Engineers revised the fueling schedule for NASA’s Artemis giant moon rocket to solve the engine cooling problem thatMonday. Agency managers hope the road will be cleared in a long-awaited test flight without a pilot,
Asked about his confidence level in the next launch attempt, mission manager Mike Sarafin said Thursday that the Space Launch System rocket, the most powerful booster NASA and its contractors have ever built, has 489 launch commitment criteria that must be met. are met to allow launch.
“We have a bunch of things that could keep us from getting away any day,” he told reporters at a news conference Thursday afternoon. “There’s no guarantee we’re going to go down (Saturday). But we’re going to show up, try and do our best.”
Sarafin and the rest of NASA’s Mission Management Team (MMT) met Thursday to look at the engine cooling problem, the vent valve leak, the valve quick disconnect, work to tighten a different seal where the liquid hydrogen lines feed propellant in the rocket propulsion system and a crack in the core stage spray insulation.
The MMT concluded that the engineers had developed sound “flight logic” in all cases and that forward thrust for launch added only a very small level of additional risk.
And so, after a detailed review and a forecast calling for a 60 percent chance of favorable weather conditions, MMT approved plans to begin pumping 750,000 gallons of cryogenic oxygen and hydrogen fuel into the SLS rocket’s two stages around 6 a.m. EDT Saturday.for blastoff at 14:17, opening a two-hour window.
Problem confirming that one of the four RS-25 core stage engines was sufficiently cooled or adapted to the extremely low liquid hydrogen temperatures during the fueling process, along with the two leaking hydrogen components, cracked insulation, and stormy weather , combined to force a launch on Monday.
The insulation problem, likely caused by thermal stresses, could have resulted in a piece falling off at some point during launch, but an analysis shows the chances of it causing significant damage are so remote, no repair is required.
The behavior of the vent valve is understood and not considered a problem, and engineers found and tightened a loose component that was likely responsible for the leak detected near the umbilicals at the base of the rocket.
The issue of engine cooling required more detailed analysis.
John Honeycutt and SLS rocket chief engineer John Blevins said a review of data from multiple sensors confirmed that all four shuttle-era engines were, in fact, properly cooled despite the temperature sensor on the No. 3 engine that showed that it was not cooling enough.
Thermal regulation is required to ensure that the bearings in powerful turbo engines remain within tight operating tolerances when they suddenly spin up to draw supercooled propellants into the combustion chamber beginning about six seconds before takeoff.
Priming is done by routing propellant through an engine’s low- and high-pressure fuel pumps, a process known as “start bleed” that circulates cold liquid hydrogen through the lines. In the process, the liquid propellant pushes out or “bleeds” the lines of hotter hydrogen, some of which may have turned to gas.
During Monday’s launch attempt, three of the engines nearly reached the target of minus 420 degrees on the hydrogen side, but engine No. 3 failed to get past about minus 380 degrees. Engineers suspect a faulty temperature sensor because other readings show good cooling
“We know we had a bad sensor,” Honeycutt said. “Since then, we’ve had time to go back and look at the data and compare multiple data sources and do some independent analysis that confirms it’s a bad sensor and we’re getting good quality propellant through the engines.”
Adding some leeway, engineers revised the fueling schedule for the second launch attempt and will begin the hydrogen launch earlier than originally planned, allowing more time for the propellant to cool the material.
Later in the countdown, the hydrogen tank will be pressurized to flight levels for a quick test, forcing more hydrogen through the lines to aid the cooling process.
Similar procedures were used before the test firing of the engine in the main stage last year and there were no problems. Blevins said the suspected sensor is not monitored by flight control software and will simply be ignored during Saturday’s launch attempt.
“We don’t need that sensor to fly,” Blevins said. “What we’re trying to do is make sure we have cold fluid (flowing through the engine) for a certain amount of time … to infer that the rest of the material is cold.”
He said “there’s no doubt we’ve got good flow through this engine.”
If no further problems arise and the weather cooperates, the countdown should finally reach zero on Saturday, beginning a ground-shaking spectacle unmatched since NASA’s legendary Saturn 5 moon rockets propelled the Apollo astronauts to the moon before from five decades.
Producing 8.8 million pounds of thrust at launch from two belt-driven boosters and four shuttle-era engines — 15 percent more than the Saturn 5 — the SLS rocket is the most powerful ever built by NASA and its contractors .
After an eight-minute ascent to an initial elliptical orbit, the core stage will fall away and the SLS upper stage will propel the unmanned Orion capsule and ESA-provided service module into an orbit for a close lunar flyby on September 8 .
The service module’s engine will put the craft into a distant orbit around the moon and bring it back to Earth for launch into the Pacific Ocean west of San Diego on Oct. 11 at around 2:10 p.m. EDT.
The primary objectives of the flight are to verify the performance of the SLS rocket and to take the Orion spacecraft into deep space. The top priority is to test its heat shield, which must withstand re-entry temperatures of up to 5,000 degrees Fahrenheit during the capsule’s high-speed plunge back to Earth.
If the Artemis 1 flight goes well, NASA plans to launch four astronauts on a flyby around the Moon in 2024, followed by a landing near the Moon’s south pole in the 2025-26 timeframe when the first woman and next man will step on the surface.
NASA plans annual flybys of the lunar surface and visits to a small space station in orbit around the Moon to conduct long-term exploration and test the hardware and procedures needed for eventual flights to Mars.
While there are no such flights to the red planet at this point, NASA sees the Moon as a critical first step toward achieving that long-term goal.
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