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NASA’s SLS rocket completes engine test on second try

Two months after an intial hot-fire test ended prematurely, the four engines on the core stage of NASA’s heavy-lift Space Launch System were fired up for the full duration of eight minutes today.

The successful engine test marks a major milestone for the rocket that’s due to get an uncrewed round-the-moon test flight off the ground late this year or in early 2022 — and for an Artemis program that’s due to put astronauts on the lunar surface in the mid-2020s.

“The SLS is the most powerful rocket NASA has ever built, and during today’s test the core stage of the rocket generated more than 1.6 million pounds of thrust within seven seconds,” acting NASA Administrator Steve Jurczyk said in a news release. “The SLS is an incredible feat of engineering and the only rocket capable of powering America’s next-generation missions that will place the first woman and the next man on the moon.”

The Aerojet Rocketdyne RS-25 rocket engines are holdovers from the space shuttle program that have been refurbished for reuse on the SLS. Those engines consume more than 733,000 gallons of super-chilled liquid hydrogen and oxygen for their full duration.

During Jan. 16’s “Green Run” test at NASA’s Stennis Space Center in Mississippi, the SLS core stage’s RS-25 engines fired for a little more than a minute before shutting themselves down. Engineers determined that the shutdown occurred when pressure in a hydraulic system exceeded its conservative pre-set limits. Adjustments were made for today’s second test at Stennis.

This time around, the engines fired for 499.6 seconds straight, achieving 109% of the power that would be required during the 212-foot-tall booster’s eight-minute ascent to Earth orbit. The engines were also put through a series of movements in specific patterns to direct their thrust.

Boeing is the lead contractor for the SLS core stage. “I want to thank the extraordinary individuals who make up the NASA, Aerojet Rocketdyne and Boeing teams who designed, developed, produced and tested the all-new SLS core stage to enable sustainable human exploration of deep space,” John Shannon, Boeing SLS vice president and program manager, said in a statement.

John Honeycutt, NASA’s SLS program manager, told reporters after the test that “everything we’ve seen in the test today looked nominal.”

NASA’s plan calls for the core stage to be refurbished and shipped from Stennis to Kennedy Space Center in Florida. Solid rocket boosters and other equipment, including NASA’s Orion crew spacecraft, will be added to the stage on a mobile launcher inside Kennedy Space Center’s massive Vehicle Assembly Building.

If all goes according to schedule, the SLS would be ready for its first-ever spaceflight by as early as November. However, NASA officials acknowledge the launch date could still slip by a couple of months.

NASA and its contractors are handling the components carefully throughout the testing cycle because they’re destined to be used for spaceflight. After the uncrewed Artemis 1 test flight, the rocket for the Artemis 2 mission is due to send astronauts around the moon in 2023, followed by the Artemis 3 moon landing in 2024 or later.

NASA’s current vision for space exploration calls for an upgraded version of the SLS to launch astronauts to Mars starting in the 2030s.

Cost overruns and development delays in the $17 billion SLS program have already led many to question whether the rocket is worth the cost, particularly if SpaceX succeeds in developing an even more powerful Super Heavy booster for missions to the moon and Mars.

The first Super Heavy prototype was unveiled today in preparation for testing at SpaceX’s Boca Chica rocket development facility in Texas.

President Joe Biden is expected to name one of the early champions of the Space Launch System, former U.S. Sen. Bill Nelson, as his choice to become NASA’s next administrator. Word of the nomination could come as soon as March 19, according to multiple news reports.

By Alan Boyle

Mastermind of Cosmic Log, contributing editor at GeekWire, author of "The Case for Pluto: How a Little Planet Made a Big Difference," president of the Council for the Advancement of Science Writing. Check out "About Alan Boyle" for more fun facts.

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