CAPE CANAVERAL, Florida - As Nasa on Saturday resumed its second effort to get its new 32-story rocket off the ground and send its uncrewed test capsule toward the Moon, engineers detected a fuel leak that potentially could lead to a new delay.

With millions around the globe and hundreds of thousands on nearby beaches waiting for the historic launch of the massive Space Launch System (SLS), a leak near the base of the rocket was found as ultra-cold liquid hydrogen was being pumped in.

Nasa said engineers would “stop flowing liquid hydrogen to the tank, close the valve used to fill and drain it,” then try to reseal it.

The space agency offered no information on the likelihood of a new delay in the Artemis program – which aims eventually to return a human crew to the Moon – following Monday’s aborted effort.

Saturday’s launch is still scheduled for 2.17pm (2.17am Sunday, Singapore time) from Kennedy Space Centre in Florida. It can be delayed by up to two hours if necessary.

“Our team is ready,” Jeremy Parsons, deputy manager of exploration ground systems at Kennedy Space Center, had said Friday.

“They are getting better with every attempt and actually performed superbly during launch countdown number one... I think if the conditions with weather and the hardware align, we’ll absolutely go.”

Though the area around the launch site will be closed to the public, an estimated 400,000 people were gathering on beaches nearby to see – and hear – the most powerful vehicle that Nasa has ever launched climb into space.

An initial liftoff attempt was thwarted by technical problems five days ago.  

The Artemis programme came 50 years after the last Apollo lunar mission.

The previous launch bid on Monday was halted by engineering snags. Nasa says technicians have since remedied the issues.  

Weather is an additional factor beyond Nasa’s control. The latest forecast saw a 70 per cent chance of favourable conditions during Saturday’s two-hour window, according to the US Space Force at Cape Canaveral.  

Before dawn, launch teams started the lengthy, delicate process of filling the rocket’s core-stage fuel tanks with several hundred thousand gallons of super-cooled liquid oxygen and liquid hydrogen propellant.

If the countdown were halted again, Nasa could reschedule another launch attempt for Monday or Tuesday.  

Dubbed Artemis I, the mission marks the first flight for both the SLS rocket and the Orion capsule, built under Nasa contracts with Boeing Co and Lockheed Martin Corp, respectively.  

It also signals a major change in direction for Nasa’s post-Apollo human spaceflight programme, after decades focused on low-Earth orbit with space shuttles and the International Space Station.  

Named for the goddess who was Apollo’s twin sister in ancient Greek mythology, Artemis aims to return astronauts to the moon’s surface as early as 2025, though many experts believe that time frame will likely slip.  

Twelve astronauts walked on the moon during six Apollo missions from 1969 to 1972, the only spaceflights yet to place humans on the lunar surface.

But Apollo, born of the US-Soviet space race during the Cold War, was less science-driven than Artemis.  

The new moon programme has enlisted commercial partners such as SpaceX and the space agencies of Europe, Canada and Japan to eventually establish a long-term lunar base of operations as a stepping stone to even more ambitious human voyages to Mars.

Spaceflight stress test 

Getting the SLS-Orion spacecraft off the ground is a key first step. Its first voyage is intended to put the 5.75-million-pound vehicle through its paces in a rigorous test flight pushing its design limits and aiming to prove the spacecraft suitable to fly astronauts.  

If the mission succeeds, a crewed Artemis II flight around the moon and back could come as early as 2024, to be followed within a few more years with the programme’s first lunar landing of astronauts, one of them a woman, with Artemis III.  

Billed as the most powerful, complex rocket in the world, the SLS represents the biggest new vertical launch system Nasa has built since the Saturn V of the Apollo era. 

Barring last-minute difficulties, Saturday’s countdown should end with the rocket’s four main RS-25 engines and its twin solid-rocket boosters igniting to produce 8.8 million pounds of thrust, about 15 per cent more than Saturn V, sending the spacecraft streaking skyward.

 About 90 minutes after launch, the rocket’s upper stage will thrust Orion out of Earth orbit on course for a 37-day flight that brings it to within 60 miles of the lunar surface before sailing 40,000 miles (64,374km) beyond the moon and back to Earth.

The capsule is expected to splash down in the Pacific on Oct 11.

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

The spacecraft also is set to release a payload of 10 miniaturised science satellites, called CubeSats, including one designed to map the abundance of ice deposits on the moon’s south pole.  

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 24,500mph (39,429kmh), or 32 times the speed of sound, on its return from lunar orbit – much faster than more common re-entries of capsules returning from Earth orbit.  

The heat shield is designed to withstand re-entry friction expected to raise temperatures outside the capsule to nearly 5,000 degrees Fahrenheit (2,760 deg C).  

More than a decade in development with years of delays and budget overruns, the SLS-Orion spacecraft has so far cost Nasa least US$37 billion (S$51.89 billion). 

Nasa’s Office of Inspector General has projected total Artemis costs will run to US$93 billion by 2025.  

Nasa defends the programme as a boon to space exploration generating tens of thousands of jobs and billions of dollars in commerce. AFP, REUTERS