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It’s finally time. After more than a decade of development, years of delays and billions of dollars of budget overruns, NASA’s Space Launch System (SLS) rocket is ready to launch with the Orion capsule atop it. If all goes well, the huge rocket will take off on its maiden voyage, the Artemis I mission, on 29 August – the first major test of NASA’s plan to return people to the surface of the moon in 2025.

The rocket was rolled out to its launch pad at the Kennedy Space Center in Florida on 17 August and it passed a flight readiness review on 22 August. “We are go for launch, which is absolutely outstanding,” said NASA’s at a press conference after the review. “This day has been a long time coming.”

SLS is the most powerful rocket ever built, producing more thrust than even the Saturn V rocket that launched the Apollo astronauts to the moon. With Orion stacked on it, it is nearly 100 metres tall – taller than the Statue of Liberty in New York.

There are a few small components of the launch that are yet to be tested, including a process called the hydrogen kick-start in which the engines are cooled down with liquid hydrogen before they fire. It couldn’t be tested during earlier “dress rehearsals” because of a hydrogen leak, and the mission’s engineers will test it on the day of the planned launch. If the leak is still there, the launch will be postponed. There are two backup launch windows, on 2 and 5 September.

If all goes well, SLS will carry Orion to an altitude of just under 4000 kilometres before the two craft separate and the rocket falls towards Earth. Orion will continue onwards to the moon, where it will spend six days in orbit before coming back home. The mission will last a total of 42 days.

One of the main goals of this flight is testing Orion’s heat shield, which will have to endure temperatures of almost 2800°C as it enters Earth’s atmosphere at upwards of 40,000 kilometres per hour. While Orion won’t have any crew aboard this time – the craft’s first crewed flight is planned for 2024 – it will carry mannequins equipped with sensors to make sure the journey would be safe for astronauts.

“This is a test flight. It’s not without risk… We are stressing Orion beyond what it was actually designed for in preparation for sending it to the moon with a crew,” said Cabana. “We want to make sure it works absolutely perfectly when we do that and that we understand all the risks.”

After Artemis I, the next flight in 2024 is planned to bring a crew of astronauts around the moon and back without landing. Then, in 2025, NASA has planned the first crewed moon landing since the Apollo 17 mission in 1972. NASA officials have said that the 2025 mission, Artemis III, will include the first woman to walk on the moon.

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