NASA’s Exploration Ground Systems (EGS) program and prime launch processing contractor Jacobs are performing final installations, functional checks, and buttoning up the Artemis 1 vehicle in the Vehicle Assembly Building (VAB) at the Kennedy Space Center (KSC) in Florida before rolling it out to its seaside launch pad for the first time. Rollout to Launch Pad 39B will be no earlier than mid-February after an engine computer needed to be replaced at the end of the year.

In addition to finishing functional checks and closing the Space Launch System (SLS) Core Stage engine compartment out for launch, EGS and Jacobs are also preparing to re-run a countdown sequencing test to verify that the ground-based launch sequencer is ready to conduct launch countdowns for the integrated Orion and SLS vehicle. The first vehicle trip to the pad will be to conduct a full launch countdown demonstration test called the Wet Dress Rehearsal.

The schedule still projects that the vehicle could be ready to launch no sooner than the end of lunar launch window in March, but doesn’t leave much time to address issues and later windows beginning in April are more realistic.

Closing out Core Stage aft compartment after engine controller replacement

With the broken Core Stage engine controller replaced over the New Year’s holidays, EGS and Jacobs were able to finish functional checkouts of the most complicated part of SLS on the evening of January 12. “We did that last night and everything worked out pretty well,” EGS Lead NASA Test Director (NTD) for Integrated Testing, said in an interview on January 13 with NASASpaceflight.

SLS is derived from the Space Shuttle vehicle and the Core Stage combines the launch systems from the reusable Shuttle Orbiter and disposable External Tank into an expendable, in-line, ground-started sustainer stage. The most complicated part of the Core Stage is the engine section where the cryogenic liquid hydrogen (LH2) and liquid oxygen (LOX) propellant is fed by the stage to the RS-25 engines.

With an engine controller that wouldn’t power up, final functional checks of the stage’s engine section components and the four RS-25s were put on hold while troubleshooting occurred from Thanksgiving through most of December. The issue also helped push the earliest lunar window that Artemis 1 could be ready for launch from February to March.

The functional checkouts of the Core Stage Main Propulsion System (MPS) and RS-25 engines verified that they are again configured and ready to be loaded and fired, this time for launch. The functional testing was the last part of Program Specific Engineering Tests (PSET) on the base elements of the new launch vehicle.

“[The testing] included all of your pneumatics and avionics checkouts of the Core Stage,” Florez said. “That [also] includes your flight readiness test of all four engines, especially after we replaced the engine controller on the number four engine.”

“Everything checked out well, we did our checks on the thrust vector control system (TVC), all the actuators. [We] gimbaled the nozzles and then we concluded the test by closing out the hydraulic system for flight and also doing a spin test of the auxiliary power units that provide hydraulic power to the engines for both steering and also for engine control.”

Credit: NASA.

(Photo Caption: The aft end of the Artemis 1 SLS vehicle is seen from the zero-level of the Mobile Launcher during Core Stage functional testing on the night of January 12. The stage’s hydraulic thrust vector control system was tested by moving the four RS-25 engines. The functional checks were the final part of Program Specific Engineering Tests on the Core Stage, which were completed that night.)

Resumption and completion of the remainder of the PSETs for the Core Stage occurred the week of January 10, with functional testing of the MPS pneumatics and hydraulics, along with the flight readiness test of the RS-25 engines being similar to the final pre-firing functional checkouts performed on the stage prior to its first tankings and test-firings at Stennis Space Center a little over a year ago as a part of the Green Run campaign for the stage.

With those functional checks complete, the Core Stage engine section can now be closed out for launch over the next few weeks. “Getting that whole engine section closed out is a big milestone towards rolling out,” Cliff Lanham, NASA Senior Vehicle Operations manager for EGS at KSC, said in the January 13 interview.

“Now that PSETs [for the Core Stage are] over, we can get into our engine final inspection and then start closing out the engine section and then finally get into the engine blanket installations.” A decision was made to have Core Stage prime contractor Boeing perform the installation of the engine-mounted heatshield (EMHS) blankets, which is the most time-consuming task in that part of preparations.

“We have engaged Boeing, they will be helping us out with the engine blankets now, so that work will be going on seven days a week and that pulled back our critical path by a few days,” Lanham noted.

The powerheads of the four RS-25 engines fit into the engine section of the stage through large openings in the boattail; the EMHS blankets are a component of the thermal protection system (TPS), enclosing those openings to provide a thermal and environmental barrier between the engine section and the outside.

Boeing conducted and supervised vehicle operations during the Core Stage Green Run at Stennis, and has already performed the lengthy installation of the EMHS blankets as a part of preparations for both Hot-Fire tests that were performed in January and March, 2021. Boeing has been performing post Green Run refurbishment and modifications on the Core Stage at KSC on a seven day per week schedule since it arrived at the launch site in late April.

That post Green Run refurbishment “traveled work” is also wrapping up. “We have one more leak check on a purge bag for the bleed [modification] that has to be completed, we’re actually planning on doing that tomorrow,” Lanham said during the January 13 interview. “In the intertank area there is some foam trimming that has to be done on the LH2 forward dome and we’re looking at finishing that up next week, so from a traveled work standpoint we are 98-99 percent complete and plan to finish that up mid next week in total.”

Final closeouts and TPS detailing work are also continuing around other areas on the integrated Orion-SLS Artemis 1 vehicle. “We’re continuing with our [Solid Rocket] Booster closeouts, all systems tunnel covers are on both the left-hand and right-hand side now,” Lanham said.

Credit: NASA/Cory Huston.

(Photo Caption: The “white room” and Crew Access Arm on the Mobile Launcher is seen backed away to the left of the Artemis 1 Orion spacecraft during a recent retraction test of the arm in the VAB. Artemis 1 is an uncrewed test flight for both Orion and SLS, but the Crew Access Arm allows NASA to install late-stow payloads in the Orion Crew Module for this mission.)

“We’ve been doing a lot of we call it RT-455 work, which is the cork material, so we’ve been working on that on both [Boosters], there’s a lot of effort there with our DFI runs, that all has to be closed out with this material, as well as the areas between the different systems tunnel covers.” RT-455 is a room temperature vulcanizing (RTV) material that is applied to exterior seams as a weather seal and for thermal protection.

“We’re looking to be done towards the end of January with the Booster closeouts, notwithstanding anything required [for] testing there,” Lanham noted. “We continue to put RTV on the exterior of the Orion as we prepare for rollout for WDR, so that work is ongoing and that is time-consuming work as well, but that’s going well.”

Remaining tests and checkout before rollout and WDR

Getting the Core Stage PSET work completed has drawn engine section closeouts more or less even with the Integrated Test and Check-Out (ITCO) schedule to rolling out to the launch pad. “Our critical path previously was running through our engine section with our blanket installation and final inspections and closeouts and then getting into confidence checks and then ultimately our final closeouts for roll,” Lanham explained.

With Boeing working on the flight EMHS blanket installations seven days a week, Lanham said, “that pulled back off our critical path by a few days and our ITCO testing basically is now our critical path.”

“Now [that] we’ve finished Core Stage PSET, [we have] ICPS (Interim Cryogenic Propulsion Stage) PSET next week, then we’ve got a Countdown Sequencing Test Run 2, and then we get into our Flight Termination System Part 1 testing, and then we get into closeouts [for rollout] and that’s kind of our critical path right now.”

ICPS is the in-space second stage on the SLS Block 1 vehicle; functional testing was partially completed in early December before the remainder was temporarily deferred. “We’ve run a lot of the tests, a lot of the guidance and flight control checks have been done,” Florez said. “We [also] completed a big chunk of the electrical portion, which includes all the flight control tests.”

“There was no issues [with the ICPS PSETs], but we had to get into [Communications] End-To-End testing,” Lanham added. “Now we’re picking up the tail end of that back up.”

The Communications End-To-End Test was conducted in mid-December; the test required reserving time with a large set of NASA’s communications resources, which Orion in particular will engage during its trip from the Earth to the Moon and back on Artemis 1.

Credit: NASA/Frank Michaux.

(Photo Caption: Members of the Artemis 1 Launch Team’s Integration Console are seen during a day of launch simulation on December 13. The launch team will be conducting and overseeing final critical pre-launch testing in addition to the countdown operations for the Wet Dress Rehearsal and the Artemis 1 launch itself.)

“That’s a very complex test, it requires multiple assets across the country,” Florez said. “It requires the Deep Space Network [and] all those ground stations, as well as the Tracking Data and Relay Satellites on orbit, so trying to schedule that up is a monumental task on its own for the amount of time that we need to test. We prioritized that test and worked other things around it, due to the assets and the schedule constraints.”

“Once we got into the test, everything went pretty smoothly for the Comm End-To-End test. We verified all the comm paths that we have. You’re essentially simulating a mission profile, so you’re making sure that you have data going through all the different legs, network legs, that you would for a mission with the different data rates and making sure that everybody that needs to receive the data and send commands can do that effectively.”

As a part of the regular schedule reworking that goes on during a launch campaign, EGS and Jacobs rescheduled the remainder of the ICPS PSETs and that work is now expected to resume early the week of January 17. “As we got the engine controller changed out, we wanted to get into Core Stage PSET immediately, so that kind of pushed the ICPS PSET to the right some,” Lanham noted. “But now we’re ready to get back into it.”

“We hadn’t started the MPS testing, we’re getting back into it now that we have some window [in the schedule],” Florez said. “What we’re focusing in on now is the MPS/Cryo tests and some of the reaction control tests.”

One issue with the ICPS was seen late last year. A leak was discovered in a portion of a gaseous helium purge line on the forward end of the ICPS, but is not seen as a constraint.

A statement from the SLS Program emailed to NASASpaceflight by NASA spokesperson Tracy McMahan said: “During checkout and testing, engineers detected a larger-than-anticipated amount of helium in the cavity between Interim Cryogenic Propulsion stage (ICPS) and the Orion stage adapter. Follow-on testing and analysis identified a helium purge line in the ICPS vent system as the probable source of the helium.”

“The purge line is part of the ground support used to purge the ICPS on the ground,” the statement continued. “At this time, the team does not believe any flight hardware action is required nor will this issue impact the wet dress rehearsal schedule. The team continues to assess test data and will closely monitor the situation during ongoing tests and checkouts.”

After the ICPS PSETs are completed, the second run of the Countdown Sequencing Test is currently scheduled for around January 24. The first run was performed on December 20.

“You’re essentially performing a launch countdown but inside the VAB, so you’re simulating some things, you obviously don’t have any [cryogenic propellant] and fluids onboard the vehicle so you have to simulate those tasks, but a lot of the [command and control computer] sequencing [is what] we’re checking out,” Florez said. “The intent there is to make sure that the software and the command and control system between the ground and the vehicle systems are talking to each other and are in sync.”

The test runs through the critical, terminal launch countdown sequence, which is executed by computers as the volume and speed of necessary, coordinated actions and verification checks increases to very high levels. The first test cutoff a few seconds earlier than was desired.

“The test went very well, we learned a lot of critical things, but towards the end of the test we learned something new that prevented us from going down further in the count,” Florez said. “The way the vehicle emulators that we use for software testing are built they behave a little bit differently [than the actual vehicle], so that’s what we learned, and due to that we’re changing the process and the procedures and [performing] the second run of the test.”

Credit: Stephen Marr for NSF.

(Photo Caption: The Core Stage intertank is seen flanked by the forward skirts of the two Solid Rocket Boosters in VAB High Bay 3 on December 20. Access inside those three areas is needed to perform final installations of Flight Termination System components and verification that the safety system is fully functional. Testing inside the intertank and forward skirts will be one of the final tasks in the VAB before the Artemis 1 vehicle rolls out to the pad, prior to both the Wet Dress Rehearsal and launch.)

The Ground Launch Sequencer (GLS) controls the terminal countdown until about 30 seconds before liftoff, when control of the countdown is divided between the SLS flight computers and the GLS. The SLS flight computers take over control of the vehicle at that point, but the GLS not only continues to monitor the vehicle performance, but also continues to control and monitor ground systems.

During the Countdown Sequencing Test the GLS was run against the real, fully-integrated Artemis 1 Orion and SLS vehicle. Emulators were still used to simulate a “wet” vehicle with the SLS stages loaded with their LH2 and LOX propellant, but the ground sequencer was working with an otherwise real set of flight computers, spacecraft and rocket hardware, and instrumentation.

The first test run didn’t quite make it through the handoff of vehicle control from the ground to the vehicle. “We got within four seconds of where we wanted to terminate the test,” Lanham said.

“And I think the fact that we did not do that handoff is exactly why, for the most part, we want to go and re-run the test, as well as picking up [changes to] the LCC (Launch Commit Criteria) limits and to get the software changed and accommodate those LCC limits.”

The highest fidelity test of the terminal countdown sequence will be performed as a part of the Wet Dress Rehearsal (WDR), where the vehicle will be fueled and prepared for ignition and liftoff just as it will be on launch day, with the countdown being stopped only a couple of seconds before engine start.

The last major ITCO test before the first rollout to the launch pad will checkout some parts of the Flight Termination System (FTS). For Artemis 1, the final installations and checkout of the FTS are divided into two parts, with first part performed before the first rollout and the WDR and the second part done back in the VAB just before launch.

Once the FTS system is fully certified with an end-to-end functional test during the second part, that signifies the beginning of a 20-day period of time where it can be used for a launch before needing to be recertified; the system won’t be fully active for the WDR, so only part of the installation and testing will be performed before the first rollout. “After we connect ordnance, we do the resistance checks and all the checkouts required on the ordnance system to make sure that it was installed correctly but it’s not necessarily the certification for launch,” Florez said.

Although the ordnance is put in place during the first part of installation, Florez explained that it is not fully connected or integrated into the system until the second part of the checkout. “You leave the ordnance installed, but it’s not connected to the vehicle, to the firing lines,” he said. “The [second part] really certifies the FTS system for launch, and that’s a test where we have live communications with the [Eastern Test] Range where we make sure that the signals are coming across.”

Credit: NASA/Cory Huston.

(Photo Caption: An engineer (left foreground) performs closeouts on the left-hand Solid Rocket Booster for Artemis 1 in the VAB on January 10. The vehicle will be outside in the weather out at the launch pad and then experience an extreme thermal environment from combustion and aerodynamic heating; room temperature vulcanizer is being applied in the gaps between the large-area/acreage thermal protection system coverings on the exterior of the vehicle.)

The first part of the final FTS install and checkout requires access to areas inside the Solid Rocket Booster (SRB) forward skirts and the Core Stage intertank; once that work is complete, which would be in early February on the current schedule, EGS and Jacobs can configure those internal volumes for rollout and start getting into final preparations to roll the Mobile Launcher with the vehicle out to Launch Pad 39B.

There are a few other tests that the processing team plans to work into the schedule before launch. “We have one other small test that we’re doing which is a test that checks out the data acquisition units — the DFI (Development Flight Instrumentation) network per-se — on Orion, ICPS, the Core Stage and Boosters, which we’re planning on running right after the Countdown Sequencing Test,” Florez said.

Another is a Launch Vehicle Stage Adapter acoustic impulse test. “That’s really a test of opportunity which is not so critical for Artemis 1, it’s critical for further missions from a data collection perspective, but we are still planning on running that,” Florez said. “We’re targeting that after we come back from WDR, we’ll be in a better configuration to run that prior to launch.”

Another task on the schedule that will be worked in parallel with critical path activities is the swap of the ICPS flight computer and batteries. Lanham said that the timing of that depends on when the flight units are delivered: “Our plan would be to get that in before WDR, but if not, then obviously we would do it post WDR, but the plan is still to swap out that box.”

Setting a launch date coupled to WDR demonstration

The Artemis 1 vehicle stacked on its Mobile Launcher will first be rolled out to Launch Pad 39B for the Wet Dress Rehearsal. The Mobile Launcher has made multiple trips to the pad on its own for different phases of Multi-Element Verification and Validation (MEV&V) and the upcoming trip to the pad is in essence the final phase of integrated testing that brings in the Orion-SLS vehicle for a full launch countdown demonstration test between the vehicle and ground elements.

Following resolution of the power failure in the RS-25 engine controller, current estimates of the soonest that the hardware could be ready to roll out to the pad for the WDR are mid-February, with the soonest that the hardware could be ready for launch in mid/late March. SLS can only launch Orion on Artemis 1 when the Moon is in the right position in its orbit around the Earth, but launch readiness is a measure of when the hardware and the people are ready to go.

Estimates of the soonest that the hardware could reach major milestones like the WDR and launch have moved around significantly. NASA also has estimates that factor in the schedule risk, given this is a new system being prepared for its first flight, which reflect additional time to deal with issues that could come up.

The risk informed estimate hasn’t changed as much; although it doesn’t predict when issues like the engine controller power failure will occur, it projects how much additional time would be needed to resolve them. That risk assessed readiness estimate has more consistently pointed at mid April, because it included many weeks of extra time to work through hardware issues and learning curve situations such as with the first Countdown Sequencing Test.

Credit: NASA/Cory Huston.

(Photo Caption: The aft end of the Artemis 1 SLS vehicle is seen in the VAB on January 10. This view of the -Z side of the vehicle is seen from the perspective of umbilical tower of the Mobile Launcher. The systems tunnel and tank pressurization lines for the Core Stage can be seen flanking one of the liquid oxygen “downcomer” feedlines that run from the LOX tank into the engine section.)

NASA will not set a launch date until after the WDR is completed and they can factor in any additional tasks with already-known work. “We’ve continually said that until we get through WDR we won’t set a launch date, so us getting out in mid-February for WDR allows them to look at March and April as opportunities,” Lanham said.

“I really can’t put my finger on it again until we come back from WDR and see if we have any issues there that we’ve got to go correct.”  After the WDR test, the vehicle and Mobile Launcher will be rolled back to the VAB for final pre-launch maintenance and servicing.

When the vehicle arrives at Pad 39B for the WDR, EGS and Jacobs will begin countdown preparations, since the test is a full launch countdown minus the last 10 seconds before liftoff. With the vehicle being prepared just as it will be for launch, NASA will have to reserve a spot on the busy Eastern Test Range calendar for the test just like the other launch providers do for hazardous operations such as launches and WDR tanking tests.

Finding a spot on the Range calendar may be another complicating factor in the overall pre-launch schedule, as planning for the Comm End-To-End test was. When NASA is ready to perform the WDR, the Range’s launch calendar may be relatively open and easier to schedule or it may be heavily booked and harder to reserve a spot.

(Lead image credit: NASA/Cory Huston)

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