NASA’s Exploration Floor Techniques (EGS) program, prime launch processing contractor Jacobs, and their Artemis launch workforce companions have tailored their countdown procedures headed into the following try and ship Artemis I on its method to the Moon. Liquid hydrogen (LH2) leaks seen whereas filling the SLS Core Stage on Launch Pad 39B on the Kennedy Area Heart (KSC) in Florida stopped previous launch makes an attempt and rehearsals within the spring and summer season.
After evaluating LH2 loading and leak decision methods throughout an illustration take a look at on Sept. 21, the launch workforce will give themselves extra time to finish the method throughout the subsequent countdown. The countdown timeline was additionally prolonged, and the workforce will take the LH2 loading course of extra slowly in hopes of lastly making all of it the way in which as much as and thru the terminal countdown.
Beginning hydrogen loading earlier, beginning extra gently
The system for loading LH2 onto the SLS Core Stage and its Interim Cryogenic Propulsion Stage (ICPS) is pressure-fed, and the launch workforce is lowering the strain used throughout the early a part of the filling course of when in comparison with earlier launch makes an attempt in late August and early September.
“We lowered the storage tank strain extra, we prolonged the sluggish fill timeline, and we additionally ended up extending the quick fill timelines as a result of the strain was decrease,” Tom Clark, Supervisor of Propulsion/Avionics Engineering with ERC, stated in a Nov. 11 interview. He’s the Core Stage Tank Propulsion Lead Engineer (TPRP) on the launch workforce.
The decrease strain, slower circulate fee procedures have been demonstrated in a tanking take a look at carried out on Sept. 21. “As soon as we bought into a quick fill configuration, we slowly raised the storage tank strain,” Clark stated. “That was the essential distinction between launch try two [on Sept. 3] and our tanking take a look at.”
A persistent leak was seen on the eight-inch diameter fill and drain fast disconnect (QD) within the LH2 Tail Service Mast Umbilical (TSMU) that connects to the Core Stage engine part, and the tanking take a look at on Sept. 21 was used to higher perceive the sealing conduct of the QD and additional develop loading methods and troubleshooting procedures.
The Artemis I car is seen on the conclusion of a tanking take a look at on Sept. 21. (Credit score: Stephen Marr for NSF)
For the upcoming launch try focusing on liftoff early on Nov. 16, one other hour was added to the size of the launch countdown by extending the primary of two built-in holds at T-6 hours and 40 minutes from two and a half hours in period to a few and a half hours. The Mission Administration Staff (MMT) will conduct a pre-tanking assembly beginning firstly of the maintain to evaluation the standing of the bottom and car techniques and the climate forecast earlier than deciding whether or not or to not gasoline SLS and make a launch try.
As soon as a “go” for tanking has been given by the MMT, after which by Artemis I Launch Director Charlie Blackwell-Thompson, the liquid hydrogen chilldown course of will now start a few hours sooner than earlier than, similtaneously liquid oxygen chilldown begins. “A part of that [extra time] is as a result of by decreasing the storage tank strain, we’re decreasing the circulate charges, so it’s going to take longer to load,” Clark stated.
“Along with that, they need [more] contingency time in there in case we’ve got to run our pre-planned contingency procedures, so if we encounter issues, they need a bit of bit extra time to do this.” SLS has a most launch window on any given day of two hours for Artemis I, so lengthening the LH2 timeline and beginning earlier ought to enhance the probabilities that the techniques and the launch workforce are able to go at opening of the launch window.
“That wasn’t an choice going into [the launch campaign] as a result of we have been borderline having the [storage] capability of hydrogen that we have to load this newer, larger car, which is why they constructed a second LH2 storage tank [at the pad],” Clark defined. “However that gained’t be out there till Artemis II.”
“After we bought in a couple of loadings, we realized we nonetheless have margin left, we nonetheless have sufficient liquid [hydrogen] left [in the storage tank] the place we have been in a position to lengthen the loading timeline.”
Each the SLS Core Stage and its ICPS in-space, second stage have been totally fueled throughout the Sept. 21 tanking take a look at. The take a look at was carried out two and a half weeks after the second launch try was scrubbed on Sept. 3 after the leak on the hydrogen fill and drain fast disconnect couldn’t be fastened.
SLS on the pad, with the in-use, 800,000 gallon LH2 storage sphere to the proper. The LH2 techniques will make use of modified, gentler pressures throughout fueling for the Nov. 16 launch try. (Credit score: Thomas Burghardt for NSF)
Following the scrub, the LH2 tail service mast umbilical was once more taken aside, this time on the launch pad. Whereas the TSMU upkeep and retesting was in work on the pad, the launch workforce revised components of its floor management software program in preparation for the tanking take a look at.
“We rewrote the process some to give you a kinder, gentler loading,” Clark defined. “Principally, what we did was we lowered our storage tank strain. We additionally slowed the chilldown part, when we’ve got the decrease circulate charges, and we tried to imitate what they have been doing at Stennis [during the Core Stage Green Run]. We tried to do it per their timeline.”
Clark famous that the brand new fast disconnect seal additionally leaked firstly of LH2 loading on Sept. 21: “Once we transitioned to quick fill, we noticed the leak indication, and it did go as much as about 7%,” he stated. “That drove us to what we name a cease circulate. We cease loading the car and we secure the whole lot at that time limit.”
At that time, the cryo loading workforce ran a pre-planned process in case they noticed a leak. With the circulate halted, they let the world across the QD heat up for a time frame after which began flowing LH2 once more; throughout the Sept. 21 take a look at, the hydrogen focus remained acceptable after that heat up and resumption of LH2 circulate.
Clark defined that the contingency process was developed based mostly on testing executed years in the past on the Launch Gear Take a look at Facility (LETF) within the KSC Industrial Space. “They have been seeing leakage down there with the preliminary testing, however they seen after they picked again up once more on subsequent runs after it warmed up some that the leak charges had improved,” he famous.
“So they really ran particular testing for that on the LETF earlier than we turned operational. We examined particularly for that, we noticed that very same statement once more, so we added that as a pre-planned contingency to our procedures.”
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The training curve for hydrogen tanking of the Core Stage at KSC has been the main target of Moist Costume Rehearsal runs in April and June after which launch makes an attempt in August and September. The configuration at Launch Pad 39B is completely different from the LETF website used for testing interfaces however not the totally built-in pad, Cellular Launcher, and car complicated.
The 39B complicated can be completely different than the take a look at stand on the Stennis Area Heart the place the Core Stage Inexperienced Run was carried out a couple of years in the past. Stennis has extra take a look at controls, but it surely has a extra compact fueling setup utilizing docked barge tanks.
At Kennedy, the EGS and contractor launch workforce remains to be experimenting to dial in repeatable settings. “Cryo techniques like predictability,” Brad McCain, Vice President and Normal Supervisor with Jacobs Area Operations Group, stated within the Nov. 11 interview. “We like the identical process again and again as a result of that offers us normally predictable outcomes, and so if you take a look at — even beginning again in April and June, you realize, we by no means loaded the identical method twice.”
“We tried to adapt and mitigate the problems that we had every time, and so each time you alter a variable or two you get completely different outcomes. For the seal leakage, we all know that thermal shocks are unhealthy for any cryo system, so that you need to decrease the thermal gradient throughout the seals.”
“With this explicit configuration, the strain shocks seem to correlate with the leakage that we’ve seen, so we need to decrease strain, which is the kinder, gentler loading that [has been discussed recently],” McCain added.
The TSMU connection was disassembled, and the seals have been changed after points in April, June, and September; the workforce is now specializing in evolving the loading course of to one thing extra repeatable. “I feel we needed to go in and take a look at the {hardware} seal,” Clark stated. “However now that we’ve executed that a few occasions, we’re extra centered on it from an operational facet of issues… what can we do to be kinder to that QD seal.”
The Artemis I car stands on Cellular Launcher-1 at Launch Pad 39B. (Credit score: Jack Beyer for NSF)
For loading liquid hydrogen at Launch Complicated 39B into the SLS liquid phases, there are three units of valves that assist management the strain and fluid circulate. There’s a valve complicated on the LH2 storage sphere after which two on the Cellular Launcher: an LH2 “skid” for the Core Stage and one for the ICPS.
The valve complicated for Core Stage LH2 on the Cellular Launcher helps a couple of set positions for filling up the stage. “It’s really a three-position valve; [in addition to the close position] one is for a sluggish fill [and] one is for a quick fill,” Clark defined.
“So as soon as we get into quick fill, it’s sort of broad open if we’re in that configuration each within the storage space and on the ML.” For fantastic management of strain and circulate on the larger, quick fill circulate fee into the Core Stage, Clark additional defined that the storage tank valves have been used. “We lowered that storage tank strain after which we deliver it up step by step so we’re slowly growing that circulate,” he stated.
The pre-planned hydrogen leak contingency process was run throughout earlier tankings with completely different outcomes; within the case of the Sept. 21 take a look at, in an effort to higher perceive the sealing conduct of the QD, the launch workforce experimented with working the contingency process utilizing the already decrease storage tank strain and by permitting the hydrogen focus stage from the leak to rise as excessive as 10% for so long as 5 minutes to see if the hydrogen ranges from the leak would stabilize and/or drop.
A hazard fuel detection system constructed into the Cellular Launcher is used to measure hint gases in enclosed areas just like the umbilical plate cavities for all of the connections from the Cellular Launcher to the rocket and spacecraft. The security system offers consciousness of a potential flammability threat from leaking propellant.
Within the case of the LH2 TSMU, the detection system measures ranges of hydrogen within the cavity between the mated floor and flight umbilical plates. These areas are additionally purged with an inert fuel like nitrogen or helium to additional scale back flammability threat.
SLS rolls out of the VAB on Nov. 4 for its subsequent spherical of launch makes an attempt in November. (Credit score: Julia Bergeron for NSF)
“They got here throughout some testing that they did again in 2011, [and] I consider that testing proved that you just really need to rise up to about 16% [hydrogen concentration] earlier than you begin getting right into a flammable situation,” Clark stated. “That was in an atmosphere that sort of mimicked our disconnect space, these areas between the plates.”
“We use the 4% [limit] as a result of that’s the very minimal that you’d get right into a flammable situation. We knew that was a really, very conservative quantity as a result of to do this you virtually need to be in a lab atmosphere and beneath excellent situations. Along with that, we’re purging these cavities with helium.”
Because it occurred throughout the Sept. 21 tanking take a look at, the excessive hydrogen concentrations went away when the circulate was stopped with the preliminary seven % leak fee, and when the strain and circulate have been extra step by step raised as part of the contingency process, the leak fee stayed beneath one % for the remainder of quick fill. NASA is utilizing the short-duration larger focus restrict in the event that they need to resolve one other leak throughout the subsequent launch try.
Trying to put all of it collectively
The launch workforce has lined all of the ground-controlled phases of the countdown at completely different factors in several Moist Costume Rehearsal (WDR) and launch makes an attempt. Floor and car points scrubbed or abbreviated previous makes an attempt, however the Sept. 21 tanking take a look at was the primary time that every one the Core Stage LH2 pre-launch loading phases have been accomplished end-to-end.
After the leak within the fill and drain QD was resolved and quick fill of the Core Stage LH2 tank was established, thermal conditioning of the 4 RS-25 Core Stage engines was began. An LH2 engine bleed is established by flowing a few of the propellant from the stage’s propellant tank via components of all 4 engines after which the LH2 is dumped overboard via a four-inch bleed QD adjoining to the fill and drain on the TSMU.
A leak on the bleed QD throughout the June Moist Costume Rehearsal countdown pressured that take a look at to be abbreviated, which prevented the complete LH2 engine conditioning sequence from being demonstrated. Points with Important Propulsion System instrumentation throughout the first launch try on Aug. 29 additionally scrubbed that countdown earlier than all of the checks may very well be accomplished.
Groups work to revive redundancy on knowledge traces from the LH2 TSMU on Sunday, Nov. 13. One redundant line has returned odd readings since Hurricane Nicole. (Credit score: Nathan Barker for NSF)
In the course of the Sept. 21 tanking take a look at, the hydrogen focus within the umbilical cavity went up once more when the LH2 bleed circulate was began. The launch workforce is taking as light an strategy to the bleed QD, however with much less choices.
“There’s no actual conditioning of the four-inch as a result of we’re working to the engine [specifications], [but] it’s a decrease circulate fee, so from that side it’s nonetheless on the similar stage as we do with the eight-inch,” Clark famous. “The engine [people] need us to start out with a principally heat engine, which is driving us to maintain that QD heat however nonetheless going at it with comparatively low strain.”
In the course of the longer, early phases of the LH2 engine bleed, the leak fee stayed inside the usual restrict. After the Core Stage hydrogen tank fueling was accomplished and the engines had been conditioned lengthy sufficient, a “pre-press” take a look at of the terminal countdown sequence for the Core Stage and RS-25 liquid hydrogen techniques was carried out.
As a result of bleed QD leak within the June WDR, the terminal countdown was run on the Orion/SLS car aside from the Core Stage liquid hydrogen techniques. Though the Core Stage has gone via its personal, standalone terminal countdown sequence twice throughout the Inexperienced Run marketing campaign at Stennis, the pre-press take a look at at KSC allowed the launch workforce to take a look at the Core Stage efficiency with the Pad 39B and Cellular Launcher techniques and will assist to dial in a few of these parameters for the following terminal countdown sequence.
In the course of the terminal countdown sequence, the Core Stage tanks are pressurized for flight and the LH2 engine bleed will increase to the next circulate fee for basically the final 4 and a half minutes earlier than ignition to assist get the engine inlet temperature and strain into their required ranges for begin.
“Shuttle had a [hydrogen recirculation] system that we’d use throughout loading and situation the engines that method,” Clark famous. “It was a two-minute terminal depend [for hydrogen on Shuttle], however they really wanted the longer bleed circulate [for SLS] as a result of they didn’t have recirc to situation the engines all through replenish.”
Artemis I on the pad forward of launch on Nov. 16. The two-hour launch window opens at 1:04 am Jap.
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“We’re nonetheless conditioning them, and we’re nonetheless flowing via them; it’s the next circulate fee, however they wanted that 4 and a half minutes minimal at flight strain flowing via the engines.”
Within the Sept. 21 take a look at, the hydrogen leak fee went above the usual restrict; that was allowed within the take a look at, once more for a short-duration, and the leak fee went down by itself.
On the following launch try, NASA shall be trying to put the whole lot collectively. They’ve run via all of the phases of launch countdown to the purpose of handing off management from the bottom to the SLS flight computer systems in bits and items, however to launch Artemis 1 they should do all of it collectively.
If they’ll apply all the teachings discovered, then they’ll get again to pathfinding once more. SLS would get management of the countdown once more at KSC, and for the primary time, the Autonomous Launch Sequencer (ALS) within the flight software program would get to run the ultimate 30 seconds of the countdown with a launch prepared car.
At current, groups are readying the Artemis I Orion spacecraft and SLS rocket for liftoff firstly of a two-hour launch window that opens at 1:04 AM EST (6:04 UTC) on Nov. 16.
(Lead picture credit score: Artemis I on the launch pad. Credit score: Stephen Marr for NSF.)
