SLS Core Stage Test Likely to Slip to December

This week's Ars Technica Rocket Report links to NASA Spaceflight (.com) reporting that NASA's giant Space Launch System (SLS) has experienced both weather and technical delays in the last several months, the end result being that the test "Green Run" planned for "early November" is looking more like late November at best and possibly December.  The Stennis Space Center is in the area of the country hammered the most by hurricanes and tropical storms this year.

Zeta was the latest hurricane to disrupt testing in the Green Run campaign for the Core Stage at Stennis; work was stopped for the sixth time by tropical weather this 2020 Atlantic hurricane season. While the storm was developing in the Caribbean last week, NASA and prime contractor Boeing were discussing technical issues revealed during Summertime Green Run testing. They will now also have to factor cleanup efforts into their go-forward plans for the final two Green Run tests.

Zeta was the third hurricane and fifth tropical system to make landfall in Louisiana. Still, it was the strongest to directly impact the New Orleans area, with the center of the storm passing over the city, MAF in New Orleans East, and then Stennis in Southern Mississippi not far from there. Weather models were in good agreement about the forecast track of the storm, but Zeta intensified more than forecast, with the storm rapidly increasing to Category Two intensity just below the Category Three threshold near landfall.

Storms are inevitable this time of year, but this year's pattern has been the most bizarre I can remember with most of them making landfall between easternmost Texas and westernmost Florida, a distance of about 500 miles.  But weather isn't their only problem.  They have hardware issues, too.

A set of countdown simulation runs, test case six of a total of eight, was completed at the beginning of October to exercise the test team and updated ground control system software, but the issues were originally seen before that. NASA and Boeing are still discussing them and analyzing data; decisions about how to proceed had not been made at the time of publication.

One issue involves one of the four liquid hydrogen (LH2) prevalves that isolate the LH2 tank from the LH2 inlets of each of the four RS-25 Core Stage engines before engine start. The prevalves open just before engine ignition and then feed propellants to the engines while they are firing. The SLS Program is continuing to discuss troubleshooting data and options to resolve the issue.

Another issue was reported with the performance of the thrust vector control (TVC) system during test case five, where the Main Propulsion System (MPS) hydraulics were thoroughly exercised. The hydraulics are used to control RS-25 engine valves in addition to the Core Stage TVC actuators that move the engines.

The TVC questions came up after digging deeper into the data from test case five. During the early part of the test, the hydraulic systems were operated using external ground power and later using the vehicle’s Core Auxiliary Power Units (CAPU).

The article goes on to say that reworking and retesting to resolve these issues will push the Hot-Fire test out of November and possibly as far as into 2021.  Prior to the hot-fire test, a Wet Dress Rehearsal was planned and a date set for "early November."  This is where Hurricane Zeta and the post-hurricane cleanup come into the picture.  Troubleshooting work that was delayed by the storm is expected to delay the Wet Dress Rehearsal, too, beyond its previous early November target.  Needless to say, there's not a lot of "early November" left!

It's a bit early to tell, but there's also a tropical storm Eta out there now that could complicate things.  The Stennis area is not in the 5 day prediction maps, but it's forecast to be west of Tampa area by next Wednesday night and headed in that general direction.

The SLS core currently at Stennis Space Center in Mississippi being put into position for testing.