NASA is making major changes to its Artemis Moon program. On Friday, Administrator Jared Isaacman announced the space agency would carry out an additional flight in 2027 to test commercial lunar landers from SpaceX and/or Blue Origin.

The first crewed mission of the Artemis program won’t land on the moon, but it aims to take four astronauts farther from the Earth than anyone has gone before.

At the core of Isaacman’s concerns is the low flight rate of the SLS rocket and Artemis missions. During past exploration missions, from Mercury through Gemini, Apollo, and the Space Shuttle program, NASA has launched humans on average about once every three months. It has been nearly 3.5 years since Artemis I launched.