Integrated ML-Pad validations almost complete
Mobile Launcher-1 (ML-1) rolled out to Pad 39B in late June for the Multi-Element V&V. Testing was interrupted for about a week in late August/early September by Hurricane Dorian, but otherwise integrated testing and checkouts of the ground systems at the pad with the systems in the LCC has continued through the Fall and is nearing completion.
“I’d say overall from a MEVV perspective we’re about ninety percent complete,” Mosedale said. “The big hitters remaining before we go back to the VAB (Vehicle Assembly Building), we’ve got testing of the Core Stage APU (Auxiliary Power Unit) spin panel.”
Credit: NASA/Ben Smegelsky.
(Photo Caption: Crawler Transporter-2 returns ML-1 to the VAB on August 30 ahead of the passage of Hurricane Dorian. The tropical storm interrupted spaceport operations at KSC for about a week. ML-1 was originally moved to Pad 39B in late June for the current MEV&V testing. Testing is planned to wrap up this month after which the ML will be moved back to the VAB again.)
“We use helium to spin up the Core Stage APUs and power the hydraulic systems prior to engine start, so we’ve got checkout of that system which is going to start this weekend,” he said at the time of the interview on November 22. “We’ve got tests of the ground cooling system for Orion and the pad ECS (environmental control system) and then a final validation of the ML fire suppression system.”
“And then we have another ISVV for the power outage and demand test, where essentially we’re going to test all of our ground systems, electrical systems response if we were to have a feeder out at the pad if we were to lose power and make sure that we’ve got redundancy in the right places, so those are the big hitters before we roll back next month.”
One of the test series already completed was one to calibrate the Ignition Over-Pressure / Sound Suppression (IOP/SS) water system timing. The large water tank at the pad is filled for ignition and liftoff and drains in a short period of time.
Over several tests, the timing of valve positions was refined to meet the IOP/SS requirements for launch. “We had to tweak the flow to ensure we had the right amount of water flowing at the right time but not too early that we impinge on the vehicle if we have an abort,” Mosedale said.
“That’s essentially what drove us to have that extra set of valves, the post-liftoff bypass valves which start the flow out of the rainbirds but we don’t go to full flow until just prior to liftoff. It was just a matter of how we had to sequence the valves with the SLS requirements for flow rate versus time and that’s how we were able to meet that requirement.”
As during a Shuttle launch sequence, the Space Shuttle Main Engines (SSME) now installed in the Core Stage start a little over six seconds before liftoff and IOP/SS water begins flooding parts of the pad.
Credit: NASA/Kim Shiflett.
(Photo Caption: Pre-liftoff water floods the ML flame hole and runs into the Pad 39B flame trench during an IOP/SS water flow test on September 13. An initial water flow can also be seen emerging from the rainbirds above on the ML deck/zero-level. Three sets of valves open in a full launch sequence to release all the water in the pad’s water tower to cover those areas while the Core Stage engines fire before liftoff and then after the Solid Rocket Boosters also fire and the vehicle lifts off and climbs away from the ML.)
“There’s three sequences of valves, you have the pre-liftoff valves that’s the flame hole and flame deflector coverage there,” he said, which open at around T-17 seconds. “We open what we call the post-liftoff bypass valves and those are the ones where we start seeing the trickle flow of water out of the rainbirds.”
“That allows us to ensure that the rainbirds are full of water once we open the third set of valves which is the post-liftoff valves and those open just prior to T-0 and that’s when we get full flow out of the rainbirds.”
The final IOP/SS test was executed by the Ground Launch Sequencer part of GFAS and included firing the set of Hydrogen Burn-Off Igniters (HBOI) positioned around the lip of the ML flame hole
As is common with other rocket engines, the RS-25s use a fuel-rich mixture during ignition and shutdown, which creates a leading and lagging buildup of hydrogen gas in the area around the engines, respectively. During ignition on the pad, the HBOIs burn excess hydrogen gas so that a large accumulation doesn’t ignite all at once.
The HBOIs are also designed to run long enough to consume any hydrogen gas lagging in the area during a possible pad shutdown after the engines reach zero-thrust, reducing the fire potential for nearby vehicle and pad equipment.
Credit: NASA.
(Photo Caption: A NASA presentation graphic showing the Hydrogen Burn-Off Igniter coverage of the RS-25 engines and Core Stage Auxiliary Power Units (CAPU) exhaust ports as viewed looking up from underneath the vehicle on the ML. )
In addition the Core Stage Auxiliary Power Units (CAPU) also exhaust hydrogen gas out of ports at the bottom of the stage’s boattail after the engines start. While the vehicle remains on the pad before liftoff, two of the HBOIs streams is aimed to cover those sets of CAPU exhaust ports.
The fire suppression/extinguishing systems at the pad and on the ML use a different water supply than the sound suppression system. “We have separate storage tanks for that, that’s outside the pad perimeter and we have essentially a special set of fire suppression pumps and that storage tank that feeds the fire suppression system as well as the post-launch washdown system,” Mosedale noted.
In addition to these tests, the hydraulically-actuated swing arms on the ML were tested out at the pad during a simultaneous retract test similar to ones conducted in the VAB.
Launch team continuing simulations
Following the remainder of the MEV&V tests, the ML is scheduled to return to the VAB by the end of the year. After a few more demonstrations and a formal acceptance review, it will be turned over from its construction team to the EGS processing team.
The launch team will continue conducting “run for record” certification simulations to get ready for Artemis 1.
“For term count (terminal countdown) sims we have ten planned between now and launch, we’ve completed one run for record sim that was back in October,” Mosedale noted. “We’ve also done one of our eight cryo load simulations earlier in April of this year both were highly successful and we learned a tremendous amount doing those sims.”
Credit: NASA/Ben Smegelsky.
(Photo Caption: A sequence showing three of the SLS swing arms as they were retracted from a connected position to their post-liftoff position in an October 4 test at Launch Pad 39B. The test was conducted on, from top to bottom, the Interim Cryogenic Propulsion Stage Umbilical, Core Stage Forward Skirt Umbilical, and Core Stage Intertank Umbilical.)
“For each one of those, it’s kind of the first time that we’ve been in that full launch day environment with the room fully staffed for a lot of folks since the end of Shuttle so those were also really big milestones for us from a EGS program perspective.”
Assembly of the first Core Stage is nearing completion at the Michoud Assembly Facility in New Orleans. Before the stage arrives at KSC for launch integration, it will first serve as a test article for the SLS Program in the Stage Green Run test campaign at the Stennis Space Center in Mississippi.
The stage will go through similar testing and checkout at KSC prior to launch, and the testing at Stennis will provide a first look at vehicle performance during those activities. The EGS launch team will monitor the full-duration stage hot-fire that is planned to culminate the campaign at Stennis along with preparatory tests.
“The effort is called ‘Green Run flight following,'” Mosedale said. “We’ll have a few folks on site there for the Green Run but we’re set up to have our Firing Room configured to receive the Green Run data and also audio of the test.”
“The complexity of the test will dictate how many folks you’ll have in the room because we’ll be following some of the earlier tests as well, the electrical checks and other things. We intend to have a team of folks, our cryo folks and others in the room when they do the tanking operation.”
“The [hot-fire test] itself at Stennis we’ll have folks in our Firing Room 1 and we’ll be following along looking at the data and that data certainly will feed back into our launch countdown timeline and also our software as well and so absolutely we’ll definitely be following along there.”
Lead image credit: NASA/Glenn Benson.
