Prior to joining NASA, he was chief of the Advanced Requirements Branch at Headquarters Air Defense Command.

[8] John Forrest, a U.S. Air Force orthopedic surgeon, was instrumental in preventing the amputation of Irwin's leg.

By his own account, the marriage failed after two years due to his poor, borderline cruel treatment of her, and he later stated that finding religion again made familial relationships much easier.

Following that assignment, Irwin served as backup lunar module pilot for the second Moon landing mission, Apollo 12.

[14] Between July 26 and August 7, 1971 – as the Apollo 15 lunar module pilot (LMP) – Irwin logged 295 hours and 11 minutes in space.

[1] This extra training is credited with allowing them to make one of the most important discoveries of the Apollo era, the Genesis Rock.

[17] The astronauts' physiological vital signs were being monitored back on Earth, and the flight surgeons noticed some irregularities in Irwin's heart rhythms.

[18] Charles Berry stated to Chris Kraft, deputy director of the Manned Spacecraft Center (MSC) at the time: "It's serious, [i]f he were on Earth.

He's getting one hundred percent oxygen, he's being continuously monitored, and best of all, he's in zero g. Whatever strain his heart is under, well, we can't do better than zero g."[18] During the post-trans-Earth injection (TEI) phase of the mission there wasn't much more for Irwin to do other than provide help with Al Worden's EVA to retrieve film magazines from the CSM's SIM bay, by donning a pressure suit and monitoring him.

[19] After the return of Apollo 15 to Earth, it was discovered that without authority the crew had taken 398 commemorative first day covers to the Moon of which a hundred were then sold to a German stamp dealer.

NASA had turned a blind eye to similar activities on earlier flights,[20] but on this occasion the administration reprimanded the astronauts, and they never received any funds from the sales.

Irwin had announced his intent to retire from the Air Force and resign from NASA prior to the reprimand.

[21] During a subsequent investigations by NASA, the Attorney General, and Congress, the astronauts surrendered the covers still in their possession; they were returned in 1983.

[21] Irwin and his wife stated that his Christian rebirth, which happened while he was in space, saved their marriage and made their lives much happier.

[25] Beginning in 1973, Irwin led several expeditions to Mount Ararat, Turkey, in search of the remains of Noah's Ark.

[26] In More Than Earthlings, Irwin wrote expressing his view that the Genesis creation narrative was real, literal history.

One occurred less than two years after Apollo 15, when Irwin was 43, while he was playing handball; he underwent an emergency triple bypass operation.

[29] Doctors from NASA doubted the incidents were related to space travel, and noted that pre-flight testing indicated him having a tendency for cardiac arrhythmias during strenuous exercise.