Artemis 1 launch attempt constraints, rocket readiness slips to mid-February 2022

by Philip Sloss

EGS has constructed a second, larger liquid hydrogen storage sphere at Launch Pad 39B to augment the existing LH2 sphere. “[That] is actually why we’re building the larger hydrogen sphere out at Launch Complex 39B — to relieve ourself of the hydrogen constraint that we have on Artemis 1,” Sarafin said.

Assembly of the storage sphere is largely complete, but it is not yet fully activated and it will not be ready to support SLS launch attempts until Artemis 2. Once available, the second tank will allow back-to-back launch attempts for both the SLS Block 1 and Block 1B vehicles and will allow additional launch attempts to be made within the same space of one week.

“We’ll do better for Artemis 2 because we have that [second] big [LH2] sphere that we’re trying to get finalized, but for now we’re still kind of stuck to the three attempts in seven days,” Spaulding said. “We certainly want to maximize our capabilities [as we progress].”

If EGS and Jacobs can complete the remaining pre-launch preparations in the VAB and at the launch pad and complete final pre-tanking countdown preparations within the 13 days currently forecast, the three vehicle tankings would fit within the rest of the overall 20-day length of time that the FTS is valid for launch use. “It fits in there kind of nicely in as much as if you take the 13 days to get to a [first launch attempt] and then you have the 7 days of launch attempts,” Spaulding said.

“[That] would get us three attempts that kind of fit exactly in that 20-day constraint. We hope that someday we’ll be able to [finish preparations] a little faster in the VAB, but it’s just the nature of having to close out those areas after you’re done that kind of drives you to where you are in getting the vehicle ready to roll out and all that.”

Although the range safety requirements and cryogenic commodity constraints would narrow down the number launch attempts available, Sarafin said that if there are no big issues with the flight hardware or the ground infrastructure, three launch attempts should provide a good opportunity to finally get the first SLS launch underway.

Credits: NASA and NASA/Glenn Benson

(Photo Caption: A slide from a NASA presentation on the new LH2 storage sphere being assembled at Pad 39B shows its relative location in the pad area. Inset in the upper right is an image taken in October 2021 of the state of construction for the new sphere. NASA plans to have the second sphere activated and online in time to support the Artemis 2 launch; the added capacity will allow launch attempts for both the SLS Block 1 and Block 1B vehicles to be conducted on back-to-back days, if necessary.)

“In general, two or three attempts has shown that we can get off [the pad] for most launch vehicles, assuming that [there is no] significant technical issue,” Sarafin said. “So we have a high level of confidence that we will be able to get off [by a third launch attempt], assuming we don’t run into a significant technical issue.”

After 20 days, requirement is to reperform the end-to-end test

If Artemis 1 hasn’t launched by the time the 20-day clock runs out, the FTS can be revalidated for another set of launch attempts by running the end-to-end test again. If the vehicle is on the pad, a rollback will be necessary, which will require breakdown of the launch countdown configuration for a return to the VAB.

As the name implies, the end-to-end test verifies that arming and destruct commands sent from range safety are correctly received and processed by the devices on the vehicle. Internal access to the SLS boosters and Core Stage is needed so that simulators can be positioned during the test to prevent an actual destruction of the vehicle.

“We do that test in the VAB because it requires access inside a couple of the compartments,” Spaulding explained. “[One area is] inside the forward skirts of the boosters, and also in the intertank area of the Core Stage; that’s where the boxes are. We have to install simulators and things like that [for the test].”

“Because we’re going to essentially demonstrate that the system works, we need to have it separated from the ordnance so we don’t send any commands to that,” he added. “So we have the simulators installed, we’ll also have to install our communication codes and things like that so we’re in a flight config. And we’ll have the range guys with us as well.”

Once the test is complete, then the 20-day clock would start again, the simulators and test equipment would be removed, the internal compartments closed out for launch, and the 13-day pre-launch sequence would need to be repeated.

Credits: NASA/Frank Michaux and Kim Shiflett.

(Photo Caption: VAB platforms, scaffolding, and test equipment are shown deployed around the forward skirts of the SLS Boosters and Core Stage intertank in the main image taken in August 2021. Inset in the lower left, an image taken from the Mobile Launcher umbilical tower during the umbilical release and retract test in late September shows the location of yellow and red-colored access doors for the Boosters and Core Stage on the -Z side of the vehicle. Without the VAB platforms, those areas cannot be safely reached for vehicle servicing and conducting tests.)

Access inside the booster forward skirts and Core Stage intertank is only available from platforms that can be extended around the vehicle in the VAB. After the Space Shuttle program, KSC ground processing returned to a “clean pad” concept of launch operations at Pad 39B, first for the since-canceled Constellation Program vehicles and then for SLS.

“We had made decisions long ago to go with a clean pad concept, and [one of the results of] that [was] we were not going to be able to access some of these areas [out at the pad],” Spaulding said. “In the previous program, you may have recalled that we had a service structure that rotated up and gave us the ability to get to those areas as well as into the body of the Space Shuttle.”

During Shuttle, vehicles were assembled in the VAB on a mobile launch platform that was moved out to the pad for the final weeks of pre-launch checkouts. The umbilical tower was part of a permanent, fixed service structure (FSS) on the Launch Complex 39 pads. A rotating service structure (RSS) connected to the FSS, and provided access to the side-mounted Shuttle orbiter for payload integration as well as access to internal compartments of the Shuttle vehicle’s liquid propellant External Tank and Solid Rocket Boosters (SRBs).

Following handover of Pad 39B from the Shuttle program to the Constellation program in mid-2009, those large Shuttle service structures were eventually demolished and removed in 2011. Spaulding noted that keeping the pad area relatively clear of vehicle umbilical towers and service structures would reduce overall maintenance costs.

“We don’t have any of that [now] because it’s not a [side-mount] vehicle [and] it’s really cost-prohibitive almost to have a lot of stuff at the launch pad sitting there not in use having to maintain [it],” he said. “So the clean pad concept was really a good one from our perspective to not have to perform maintenance all the time and just roll out the tower when we’re ready to go with the vehicle.”

But Spaulding said it does mean less servicing can be done at the pad. “It doesn’t give you access to all of those areas [at the pad],” he said. “That access in the VAB comes from moveable platforms that are part of the VAB itself, and it does not exist at the pad.”

The SLS Mobile Launch, a hold-over from Constellation, on a modified Apollo-era crawlerway transporter arrives at LC-39B for testing. (Credit: Stephen Marr for NSF/L2)

For SLS, vehicle integration, testing, and checkouts are completed in the VAB; after rollout to the pad by a crawler transporter, the Mobile Launcher is set down onto pedestals and connected to the pad electrical, fluid, and environmental control services.

Decision point for starting the clock in the VAB

NASA will ultimately have to make a decision of when to proceed with the installation of the FTS batteries and when to run the FTS end-to-end test. Since the 20-day clock would be critical to the schedule, the timing of the test relative to other final launch preparations could be different during this first-time experience when compared to a more standardized processing flow in the future.

The vehicle and Mobile Launcher will be back in the VAB following a full run-through of the launch countdown timeline called the Wet Dress Rehearsal (WDR). Once the vehicle arrives at the pad on the Mobile Launcher for the WDR, ground crews will first go through the pre-countdown preparations at the pad. Pad connections to the Mobile Launcher and SRB hydrazine servicing will be conducted on the flight vehicle in a nearly ready-to-launch configuration.

Once back in the VAB, final configuration of the FTS for launch is the primary task, which includes battery installation, ordnance installation, and the time-critical end-to-end test suite. “That’s the bulk of what we do when we come back with those tests,” Spaulding said.

“We do a couple of things. [We have to install] the batteries, we have to install the simulators onto the equipment, onto the firing lines, and some of the other areas because we need it isolated from the system. We do have some ordnance that we’re going to install, too; we’ll do that before we get into the end-to-end test.”

“We do the end-to-end test on the Core Stage and then a test on the boosters [as] part of the end-to-end test on those flight termination systems,” he added.

Credit: NASA.

(Photo Caption: An excerpt from a February 2021, Artemis 1 mission availability document revision produced by the Mission Analysis & Integrated Assessments (MAIA) group within NASA’s Exploration division. The excerpt was shared on the NSF forums by a poster who obtained it through a Freedom of Information Act (FOIA) request. Launch attempts for Artemis 1 not only have to be synchronized with lunar launch opportunities but also with ground infrastructure and Eastern Test Range safety requirements.)

ESD and the EGS, Orion, and SLS programs within the division will also be working to be ready to conduct the final pre-flight reviews when the hardware is ready to fly, and one of big decision points will be proceeding into the FTS end-to-test.

“There are decisions that definitely have to be made, both to do the wet battery activation — because we need those flight [FTS] batteries installed — and then to proceed down that path to get to the end-to-end test and get ready to roll out [for launch],” Spaulding said. “There will be other reviews after that decision, final ones, to make sure that we’re able to roll out, and there’s a number of different milestones and milestone reviews along the way.”

“Definitely there is a management decision that says ‘we understand where we are from a constraint perspective and the ability to get off the ground before we do [the test] because that starts those two timers,’ I’ll call them. So those are big milestones that fall into some of our other reviews as well to give us a go to press on to do that.”

Other work in the VAB after the vehicle and Mobile Launcher return from the WDR includes preflight stowage of mission equipment inside Orion and removal of some ground test instrumentation. Any additional work or maintenance necessary after the WDR on the flight hardware, Mobile Launcher, or equipment at the pad would factor into when the FTS end-to-end test takes place.

In part due to the time constraints imposed by the 20-day clock, the launch processing teams will begin working seven days a week when the FTS end-to-end test is performed. Teams are already divided into multiple work shifts and working six days a week, but beginning with the FTS test they will be working around the clock to complete launch preparations, 24/7.

Lead image credit: NASA/Frank Michaux.

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