September 15, 2020.
Final preparations are in work to ready the first Space Launch System (SLS) Core Stage flight article for its first-ever propellant loading in the B-2 Test Stand at NASA’s Stennis Space Center in Southern Mississippi.
Prime contractor Boeing is leading the Green Run test campaign for the central component of the space agency’s new launch vehicle as the test team approaches the critical Wet Dress Rehearsal (WDR) now tentatively targeted for early November.
The WDR is the seventh of eight Green Run test cases and the precursor to a full-duration Hot-Fire test of the stage once the tanking test is completed.
Final closeouts of the stage to configure it for its first live countdown will take up much of the remaining time before the full Green Run team meets for a Test Readiness Review (TRR); the meeting is planned two days before the test to verify that the vehicle, the test stand, and the test team are ready to proceed.
In the WDR, the Core Stage will be prepared for ignition exactly as it will for the Hot-Fire and for a launch, activating all its systems to run together and meet all their firing criteria before the countdown is stopped several seconds before engine start.
A couple of days after the Green Run test team completed the series of simulation practice runs that made up most of test case six in early October, Hurricane Delta became the fifth tropical weather system to disrupt the work schedule at Stennis.
Coupled with a two-month standdown from March to May due to the COVID-19 pandemic, natural causes are expected to stretch the Green Run campaign out to a full year; the stage arrived on NASA’s Pegasus barge at Stennis on January 12, 2020, and the current plan has Pegasus departing with the SLS Core in mid-January, 2021, assuming things go well with the last two Green Run tests.The Mississippi space center returned to normal hurricane status on October 10 and back on-site, final preparations for the big Wet Dress Rehearsal and Hot-Fire tests resumed
“The next thing that we had to go do was load the new version of Stage Controller software, so that’s behind us and now what we’re doing is doing the last set of safing checks that basically validate that the new load of software is working just like the old one did,” Mark Nappi, Boeing Green Run Test Manager, said on October 15
(Photo Caption: Boeing Green Run Test Manager Mark Nappi (left) is one of the NASA and Boeing SLS officials briefing agency administrator Jim Bridenstine (middle) while standing under the Core Stage in the B-2 Test Stand at Stennis on February 10. Mr. Bridenstine is situated under the boattail’s “manhole,” which provides one of the access points into the engine section/boattail compartment. The nozzles of the four RS-25 engines are covered with yellow bagging in part to keep the engine components dry.)
Internal work platforms are deployed in the dry volumes of the Core Stage, the forward skirt, intertank, and engine section for pre-launch processing and then must be removed before flight or flight-like operations such as the final two Green Run tests
After completion of test case six, NASA and Boeing announced a forecast for the final two big Green Run tests on October 13
The vehicle will be all powered up and the team will be on console and then we’ll start the loading of the 537,000 gallons of liquid hydrogen and the 196,000 gallons of liquid oxygen,” John Shannon, Boeing’s Vice President and Program Manager for SLS, said
“The test readiness reviews are normally conducted the day before the test starts, so we start Test Case Seven on the 28th is what we’re planning right now and so the TRR will be on the 26th,” Nappi said prior to the delay
“So that’s where we’ll start test case seven and then it’s a four-day test
Two days into it we start tanking, so it’s a pretty short-duration type of operation.”
“So there’s some work that we’ll do on the vehicle and there’s some work that Stennis will do leading up to the official start and call to stations for test case seven.”
The large, 212-foot long Core Stage will require all six of the space center’s LOX and LH2 barges to be docked at the B Test Complex
At the conclusion of the TRR, the SLS management team would give a go to start the test a day or two later
The countdown clock won’t start until later in the test, but Nappi noted the WDR is a launch countdown type of operation
(Photo Caption: Green Run infographic of the propellant storage that will be used to fill the Core Stage during the Wet Dress Rehearsal and Hot-Fire tests. Stennis Space Center uses barges docked to its A and B Test Complexes to support testing “hydrolox” rocket engines and rocket stages. The SLS Core Stage Green Run will use most of the barge propellant capacity and all six positions at the B Test Complex will be occupied for the two fueled Green Run tests.)
Nappi explained that it takes about three days of preparations to protect the Core Stage and the test stand against tropical storm force winds and weather conditions
The schedule impact each time the Green Run team had to stop and protect the hardware was different from one storm to the next, in part depending on the timing of the approach and what test work was being performed
If a go is given to proceed, the primary test team will be on console in the test control center and they will begin final tanking preps
Loading the Core Stage with propellant is a major objective of the test; it will be the first time in the SLS Program that a full-scale article is filled with its flight load of LOX and LH2
“The first fun thing is going to be to thermally condition the tank, where you put a little bit of cryos in and you start to chill the tank down before you go into what you call the fast fill time-frame and then it’s going to be a lot of looking at stable replenish and make sure we can keep pressure on the tank,” Shannon said back in January when the stage completed production at the Michoud Assembly Facility and was transported to Stennis
(Photo Caption: The top of the -Z side of Core Stage-1 in the B-2 Test Stand at Stennis in late January, showing fire-extinguisher water lines and platforms around the forward skirt and liquid oxgyen tank. The first working stage article will go on to Kennedy Space Center to help power the Artemis 1 mission to the Moon.)
The countdown and the pre-ignition cutoff is the other major objective of the WDR test; the test team will be running a live, fueled Core Stage through a terminal countdown for the first time
The terminal sequence was simulated during test case six but a full-up, final countdown requires the ground control and test stand infrastructure to support preparing the Core Stage to fire its engines under launch conditions
The vehicle’s Core Stage Auxiliary Power Units (CAPU) will be started and the hydraulic systems will be tested by running the four RS-25 engines through a canned sequence of movements
The countdown will be taken all the way down to a few seconds before the hand-off of control from the Stage Controller to the Core Stage flight computers
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