NASA EGS completes first SLS Mobile Launcher fueling tests

by Philip Sloss

Across two weekends in November NASA Exploration Ground Systems (EGS) and prime Test and Operations Support Contractor (TOSC) Jacobs successfully completed the first flow tests of liquid hydrogen (LH2) and liquid oxygen (LOX/LO2) between the refurbished and updated Launch Pad 39B infrastructure and Mobile Launcher-1 (ML-1) at the Kennedy Space Center (KSC) in Florida.

The integrated propellant loading test of the pad and the mobile launcher (ML) was a major objective of the Multi Element Verification and Validation (MEV&V) campaign ahead of the launch of Artemis 1, the first joint mission across the EGS, Orion, and Space Launch System (SLS) programs. The test campaign started at the beginning of the summer and is expected to conclude by the end of the year.

The flow test of cryogenic LH2 and LOX was the first of three flows to be completed ahead of launch; the next one will be during the Artemis 1 Wet Dress Rehearsal (WDR) to fuel the Artemis 1 launch vehicle for the first time ahead of the countdown for its first launch, expected in 2021.

Integrated propellant flow test success

The Cold Flow Test or Integrated System Verification and Validation (ISVV) 17 was conducted over two Saturdays last month, November 9 and 16. “Completion of ISVV 17 was a huge milestone for EGS as we work toward Artemis 1 launch,” Wes Mosedale, Lead NASA Test Director in the Test, Launch, and Recovery Management Branch of EGS, said in a recent interview.

“The test went extremely well, we didn’t have leaks on either system. I’d say lessons that we learned and things that we may go tweak in our procedures, none of those require us to do another loading operation with the ML at the pad so from an EGS perspective the next the cryos will be during wet dress.”

“One of the things our launch director Charlie (Charlie Blackwell-Thompson) reminded us at our pre-test briefing going into these is that we’re going to flow cryos three times prior to Artemis 1 launch and ISVV 17 was one of those,” he added. “We have that behind us now so the next time we flow cryos out at the pad will be for wet dress and then for launch, so getting these tests behind us was a huge step.”

Credit: NASA/Ben Smegelsky.

(Photo Caption: A November 8 view looking down the length of LH2 cross-country lines that run from the storage tank in the northeast corner of the Launch Pad 39B infield to the Mobile Launcher. Lines allow hydrogen to flow from the sphere to the ML and the vehicle and also, via separate lines, from the vehicle back out to a safe vent location.)

The two liquid propellant commodities were tested individually with Mobile Launcher-1 (ML-1) hard-down at Pad 39B; flowing liquid oxygen from the pad storage sphere to the ML was tested first on November 9, followed by LH2 on the 16th. SLS uses both solid and liquid propellant; the Solid Rocket Boosters are filled with solid-propellants months and years before launch day, but the two liquid-fueled stages, the Core Stage and Interim Cryogenic Propulsion Stage (ICPS), are loaded hours before a scheduled liftoff.

“Part of our objective going into this was not only to validate our flow sequencing and timelines but also the preparations that we do which are part of our critical path in launch countdown to get to tanking,” Mosedale said. “So technically for both LOX and hydrogen each one of those tests started the day before with the preparations at the storage area because that’s part of our path to get the pad closed out for tanking.”

“The actual flow themselves I’d ballpark it at about six hours for the actual load portion. We did the LOX and hydrogen a little bit different, there were some lessons learned based off of the first time we did LOX.”

“For LOX we did a lot of the storage area preparations on that Saturday that we did the test so that drove our timeline to be a little bit longer for the team,” he added. “We had several hours of storage area preparations on the ninth before we got into the flow.”

“On the tail end of LOX because of the inerting is a little bit easier, the post test portion on that Saturday wasn’t as long but the team worked essentially a twelve-hour day. For hydrogen we got a lot of the storage area preps done the Friday before and so essentially we came in on the sixteenth and started working the final preps of the storage area which is opening the block valves and then getting the pad cleared and then we were ready to get into flow pretty early that morning, seven or eight o’clock I think it was.”

ISVV 17 was an integrated test of the pad and the ML together. “This being an integrated V&V (verification and validation test) we didn’t have separate test objectives,” Mosedale noted. “By nature between the ML and the Pad it was an end-to-end [test] for LO2 performing the modified vehicle loading profile through both the Core Stage and upper stage (ICPS) skid back to the dump basin and really what we wanted to do was get liquid temperatures and pressures at both the skid inlets for both the Core Stage and upper stage.”

“Likewise for LH2 same thing, we wanted to work through that vehicle loading profile, get liquid to both the Core Stage and upper stage skid for LH2 back through the liquid separator and out to the flare stack,” he added. “For LH2 side we wanted to get some data on the Core Stage engine bleed valves, which is new for us and then test the upper stage replenish flow and then this was our first time with the liquid separator seeing hydrogen as well.”

Test configuration, flow paths

The propellants were fed through the launch pad and mobile launcher cryogenic loading infrastructure as remotely commanded from Firing Room 1 of the KSC Launch Control Center (LCC). EGS is in late stages of development of the Ground Flight Application Software (GFAS) and overall Spaceport Command and Control System (SCCS) that manages ground processing, integration, checkout, and launch of Orion and SLS vehicles.

The ISVV 17 tests were the first opportunity to command and control the real propellant loading subsystem hardware. “We’ve tested the subsystem end to end, all the valves, pressure transducers, everything was checked out prior to cryo flow from the firing room and then we also did a series of simulations specifically for this test event,” Mosedale explained.

“We had our ground models in the exact configuration that we did for this test and we ran through a simulation both for LOX and hydrogen with some problem scenarios thrown in. That really helped us both flesh out our procedure and make sure our loading procedure for this test was correct and also make sure to practice our problem reporting and anomaly discussion and work those out as well.”

Credit: NASA/Cory Huston.

(Photo Caption: An engineer monitors systems from one of the firing rooms in the Launch Control Center at KSC during a cryogenic loading simulation in April. Many of the same members of the launch team participated in the recent cryogenic loading test, which was orchestrated by EGS command and control software.)

Without the vehicle in place, loading operations were commanded manually by launch team engineers in the firing room. “From a sequencing perspective the loading operation was done very manually and that’s really just an artifact of the configuration we were in and not having the vehicle and all those sensors on the vehicle which our software sequencers use to trigger the loading operations, so that part of the operation was done manually versus on launch day a lot of that process will be automated,” Mosedale noted.

The SLS Core Stage and ICPS have sensors inside their LOX and LH2 tanks that signal when the quantities reach different levels there. This is used in both directions: during propellant loading as the liquid-level sensors are covered, those indications are used to adjust the speed of the filling operation; during flight as the stage engines drain the tanks and the sensors are uncovered, those indications are monitored by vehicle flight control systems to ensure all engines are shut down before the tanks are empty.

LOX is the denser of the two liquids and is fed from the large storage sphere in the northwest corner of the pad to the vehicle using pumps. Since SpaceX took over control and operation of Pad A at Launch Complex 39, NASA grabbed the Shuttle-era pump set there as cold spares for the two Pad B pumps.

“There’s two pumps that are in place, the other two are essentially spares so they’re not physically installed in the system,” Mosedale explained. “For loading, we use a single pump and then the other pump is there as a backup.”

“We’ll have the ability on launch day, of course, if we have an issue with the pump — leak, the seal, whatever it might be — to be able software-wise to switch between the pumps.”

Credit: NASA/Ben Smegelsky.

(Photo Caption: Jacobs engineers Josh Jones, Jim Loup and Rene DeLaCruz inspect equipment surrounding the liquid oxygen storage sphere at Launch Pad 39B on November 8. They are standing in and around the two pumps used for transferring LOX from the sphere to the Mobile Launcher and the SLS vehicle’s liquid-fueled stages.)

LH2 is less dense and doesn’t require pumps to feed it from the storage sphere to the ML and onto the vehicle. “Between the storage tank pressure and the valves that we have in the system at the cryo skid we manage the hydrogen,” Mosedale said.

“It’s a pressure loading operation so we push it up using the storage tank pressure and then we control the flow rate between the pressure at the storage tank and the variable position valves that we have controlling the flow rate there at the cryo skids between the Core Stage and upper stage.”

As with validation of the propellant loading systems at the Stennis Space Center that will be used for the Core Stage Green Run test planned for next year, additional test equipment was put in place for ISVV 17 to account for the lack of a vehicle. “We did have to have some special test equipment as a result of us not having the flight vehicle,” Mosedale said. “On the Core Stage, we had temporary blind flanges installed on the LO2 fill and drain line, the flex hoses, and the engine bleed line flex hoses there on the TSM (Tail Service Mast) plate interface.”

“And then for LO2 upper stage, we had temporary blind flanges installed on the upper stage umbilical flex hose.”

“For the hydrogen side kind of a similar configuration we had a turnaround tool that was installed in what we call the TSM ‘bathtub’ which is essentially kind of the bottom of the TSM and that turnaround tool was essentially a jumper flex hose that allowed us to go from the LH2 fill and drain line back out to the engine bleed line, so it allowed us to have that flow path configuration for this test,” Mosedale added. “Similarly for the LH2 upper stage, we had a blind flange that was installed on that LH2 flex hose.”

Credit: NASA/Ben Smegelsky.

(Photo Caption: A November 8 view from the ML deck/zero-level of the two Tail Service Mast Umbilicals (TSMU) with their umbilical arms extended for the ISVV 17 tests. The LO2 TSMU is on the right (foreground), LH2 TSMU left (background), corresponding to the layout of the storage spheres in the pad infield (LO2 northwest, LH2 northeast). The ground-side umbilical plates were not part of the configuration for these tests without a vehicle in place.)

Although there is no vehicle stacked on the Mobile Launcher, Mosedale noted that they did test the overall propellant flow sequence. “From a sequencing perspective, we did this just like we would on launch day, chilldown, slow fill, fast fill, topping, replenish,” he said.

“The flow rates aren’t the same as we’ll have against the vehicle so we didn’t necessarily dwell at each phase for the same duration we would on wet dress or launch day but we absolutely did follow the sequences on the LOX side and the different pump speeds as we worked through the fill operation and on the hydrogen side the storage tank pressure and the valve configuration as we worked through the different phases of loading.”

The turnaround tools allowed NASA and Jacobs to test flow paths that will be used to fill the vehicle and then to keep it filled. For this vehicle the cryogenic propellant is stored near its boiling point; as some of that propellant boils off and becomes gaseous, it is vented away from the vehicle.

“On the LO2 side our flow path was from the LO2 sphere we pump it up through the ML,” Mosedale explained. “For Core Stage, we go through the LO2 replenish valve on the Core Stage skid and then back out of the TSMU vent valve and then out to the LO2 dump basin.”

“Similarly for LO2 upper stage, the flow went up the tower to the upper stage replenish valve and then back out of the drain valve there and out to the dump basin. On the hydrogen side we went from sphere up to the Core Stage skid valve on the ML through that turnaround tool which I described in the bathtub and then to the engine bleed lines and then out to the liquid separator and then to the flare stack and then again for the upper stage very similar up the tower to the upper stage skid valves and then back out of the drain valves and down to the separator and to the flare stack.”

Credit: NASA/Ben Smegelsky.

(Photo Caption: The flare stack used to safely consume hydrogen that boils off from liquid to gas during the fueling process can be seen to the left of the Pad 39B water tower. In addition to hydrogen boil-off that is vented from the top of the propellant tanks of the SLS liquid stages, some LH2 used for conditioning engine equipment also exits the vehicle. A liquid hydrogen separator, which is obscured in this image to the left of the base of the flare stack, provides a temporary holding location to allow the liquid “engine bleed” to boil off before it is also vented to the flare stack.)

“With the exception of having the umbilical plates there which we didn’t have we tested the system essentially end-to-end,” he said.

In addition to filling the propellant tanks, a smaller quantity of both commodities is flowed through the engine equipment and the feedlines and in the stage to condition them for ignition and mainstage operation. In contrast to the Shuttle, where the LH2 engine bleed was recirculated back into the External Tank, both commodities exit the Core Stage.

The RS-25 LH2 engine bleed required the addition of a hydrogen separator tank in between the ML and the launch pad’s flare stack to ensure that the liquid can expand to gas before it reaches the flare stack to be safely burned.

“We size the separator to keep up with what we think is the max flow coming out of the bleed system with some margin,” Mosedale noted. “With the flow rates that we had with the turnaround tool installed and the configuration I don’t think we were at the flow rates we will see on launch day, but certainly we did get liquid in the separator and we were looking at the back pressure there that it caused on the system which was within what we expected and then the boiloff rates.”

With the vehicle stacked on the ML, the other flow path would be to drain the SLS liquid-fueled stages after a scrubbed launch attempt or tanking test such as the wet dress rehearsal (WDR) which is planned as part of Artemis 1 launch preparations.

“The flow path is essentially the same as it was going to the vehicle just in reverse when we push it back out of the vehicle,” Mosedale said. “We couldn’t test that in this configuration but certainly as we go through our cryo load simulations and launch countdown simulations that will be part of those demonstrations, so we’ll do that against the models and emulators.”

In addition to the propellant flows themselves, other systems integral to a safe load operation were tested.

“For this test, it was really the systems that are directly supporting cryos, so for the hydrogen test haz gas (hazardous gas detection) was obviously a big one, the leak and fire detectors that we have throughout the piping from the storage area all the way through the ML,” Mosedale noted. “That system worked well for us.”

“Other subsystems that we had [supporting], ground power was one of them. We had engineers supporting should we have a power issue or something like that and we need to transition to batteries.”

“We use a lot of GN2 (gaseous nitrogen) and helium during the test so it was a good test of our pneumatic systems that support,” he added. “And then, of course, our command and control system; for the cryo guys it’s the same consoles that they’ll be sitting at on launch day so from that perspective [it was] another good test of our command and control system.”

The pneumatic systems complement the hazardous gas detection system, which includes sensors looking for leaks on and off the vehicle. Gaseous helium and nitrogen are used to mitigate the flammability of any potential leaks. A purge of the gases is maintained in enclosed areas.

“Nitrogen we use for purges for electrical enclosures and things like that,” Mosedale said. “And then on the LOX side to purge out the lines; we use helium on the hydrogen side to purge those lines out.”

One of the liquid oxygen skids on the Mobile Launcher. Credit: NASA/Ben Smegelsky.

Although based in large part on Space Shuttle rocket engines, SLS is a larger rocket than Shuttle, with an integrated ICPS upper stage. In addition to the propellant flowing into Tail Service Mast Umbilicals (TSMU) at the bottom of the Core Stage, lines run well up the tower of the ML to the swing arm that connects to the ICPS for fill and drain.

“Certainly it’s more complex for us [now],” Mosedale said. “During the Shuttle days we had a single tank so the sequencing of the flow both between LOX and hydrogen and then again between the Core Stage and upper stage is something new for us.”

“We demonstrated that specific sequence as we transition through the different phases of Core Stage and then get into replenish there and then get into upper stage, the same thing there and we went all the way through that loading sequence to the point where we had both stages in the replenish configuration like we would as we get toward terminal count.”

“I don’t think I can go too deep into the details from an export control perspective but we start with Core Stage LOX,” he added. “We have to delay the start of Core Stage LH2 to satisfy some thermal constraints there, so those are definitely tied together.”

“For each of the commodities, we get into replenish on the Core Stage before we start flow for the upper stage.”

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