduce the cost to build new engines and the time it takes to field them.

In addition to the new MCC and pogo accumulator on E0525, the insulation for the high-pressure fuel turbopump is another affordability improvement being demonstrated. “[The] heritage SSME system was effective, it was good, but it was multiple pieces that would get clam-shelled around the engine,” Adamski explained.

“We’re going to be using a different type of insulation system which is used on RS-68, on their fuel pump. We’re pretty much going to clamshell a mold around it and then you inject the foam inside that mold and so you use that as the insulation system. It’s very effective and much cheaper and much easier to work with than what we were using before, so we’re going to be demonstrating that on the high-pressure fuel pump.”

Administrator visit

NASA Administrator Jim Bridenstine took office in late April and is currently touring several NASA centers and facilities. Last week, he visited Kennedy Space Center in Florida following the introduction of the first astronaut crews for the initial Commercial Crew Program missions flying on the SpaceX Dragon and Boeing Starliner vehicles to the International Space Station.

On Monday, Mr. Bridenstine visited the Michoud Assembly Facility in New Orleans, where parts of NASA’s Orion spacecraft and SLS launch vehicle are manufactured and assembled. Tomorrow, he will visit the Marshall Space Flight Center in Huntsville, Alabama.

Past downtime, future tests

After the Retrofit 1a test series was completed in late February, the A-1 test stand went a maintenance and upgrade period. During that time, the test stand was outfitted with a new thrust vector control (TVC) system that will see use during the next development test series, called Retrofit 2. E0528 is pointed at that test series, which will include new units of all the components being demonstrated in the first two retrofit series along with new flex hoses.

E0525 was installed in the A-1 stand in late July. Prior to that, the first AR-22 engine went through a rapid-turnaround demonstration in the stand in late June and early July. The AR-22 is Aerojet Rocketdyne’s other SSME derivative, composed entirely of SSME hardware from earlier in the Shuttle Program with the exception of the new Honeywell ECUs.

After Tuesday’s hot-fire, E0525 will be turned around for the second Retrofit 1b test in early September. ECU FM14 will be installed on the engine for that test, which is currently scheduled for early September.