KENNEDY SPACE CENTER, Fla. (AP) — NASA's Artemis II flight crew and launch teams conducted a Countdown Demonstration Test on Dec. 20, 2025, at Kennedy Space Center in Florida. The four astronauts—Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen—participated in the simulation. The test replicated launch procedures without an actual liftoff.
The demonstration validated the launch timeline for Artemis II, NASA's first crewed mission using the Space Launch System rocket and Orion spacecraft. Crew members donned Orion crew survival system spacesuits in the Neil A. Armstrong Operations and Checkout Building. They then performed a historic astronaut walkout and boarded the Orion spacecraft atop the SLS rocket. The exercise simulated the countdown to T-0, according to NASA officials.
Wiseman serves as mission commander, with Glover as pilot, Koch as mission specialist and Hansen as mission specialist, NASA said. Hansen represents the Canadian Space Agency. The team practiced suit checks, crew boarding and ground operations in the Launch Control Center firing rooms.
The test marks a key milestone ahead of the planned launch no later than April 2026, NASA stated. Artemis II will send the crew on a 10-day lunar flyby mission. It builds on the uncrewed Artemis I flight in 2022, which tested the SLS and Orion systems in orbit around the moon.
"This test marks the passage of a key milestone on America’s journey to the launchpad. We have many more to go," NASA said in a statement published Dec. 23, 2025.
The walkout echoed traditions from the Gemini, Apollo and space shuttle programs, as well as recent Commercial Crew missions, according to NASA. Crew members exited through double doors at the Armstrong building and proceeded to the launch pad.
Launch teams rehearsed procedures to ensure synchronization between the crew and ground personnel. The simulation focused on timeline validation and equipment checks, NASA reported. No issues were disclosed in the agency's initial release.
Artemis II will demonstrate capabilities for deep-space missions, including life support and navigation systems, according to NASA. The mission aims to fly the crew approximately 7,000 kilometers from the lunar surface for imaging and science operations.
"Artemis II builds on the success of the uncrewed Artemis I in 2022, and will demonstrate a broad range of capabilities needed on deep space missions," NASA stated in its mission overview.
The flight will advance NASA's goal of establishing a sustainable presence on the moon, targeting the south polar region for future landings. It will also support preparations for crewed missions to Mars, according to agency documents.
NASA highlighted the event in its 2025 year-in-review materials, describing it as part of accelerated exploration efforts. The agency published details on its website and NASA+ platform on Dec. 23, 2025, listing it among top recent news items.
The Countdown Demonstration Test, or CDDT, serves as a full dress rehearsal for launch operations. It de-risks the process by identifying potential issues before the actual flight date, NASA explained.
Artemis II represents the first U.S. crewed lunar mission since Apollo 17 in 1972. The program involves international partnerships, including Canada's contribution of Hansen to the crew.
Ground teams at Kennedy Space Center managed the test from the Launch Control Center. They coordinated with the crew to simulate all pre-launch activities up to the point of ignition.
NASA plans additional milestones before the 2026 launch window. These include further system checks and integration tests for the SLS and Orion.
The mission will test hardware for future elements, such as the Gateway lunar space station and Starship human landing system, according to NASA.
Science objectives include collecting data on lunar geology and radiation exposure in deep space. This information will inform Artemis III, which targets a crewed landing at the moon's south pole.
"NASA’s Artemis II mission... will advance the agency’s goal to land astronauts at the Moon’s south polar region and will help set the stage for future crewed Mars missions," NASA said in an August 2025 science overview.
The crew completed the test without reported anomalies. NASA described the event as a success in advancing the Artemis program's timeline.
Historical context ties the walkout to over 60 years of Space Coast traditions. Previous programs used similar rehearsals to ensure mission readiness.
Artemis II's launch is targeted for early 2026, with the exact date dependent on final preparations. NASA officials emphasized the test's role in maintaining schedule momentum.
The agency continues to partner with commercial entities, including SpaceX for related crew transport. These collaborations support broader exploration goals.
NASA released images of the event, credited to photographer Glenn Benson. The photos show the crew in suits during the walkout and boarding.
The test lasted several hours, simulating the full countdown sequence. Crew members remained in the spacecraft for the duration of the rehearsal.
This demonstration follows Artemis I's successful 25.5-day mission in 2022, which validated the rocket and capsule for human flight.
NASA's Artemis program aims to return humans to the moon and establish long-term operations. It positions the U.S. in the ongoing international race for lunar exploration.
Officials noted the CDDT's importance in a year marked by multiple exploration achievements. The test underscores progress toward sustainable deep-space travel.
