NASA announced that Apollo 10, scheduled for launch May 18, would be a lunar orbit mission during which two astronauts would descend to within 15,240 meters of the moon's surface.

The decision followed reviews of technical and operational data from the Apollo 9 earth-orbit mission. The prime crew would be astronauts Thomas P. Stafford, spacecraft commander; John W. Young, command module pilot; and Eugene A. Cernan, lunar module pilot. Backup crew members were L. Gordon Cooper, Jr., Donn F. Eisele, and Edgar D. Mitchell. With the exception of the actual landing, the mission plan was the same as for the lunar landing mission. Stafford and Cernan were to enter the LM, separate from the CSM, descend twice to within 16 kilometers of one of the preselected landing sites, and then rendezvous and dock with the CSM. Because of propellant limitations in the ascent stage, landing and subsequent liftoff from the moon would be impossible.