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.
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. Should the countdown be delayed beyond the two-hour window targeted for liftoff, NASA has set Sept. 2 and Sept. 5 as alternative launch dates.
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.
Orion will be carrying a simulated crew of three - one male and two female mannequins fitted with sensors to measure radiation levels that a real-life crew would encounter.
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. Those include SpaceX's heavy-duty Starship launch and lunar-landing vehicle, still under development, and components still to be constructed including an orbital fuel depot and space tankers. Even the new moon-walking suits remain to be designed.
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.