Artemis II just reached a point of no return. Next stop: The moon.

Artemis II has officially left Earth's neighborhood, with the Orion spacecraft now on a three-day leg of the deep space journey toward the moon.

After NASA polled "go" on translunar injection — or TLI, the key engine firing — flight controllers commanded the maneuver just before 8 p.m. ET on Thursday, April 2, less than 24 hours after the historic mission launched from Kennedy Space Center in Cape Canaveral, Florida. 

For the U.S. space agency, this moment is the real point of no return in a carefully orchestrated test flight. It's the last major engine firing of the mission. The burn not only pushes the capsule toward the moon, it also serves as the same critical maneuver that will eventually bring the astronauts home. 

That's riskier than NASA's usual spaceflights. On the International Space Station, astronauts circle Earth every hour and a half. If something goes wrong, they're never more than about 90 minutes from an emergency landing. But on Artemis II, as soon as controllers take this step, NASA has committed to the rest of the mission, save a couple of options for a U-turn, said crewmate Christina Koch. 

"Wrapping our heads around that is very interesting," said Koch, who is heading up those procedures, during a pre-launch news conference. "Before we go into some of our entry [simulations], we talk about how, 'Hey, there's no canceling the countdown on this — we are re-entering,' but the truth is, we are re-entering at the moment we do TLI."

The 10‑day Artemis II flight, led by Commander Reid Wiseman, pilot Victor Glover, and mission specialists Jeremy Hansen and Koch, aims to pave the way for a moon-landing during Artemis IV as early as 2028. This mission tests the resources needed for that upcoming journey: NASA's powerful rocket, the Orion spacecraft, and the teams on the ground who guide them. 

In future Artemis missions to the moon, the agency wants astronauts to practice living for longer periods away from Earth before pushing on to Mars, where crews will need far more extraterrestrial survival skills. 

So far the crew has set up the spacecraft toilet — with a few setbacks — and performed a piloting demonstration for steering toward and around the spent propulsion system. The exercise was meant to test how Orion's manual controls handle, as this will become necessary in future missions for docking with moon landers in space. 

The astronauts are also acclimating to life inside the capsule. The cabin has had unexpectedly cold temperatures. The crew unpacked extra long-sleeve shirts from their suitcases to try to warm up. 

At the end of Flight Day 1, the astronauts' sleep was disrupted by a middle-of-the-night, brief engine firing to adjust Orion's orbit around Earth. The ill-timed operation was part of the plan, and the crew returned to their sleeping bags for a few more hours of rest before the translunar injection burn. 

Koch set up Orion's system for the burn, performed by Orion's main engine on the European Service Module. The system provides enough thrust to accelerate a car from zero to 60 mph in less than three seconds.

The roughly six-minute engine firing was necessary to speed up the spacecraft so that it could escape Earth's gravitational pull. This technique allows the astronauts to travel without having to make major course corrections along the way. 

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The burn has reshaped the spacecraft's path into a long loop that will carry them out a quarter‑million miles from home. It will also harness the moon's gravity to slingshot Orion back to Earth. This is the first time since 1972 that humans have left Earth's orbit. 

The mission configuration is what's known as a free-return trajectory, said Lakiesha Hawkins, an exploration systems development administrator.

"This is something that we've experienced before," she said. "If you recall in your history, we did that on Apollo 8 and Apollo 13."