NASA is changing the script for the second launch attempt of the SLS moon rocket

NASA’s Space Launch System rocket sits on the launch pad in Florida. (NASA Photo/Joel Kowsky)

NASA is counting down once again to the first launch of the Space Launch System rocket for an uncrewed test flight around the Moon that is expected to set the stage for future lunar landings.

The launch from the Kennedy Space Center in Florida is scheduled during a two-hour window starting at 2:17 p.m. ET (11:17 a.m. PT) on Saturday.

Live online coverage of the tank operations will begin at 2:45 am. PT on NASA TV. Full launch coverage in English will begin at 9:15am. PT, with coverage in Spanish beginning at 10 a.m. PT. (See the full schedule.)

The launch of the SLS rocket — which surpasses the Apollo-era Saturn V as the most powerful launch vehicle ever built for NASA — should be an impressive sight. But this is just the beginning for a 38-day mission that marks the first time in nearly 50 years that a spacecraft designed to carry humans has made it all the way to the moon.

NASA’s mission plan calls for SLS to send an Orion spacecraft on a journey that will come as close as 60 miles to the lunar surface and extend up to 40,000 miles beyond the moon.

This time, Orion won’t be carrying humans. Instead, three mannequins equipped with sensors will collect data on radiation exposure and other environmental conditions inside the capsule. There will also be an Alexa-like virtual assistant nicknamed Callisto, which is provided by Amazon in partnership with Cisco and Lockheed Martin.

One of the mission’s key moments will come when the Orion spacecraft hits the atmosphere at 25,000 mph on its way back into a dive in the Pacific Ocean. This will put Orion’s heat shield to its most severe test, with temperatures ranging up to 5,000 degrees Fahrenheit.

If this test flight goes well, it would pave the way for NASA to send a crew of astronauts on a similar flight around the Moon for Artemis 2 in the 2024 timeframe. The landmark lunar landing would come on Artemis 3 in 2025 or in 2026.

NASA aborted its first launch attempt on Monday, largely due to an issue with the cooling process for the four Aerojet Rocketdyne RS-25 rocket engines in the Boeing-built SLS core stage.

The pre-launch procedure requires “bleeding” some of the supercooled liquid hydrogen fuel from the SLS tank to bring the engines’ temperature down to the required level of about 420 degrees below zero F. During Monday’s refueling operation, a sensor indicated that one of the engines was not cooling sufficiently.

Engineers were unable to fix the problem in time for launch, forcing a crash. They then suspected that the problem was due to a faulty sensor rather than a failure of the cooling system itself.

For this effort, the rules governing the process have been rewritten to account for a wider variety of data from a variety of sensors — and to ignore readings from the suspect sensor if necessary.

In addition, the cooling process, also known as “start bleed”, will be conducted during an earlier phase of the fueling process, at approximately 8 am. ET (5 a.m. PT). Mission managers made this change because the process worked flawlessly earlier in the countdown during a “Green Run” engine test in March.

In recent days, workers at the launch site have also refined and repaired some of the components that caused other concerns during Monday’s countdown — for example, a leak in the rocket’s fuel supply lines.

Tanker trucks deliver liquid hydrogen to storage tanks at the Kennedy Space Center.  (NASA photo/Bill Ingalls)

Tanker trucks deliver liquid hydrogen to storage tanks at the Kennedy Space Center. (NASA photo/Bill Ingalls)

Technical glitches aren’t the only concerns that could prevent takeoff: stormy weather could also force a postponement. Forecasters estimate there is a 60 percent chance of acceptable weather at the start of Saturday’s launch window, rising to more than 80 percent by the end of the two-hour window.

“On any given day, there’s about a 1 in 3 chance we’re going to grind for whatever reason,” said Melody Lovin, weather officer for the US Space Force’s Space Launch Delta 45. “Of those chances we clear, there’s about a 50% chance it’s due to the weather.”

PREVIOUSLY: Why NASA’s first moon rocket launch is a big deal

If Saturday’s launch attempt has to be called off, the next opportunity would come on Monday or Tuesday. If that opportunity is missed, the SLS will have to move off the launch pad for a test of the flight termination safety system, said Jeremy Parsons, associate director of ground exploration systems at the Kennedy Space Center.

The Artemis moon program, named after the mythological moon goddess who was Apollo’s sister, underscores NASA’s leadership role in exploration beyond Earth. That role has been somewhat controversial in recent years due to years of delays and billions of dollars in cost overruns associated with the SLS-Orion program.

A successful mission would arguably raise the space agency’s profile compared to commercial space ventures like SpaceX and Blue Origin, while a less-than-successful mission could intensify the debate over whether NASA should deliver more than its role in these commercial enterprises. (SpaceX is already set to provide a lunar lander for the Artemis 3 mission, based on its Starship rocket design.)

“Both Blue Origin and SpaceX built reusable heavy-lift rockets at their own expense and are already suppressing the government’s rocket that receives billions of our tax dollars,” former NASA contributor Lori Garver wrote in her recent op-ed. memoir, “Escaping Gravity.”

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