NASA looking at SLS certification schedule changes in ‘Drive to EM-1’

NASA is looking at deferring some programmatic certification activities until after the Exploration Mission-1 (EM-1) flight in addition to its other initiatives to shorten the schedule to the inaugural launch. The goal remains to find ways to move the launch date back into late 2020 from the current Spring 2021 forecast.

In a May 15 internal email NASA Exploration Systems Development (ESD) head Bill Hill provided a status on the multi-phase schedule reduction process that the civilian space agency is working through.

With the Space Launch System (SLS) Core Stage Green Run still on the schedule, analysts continue to comb through the work details looking for ways to streamline that and other downstream activities.

ESD, which oversees the Exploration Ground Systems (EGS), Orion, and SLS programs and is responsible for cross-program systems integration, is now also looking at moving some design-level certification work of the SLS vehicle that will fly EM-1 until after the test flight.

The programmatic focus would be on the EM-1 mission-level certification, moving the full certification of the design into preparations for Exploration Mission-2 (EM-2), which will be the first crewed ESD mission.

Looking at moving SLS development milestones after EM-1 test flight

“Although we have already implemented significant changes to improve [schedule] performance and have seen positive results from those changes, I believe that there is more we can do to challenge our team to accomplish the objectives of the Agency,” Hill wrote to his team.

“With this e-mail, I am implementing the next phase of that process. The goal is to accomplish three objectives to allow us to work towards an EM-1 launch readiness window of late 2020 with a risk-informed date that extends into 2021.”

Mr. Hill is NASA’s Deputy Associate Administrator of ESD, which falls under the Human Exploration and Operations Mission Directorate (HEOMD).

The Green Run acceptance test of the first SLS Core Stage in the B-2 Test Stand at the Stennis Space Center is the longest activity on the schedule and one of the objectives is to shorten that timeline; another objective is to look at reducing the launch processing schedule after delivery of all the vehicle hardware to EGS at the Kennedy Space Center (KSC) in Florida.

The newest initiative is looking at deferring some of the SLS Program’s development milestones until after EM-1 but before EM-2. The baseline plan for SLS was to certify the design of its initial operating capability before the EM-1 launch; for SLS, that Block 1 Crew configuration consists of the Core Stage, two five-segment SLS Boosters, the Interim Cryogenic Propulsion Stage (ICPS), and adapters that connect the liquid propellant stages and the Orion spacecraft payload.

Credit: NASA.

(Photo Caption: SLS Block 1 Crew configuration, which provides the initial operating capability for the program with the EM-1 launch. The same configuration will fly EM-2 following additional certifications and outfitting to formally crew-rate the design.)

ESD is in charge of integration of EGS, Orion, and SLS, making sure that all three programs work together in addition to meeting their own individual requirements. “I am also directing ESD to focus activities by emphasizing the flight test nature of EM-1,” Hill wrote. “By focusing more on the flight test aspects, it may be possible to defer certain design certification activities to obtain schedule efficiencies for the EM-1 launch.”

“The goal is to advance the availability of flight test data acquisition while accepting an increased, but reasonable level of risk,” he explained. “This flight test approach will focus efforts on the EM-1 mission certification process rather than generic full-up design certification of the Block 1 design. Under this approach, full-up Block 1 design certification will occur before the EM-2 crewed flight.”

Both EM-1 and EM-2 will fly the same SLS Block 1 Crew configuration, since EM-2 was rebaselined last year following Fiscal Year 2018 directives from Congress.

EM-2 is expected to be the second SLS launch, and much of the design for the second vehicle is largely frozen with Core Stage structures already manufactured and most of the motor segments for the EM-2 boosters already through propellant casting. The RS-25 engines for the second flight are already essentially ready to fly and the ICPS is a derivative of production Delta 4 Heavy upper stages.

The Core Stage is the newest piece of SLS, and prime contractor Boeing along with NASA have been challenged establishing the end-to-end process to build the first article. Delays in manufacturing and assembly have contributed to the formal EM-1 launch date commitment moving from November, 2018, to June, 2020; less-formal forecasts factoring in more recent delays currently estimate readiness in Spring 2021.

Credit: NASA/Steven Seipel.

(Photo Caption: The liquid oxygen (LOX) tank for Core Stage-2 stands in Cell A of Building 110 at the Michoud Assembly Facility (MAF) behind the forward join of Core Stage-1 on April 15. Now all on hand at MAF, some of the structural elements for the second Core Stage have been there for years and most of them are now in assembly.)

“First time production for highly complex and critical human spaceflight development is challenging and is not unique to any one program, organization, or Agency,” Hill wrote. “It is a universal challenge that has to be addressed by all. For Exploration Systems Development (ESD), these challenges have negatively impacted our cost/schedule objectives for Exploration Mission (EM) – 1 launch readiness.”

The agency took a more aggressive look at pruning the EM-1 schedule earlier this year as the readiness date moved well away from the previous June, 2020 commitment into 2021, even studying a move of the critical Orion test mission to a domestic, commercial heavy-lift launcher already in service.

Still working on streamlining Green Run, launch processing schedules

Deletion of the Green Run acceptance test of the first flight Core Stage (Core Stage-1) from the schedule is still officially under consideration, but skipping it is also considered risky, and NASA is also looking to conduct the test campaign as fast as they can. Boeing is targeting completion of Core Stage-1 by the end of the year, and it would then ship to Stennis.

The Green Run acceptance test is the first opportunity for the SLS Program to fully operate and checkout any Core Stage; the test campaign is expected to take so long because most of the work at Stennis will be ‘first-time ever’ operations for the program, including fueling activities and ultimately firing the stage for a full flight-duration of more than eight minutes.

“The goal is to complete green run in less than 6 months, by June of 2020, recognizing that there are schedule risk challenges and potential unknown-unknowns that could extend that date,” Hill wrote. “This activity has the potential to reduce green run test time by 4 months; if that is achieved, it would support an EM-1 launch readiness window in 2020.”

Credit: NASA/Eric Bordelon.

(Photo Caption: The engine section is lifted out of Cell A at MAF earlier this year after the boattail structure was bolted to its underside. Integration of all the equipment inside the engine section took much longer than NASA and Boeing expected, significantly contributing to the schedule delays that NASA is now trying to mitigate.)

In parallel with the Green Run stage test schedule, the EGS Program is looking at its KSC schedules once it receives all the EM-1 hardware; in addition to the eventual delivery of the Core Stage from Boeing, Lockheed Martin plans to turn over the Orion spacecraft for EM-1 to EGS early next year. NASA has been looking at the schedule of activities to stack the SLS and Orion vehicles in the Vehicle Assembly Building (VAB).

“To improve final integration at KSC, I have instructed our Exploration Ground Systems (EGS) team to implement specific EGS schedule reduction efforts from the Schedule Risk Reduction Team findings,” Hill wrote. “These include elimination of the partial stack modal test (PSMT) and the removal of critical path time for surveying vehicle markings through imagery.”

The PSMT was to characterize the modal properties of only the mated Core Stage and SLS Boosters and was expected to take over three weeks.  Most of the time allocated for the test was getting set up to run it, and no other stacking work could be done in parallel.

An integrated modal test (IMT) of the fully mated vehicle is also on the schedule; however, the test set up work could be done in parallel with other stacking activities and first-time vehicle testing in the VAB.  The optical reference marking survey was planned in between an Umbilical Release and Retract Test and the IMT.

“The outcome of these changes indicates that if the core stage is delivered to KSC in the June 2020 time frame, it would be possible to launch in late Fall 2020,” Hill added. “Clearly, this does not account for additional schedule risk evaluations or potential unknown-unknowns.”

Previous initiatives continue

In addition to the ongoing, detailed schedule audit, already implemented work changes continue on the front end of the remaining schedule. NASA and Boeing changed the sequence of final assembly work for Core Stage-1 so that checkout work of the engine section wouldn’t hold up parallel activity on the other parts of the stage.

The forward join of the top three sections of the stage joined the liquid hydrogen (LH2) tank and the engine section / boattail assembly in the Final Assembly area in mid-April. Boeing said it expects mating of the LH2 tank and the forward join to begin this week, on the recently-established schedule.

Credit/NASA.

(Photo Caption: The Core Stage Pathfinder is backed out of NASA’s Pegasus barge by the Multi-purpose Transportation System (MPTS) at the Stennis B Test Complex following shipment from MAF in early May. The non-working article replicates the size, weight, and balance of a Core Stage and will be used for handling practice; it will be lifted, set down, and bolted into the B-2 position (upper right) in the coming weeks.)

The Core Stage Pathfinder, a non-working, full-scale model, arrived at Stennis on May 2 to allow lift crews there to practice handling a stage, putting it into the stand, and taking it out. The Pathfinder imitates the weight, center of gravity of the stage and its outer mold line in low fidelity; in addition to testing the stand’s hold down structural attachments, the test stand team will also get to fit check access platforms and umbilical carriers.

Although the schedule analysis isn’t done, the long-deferred, initial Flight Readiness Analysis Cycle activity for EM-1, called FRAC-0, is now planned to start in June. “At this time, a risk-informed date will lead us to a Spring 2021 launch,” Hill wrote. “We are having our baseline schedules reviewed independently to evaluate incorporation of potential risk factors, and that evaluation will be based on a schedule that does not consider the improvements noted above, because they are still in work.”

“With the actions above, I am challenging our teams to do better. ESD will plan for and execute to the most aggressive schedule to have an opportunity to build margin and launch as early as possible, with the goal of launch in late 2020. Therefore I have also instructed our SE&I (Systems Engineering and Integration) team to use a launch window starting in November 2020 to anchor our next loads and trajectory analysis cycle that will start in June.”

Lead image credit: NASA/Eric Bordelon.

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