NASA completes Exploration Upper Stage CDR, focuses new office on SLS Block 1B development

by Philip Sloss

“You can cut a lot of mass out of the design if you’re optimizing toward a lunar mission, and that mass can then go to the co-manifested payload along with the Orion,” he added. “So that was the motivation.”

“During the stand down between 2018 and really January of 2020, there was a small team from Boeing along with our NASA folks, with Boeing also engaging their suppliers, to look at what the major systems trades and, at the top level, what changes would [be necessary] to make that optimization,” Holloway continued. “We did it on task orders, and the results of that were propagated into the EUS design after we got turned on in January 2020.”

According to a recent Government Accounting Office (GAO) report, planning for EUS and Block 1B was whip-sawed early in 2020 by changing plans for the first crewed Artemis lunar landing by the end of 2024. The goal to return U.S. astronauts to the Moon in less than four years continues to be the agency’s highest priority, and early last year the SLS Program was asked to work to a first Block 1B launch in September 2024 in the vehicle’s cargo configuration, presumably in support of launching a human lunar lander spacecraft that has yet to be selected.

Following the departure of Human Exploration and Operations Mission Directorate (HEOMD) Doug Loverro, the first Block 1B launch was moved back to early 2026 and changed back to the crew configuration. The EUS CDR tried to take into account differences between the crew and cargo configurations, both of which NASA eventually plans to use.

“As the missions and the manifest have evolved, the EUS design has evolved with them. And we have switched a couple of times between cargo and crew,” Wofford said. “The recent CDR that we did is applicable to both cargo and crew.”

“In almost all cases, the cargo requirements envelope the crew requirements, so they’re more severe than the crew requirements, and cargo loads and environments are usually more severe than those for crew. There are a few poke outs or cases where the crew requirements are unique, and those differences were carefully noted in the CDR and are being addressed with RIDs (Review Item Discrepancies) and action items.”

Credit: NASA.

(Photo Caption: NASA recently updated their renders of the EUS to more closely resemble the current design. The render on the left depicts an old, slightly longer version of the stage; however, the RL10 engine configuration shown is not the correct one for EUS. The render on the right was updated to reflect the smaller liquid oxygen tank and correctly depicts the RL10C-3 engine configuration that will be used on the new SLS upper stage.)

New office focusing on Block 1B development

The Block 1B upgrades for the SLS vehicle are a long-term priority for the program, which dedicated resources to a new organization beginning in 2020 to continue development of EUS and Block 1B while much of the focus elsewhere is on completing preparations for SLS Block 1’s first launch on Artemis 1.

Wofford was named manager of the Block 1B/Exploration Upper Stage Development Office within NASA’s SLS program last Summer. “The reason they set up the office the way that they did was two-fold,” he explained.

“Number one, the EUS function was originally in the Stages office, and the Stages office was up to their eyeballs in alligators trying to get Artemis 1 and Core Stage-1 off the ground. So they had Core Stage-1 production gearing up towards Green Run and gearing up towards first flight. So Stages dance card was full, and you needed to carve the EUS effort out from under them so that they could accomplish Artemis 1.”

“So that’s reason number one. Reason number two was [that] the program wanted to dedicate the Block 1B office to possibly doing things a little different, a little bit different decision velocity, a little bit streamlined integration relationship. So part of my charter was to figure out how to do that with our Boeing partners.”

NASA and Boeing had already started changing their working relationship in 2019 in order to accelerate the EUS and Block 1B development timeline. “We do a lot of things concurrently with our Boeing partners instead of serially,” Wofford said.

“The way things traditionally work is the contractor does their thing with it, then they toss it over the fence to the government and the government does their thing with it and there’s some iteration back and forth on that, which can be time-consuming. When we started this before COVID, the original plan was for my team to be co-located at the Boeing offices where we could work really fast with each other.”

Wofford noted that Boeing has established a similar office within their SLS organization. “We still work really fast with each other, but we’re doing it virtually in this COVID environment instead of all together in one office,” he noted. There are plans to resume co-located work in the future when conditions are safe.

As a part of doing things differently, the new office is an outlier within the program. The SLS Program sits within the overall Exploration Systems Development (ESD) division of the Human Exploration and Operations area of NASA.

In the hierarchical structure, ESD is at Level 1 and provides integration for the three Level 2 programs — Exploration Ground Systems (EGS), Orion, and SLS — which operate independently of each other. The various SLS element offices reside at Level 3 and represent different parts of the vehicle such as the Booster Element (Solid Rocket Boosters), Stages Element (Core Stage), and the Liquid Engines element (RS-25 and RL10).

The new office is different than the Level 3 element offices. “We are a little bit of a hybrid in the organization,” Wofford explained. “We are more than an element office but we are less than the program office, so we kind of straddle that line.”

“Within my office, we’re responsible for EUS, ‘lock, stock, and barrel,’ but we also have strong integration with some of the other things that we touch. So all of the other hardware elements that go into Block 1B, we have a really strong matrix support and a strong integration relationship with those offices.”

“So it’s kind of what we call ‘Level Two and a Half,'” Wofford added. “It’s not quite Level 3, which is an element-level office, but it’s not quite Level 2, which is the [NASA SLS Program Manager] level. The advantage of this is that I do report directly to [the NASA SLS Program Manager,] Mr. Honeycutt, and I do have responsibility for the entire Block 1B vehicle. So it’s a strong concept.”

Credit: NASA and NASA OIG

(Photo Caption: A composite of NASA and NASA Inspector General Office diagrams showing the different organizational levels inside and outside the SLS Program. The new Block 1B/EUS Development Office (not shown in this diagram) is said to be a hybrid, like a Level 2.5 below the program level itself.)

“We also have a really strong integration function with Level 2, the SE&I (Systems Engineering and Integration) people that do the vehicle engineering tasks. And then each of my subsystem managers reaches out to those organizations and works closely with them on a daily basis in addition to what they do with Boeing.”

With the Critical Design Review for the stage is complete, Block 1B development efforts continue at Marshall as EUS manufacturing is slated to begin at Michoud in the summer. “EUS is kind of the long pole in the tent, but it’s not the only part involved in flying the Block 1B variant of the SLS vehicle,” Wofford said.

“There’s the Universal Stage Adapter, which is being managed by the SPIE (Spacecraft Payload Integration and Evolution) organization. That’s the adapter that goes between the Orion vehicle and the EUS.

“The biggest area besides EUS and the Universal Stage Adapter that’s being worked on is in terms of avionics and software [development] and the vehicle engineering tasks, the analysis tasks like trajectories and loads and environments and performance projections and that sort of thing.”

“So [there’s a] big integration effort involved in certifying and developing the new vehicle,” Wofford added.  He also noted that the SLS Program is currently planning to hold the Critical Design Review for the integrated Block 1B vehicle in mid-2022.

The SLS Block 1B cargo, EUS, and interstage. (Credit: NASA)

In addition to the new office, NASA and Boeing have also tried to incorporate lessons learned from building the Core Stage manufacturing and production infrastructure from the ground up. “We took the lessons learned from the Core State manufacturing and propagated a lot of that back into the process and design of the upper stage,” Holloway noted.

“Things like getting manufacturing engineering involved in evaluating the designs and signing off on the drawings early, rather than just receiving them after CDR to build, and doing integration mockups to help with layouts and routing and installation before those designs are finalized… [that 2018 to 2020] stand down gave us that opportunity to evolve the design to maximize the co-manifested payload to the Moon, and it also gave us the time to evolve the process, if you will, to make sure that the manufacturing side of EUS, when we get there, doesn’t run into a lot of the same problems that Core Stage found when they trailblazed for us.”

The SLS Program also works with the Kennedy Space Center-based EGS Program to support the eventual launches of Block 1B vehicles, but the programs have different responsibilities. While SLS is maturing the design of EUS and Block 1B, EGS is building Mobile Launcher-2 and evolving their hardware and ground-based launch control software infrastructure for the later vehicle.

The recent GAO-21-105 audit noted that the Artemis 4 mission that would debut Block 1B and EUS is forecast to launch in March 2026.

(Lead image credit: Nathan Koga for NSF.)

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