Apollo 13 was the seventh crewed mission in the Apollo space program and the third meant to land on the moon. The craft was launched from Kennedy Space Center on April 11, 1970 but, the lunar landing was aborted after an oxygen tank in the service module (SM) failed two days into the mission. The crew  instead looped around the Moon and returned safely to Earth on April 17. A routine stir of an oxygen tank ignited damaged wire insulation inside it, causing an explosion that vented the contents of both of the SM’s oxygen tanks to space. Without oxygen, needed for breathing and for generating electric power, the SM’s propulsion and life support systems could not operate. The CM’s systems had to be shut down to conserve its remaining resources for reentry, forcing the crew to transfer to the LM as a lifeboat. With the lunar landing canceled, mission controllers worked to bring the crew home alive.

Although the LM was designed to support two men on the lunar surface for two days, Mission Control in Houston improvised new procedures so it could support three men, for four days. The crew experienced great hardship, caused by limited power, a chilly and wet cabin, and a shortage of potable water. There was a critical need to adapt the CM’s cartridges for the carbon dioxide scrubber system to work in the LM; the crew and mission controllers were successful in improvising a solution. The astronauts’ peril briefly renewed public interest in the Apollo program; tens of millions watched the splashdown in the South Pacific Ocean on their televisions. An investigative review board found fault with preflight testing of the oxygen tank and Teflon being placed inside it. The board recommended changes, including minimizing the use of potentially combustible items inside the tank; this was done for Apollo 14.

In 1961, U.S President John F Kennedy challenged his nation to land an astronaut on the moon by the end of the decade, with a safe return to Earth. NASA worked towards this goal incrementally, sending astronauts into space during Project Mercury and Project Gemini, leading up to the Apollo space program. The goal was achieved with Apollo 11, which landed on the moon on July 20, 1969. Niel Armstrong and Buzz Aldrin walked on the lunar surface while Michael Collins orbited the Moon in Command Module Columbia. The mission returned to Earth on July 24, 1969, fulfilling  Kennedy’s challenge. 

NASA had contracted for 15 Saturn V rockets to achieve the goal; at the time no one knew how many missions this would require. Since success was obtained in 1969 with the sixth Saturn V on Apollo 11, nine rockets remained available for a hoped-for total of ten landings. After the excitement of Apollo 11, the general public grew apathetic towards the space program and Congress continued to cut NASA’s budget; Apollo 20 was canceled. Despite the successful lunar landing, the missions were considered so risky that astronauts could not afford life insurance to provide for their families if they died in space.