NASA starts counting down the lunar rocket’s fourth fuel test

The countdown clock began ticking on Saturday for NASA’s fourth attempt to complete a countdown and fuel test of the lunar rocket Space Launch System, a requirement before the huge booster can be cleared for launch on its long-awaited maiden flight.

“No one wants to get through this more than the EGS (Exploration Ground Systems) team, and all our teams … to get this vehicle on the tank, understand where we’re going in the terminal count and then come back … out for launch, “said Jim Free, director of exploration development at NASA’s headquarters.

The countdown began at 5:30 p.m. EDT, and if all goes well, the two-day test will tick into the final hours Monday morning, as engineers plan to remotely load the rocket’s first and second stages with three-quarters of a million gallons of super-cold liquid oxygen and hydrogen fuel.

A full moon sits behind NASA’s Space Launch System rocket on top of pad 39B at the Kennedy Space Center. On Saturday, NASA began a two-day ordeal countdown and fuel test to clear the way for an un Piloted flight beyond the moon and back late this summer.

William Harwood / CBS News

Launch Director Charlie Blackwell-Thompson and her team plan to count down to T-minus 33 seconds and then perform a recycle that will mimic an unplanned team before counting all the way down to just within T-minus 10 seconds. At that point, just before the rocket’s four main engines were to begin their launch sequence in an actual launch, computers would stop the test.

The goal is to ensure that complex launch control software, the rocket’s electrical, mechanical and propulsion systems, together with their interface with launch ramp support equipment, will work together as needed to safely launch the most powerful booster ever built for NASA.

These complexities were demonstrated in three previous attempts to supply fuel to SLS when engineers encountered problems with launch ramp subsystems, unexpected fuel temperature and pressure deviations, a jammed upper-stage helium valve, and leaks in a fixture connecting a hydrogen fuel line to the rocket’s first stage.

Originally pulled out to pad 39B at the Kennedy Space Center on March 18, NASA moved the 330-foot SLS rocket back to the Vehicle Assembly Building on April 25 to replace the helium valve, fix the hydrogen leak, and perform several other upgrades and improvements.

Hydrogen leaks are notoriously difficult to detect and eliminate because they usually do not appear until the hardware is exposed to cryogenic temperatures. But Free is optimistic that the work of tightening up a flange in the fuel line coupling has solved the problem.

The Space Launch System rocket is the most powerful booster ever built for NASA, it is 330 feet high and capable of generating 8.8 million pounds of thrust when ascending.

William Harwood / CBS News

“We fixed some things we saw around the area where we saw the leak, including going back to some of the procedures we used and the knowledge from the shuttle days, which we really benefited from,” he said. “Of course we will not know the results of it until we actually flow liquid hydrogen at the pad.

“We also worked on some of the loading procedures,” he continued. “We saw some things with LOX (liquid oxygen) and hydrogen that our team was actually able to go back in (and) automate these procedures, which we know will help us during the upcoming flow.”

Along with addressing the hydrogen leak, engineers replaced the helium valve after finding some rubber residue stuck in the mechanism. They also modified fuel procedures to eliminate some of the pressure and temperature problems experienced earlier.

Mounted on top of a powerful belt conveyor, the SLS rocket and its mobile launch stage were pulled back to the launch pad on June 6, setting the stage for the weekend’s fourth attempt to complete the exercise.

Assuming the test goes well, NASA will move the rocket back to VAB once more for final flight preparations.

NASA hopes to finally launch SLS at the end of August, and reinforce an un piloted Orion crew capsule on a test flight beyond the moon and back. The first pilot mission, an aircraft carrying four astronauts around the moon, is scheduled for 2023 with a landing in the 2025 time frame.