US: Nasa megarocket Artemis I set for debut test launch to moon today

Nasa's colossal next-generation megarocket was set for its long-awaited debut launch on Monday, on an uncrewed, six-week test flight around the moon and back, marking the first mission of the space agency's Artemis program, the successor to Apollo.

The 32-story-tall, two-stage Space Launch System (SLS) rocket and its Orion crew capsule were due for blast-off from the Kennedy Space Center in Cape Canaveral, Florida, during a two-hour launch window opening at 8.33am EDT (4.33pm UAE time).

The maiden voyage of the SLS-Orion — a mission dubbed 'Artemis I' — is intended to put the 5.75-million-pound vehicle through its paces in a rigorous demonstration flight which will push its design limits, before Nasa deems it reliable enough to carry astronauts.

Billed as the most powerful, complex rocket in the world, the SLS represents the biggest new vertical launch system the US space agency has built, ever since the Saturn V flown during the Apollo moon programme of the 1960s and 1970s.

The spacecraft was slowly trundled to historic Launch Pad 39B earlier this month, following weeks of final preparations and ground tests. Last week, Nasa officials concluded their flight readiness review, declaring that all systems were "go for launch".

One issue cited by Nasa officials last week, as a potential show stopper for Monday's launch, would be any sign during rocket fuelling that a newly-repaired hydrogen line fitting had failed to hold.

If the countdown clock is halted for any reason, Nasa has set September 2 and September 5 as backup launch dates.

Barring last-minute technical difficulties or unfavourable weather, Monday's countdown should end with the rocket's four main R-25 engines and its twin solid-rocket boosters igniting to produce 8.8 million pounds of thrust — about 15 per cent more thrust than produced by the Saturn V, sending the spacecraft streaking skyward.

About 90 minutes after launch, the rocket's upper stage will thrust Orion out of the Earth's orbit on course for a 42-day flight that brings it to within 60 miles of the lunar surface before sailing 64,374 km beyond the moon, and back to Earth. The capsule is expected to splash down in the Pacific on October 10.

Although no humans will be aboard, Orion will be carrying a simulated crew of three — one male and two female mannequins — fitted with sensors to measure radiation levels and other stresses that real-life astronauts would experience.

A top objective for the mission is to test the durability of Orion's heat shield during re-entry, as it hits Earth's atmosphere at 39,429 km per hour, or 32 times the speed of sound, on its return from lunar orbit — much faster than more common re-entries of astronaut capsules returning from low-Earth orbit.

"That's our highest priority that we have to accomplish," lead flight director Rick LaBrode said of demonstrating the heat shield's ability to withstand re-entry friction, expected to raise temperatures outside the capsule to nearly 2,760°C.

"That's what's going to keep the capsule together and save the astronauts."

Back to the moon

Nasa's Artemis program — named for the goddess who was Apollo's twin sister in ancient Greek mythology — aims to return astronauts to the moon's surface as early as 2025, and to establish a long-term lunar colony as a stepping stone to even more ambitious future voyages, such as sending humans to Mars.

More than a decade in development with years of delays and billions of dollars in budget overruns, the SLS-Orion spacecraft has so far cost Nasa at least $37 billion, including design, construction, testing and ground facilities.