Artemis II: A Guide to the NASA Mission’s Key Terms & Milestones

NASA teams are finalizing preparations for the Artemis II mission, with the Space Launch System rocket positioned at Launch Complex 39B at the Kennedy Space Center. The agency targets a launch date of April 1, 2026, marking the beginning of a 10-day crewed journey that will venture farther into deep space than any human has traveled before.

This operation represents the first crewed flight of the Orion spacecraft and the first time humans have traveled beyond low Earth orbit since the Apollo 17 mission in 1972. The mission will carry four astronauts: NASA commanders Reid Wiseman, Victor Glover and Christina Koch, alongside Canadian Space Agency astronaut Jeremy Hansen. According to mission data, the flight is expected to set several human spaceflight records. Glover is positioned to grow the first person of color, Koch the first woman, and Hansen the first non-U.S. Citizen to travel to the Moon’s vicinity.

Pre-Launch Procedures and Terminology

As ground teams advance through the countdown, specific technical terminology will define the status of the vehicle. The rocket, known as the Space Launch System (SLS), will be loaded with cryogenic propellants. Personnel refer to liquid oxygen as LOX and liquid hydrogen as LH2. The fueling process occurs in multiple phases, including slow load, fast load, top-off, and replenishment.

Timeline management during this phase relies on two distinct clocks. L Minus indicates the time remaining until liftoff in hours and minutes. T Minus corresponds to specific events within the launch countdown sequence, such as the retraction of the crew access arm or engine ignition. If the launch team announces a hold, this signals a planned stoppage in the countdown. During a hold, the T Minus clock pauses to allow for tasks or to align the liftoff with a specific window, while the L Minus clock continues to run.

Hours before departure, the crew will enter the White Room, a controlled environmental area where they will don helmets and gloves. This precedes ingress, the process of boarding the Orion crew module, which will serve as their habitat for the duration of the mission. The spacecraft and rocket sit atop a mobile launcher, a ground structure used for testing, maintenance, and transport to the launch pad.

Liftoff and Ascent Sequence

The ground launch sequencer, a computer system responsible for commanding liftoff, will initiate the terminal count. This automated phase covers the final 10 minutes before departure. Following engine ignition and the activation of solid rocket boosters, the vehicle will undergo umbilical separation. This step disconnects power cables and fuel lines, representing the final physical link to the ground before the rocket ascends.

During the climb, the flight profile involves several critical stages. The core stage serves as the backbone of the rocket, housing engines, fuel tanks, and avionics—the electronic navigation and control systems. The solid rocket boosters are designated as SRBs. The launch abort system, known as LAS, remains ready during ascent. Two of its three motors can return the Orion capsule safely to Earth in the event of a malfunction, while the third motor is used to jettison the system shortly after liftoff if the launch proceeds nominally.

Approximately eight minutes after launch, the core stage will reach Main Engine Cutoff, or MECO. This event signals the shutdown and separation of the SLS core stage from the Interim Cryogenic Propulsion Stage (ICPS) and the Orion spacecraft. Following this separation, a zero-gravity indicator—a stuffed animal selected by the crew—will float within the cabin, visually confirming the astronauts have reached a space environment.

Orbital Maneuvers and Lunar Transit

Once in space, the mission relies on a series of ignitions, moments when the propulsion system activates to maintain trajectory or achieve novel orbits. Approximately 49 minutes after launch, the ICPS will perform a perigee raise maneuver. This ignition increases Orion’s altitude, placing it into a stable low Earth orbit.

Roughly one hour into the flight, the ICPS will ignite again for an apogee raise maneuver, pushing Orion into a higher orbit. Following this burn, the ICPS will separate from the spacecraft. Before the propulsion stage eventually disintegrates upon reentry over the Pacific Ocean, the Artemis II crew will practice proximity operations. They will maneuver Orion toward and around the ICPS, a demonstration of piloting skills required for future missions.

On the first day of flight, an additional perigee raise ignition will position Orion optimally for the translunar injection burn. This critical maneuver occurs on the second day and increases the spacecraft’s velocity, allowing it to depart circular Earth orbit and enter an elliptical trajectory toward the Moon. This will be the final major engine firing of the mission. The Orion service module, which provides power, propulsion, and thermal control, will deliver the thrust necessary to begin a four-day journey around the Moon.

Lunar Flyby and Return Trajectory

During the subsequent days, small trajectory correction ignitions will ensure Orion maintains the correct path. On the fifth day of flight, the spacecraft will enter the lunar sphere of influence, the point in space where the Moon’s gravity becomes stronger than Earth’s. The mission plan calls for Orion to fly around the far side of the Moon, reaching a distance of approximately 4,700 miles beyond the lunar surface.

After exiting the lunar sphere of influence, three small ignitions will secure the correct trajectory for splashdown, with the final adjustment occurring on the 10th day. Prior to reentry, the service module will separate from the crew capsule to expose the heat shield. This shield is designed to protect the astronauts during atmospheric reentry, where the spacecraft will travel at speeds of about 25,000 miles per hour.

Following the heat of reentry, drogue parachutes will deploy to begin slowing the descent, followed by pilot parachutes that deploy the three main parachutes. These reduce the capsule’s speed from approximately 209 miles per hour to 27 miles per hour. Once velocity is sufficiently reduced, the capsule will splash down in the Pacific Ocean off the coast of California. Recovery forces from the U.S. Navy are scheduled to retrieve the crew and vehicle.

The Artemis program is scheduled to continue with additional lunar missions later this decade, including an eventual arrival on the lunar surface.