![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/01\/P1120473.35pct.jpg\")
<\/p>\nActivation of the B-2 test stand at Stennis Space Center in Mississippi for the \u201cGreen Run\u201d test campaign of the first Space Launch System (SLS) Core Stage is almost complete and NASA and its contractor workforce are moving into practice and simulations of the upcoming tests while finishing up remaining tasks. The B-2 position of the test stand has been used for stage testing from Saturn to Shuttle to Delta IV, and NASA is planning to set up the first Core Stage there in the second half of 2019.<\/p>\n
A series of tests in the Fall of 2018 verified the working operation of critical cryogenic propellant management and environmental control systems for Core Stage service and support. Over the past six years, the Shuttle-era B-2 test stand structure was restored, construction of additional structure for SLS completed, and outfitting and activation of test stand and test control center systems are almost complete.<\/p>\n
The final major structural pieces, the two forward hold downs called \u201cyellow boxes,\u201d were also installed in late 2018. A \u201cform and fit\u201d Pathfinder test article is planned to arrive in the early Spring to practice lifting and handling the real thing when it finally arrives at Stennis.<\/p>\n
Wrapping up activation<\/p>\n
The systems that will flow hazardous fluids and gases to the vehicle were tested in the Fall following their activation. As noted in the November Lagniappe issue, systems that flow cryogenic liquid oxygen (LOX) and liquid hydrogen (LH2) propellant from storage locations into the stand were tested individually.<\/p>\n
The High-Pressure Gas Facility (HPGF) at Stennis was also tested in October to verify recent upgrades to meet the gaseous nitrogen requirements of the Core Stage. \u201cWe pretty much to date have finished all the restoration,\u201d Bryon Maynard, Project Engineer for NASA\u2019s SLS Core Stage B2 Green Run Project said during an interview on December 20, just prior to NASA\u2019s closure by the ongoing, partial U.S. government shutdown.<\/p>\n
\u201cWe\u2019ve pretty much finished all the construction work for the SLS and we\u2019re pretty much down to our last activation test in the fluids area, cryogenics, which is the LOX replenishment.\u201d<\/p>\n
<\/p>\n
Recent view of the stand at the Stennis B Test Complex, with the B-1 position on the left and the B-2 position on the right. Credit: Philip Sloss for NSF\/L2.<\/p>\n
LOX and LH2 are supplied to the B-stand by barges, with up to three barges for each commodity that can be docked simultaneously in the area; the stand itself also has a tank for storing LOX. When the stage is in place, the propellant will flow up to the tail service mast (TSM) umbilical plates on the +Z side of the engine section and into the vehicle.<\/p>\n
Without the vehicle, special equipment was used for activation testing. \u201cFor hydrogen we\u2019re probably within about thirty, forty feet of the umbilical because we have to put activation spools in because we\u2019ve got to send the hydrogen back to the flare stack,\u201d Maynard explained.<\/p>\n
\u201cSo you\u2019ll see the line come up short of the umbilical maybe by thirty, forty feet and then we hook up an activation spool that goes to our vents. That last thirty feet of pipe that we have to put back in doesn\u2019t affect the overall system. We\u2019ve pretty much got ninety-nine percent of it [activated].\u201d<\/p>\n
The equipment that connects directly to the vehicle umbilical plates will be installed after activation. \u201cThat\u2019s our special test equipment, so once we finish activation on the facility then we\u2019ll put that last piece in there,\u201d Maynard said.<\/p>\n
During fueling, liquid oxygen and liquid hydrogen that boil off or are used for chilling down propellant and engine hardware exit the vehicle through vent and bleed lines. The highly flammable hydrogen is directed to a flare stack at a safe distance from the stand where it is burned off, while the oxygen is dumped out to a pit set away from the stand on the opposite side.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/01\/P1120563.35pct.jpg\")
<\/p>\n
One of the two \u201cyellow boxes,\u201d the forward hold-downs for the SLS Core Stage, on Level 19 of the B-2 stand. The structures were added to the stand in the second half of 2018. Credit: Philip Sloss for NSF\/L2.<\/p>\n
The HPGF supplies commodities such as air, gaseous helium, gaseous nitrogen, and gaseous hydrogen to the different test complexes at Stennis. It was upgraded to support the gaseous nitrogen demands of the Core Stage during tanking operations. As a part of the environmental control system (ECS) for the vehicle, a ground supply of temperature and humidity controlled air is typically run through the dry sections (forward skirt, intertank, and engine section).<\/p>\n
During and around fueling operations while the cold, flammable liquids and gases are in the vicinity, that air-conditioning is switched over to heated nitrogen gas and the stage needs a lot of it with various vent doors kept open. \u201cWe have to maintain a high flow to keep basically a kind of positive pressure inside the area,\u201d Maynard explained.<\/p>\n
\u201cWhen they go up for flight they always want to make sure they equalize, so there\u2019s these vents open. So you kind of have to feed enough so that the outside air doesn\u2019t come back in and so during cryogenics, we\u2019ll use nitrogen,\u201d he added.<\/p>\n
\u201cYellow boxes\u201d one of the final additions for SLS<\/p>\n
In contrast to the single position A-1 and A-2 test stands nearby that have supported testing LOX\/LH2 stages and engines in the past and present, the B Test Complex at Stennis has a dual position stand with the B-1 and B-2 positions co-located. The B-1 position in the stand is currently used for acceptance testing Aerojet Rocketdyne RS-68 flight engines for use in United Launch Alliance (ULA) Delta IV Common Booster Cores (CBC).<\/p>\n
The B-2 position originally supported development and acceptance testing of Saturn V S-IC first stages in the mid to late 1960s. It was modified for Space Shuttle Main Propulsion Test Article (MPTA) testing in the late 1970s and early 1980s, and then supported Delta IV CBC testing during its development in the late 1990s and the turn of the century.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/01\/B-2-Stand-SIC-CBC-Tests.jpg\")
<\/p>\n
A composite of historical uses of the B-2 test stand. Left, a Saturn V S-IC stage is fired in the 1960s. Right, a Delta IV Common Booster Core (CBC) stage is fired in the early 2000s. Credit: NASA.<\/p>\n
\u201cThe B-2 test stand has always been used for stages, Saturn, Shuttle, Delta 4, and this one,\u201d Maynard said, referring to SLS.<\/p>\n
\u201cAround 2009-10, we were given marching orders to do an assessment on refurb-ing (refurbishing) the stand. And then about 2012 we got the go to go ahead and do it.\u201d<\/p>\n
\u201cBasically there was a lot of rusted structural steel, a lot of rework,\u201d he added. \u201cThe structure left over from the Saturn and the Shuttle Program is all the grey stuff down.\u201d<\/p>\n
\u201cNow we did take this grey structure right here, we actually lifted it up and moved it back twenty feet,\u201d he continued. \u201cIt saved us a boatload of money and a lot of mass that we would have had to build extra on the backside. And then all the white structure up above, all the way up is all put in specifically for SLS.\u201d<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/01\/B-2-MPTA-Structure-Move-Aug-2014.jpg\")
<\/p>\n
Before\/after images of the move of the Main Propulsion Test Article (MPTA) structure on the B-2 stand in August, 2014. Credit: NASA.<\/p>\n
Some subsystem activation work began while construction was winding down, but activation activities have been going on through 2017 and 2018.<\/p>\n
One of the final custom structural pieces installed for the SLS Core Stage were the two \u201cyellow boxes\u201d up near the top of the stand. Similar to the Space Shuttle External Tank, the thrust beam that runs through the stage\u2019s intertank takes most of the vehicle thrust loads from the two Northrop Grumman Solid Rocket Boosters (SRB) and the four Aerojet Rocketdyne RS-25 engines.<\/p>\n
The yellow boxes are the two forward hold-down structures that will do most of the work holding the stage in place in the stand, attaching to either end of the intertank thrust beam at the forward SRB attach points. \u201cWe just finished yesterday actually the last torquing of the bolts, so they are now firmly installed,\u201d Maynard said during the interview in December.<\/p>\n
He also noted that one of the hold-downs weighs a little more than the other, but the average between them is about sixty-five thousand pounds.<\/p>\n
Remaining activation tests<\/p>\n
There were still a few systems going through activation testing at the end of December. At the time of the interview, the other liquid oxygen system was being tested. \u201cOn the LOX side we have two systems,\u201d Maynard noted. \u201cOne is a very high flow system to do the fast fill on the vehicle and then we have another system to keep the replenishment going.\u201d<\/p>\n
\u201cWe have barges for hydrogen, three docks, that provides us enough hydrogen to go into the vehicle,\u201d he explained. Then on the LOX side we have three LOX positions and that provides enough for the fill and then we have our day tank which is what we\u2019re activating today for replenishment.\u201d<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/01\/P1120572.35pct.jpg\")
<\/p>\n
A view looking south from Level 19 on the B-2 stand. Lower left, the docks for barges that supply cryogenic propellants to the stand. Center right, the hydrogen flare stack for B-2 is the right most stack in the image. The two test control centers (TCC) in the background are the original TCC (upper left) that is used for RS-68 testing in the B-1 stand, and the blue-roof TCC that will be used for SLS Green Run testing. Credit: Philip Sloss for NSF\/L2.<\/p>\n
\u201cYou get better quality LOX in there because that\u2019s kind of what you want to do in your replenishment \u2014 you don\u2019t want to put a lot of heat back into the system.\u201d<\/p>\n
Asked about other services for the Core Stage, he said: \u201cSo you\u2019ve got helium \u2014 we\u2019ve almost wrapped up all of our helium testing, which is providing the purges and stuff that the engines require from helium through the vehicle. We also have helium to press up the bottles on the vehicle, so we\u2019ve tested that.\u201d<\/p>\n
\u201cThere\u2019s also what we call the CAPU (Core Auxiliary Power Units) spin-start,\u201d he added. \u201cBefore the engine starts we have to spin them up, so that\u2019s what we use the helium [for].\u201d<\/p>\n
Maynard noted activation work that\u2019s left for the stand: \u201cRight now we\u2019re doing the LO2 replenishment system and then I think the last fluid system we have to check is our hydraulics, which is the hydraulics that we would connect up to the vehicle to gimbal the engines without the CAPUs. So that\u2019ll be sometime early next year.\u201d<\/p>\n
\u201cThe rest of the stuff is kind of here and there, we\u2019re really getting down to the end of our punch list.\u201d<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/01\/B-2-Water-Testing-Deluge.60pct.jpg\")
<\/p>\n
An image from a drone taken during a December, 2017, test of the B-2 water deluge system. Credit: NASA.<\/p>\n
Once the stage is set up in the stand for Green Run, the SLS Program based at the Marshall Space Flight Center in Huntsville, Alabama, and Stages prime contractor Boeing will be in charge. \u201cNot to be sly, but the way we\u2019re involved we\u2019re actually a filling station,\u201d Maynard observed.<\/p>\n
\u201cWe\u2019re going to fill it up, but after we fill it up it is Marshall and Boeing all the way. We\u2019re a gas filling station.\u201d<\/p>\n
Stage test firing demands lots of water<\/p>\n
Testing and activation of other B-2 subsystems occurred over the last several months. The hot-fire test which culminates the Green Run campaign for the flight stage will require a lot of water to protect the flight and ground hardware.<\/p>\n
The flame bucket will be deluged with water, similar to single-engine tests in other stands at Stennis; however, additional measures are needed for sound suppression, to protect the Core Stage from the noise that it makes during the eight-plus minutes it is firing while it is held in place.<\/p>\n
\u201cIf you leave the pad, you\u2019re basically flying away from that acoustic energy, but we\u2019re staying in the stand and we\u2019re basically beating the vehicle with that acoustic energy for five-hundred seconds,\u201d Maynard explained. \u201cSo to knock off that acoustic energy we put in an acoustic ring above the aspirator.\u201d<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/01\/B-2-Water-Testing-Aspirator-01.jpg\")
<\/p>\n
An image of the aspirator for the B-2 stand during a water flow test in May, 2018. Credit: NASA.<\/p>\n
\u201cAnd so basically the water is coming across normal to gravity right under the nozzles and that will absorb some of that acoustic energy.\u201d<\/p>\n
In addition to the flame bucket deluge and sound suppression water, plumbing for fire extinguisher (firex) water is also installed on the stand. The facility water supply can be routed to the firex system in case it is needed for contingencies with the vehicle and\/or stand.<\/p>\n
\u201cThe way that would work on the deluge is during the test all the water is going to the bucket or the acoustic ring,\u201d he explained. \u201cIf there is an event then what they\u2019ll do is shut off the risers going to the bucket, at the same time they would open up the valves that would send the water up into these water cannons and the ring here.\u201d<\/p>\n
There are firex rings on the stand at different levels to provide coverage of the vehicle\u2019s exterior.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2019\/01\/P1120532.35pct.jpg\")
<\/p>\n
A few of the semi-circular rings that are part of the firex system, as seen looking up from Level 19 to the top of the B-2 structure constructed for SLS. Credit: Philip Sloss for NSF\/L2.<\/p>\n
The Test Control Center (TCC) that will be used with the B-2 stand for the upcoming Core Stage tests is one that had been intended to be used for the A-3 stand instead of the existing control center for the B complex. \u201cBecause of B-1 testing and the amount of people and stuff that we use, we had already \u2018refurb-ed\u2019 the test center there for A-3, so it was in a really great state so we just said \u2018hey why don\u2019t we just add some more copper, connect it to the B-stand?’\u201d Maynard explained.<\/p>\n
\u201cAnd so we\u2019ll run the whole system from what we used to call the DAF, the Data Acquisition Facility.\u201d The A-3 stand was built for the Constellation program; following cancellation of Constellation at the beginning of the decade, the stand was mothballed.<\/p>\n
\u201cThe control center is pretty much ready to go,\u201d he noted. \u201cThat\u2019s part of our activation is to wring out the control center.\u201d<\/p>\n
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