The success of Artemis I is establishing, the foundation for NASA’s newest push to the Moon. Its early success will pave the way to the next mission, Artemis II. The first flight of the Artemis Program ended with a successful splashdown in the Pacific Ocean on December 11. And now, NASA will review the data of Artemis I’s voyaging spacecraft, Orion, to prepare for Artemis II.

If the information leads to another launch-worthy vehicle, NASA will place the Artemis II mission into space at a tentative future date, perhaps in the next couple of years. When it takes off, Artemis II will bring the first humans back to the lunar environment since Apollo 17 in 1972. (Humans will step foot on the Moon in the subsequent mission, Artemis III.)

Both missions have a common goal: to find out how, exactly, humans can return to deep space, and perhaps one day reach Mars. But they are designed differently.

Inverse breaks down what you need to know about how the two missions vary.

Artemis I vs Artemis II flight plan and timespan

Artemis I spent twice as long in space than Artemis II will.

The Artemis I mission length time was 25.5 days. When Artemis I finally lifted off from NASA’s Kennedy Space Center in Florida on November 16, the world witnessed the first integrated demonstration of the Space Launch System(the lower, orange part of the towering vehicle), the Orion capsule on top, and the Exploration Ground Systems. The mission flew Orion to the Moon, enter a distant retrograde orbit (DRO), and then debuted a “skip entry” return in Earth’s atmosphere ahead of splashdown as Orion came back faster and hotter than any previous spacecraft designed for humans.

Orion entered DRO on November 25, and left this orbit just shy of a full week, on December 1. The mission went so well that NASA gave Orion seven new objectives to complete in DRO, that could help engineers better prepare for Artemis II and beyond. These included firing engines for about 100 seconds at a time, versus the 17-second maximum for single burns on Artemis I, and seeing solar array response. “We were looking at longer burn times that we know we’re going to need for future missions,” Debbie Korth, Orion Program Deputy Manager, told reporters on December 5. The team also elected to configure the heating systems on Orion’s powerhouse, the service module, to the settings they estimate for Artemis II. “We’re getting much better thermal response than we had originally anticipated… so this will help us refine those models, and be able to offer more capability as we move forward in the future missions,” Korth added.

Ten days later, it splashed down into the Pacific Ocean off the coast of California, where teams mobilized on behalf of NASA’s Exploration Ground Systems and the U.S. Navy to retrieve the uncrewed capsule.

But Artemis II — the crewed flight test — will only last 10.5 days. After launch, Artemis II will travel on a highly elliptical orbit around Earth for one day, and following that, Orion will soar towards the Moon. NASA will evaluate life support systems as part of its first day’s agenda.

“And at the end of that one day in high Earth orbit, Orion will essentially perform a mission completion maneuver… and put itself on a free return trajectory about four-and-a-half days out and four-and-a-half days back,” Mike Sarafin, Artemis I mission manager, told reporters on November 29, during a media briefing to announce that the Artemis I Orion had reached its farthest point from Earth.

The free return trajectory involves a trip from low-Earth orbit (LEO) out to the Moon and back. Renowned aeronautical engineer Angelo Miele described this trajectory as “where propulsive maneuvers are employed only at the departure from LEO and return to LEO.” According to Miele’s obituary from Rice University, “symmetric free-return trajectories were used by NASA in the missions from Apollo 1 to Apollo 11.”

Artemis Moon astronauts and mannequins

The only passengers on the Artemis I Orion capsule were bionic. The European Space Agency (ESA) supplied two female mannequin torsos, Helga and Zohar, to ride onboard. But arguably the most important human-like rider on Orion was “Commander Moonikin Campos,” a full dummy fitted with sensors and seated in an actual astronaut chair. ESA (which provided the European Service Module that propeled Orion through space) and NASA will review data across these experiments to shape how they’ll approach the crewed flight test, Artemis II.

The mannequins will give radiation data. One is fitted with protection, the other went bare around the Moon. Scientists will analyze the dosimeter data to learn more about what sort of exposure to highly-energized particles a crew could experience flying through space. The Moonikin’s seat also captured vibration data, to see how the force of splashdown transferred into the seat. Landing is the end of the mission, and it is one of the most critical safety phases to get correct.

Unique lunar orbits

The first Artemis astronauts to plant boots on the Moon will travel in a near rectilinear halo orbit (NRHO) as part of Artemis III. NRHO is an ideal but tricky path along the gravitational boundaries of Earth and its natural satellite. NASA’s CAPSTONE spacecraft is currently evaluating this flight path and its dynamics, but Artemis I and Artemis II are not in this orbit.

To test its systems, Artemis I flew around the Moon in DRO, another type of stable, fuel-efficient path. Artemis II will take humans into orbit around the Moon — but not land them — via a free return trajectory to and from Earth. Think of the classic spacefaring film Apollo 13 to better understand the journey Artemis II will take around the Moon, minus the frightening scenarios.

The Long Road Ahead — Both Artemis I and Artemis II are setting the baselines for Artemis III, when the first humans will land on the Moon since Apollo. NASA administrator Bill Nelson reiterated to reporters on November 29 that one of the two astronauts to touch the lunar regolith will be the first woman on the Moon. NASA has said that the Artemis Program also seeks to bring the first person of color to that far outpost.

Artemis I and Artemis II will pave the path for the more ambitious missions in development, by proving SLS’ performance, demonstrating Orion’s capabilities, and collecting data about the deep space environment.

One future spacecraft for the Artemis Program is in the works: an orbital facility around the Moon called Gateway. This lunar outpost would ride on the NRHO path CAPSTONE is traveling. Ideally, Gateway would be there for at least 15 years.

Jim Free, associate administrator for NASA’s Exploration Systems Development Mission Directorate, said last August that NASA is currently defining these later Artemis missions. By the time the space agency reaches the planning of Artemis IV, it will be “emotional.”

“At that point, we’re full steam ahead into our missions.”

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