Boeing works towards SLS Core Stage Green Run checkouts after completing first test

by Philip Sloss

Systematic checkout will verify stage is ready for fueling and test fire

Both the Core Stage and significant elements of the test stand infrastructure beyond the Stage Controller are new; the checkouts ahead of the fueling and test-firing will validate that everything is in working order and plays nicely with each other. The power-up testing will methodically build in scope from a few subsystems to the complex integrated tests short of hazardous operations.

“This is the first time that this vehicle will see this Stage Controller software, which together are seeing the stand,” Nappi explained. “It’s the first time all three of these are coming together and in order for us to get to a point where we feel safe enough to put hazardous commodities on here being the Wet Dress Rehearsal, LH2 and LOX, we’re going to wring those systems out very slowly and in a incremental fashion that is very deliberate so that we make sure that everything is working like it’s supposed to.”

“What we’re going to do is there’s hundreds of commands, we’re going to send commands and we’re going to look for the indications to come back,” he said. “Send another command, look for the indications to come back. We’ll do that on all the black boxes, checkout all the heaters, and we do it in a very incremental fashion so that by the time we’re ready to do Wet Dress, we’ve validated and verified that every one of those functions work like they’re supposed to.”

Credit: NASA/SSC.

(Photo Caption: Core Stage-1 is lifted up vertically above the tarmac at the B Test Stand at Stennis on the morning of January 22. Winds finally relaxed enough to lift the stage into the B-2 position of the stand on the right.)

At the outset of the checkout, powering up the stage in the stand will validate several fundamental things.

“The first thing that we’ll do is we’ll get power on the vehicle and that will validate a number of things,” John Cipoletti, Launch Team Lead and Green Run Deputy for Boeing, said. “We’ll validate that the B-2 stand can give us the proper power and current, it’ll verify that the Stage Controller can actually command the vehicle to power up and that we’re going to get telemetry off of the vehicle down through the Stage Controller and out to our test team, so that’s the very first item.”

“It sounds pretty basic but will the computers come up, form what we call a Flight Computer Operating Group (FCOG), will they communicate to the stand, will they communicate to the Stage Controller, will we see that data, and can we charge and discharge the batteries, so that’s the very first thing we do and it validates a lot of the interfaces believe it or not with a very small, incremental step.”

NASA developed the software that runs on the vehicle’s flight computers. For flight, the computers will run the standard Flight Computer Application Software (FCAS); however, a variation of FCAS is loaded on the computers for the Green Run campaign.

“The latest version of what they call the Green Run Application Software, affectionately called GRAS was loaded at MAF,” Cipoletti noted. “We have built into our test sequence, because they may provide us an update, to do another load if necessary.”

Credit: NASA/SSC.

(Photo Caption: Modal test instrumentation can be seen on the -Y side of Core Stage-1 after it was rotated to vertical on January 22. Both LOX feedlines (also known as downcomers) can be seen, along with the systems tunnel on the right side.)

Cipoletti explained the outline of the testing sequences. “The avionics team is going to progress through a number of tests of what we’d like to call internal connections,” he said. “The vehicle was tested during FIFT (Final Integrated Functional Test) at MAF but we’ve now sent it on its way to Stennis and we just want to make sure all the avionics are still working fine, so we’ll power up every electronics box on the vehicle and then look at their built-in test and then look at the data we’re seeing and make sure that everything is within normal parameters.”

“There’s some interest in how our redundant inertial nav (navigation) units work, so we’re going to send them through a navigation cycle, gyrocompass align cycle, and go inertial.”

The test team will then test some direct ground commanding legs to the vehicle. Typically commands to the stage to take a particular action go through the flight computers to perform those actions; however, a small set of hardware that is used before ignition is commanded and controlled directly from the ground.

“Once the avionics team is satisfied that all the LRUs (line replaceable units) are working then we’re going to test the stand interfaces fully for heater power because we have a lot of different heaters on the vehicle for when we go into cryo load,” Cipoletti explained. “That’s kind of a dance between the Stage Controller and the stand [power] supply from Stennis.”

“The stand gives all of the electrical power but the Stage Controller runs the control loops on the heaters, so we make sure all those heaters work. That’s the first sequence of tests, it’s probably about five days worth of testing give or take a little bit and we’ll take a look at the data.”

Credit: Philip Sloss for NSF.

(Photo Caption: Core Stage-1 in the B-2 test stand position on February 10. Much of the modal testing instrumentation wiring runs have been removed from outside of the stage. Sensor island circles will remain dotting the stage, seen here most prominently on the LOX tank; those contain development flight instrumentation (DFI) that will be transmitted to the ground in real-time during flight.)

After that, the test team will move into sequences with more choreography across the flight systems and the ground systems. They will start by validating critical safing sequences will protect the vehicle and the ground at different points during hazardous operations from fueling the vehicle to firing the stage.

“The next thing we do is wring out some more of the stand and the Stage Controller interfaces and make sure that we can control the vehicle and safe it, make sure that the Stage Controller after it’s been tested and connected to the vehicle will properly flag conditions that are off-nominal,” Cipoletti said. “And then there’s a series of safeguards we have that we need to test and we call this our safing checks.”

When necessary the vehicle and ground computers will need to automatically stop and/or back out of different situations and transition back to a safe, stable configuration and there are multiple command legs available to initiate safing.

“There’s a way for the Stage Controller to command the vehicle to shut down and there’s two paths for that,” Cipoletti explained. “We’re going to make sure both paths work and then there’s an emergency command that we can send from the stand through the vehicle if we lose communication with the vehicle through its downlink and downlist and uplink and that’s a hard line. We’ll check to make sure that that hard line works so that we have all of our emergency safing in place.”

Later test sequences bring up propulsion, hydraulics, and engines

The power-up testing will build up to more complicated testing of multiple systems and their interactions. Next is the Main Propulsion System (MPS) leak and functional suites of tests.

“The next thing we’ll do is now bring up a little more complexity with our Main Propulsion System,” Cipoletti said. “We’ll make sure all of the fluid connections through the umbilicals are leak tight, the helium, nitrogen, and we’ll check the hydrogen and oxygen lines with helium and nitrogen as well.”

“And then make sure that all the main propulsion valves inside, that we can command them, we can move them open and close, see the appropriate talkbacks so that we know we have control of the Main Propulsion System in an ambient environment and that’s our MPS Leak and Functional. All the time that we’re moving these valves we’ll be checking different connections that are fresh at the stand to make sure that you get the right flow and we don’t see leaks.”

Credit: Philip Sloss for NSF.

(Photo Caption: Two technicians (middle left) can be seen to the right of the red central tower on Level 19 of the B Test Stand on February 10. Weather is an issue that is monitored closely and it was said that the winds were too high at times to work up at the levels seen in the top of the image where the forward skirt is positioned.)

Then the test team will test that the vehicle can operate some of the moving parts of the RS-25 engines, running through some of the critical engine sequences in unfueled conditions at ambient temperature.

“We finally build to what is actually the most integrated test just prior to Wet Dress,” Cipoletti said. “It’s called the TVC (thrust vector control) hydraulic checkout and engine checkout. For that test to be [run] satisfactory, both the MPS system has to be up and running, the Core Stage engines, the RS-25s are connected and tested and the vehicle hydraulic system is tested.”

“We run the first part of that test on hydraulic power from the stand. The RS-25s will go through a series of tests to make sure that they can go through their start sequence, stop sequence, make sure the igniters work, make sure all the valving is working within their calibration parameters. For the engines to be able to do that our MPS system has to be up and providing proper pneumatic support to the engines.”

“We’ll then through both the hydraulic and pneumatic shutdown procedure and when the engines are finished with that, the whole sequence really is a flight readiness test,” Cipoletti added. “Then we’ll switch over to concentrate on the hydraulics on the Core Stage.”

“The TVC team will test their ability to control the actuators, both command and their fault detection system. When that’s complete and we fill the reservoirs, we’ll disconnect the ground hydraulics and we’ll be fully ready for operating in a flight condition, so when we’re in that condition we’ll turn on the circulation pumps to keep the hydraulic fluid at the right temperature during cryo load.”

“After the circulation pumps are tested we’re going to provide ground helium and spin the whole system up using ground helium and making sure that the CAPUs (Core Auxiliary Power Units) can provide full pressure,” he said.

Credit: NASA/SSC.

(Photo Caption: Another image of Core Stage-1 in the B-2 Test Stand position on January 24 shortly after it was initially installed.)

The CAPUs are significantly-modified Shuttle APUs; in Shuttle, turbines were driven by hydrazine carried onboard the orbiters. In the Core Stage, the hydrazine elements were removed and the turbines are now driven by pressure from the RS-25 engines while they are running; prior to engine start, the CAPUs are driven by a helium spin-start ground system.

“At that point, we’ll look to Mark and say we’re ready for Wet Dress,” Cipoletti said.

The NASA and Boeing engineering community will review all the data from power-up testing in the lead up to the Wet Dress Rehearsal and hot-fire tests. The stage will be configured for both tests, with the intent to leave it in that pseudo-flight set up while the test team at Stennis recycles the ground systems and replenish propellant and other commodities to turn around, refuel the stage, and finally fire it for the first time.

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