After stacking the stages of the Space Launch System (SLS) rocket for NASA’s Artemis 1 mission in June and July, EGS and TOSC powered up the Core Stage for the first time in the Vehicle Assembly Building (VAB) at the Kennedy Space Center (KSC) in Florida on August 6. The initial power up was a significant milestone in pre-launch processing, marking the beginning of the systematic checkouts of the vehicle and ground systems that will be used for the first launch on Artemis 1.
Just prior to powering up the Core Stage, the four umbilicals that connect ground services from the Mobile Launcher were attached to quick disconnect plates on the stage’s three major equipment bays: the forward skirt, intertank, and engine section. The Integrated Operations team of EGS and Jacobs and the SLS prime contractors are working almost around clock in the VAB to get through all the installations, checkouts, and special tests in time for a launch no earlier than the end of 2021, but more likely in early 2022.
Core Stage power-up begins interface verification testing
The initial power-up of the Core Stage was commanded from the Launch Control Center in the Launch Complex 39 area at KSC on August 6. It was the first power up of the stage since it was in the B-2 Test Stand at the Stennis Space Center in April at the end of the SLS Green Run design verification campaign.
The EGS ground-based command and control at KSC is a different system than the Boeing Stage Controller system used at Stennis for Green Run campaign, so the first SLS power up was a significant event EGS and their first launch campaign for the KSC Spaceport Command and Control System as well as for the overall ground infrastructure. “Our initial power up for the Core Stage is planned for [Aug. 6], so that’ll be a big milestone for us and the team,” Cliff Lanham, NASA Senior Vehicle Operations manager for EGS at KSC, said in an interview the day before on August 5.
Core Stage power up also kicked off parts of the Interface Verification Test (IVT), which is one of the first big tests in the pre-launch Integrated Test and Check-Out (ITCO) campaign of the Artemis 1 vehicle. For this first interface test, performed only on the Artemis 1 SLS vehicle elements, the launch team will verify the ability of the ground systems to command the vehicle and monitor the health and status of its systems.
“It’s verifying the interfaces from the ground systems to the vehicle systems and also from vehicle to vehicle systems before we progress with more dynamic testing through our scheduled flow,” Dan Florez, EGS Lead NASA Test Director (NTD) for Integrated Testing, said in a May interview.
“We want to make sure electrical interfaces are correctly mated. We’ll go through a series of vehicle leak checks, make sure all of those are good from a ground perspective and that data is essentially looking good as we perform further integrated testing downstream as a readiness check to make sure all the systems are looking good and performing nominally,” Danny Zeno, senior NTD who oversees Integrated Test for EGS, added.
Additional connections between the SLS vehicle elements and the Mobile Launcher are still in work, so the initial Core Stage power up was planned as an early opportunity to get a “first look” at the interfaces between the ground and the most complicated element of the vehicle and if there were any issues the team could start analyzing in parallel with the other work.
“Our work getting the Boosters powered up in conjunction with the Core Stage is out in mid-August, so the opportunity is here to go ahead and power-up and potentially buy down some risk for us by getting the Core Stage piece powered up,” Lanham said. “We decided to go ahead and pull this test in as a Core Stage standalone only test to try and get ahead of any issues we may find.”
Lanham noted that the Core Stage was planned to be powered up for about 24 hours in this initial test. In addition to collecting data on the vehicle and ground systems and their interaction, he said the power up also provided an opportunity to load updates for the SLS flight software to the three flight computers and to the RS-25 engine control software that runs on engine controller units on each of the four Core Stage engines.
“It’s really getting powered up, [checking] some health and status, [getting] the flight software load done — there’s an engine controller software load as well that we’ll do and then we’ll power down and then get ready for the Booster-Core Stage integrated power up later in the month,” he said.
“We’ll encounter some problems, but that’s the intention is to learn the vehicle [and] flush out problems as we press more into the ITCO timeframe.”
(Photo Caption: Black, rectangular, transportation cover plates denote the locations of the four umbilicals on the Core Stage in this composite image. The forward skirt and intertank umbilicals are on the upper part of the -Z side of the stage; the two tail service mast umbilicals are near the bottom of the engine section, where propellants flow into the vehicle storage tanks.)
Stacking hardware takes back seat to connecting systems
Work in the VAB increased in complexity after the two SLS stages were lifted and mated in VAB High Bay 3. The Core Stage was lifted and mated to the boosters on the Mobile Launcher in mid-June, and the in-space Interim Cryogenic Propulsion Stage (ICPS) was placed on top of the interstage Launch Vehicle Stage Adapter in early July.
Since the last stacking, Lanham said the Integrated Operations team has been busy at work sites inside and outside the SLS. “We are continuously busy up and down the stack as we go, and there’s never really a downtime; we’re pretty much continuously working,” he explained.
After the Core Stage was mated to the boosters, Jacobs, the prime TOSC, began work to open up the Core Stage equipment bays and establish work access inside the dry volumes: the forward skirt, the intertank, and the engine section. Installing the intricate work platforms inside the stage around spaceflight system equipment was another first time operation for the SLS teams.
“To get into the [dry] volumes, we had to put in access, and [it] is fairly complex to the get access into these volumes as you can imagine,” Lanham said. “You’re trying to get people in there to work without damaging any of the hardware inside.”
Once the internal access kits were set up, Jacobs started preparations for powering up the vehicle while Boeing resumed “traveled” work tasks from the Green Run.
“Inside the engine section, Boeing has been doing some of their traveled work,” Lanham said. “They’re getting into the [Main Propulsion System prevalve] clutch [repairs]. We’ve also been doing a lot of booster cable work and pyro work as well, and then, in addition, we’ve had the stacking operations for the Launch Vehicle Stage Adapter and the ICPS.”
The Mobile Launcher systems are also being configured, with connections now being made to the SLS umbilicals. “We do what’s called our O&M (Operations and Maintenance) control requirement checkout, so essentially we’ve been checking out our systems as we’ve been preparing to mate them to the vehicle,” Lanham said.
“We do some final arm swings and that type of stuff to make sure everything is good to go as we get ready to attach to the vehicle. We’ve done similar work with our environmental control system, doing final checkouts, because that is key to powering up the vehicle is to have the environmental control in place for all the different volumes.”
As Core Stage prime contractor, Boeing orchestrated much of the Green Run operations at Stennis; the Artemis 1 flight article is the only one planned for use as a propulsion test article as it was for Green Run, and Boeing is working on tasks carried over from the Stennis tests.
“We handed the vehicle over to NASA and did what’s called the ‘DD250’ [transfer of responsibility government document] sign-off right when we came off the barge and rolled it into the VAB [in late-April],” John Shannon, Boeing’s Vice President and Program Manager for SLS, said in a July interview. “So the TOSC team with Jacobs under Exploration Ground Systems has taken over work on the vehicle, but there were some exceptions to that that were negotiated prior to handing over.”
Part of the work is the remainder of the thermal protection system (TPS) repairs and refurbishment on the outside of the Core Stage. The initial month following the stage’s arrival at KSC was taken up with TPS repairs from the Green Run Wet Dress Rehearsal and Hot-Fire tests, with the majority of that work performed with the stage in its horizontal shipping orientation in the VAB Transfer Aisle.
“We did some external things that would have been difficult to get to as the vehicle is vertical,” Shannon noted. “Places where the platforms were either covering the area that we needed to work or [where] you would have had to build significant scaffolding on the platform. So if we could get to it in the Transfer Aisle, we did it there.”
(Photo caption: The Artemis 1 Core Stage under going pre-mate and traveled work operations in the transfer aisle of the VAB.)
The spray-on foam insulation (SOFI) work was additionally complicated due to the development flight instrumentation the vehicle is equipped with. “The TOSC team did a really nice job of building up of fairly sophisticated set of scaffolding that protected the vehicle and gave us access, and we went in and took a look at some of the strain gauges that were on the external part of the vehicle underneath the foam,” Shannon said.
“We repaired some [foam] areas specifically in the hydrogen tank/intertank flange area that had either had a void due to cryo-pumping or some other damage, fixed all of that [while horizontal].” After the stage was vertically attached to the boosters on the Mobile Launcher in High Bay 3, the remainder of the work is now being completed in parallel with all the other pre-launch preparations.
With the first Core Stage power-up underway, work continues to prepare the boosters and ICPS systems for power up later in August. “The plan is to get the boosters ready, finish up the crossover work, get everything connected and then we’ll power up the Core Stage and boosters together. And then we’re planning for — not too long thereafter we’ll get into ICPS,” Lanham said.
Lanham noted that preparations to connect the ICPS Umbilical (ICPSU) to the ICPS are also being worked in parallel: “At this point we still have to get the ICPSU umbilical plates built up, and then we’ll go ahead and integrate the ICPSU to the ICPS — which will allow us to get into the next piece of that initial IVT testing.”
Managing schedule, moving around tasks for a better fit
EGS and Jacobs are managing all the different blocks of work within the overall Artemis 1 schedule. Artemis 1 is the first time launch crews are working with Orion and SLS flight hardware, and once the Core Stage was mated to the boosters, activity on the different paths and branches of work could start in parallel both inside the VAB while Orion spacecraft preparations could pick up elsewhere at the space center.
With the expansive branches of work, the forward schedule is being evaluated frequently to try to minimizing expansion of the overall timeline. “We drive our schedule to the critical path, and we are evaluating our plans [daily] because issues pop-up, non-conformances occur,” Lanham said. “[As an example,] we might have personnel issues that don’t allow someone to progress, so we are continuously re-flowing our schedule to be the most efficient, effective way to get everything done.”
Some work blocks are being rearranged on the calendar where there is a better fit. Two examples were more visible tasks that originally had been planned for earlier in the schedule: stacking of passive test articles and SOFI foam work.
While stacking of the vehicle is a main priority, the last two elements for Artemis 1 VAB testing are passive articles to be stacked on top of the ICPS. This work was temporarily set aside because it isn’t critical path work and delaying it wouldn’t affect the schedule.
Likewise, the bolted flange between the bottom of the LVSA and the top of the Core Stage forward skirt needs to be closed out with SOFI sprays around the circumference. The baseline plan had the LVSA foam spray work on the flange beginning shortly after the LVSA was mated to the Core.
“LVSA foaming and stacking have not been critical path items for us, so they can move around,” Lanham said. “So we have done that, and that’s just typical of what our job is.”
More critical to getting the active SLS systems powered up and talking to the ground control systems was connecting the four servicing umbilicals from the Mobile Launcher to the Core Stage. “The LOX (liquid oxygen) tail service mast umbilical (TSMU), the [liquid] hydrogen tail service mast umbilical, the CSITU (Core Stage Intertank Umbilical), and CSFSU (Core Stage Forward Skirt Umbilical) have all been integrated to the vehicle, and so that was another big achievement for the team: first time connecting to the vehicle,” Lanham said.
After a lot of preparation, the umbilical arms were swung into position, and the ground-side umbilical plates were connected to the vehicle-side plates in late-July prior to the initial power-up. Lanham added that he is seeing the teams work through the learning curve of first-time, hands-on work.