NASA’s Space Launch System (SLS) Program is pursuing ways to accelerate development of the on-again, off-again next evolution of the launch vehicle. The main change from the initial Block 1 vehicle to the Block 1B version of the rocket is the larger, higher performance Exploration Upper Stage (EUS).



Delays primarily with Core Stage production slowed development of EUS and Block 1B as NASA and prime contractor Boeing shifted resources away from the new upper stage. EUS and Block 1B became more controversial over a year ago when the Trump White House concluded that they were unnecessary and began advocating defunding the project; however, key members of Congress remain supporters and funding was restored for the current U.S. fiscal year.

SLS and Boeing began organizational changes prior to the coronavirus disease 2019 (COVID-19) pandemic, relocating NASA people working on EUS development to Boeing offices near the program’s home at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama. The new stage and vehicle design have the potential to deliver over forty metric tons of payload to the Moon in a single launch, which would provide additional flexibility for designers of spacecraft and operational concepts.

Although they were forced like everyone else to adapt their plans to social distancing, the program and prime contractor are continuing to move forward while teleworking and hope to conduct a Critical Design Review (CDR) by the end of the 2020 calendar year.

Moving the architect in with the builder, increased emphasis on the cargo version

Exploration Upper Stage teams working at MSFC for the SLS Program headquartered there had recently moved from worksites in the center to Boeing offices outside the gates of the Redstone Arsenal where MSFC is located.

“We had just initiated a partnership with Boeing where we co-located all that NASA EUS team in the same building with [Boeing’s] EUS team,” NASA SLS Program Manager John Honeycutt said in an April 10 interview. “The intention there was to have the builder working with the architect so that there’s no surprises when you get to the end and you know you’ve got a good, producible design.”

Honeycutt is calling the overall effort, which includes co-locating the teams, an accelerated development activity. Prior to the disruptions brought on by the COVID-19 pandemic, he was looking to hold the Critical Design Review (CDR) by the end of the calendar year, which would be the end of the first quarter of fiscal year (FY) 2021.

(Photo Caption: A graphic showing elements of the Exploration Upper Stage design as updated in 2019. The stage will be built by Boeing and is powered by four Aerojet Rocketdyne RL-10C3 engines. The C3 version of the engine has a two-piece, fixed carbon-carbon nozzle extension attached to the nozzle. In contrast, the RL-10 version used for ICPS has a longer, three-piece nozzle extension that is partially deployed after stage separation and before the first engine start. The engine nozzle is regeneratively-cooled; the nozzle extension radiates away heat.)

“I’ve challenged the team to get it done early in FY ’21 so I’m looking forward to them getting it done probably within the first three or four months of FY ’21,” Honeycutt noted. “That was before the virus and so I don’t understand the impacts there and so we’ll have to go make some adjustments. I’ll get a better view of their schedule as they move over the course of the next three weeks.”

Part of the accelerated development activity is to take another look at the overall requirements with an eye towards shortening the schedule to the first flight.

“The thing that we were going to be able to do with this co-location activity is [to better evaluate if there is] leeway relative to any requirements that the team may find where we might be willing to take some [schedule] relief and expedite that,” Honeycutt said. “John [Shannon] and I agreed that was going to be a huge benefit to us.” Shannon is Boeing’s Vice President and Program Manager for SLS.

“Now that said we’re continuing moving on with that activity but the team is doing it in a virtual environment. From what I see right now we’re on a good pace to have a good shot at [CDR] early in FY ’21.”

“They are teleworking but since this is a development activity we really haven’t changed any of our expectations on dates or productivity and that team so far is just knocking it out of the park on just staying on track with their planning and their development work,” Shannon added. “I think that while we’re off the floor at MAF (Michoud Assembly Facility), most of the EUS work to update the tools had already been done, so now it’s just making sure the design is right, getting the agreements with the suppliers, and working through the process to get to that Critical Design Review at the end of the year.”

The initial Block 1 version of SLS is going through human-rating certification to be able to launch crew on Orion spacecraft beginning with the Artemis 2 launch. In the past Block 1B was planned to quickly replace Block 1 as a crew launcher for lunar missions; now SLS and Boeing are looking at whether some human-rating requirements could be deferred so that the Block 1B Cargo version could launch sooner, complementing Block 1 Crew first and replacing it later.

“My direction to the team is we want to do it smart and if it makes sense to integrate any piece of the human rating for the Block 1B without a tremendous schedule impact we need to go ahead and do that, and then for the things that kind of break us in getting up Block 1B Cargo we’ll have to put those on the shelf,” Honeycutt said.

“Probably the big one is going to be the activity associated with avionics and the human rating there. We’ll end up pushing that out but certainly anything that makes sense to do and saves us money and keeps us on track we’ll look strongly at doing that.”

The Block 1B Cargo variant can deliver more payload mass to a trans-lunar trajectory than the Block 1B Crew version for Orion because the latter launches with additional structural and safety hardware such as the stage adapter that connects the spacecraft to the rocket and Orion’s Launch Abort System (LAS) that doubles as an aerodynamic fairing and crew escape system during the first approximately three minutes of flight. In contrast, on cargo vehicles the payloads attach almost directly to the rocket, have less complicated aerodynamic fairings, and no escape system requirements.

(Photo Caption: A chart of payload fairing options from the most recent public release of the SLS Mission Planner’s Guide in December, 2018. Two options for early Block 1B Cargo missions would be the 8.4-meter USA (Universal Stage Adapter) PLF and the 8.4-meter Short PLF shown in the middle of the chart. The USA was already in development as the Block 1B Crew configuration was expected to fly first. The 8.4m Short PLF designed for Cargo configurations would provide almost double the usable volume of the USA-derived fairing.)

In addition to development of the upper stage, the SLS Program would need to complete first-flight development of the payload attachment system elements. The Universal Stage Adapter (USA) already in development by Dynetics for SLS Block 1B Crew could be modified for payloads with lower volume requirements, but a longer, larger 8.4 meter wide fairing would provide almost twice as much usable volume.

The Exploration Ground System (EGS) Program at the Kennedy Space Center (KSC) in Florida would also need to complete development and assembly of Mobile Launcher-2 (ML-2), which will be used to launch Block 1B vehicles from Launch Pad 39B at KSC.

Doubt about EUS future remains with sustained White House opposition

EUS and Block 1B development remains controversial even as SLS and Boeing move to streamline work. The White House remains strongly opposed to any further EUS/Block 1B spending, which they argue is unnecessary for a long time.

In the President’s Fiscal Year 2021 Budget Request published in February, the Office of Management and Budget highlighted the cost savings of cancellation, saying that SLS “is facing significant cost, schedule, and management challenges resulting in billion dollar cost overruns and multiple-year delays” and that NASA should focus on flying the first SLS flight “before engaging on a costly multi-year Block 1B upgrade program that is not needed for lunar exploration over the next decade.”

“Competitively procuring commercial launch vehicles to carry cargo as a complement to crewed SLS launches will speed up lunar exploration plans and save money in 2020 and future years that will be critical for supporting exploration activities on the lunar surface in a sustainable manner,” they added. Defunding EUS and ending further development was first proposed by the White House in their FY 2020 budget proposal.

The upgrades have key supporters in Congress, though, and appropriation bills passed there have consistently included language over the last decade mandating higher SLS performance and funding since FY 2016 specifically for EUS. Development was suspended and the EUS budget was cut from $300 million to $150 million in FY 2019 to focus on finishing the Block 1 vehicle and flying it for the first time on Artemis 1; NASA was already re-evaluating schedules that forecast the Artemis 1 launch in 2021 before COVID-19 became another factor.

Boeing’s redesign of the stage was completed last year and approved by NASA and the prime contractor made the Block 1B part of the foundation for its Human Landing System (HLS) proposal submitted in November for Artemis, which prioritizes the goal of landing U.S. astronauts on the Moon again by the end of 2024 during the Artemis 3 mission. Boeing’s proposal would require delivery of both the first EUS for flight and two Core Stage units by the middle of 2024, a time-frame where NASA only expects a single Core.

Top NASA officials expressed skepticism for both possibilities during Congressional testimony in the middle of 2019 and again late in the year that EUS could be ready for a first launch in time to support the prime Artemis objective. Congress included $300 million for EUS in the FY 2020 budget, but the White House continues to advocate canceling the effort altogether.

(Photo Caption: A slide from a February presentation by the SLS Program showing characteristic energy (C3) performance for different heavy-lift launch vehicles. The curves for the two SLS cargo configurations appear to based on a data update more recent than the late 2018 Mission Planner’s Guide numbers. As the chart states the data for the commercial vehicles is from NASA’s Launch Services Program (LSP); what isn’t clear is how recently the LSP data plotted here was updated.)

NASA’s FY 2021 budget submission in February deletes funding for not only EUS but also ML-2, which would be unnecessary if EUS is canceled. “Although NASA began design and construction of the second mobile launcher platform, additional funding to complete the project is being deferred,” the submission notes. “NASA does not have plans to utilize the second mobile launcher in the near-term.”

Even with recent hints of changes, given the strong opposition from the White House, any involvement of EUS and Block 1B in NASA’s Artemis architecture would be a significant departure from the agency’s plans.

As noted by OMB, with the initial configuration behind schedule, still in development, and yet to fly for the first time, the only role SLS currently has in Artemis is as a crew launch vehicle. All the enabling infrastructure in the Artemis reference architecture from Gateway modules to lunar lander stages to surface logistics will be launched on commercial rockets such as the SpaceX Falcon Heavy that is flying today and others in private development that NASA does not have to directly fund.

The Block 1B Cargo variant is only being advocated outside the space agency in alternate lunar architectures. Studies such as one published by Aerojet Rocketdyne concluded that the higher predicted performance capability of SLS to the Moon would reduce the complexity of the lunar lander spacecraft and the landing mission itself, which would reduce HLS development risks to the end of 2024 goal.

(The study is available in the Future In-Space Operations (FISO) Telecon Presentations Archive. Titled “Analysis of the Utility of Various Human Landing System Architectures,” it was presented on January 29.)

Lead image credit: Nathan Koga for NSF.

