Colonel Carr was one of the 19 astronauts selected by NASA in April 1966. He served as a member of the astronaut support crews and as CAPCOM for the Apollo 8 and 12 flights, and was involved in the development and testing of the lunar roving vehicle which was used on the lunar surface by Apollo flight crews.

Carr was commander of Skylab 4 (third and final manned visit to the Skylab Orbital Workshop), launched November 16, 1973, and concluded February 8, 1974. This was the longest manned flight (84days, 1 hour, 15 minutes) in the history of American manned space exploration to date. He was accompanied on the record-setting 34.5-million-mile flight by Dr. Edward G. Gibson (science pilot) and William R. Pogue (pilot). The crew successfully completed 56 experiments, 26 science demonstrations, 15 subsystem detailed objectives, and 13 student investigations during their 1,214 revolutions of the earth. They also acquired extensive earth resources observations data using hand-held cameras and Skylab's Earth Resources Experiment Package camera and sensor array. They logged 338 hours of operation of the Apollo Telescope Mount which made extensive observations of the sun's solar processes.

From February 1974 until March 1978, Colonel Carr and his Skylab 4 teammates shared the world record for individual time in space: 2,017 hours 15 minutes 32 seconds, and Carr logged 15 hours and 48 minutes in three EVAs outside the Orbital Workshop.

In mid 1974 Carr was named head of the design support group, within the astronaut office, responsible for providing crew support to such activities as space transportation system design, simulations, testing, and safety assessment, and for development of man/machine interface requirements.

Carr retired from the United States Marine Corps in September of 1975 and from NASA in June of 1977. He is a Senior Consultant on Special Staff to the President of Applied Research, Inc., headquartered in Los Angeles, California, with offices in Santa Clara, California, and Houston, Texas.

Currently, Colonel Carr is President of CAMUS, Inc., Little Rock, Arkansas, and Director of the Arkansas Aerospace Education Center, Little Rock, Arkansas.

Carr is also working with fellow astronaut William Pogue on the Boeing Company's International Space Station Project, specializing in assembly EVA.