Countdown clocks began on Saturday for NASA’s fourth attempt to complete a dress rehearsal countdown and refueling test of its Space Launch System moon rocket, a requirement before the massive booster could be cleared for the launch of its long-awaited maiden flight.
“No one wants to go through this more than the Exploration Ground Systems (EGS) team and all of our crews…to get this vehicle filled, figure out where we are in the terminal count, and then come back…ready for launch,” said Jim Free, director of exploration development at NASA Headquarters.
The countdown began at 5:30 p.m. EDT and if all goes well, the two-day test will enter its final hours on Monday morning, when engineers plan to remotely load the rocket’s first and second stages with three-quarters of a million gallons of supercold. liquid oxygen and combustible hydrogen.
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Launch Director Charlie Blackwell-Thompson and his team plan to count to T-minus 33 seconds and then perform a recycle that will mimic an unplanned wait before counting to T-minus 10 seconds. At this point, just before the rocket’s four main engines begin their start-up sequence during an actual launch, the computers will shut down the test.
The goal is to ensure that the rocket’s complex launch control software, electrical, mechanical and propellant systems, and their interfaces with launch pad support equipment, will work together as needed to launch. safely the most powerful thruster ever built for NASA.
These complexities have been exposed in three previous attempts to power the SLS as engineers encountered issues with launch pad subsystems, unexpected propellant temperature and pressure excursions, a stage helium valve blocked top and leaks in a fitting that connects a hydrogen fuel line to the rocket. first stage.
Originally transported to pad 39B at Kennedy Space Center on March 18, NASA moved the 330-foot-tall SLS rocket to the Vehicle Assembly Building on April 25 to replace the helium valve, repair the hydrogen leak and perform several other upgrades and improvements.
Hydrogen leaks are notoriously difficult to identify and eliminate because they usually don’t show up until the material is exposed to cryogenic temperatures. But Free is optimistic that working to tighten a clamp in the fuel line connector fixed the problem.
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“We’ve fixed some things that we saw around the area where we saw the leak, including going back to some of the procedures that we used and the shuttle days know-how, which we really benefited from,” said he declared. “Obviously, we won’t know the results of this until we actually get the liquid hydrogen to flow through the buffer.
“We also worked on some of the loading procedures,” he continued. “We’ve seen some things with LOX (liquid oxygen) and hydrogen where our team has been able to actually go back (and) automate those procedures, which we know will help us in the flow to come.”
In addition to fixing the hydrogen leak, engineers replaced the helium valve after finding a bit of rubber debris lodged in the mechanism. They also changed fueling procedures to eliminate some of the pressure and temperature issues previously encountered.
Mounted on a powerful tracked transporter, the SLS rocket and its mobile launch stage were brought back to the launch pad on June 6, setting the stage for this weekend’s fourth attempt to complete the rehearsal.
Assuming the test goes well, NASA will move the rocket to the VAB once more for final flight preparations.
NASA hopes to finally launch the SLS in late August, propelling an unmanned Orion crew capsule on a test flight past the moon and back. The first piloted mission, a flight carrying four astronauts around the Moon, is scheduled for 2023 with a landing in 2025.
William Harwood
