NASA SLS Green Run Testing Complete, Boeing Readies Core Stage for Tow to Florida

by Philip Sloss,

NASA’s Space Launch System (SLS) program and prime Core Stage contractor Boeing wrapped up the Green Run testing campaign on the Artemis 1 flight article at the Stennis Space Center and are readying the vehicle for its long-awaited shipment to the Kennedy Space Center (KSC) in Florida. After reviewing the performance of the vehicle from its second test-firing in mid-March, NASA and Boeing agreed that the stage could be reconfigured from testing to launch.

While refurbishment activities continue, the team at Stennis has also started disconnecting the stage from the test stand to prepare for departure from Stennis. Weather will be a key factor in when the stage can be put on board the agency’s Pegasus barge to start the waterway tow trip from Stennis to Kennedy, but a late-April arrival at KSC is still possible — with KSC schedules currently forecasting attachment of the Core Stage to the SLS Boosters in the Vehicle Assembly Building in mid-May to prepare for launch of Artemis 1.

Core Stage Green Run testing officially completed

A break of configuration review was held on April 2 to determine if all the different agency and contractor teams were ready to proceed from Green Run testing to departure preparations. The stage and its four Aerojet Rocketdyne RS-25 engines are being refurbished in the B Test Stand at Stennis where Core Stage-1 remains installed in the B-2 position.

The review covered both the March 18 Hot-Fire test (called test case 8) and post-firing refurbishment activities (called test case 9). It is a part of the methodical process that NASA, Boeing, and all the SLS Core Stage technical stakeholders are going through to make sure that good data was collected from the test, that it covered all the required areas, and that the vehicle’s performance was consistent with expectations. The review also went over the health and status of the flight hardware and whether it was in good shape for the upcoming trip.

After reviewing data from the last test-firing as well as the refurbishment activities so far, NASA and Boeing agreed that Green Run testing was complete and that the stage could be taken out of test configuration.

In addition to the refurbishment work to get the program’s first flight article ready to put back on NASA’s Pegasus barge, the stage also needs to be disconnected from the test stand. The Stennis B-2 stage testing position in the dual-position B Test Complex provides the same ground-to-vehicle connections as the Core Stage will need for countdown and launch at KSC. Now that testing is complete, those four umbilical plate connections can be disconnected.

Before disconnecting the ground-side umbilical plates from the vehicle-side, the NASA-developed SLS flight software was loaded on the three SLS flight computers situated in the forward skirt. The Flight Computer Application Software (FCAS) will command and control the Core Stage and Boosters on the SLS Block 1 vehicle, and the software update replaces the previously-loaded Green Run Application Software (GRAS).

GRAS was branched from the FCAS code and customized for the test-specific, Core Stage-only configuration in the stand at Stennis.

In parallel with the stage activities, NASA and Aerojet Rocketdyne completed their data review of RS-25 engine performance during the second hot-fire test. The four former Space Shuttle Main Engines were essentially test support equipment for the Core Stage Green Run design verification campaign, and they operated nominally during the test.

The final tests in the Green Run stage campaign, where the vehicle was taken through multiple end-to-end countdown sequences, also allowed SLS and Aerojet Rocketdyne to fine-tune the countdown timeline to prepare the engines for ignition in the SLS vehicle. The SLS operating conditions are more extreme than Shuttle, requiring the engines to run at higher power levels with extended ranges for propellant temperature and pressure.

Currently, drying, inspections, and leak checks of the engines are almost complete. Once those are done, the engines will be ready to support the upcoming removal of the Core Stage from the test stand and the barge trip on Pegasus to the Kennedy Space Center launch site where final preparations for the launch of the Artemis 1 uncrewed lunar mission will take place.

Once the hands-on refurbishment work inside and outside are completed, Boeing will close out the stage’s unpressurized dry volumes. Platforms installed inside the forward skirt, intertank, and engine section will be disassembled and removed and then ground support equipment (GSE) doors will be installed.

External access platforms around the Core Stage will be retracted and then the test stand’s derrick crane will be positioned to hook up to the “lift spider” that remains attached to the top of the stage.

EGS continuing to process Orion and SLS hardware for launch integration

At Launch Complex 39 and other Kennedy Space Center facilities, Exploration Ground Systems (EGS) continues processing the rest of the Artemis 1 flight vehicle hardware. Loading of hypergolic propellants on the modules of the Orion spacecraft is underway in the Multi-Payload Processing Facility (MPPF).

Nitrogen tetroxide, also called mixed oxides of nitrogen (MON-3), was loaded on Orion’s European Service Module (ESM) at the end of March. Loading of the hypergolic oxidizer was completed on March 31, and the oxidizer tanks were pressurized for flight the next day.

EGS and prime test and operations support contractor (TOSC) Jacobs are reconfiguring equipment in the MPPF to service the mono-methyl hydrazine (MMH) tanks next. MMH loading is expected to begin early in the week of April 12.

The SLS Boosters are stacked on Mobile Launcher-1 in High Bay 3 of the VAB, and closeout work continues as the EGS Integrated Operations team awaits the arrival of the Core Stage. Closeout of all ten field joints in the two five-segment solid rocket boosters (SRB) is complete, and the wiring for development flight instrumentation (DFI) on this first SLS flight vehicle is being routed in the systems tunnel of each booster assembly.

When the Core Stage arrives at KSC, the SLS vehicle elements will first be stacked with a Mass Simulator for Orion (MSO) for some of the first-flight specific development tests that will be carried out in the VAB.

After the Core is attached to the Boosters, the Launch Vehicle Stage Adapter (LVSA) will be lifted on top of and bolted to the Core Stage forward skirt. The Interim Cryogenic Propulsion Stage (ICPS) is currently rooming with Orion in the MPPF where its next work will be synchronized to SLS stacking progress. When the schedule converges on a more specific “need date” for the ICPS in the VAB, the upper stage’s attitude control system tanks will be filled with hydrazine ahead of that.

At that point, the United Launch Alliance (ULA) Delta IV upper stage derivative will be moved to the VAB and lifted into the High Bay 3 integration cell and placed on top of the LVSA.

New schedule forecasts, finalizing EGS pre-launch testing and mission plans

Artemis 1 is the first joint mission across the programs within the Exploration Systems Development (ESD) division of NASA’s Human Exploration Operations Mission Directorate (HEOMD). The EGS, Orion, and SLS programs are nearing readiness to support another methodical testing and checkout campaign at Kennedy with the Artemis 1 Orion/SLS vehicle integrated to the EGS ground control systems and infrastructure.

EGS is responsible for launch operations at the beginning of a mission and landing and recovery operations at the end. Test plans for the pre-launch Integration Test and Check-Out (ITCO) in the VAB and post-splashdown Landing and Recovery recently reached a “freeze point” level of maturity, and in early-April an internal program control board reviewed specifications, operational requirements, launch commit criteria (LCC), and landing and recovery plans ahead of proceeding into that work in the next few weeks.

A Systems Acceptance Review/Operations Readiness Review (SAR/ORR) for ITCO is planned for the end of April, anticipating the beginning of SLS vehicle power-up and the beginning of testing in the VAB soon thereafter. Short-term forecasting shows the Core Stage’s arrive at KSC early in the week of April 26 and that mating of the Core Stage to the Boosters could occur around May 11.

With the progress on Core Stage refurbishment at Stennis, the formal completion of Green Run testing, and configuration of the stage to leave Mississippi, that tentative forecast of a Core Stage mate to the SRBs in mid-May will be highly dependent on some good luck with the weather.

Calm winds in the Stennis area are required for several hours so that the derrick crane at the B Test Stand can safely remove the Core Stage from the B-2 position. When the stage arrived at Stennis in January 2020, crews had to wait about a week for good weather to safely maneuver the stage into the stand.

The full removal operation will require the stand’s crane to carefully lift the stage up and out of the stand and then swing it over to the tarmac. While the stage hangs from the crane, teams will connect a commercial trailing crane to the engine section to help rotate the stage from vertical to its horizontal orientation for transport.

When the weather cooperates long enough to remove the stage from the stand and then perform the two-crane breakover, the Core will be reinstalled on its ground transporter, called the Multi-Purpose Transportation System (MPTS), with the connected lift spider on the front being set down on another fixture to support the weight of that GSE hardware.

After the stage is secured to the MPTS and the lift spider is taken off the stage, the transporter can be rolled onto Pegasus for the trip. Depending on weather and sea conditions, the tow trip for Pegasus with the Core Stage onboard should take around a week.

Once the Core Stage arrives at KSC, EGS is realistically projecting it will take 10 months to get the vehicle and ground infrastructure ready for their first launch. However, there is at least one optimistic timeline showing a “work to” launch date of November 4.