Before joining NASA as a member of the first group of scientist-astronauts in June 1965, he worked at the U.S. Geological Survey's Astrogeology Center at Flagstaff, Arizona, developing geological field techniques that would be used by the Apollo crews.
Following his selection, Schmitt spent his first year at Air Force UPT learning to become a jet pilot.
Upon his return to the astronaut corps in Houston, he played a key role in training Apollo crews to be geologic observers when they were in lunar orbit and competent geologic field workers when they were on the lunar surface.
After each of the landing missions, he participated in the examination and evaluation of the returned lunar samples and helped the crews with the scientific aspects of their mission reports.

Schmitt spent considerable time becoming proficient in the CSM and LM systems.
In March 1970 he became the first of the scientist-astronauts to be assigned to space flight, joining Richard F. Gordon Jr. (Commander) and Vance Brand (Command Module Pilot) on the Apollo 15 backup crew.
The flight rotation put these three in line to fly as prime crew on the third following mission, Apollo 18.
When Apollo 18 and Apollo 19 were cancelled in September 1970, the community of lunar geologists supporting Apollo felt so strongly about the need to land a professional geologist on the Moon, that they pressured NASA to reassign Schmitt to a remaining flight.
As a result, Schmitt was assigned in August 1971 to fly on the last mission, Apollo 17, replacing Joe Engle as Lunar Module Pilot.
Schmitt landed on the Moon with commander Gene Cernan in December 1972.

Schmitt claims to have taken the photograph of the Earth known as The Blue Marble, possibly one of the most widely distributed photographic images in existence.
NASA officially credits the image to the entire Apollo 17 crew.

While on the Moon's surface, Schmitt — the only geologist in the astronaut corps — collected the rock sample designated Troctolite 76535, which has been called "without doubt the most interesting sample returned from the Moon".
Among other distinctions, it is the central piece of evidence suggesting that the Moon once possessed an active magnetic field.

As he returned to the Lunar Module before Cernan, Schmitt is the next-to-last person to have walked on the Moon's surface.
Since the death of Cernan in 2017, Schmitt is the most recent person to have walked on the Moon who is still alive.

After the completion of Apollo 17, Schmitt played an active role in documenting the Apollo geologic results and also took on the task of organizing NASA's Energy Program Office.
Before joining NASA as a member of the first group of scientist-astronauts in June 1965, he worked at the U.S. Geological Survey's Astrogeology Center at Flagstaff, Arizona, developing geological field techniques that would be used by the Apollo crews. Following his selection, Schmitt spent his first year at Air Force UPT learning to become a jet pilot. Upon his return to the astronaut corps in Houston, he played a key role in training Apollo crews to be geologic observers when they were in lunar orbit and competent geologic field workers when they were on the lunar surface. After each of the landing missions, he participated in the examination and evaluation of the returned lunar samples and helped the crews with the scientific aspects of their mission reports.
Schmitt spent considerable time becoming proficient in the CSM and LM systems. In March 1970 he became the first of the scientist-astronauts to be assigned to space flight, joining Richard F. Gordon Jr. (Commander) and Vance Brand (Command Module Pilot) on the Apollo 15 backup crew. The flight rotation put these three in line to fly as prime crew on the third following mission, Apollo 18. When Apollo 18 and Apollo 19 were cancelled in September 1970, the community of lunar geologists supporting Apollo felt so strongly about the need to land a professional geologist on the Moon, that they pressured NASA to reassign Schmitt to a remaining flight. As a result, Schmitt was assigned in August 1971 to fly on the last mission, Apollo 17, replacing Joe Engle as Lunar Module Pilot. Schmitt landed on the Moon with commander Gene Cernan in December 1972.
Schmitt claims to have taken the photograph of the Earth known as The Blue Marble, possibly one of the most widely distributed photographic images in existence. NASA officially credits the image to the entire Apollo 17 crew.
While on the Moon's surface, Schmitt — the only geologist in the astronaut corps — collected the rock sample designated Troctolite 76535, which has been called "without doubt the most interesting sample returned from the Moon". Among other distinctions, it is the central piece of evidence suggesting that the Moon once possessed an active magnetic field.
As he returned to the Lunar Module before Cernan, Schmitt is the next-to-last person to have walked on the Moon's surface. Since the death of Cernan in 2017, Schmitt is the most recent person to have walked on the Moon who is still alive.
After the completion of Apollo 17, Schmitt played an active role in documenting the Apollo geologic results and also took on the task of organizing NASA's Energy Program Office.
Harrison Schmitt