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For this special ground test firing, the three flight computers on the Core are running Green Run Application Software (GRAS), a variation of the Flight Computer Application Software (FCAS) they will run for Artemis 1 and beyond. Just as planned for launch, engine start commands were issued beginning at T-6.6 seconds to the four RS-25 engines individually at 120-millisecond intervals.<\/p>\n
The engines start to 100 percent of rated power level as they did in their Space Shuttle Main Engine (SSME) days. Now, with SLS, at T-0 they throttled up to 109 percent of their original, 1970s rating. The engines fired for about 499 seconds, with a final test objective to let the RS-25s run until they uncovered the low-level sensors in the LOX tank which triggered shutdown.<\/p>\n
\u201cFrom our initial look at all the data, we achieved all the test objectives even the secondary objectives,\u201d John Shannon, Boeing\u2019s Vice President and Program Manager for SLS, said in a briefing a few hours after the test. \u201cWe did see a LOX low-level cutoff and the system behaved exactly as it should and so we\u2019re very excited about the data that we\u2019ve gotten.\u201d<\/p>\n
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\u201cIt\u2019s terabytes and we\u2019ll be working through that over the next couple of weeks as we do very detailed inspections of the hardware, but the initial look is that everything worked perfectly,\u201d he added.<\/p>\n
\u201cWe also can\u2019t forget to say that it wasn\u2019t just the vehicle that worked perfectly today it was the B-2 Test Stand and the work that the Stennis Space Center did to pull off an amazing test like this was unbelievable and all of their systems worked exactly like they should.\u201d<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2021\/03\/NHQ202103170001large.jpg\")
<\/p>\nCredit: NASA\/Robert Markowitz.<\/p>\n
(Photo Caption: The B Test Stand with Core Stage-1 installed in the B-2 position at the Stennis Space Center dances with lightning on the night of March 17. The weather was a challenge for the test team to complete preparations for propellant loading the next morning, but the pre-tanking management meeting was able to be held on schedule.)<\/em><\/p>\n
A repeat of the test was necessary when the first attempt on January 16 stopped 67 seconds into the planned eight-minute plus long firing, when the first hydraulic thrust vector control (TVC) engine gimbaling test caused pressures and reservoir levels to drop farther than analytical models and subsystem-level bench testing had predicted.<\/p>\n
A strong weather front passed through the area on March 17 the night before the second test, bringing lightning, heavy rain, and high winds to Stennis and threatening to slow final test preparations.<\/p>\n
\u201cWe actually had a weather challenge last night,\u201d Julie Bassler, NASA SLS Stages Element manager, said in the post-test briefing. \u201cWe were watching the bad storms come through but we had a Stennis team that was on the ready and they came out around 2 am and got on the facility and finished up our pre-test work that we needed to do out on the stand.\u201d<\/p>\n
\u201cAt 5:30 when the test team came in we had an all-clear sign and we were ready to go into test. At 6 am we did our tanking \u2018go\/no-go\u2019 and we had no anomalies, no issues were being worked, and that was pretty much the way the whole day went,\u201d she added.<\/p>\n
This was the second full terminal countdown that the test team conducted, tanking the stage, conditioning the propellant to reach engine \u201cstart box\u201d requirements, and then initiating the automated final, 10-minute pre-ignition sequence.<\/p>\n
The test team has used data and experience gained from previous Wet Dress Rehearsal and Hot-Fire tests to fine-tune procedures and protocols for both the countdown and the hot-fire test sequence. Data from the system response in the first Hot-Fire test was also used re-calibrate analytical modeling and NASA said an early look at data from the second test indicates the updated model predictions were close to actual performance.<\/p>\n
\u201cWe had no major issues and we went all the way up to the T-10 minutes and we did our hold and checked everything and did our final go\/no-go from the test team and went right into the hot-fire,\u201d Bassler said. \u201cAll the data that we\u2019re seeing now [indicates] everything looks like we were right down the middle of our modeling and our analysis.\u201d<\/p>\n
The 500 second engine firing was punctuated by three stressing engine gimbaling profiles. The first TVC test began at T+60 seconds and ran for about 30 seconds, with all four engines were being simultaneously driven in a small circle at high rates.<\/p>\n
Within that first gimbal test with the engines moving in circles they were throttled down from 109 to 95 percent at T+65 seconds, which put additional demand on the hydraulic systems that also control engine valve positions. At T+87 seconds, the engines were throttled back up to 109 percent while still in motion.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2021\/03\/BCK_4602.small_.jpg\")
<\/p>\nCredit: Brady Kenniston for NSF<\/p>\n
(Photo Caption: The flight article for Artemis 1, Core Stage-1, fires in the B-2 position of the B Test Stand at Stennis Space Center on March 18. The second Hot-Fire ran a full 500 seconds in duration, accomplishing all planned test objectives.)<\/em><\/p>\n
A two-minute suite of sinusoidal frequency response test (FRT) engine movements began at T+2 minutes, 30 seconds, followed by a second circular motion TVC test that ended a few seconds before shutdown.<\/p>\n
\u201cThe gimbaling that we did and the engine throttling all matched exactly what we predicted,\u201d Bassler said. \u201cThe team will go through and look at that data but we saw nothing anomalous there.\u201d<\/p>\n
\u201cIt looked really smooth and the data that we do have we\u2019re going to have to go through that more thoroughly but it is looking like we have a very strong TVC system and we hit all the ends of the boundaries. We were testing the limits to make sure that we could fly through any kind of environment and since this is a generational vehicle it\u2019s something we wanted to test for all future Core Stages and Artemis missions.\u201d<\/p>\n
The engines were also throttled down to 85 percent before shutdown. \u201cWe collected a lot of data today,\u201d Shannon noted. \u201cBeing able to see the hydraulic system work with very little propellant in the tanks with some aggressive gimbaling was a stress test for the vehicle and it just gives us great confidence the vehicle can handle exactly what it was designed for.\u201d<\/p>\n
\u201cThe vehicle really performed like a champ today.\u201d<\/p>\n<\/p>\n