(Reuters) – NASA will take a giant leap towards putting “footprints on the moon dust” for the first time since 1972 with Monday’s launch of the Artemis 1 mission, astronaut Stanley Love told Reuters.

A half century after the end of NASA’s Apollo era, the U.S. space agency’s long-anticipated bid to return astronauts to the moon’s surface remains at least three years away, with much of the necessary hardware still on the drawing board.

But the debut launch of its next-generation megarocket, the Space Launch System (SLS) and the Orion crew capsule it is designed to carry will set it back on course for the moon and then onwards to Mars, Love said.

“This is the single step that starts the journey of a thousand miles,” said Love, who is also a planetary scientist.

“We hope to have a sustainable presence on the moon, maybe with bases, research stations… and that is all focused on taking that next great step about a thousand times further into space than the moon, in rough numbers, to the planet Mars,” Love added.

The combined SLS-Orion spacecraft is due for blastoff from the Kennedy Space Center in Cape Canaveral, Florida, sending the uncrewed capsule around the moon and back to Earth on a six-week test flight.

The journey is intended to put the SLS vehicle through a rigorous stress test of its systems during an actual flight before it is deemed ready to carry astronauts.

Love, who as the Deputy Chief of the Astronaut Office’s Rapid Prototying Laboratory, develops Orion’s cockpit displays and controls, said the most important part of the inaugural Artemis mission will be to test the heat shield on the crew capsule.

“The main point of the flight doesn’t happen until the last few minutes when we come plunging back into the Earth’s atmosphere after falling from the moon at something like 24,000 miles an hour, 5000 degrees on that heat shield, and we hope it stays nice and cool on the other side of that heat shield where we’re going to put the people one day,” Love said.

Three mannequins with sensors to test for flight stress and lunar radiation will be in the Orion vehicle for the Artemis 1 mission, Love said.

The SLS represents the biggest new vertical launch system NASA has built since the Saturn V rockets flown during its Apollo moon program of the 1960s and 1970s.

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

Congress has steadily increased NASA’s budget to include funds for Artemis. Among the greatest financial beneficiaries are the principal SLS and Orion contractors – Boeing and Lockheed Martin, respectively.

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 as early as 2025 and establish a long-term lunar colony as a steppingstone to even-more-ambitious future voyages sending people to Mars.

Twelve astronauts walked on the moon during six Apollo missions from 1969 to 1972, the only spaceflights yet to place people on the lunar surface. All of those explored regions around the lunar equator.

A successful SLS-Orion launch is a crucial first step. The towering spacecraft, 322 feet (98 meters) tall, was slowly trundled to Launch Pad 39B last week following weeks of final preparations and ground tests.

Love, who has been an astronaut since 1998, flown on the space shuttle and taken two spacewalks, is clear-eyed about the potential risks of Monday’s launch.

“I would say I am optimistic, but I am well aware of the risks,” Love said. “I know where the weak points are, and I know that there’s risk associated with each to those weak points.”

The purpose of Artemis 1, Love said, is “to find the areas that we didn’t know to be worried about so that we can find them and fix them.”

Barring last-minute technical glitches or unfavorable weather, the four main SLS engines and its solid-rocket boosters are set to ignite at 8:33 a.m. EDT (1233 GMT) on Monday, sending the spacecraft streaking skyward.

Following separation from the rocket’s upper stage more than 2,300 miles (3,700 km) from Earth, Orion’s thrusters are due to fire to set the capsule on its outbound course, bringing it as close as about 60 miles (100 km) from the lunar surface before traveling roughly 40,000 miles (64,400 km) beyond the moon and back to Earth. The capsule is due for an Oct. 10 Pacific Ocean splashdown.

If successful, Artemis I would pave the way to a first crewed SLS-Orion mission, an out-and-back flight around the moon designated Artemis II, as early as 2024, followed a year or more later by an Artemis III trip to the lunar surface.

Artemis III will be much more complex, integrating the SLS-Orion with spacecraft to be built and flown by entrepreneur Elon Musk’s company SpaceX.

The plan would be for a four-person Orion crew to dock in space with a SpaceX lander to ferry two astronauts to the moon’s surface for nearly a week.