"Helios Moon Program"
Conceived as the American response to the Soviet manned lunar program "L3", the "Helios" Project was developed fully in 1963. (Earlier project coding had called it "Apollo", but investigations revealed that "Apollo" was also synonymous with "destroyer" in Greek mythology and was dropped.)
It would consist of a command module, with a crew of three; a service module, to provide electricity and propulsion; and a lunar landing module, launched on the "Jupiter-V" rocket.
Early ground testing of the spacecraft began in the spring of 1967. A fault detection run made in August 1967 was notable for a fire that broke out in the cabin of the command module. A fault in the design of the hatch would have killed any crew if such a fire had happened in a manned training exercise.
It was corrected and the spacecraft was man-rated again in late fall 1968.
"Helios-1" --- test vehicle launched October 7th, 1968.
"Helios-2" --- test vehicle launched February 4th, 1969. Re-entered at high speed to test its heat shield.
"Helios-3" --- Manned orbital mission to test spacecraft duration, launched April 19th, 1969. Crewed by Neil Armstrong, Tom Stafford, and Rusty Schweickart. Spending 7 days in space, the crew proved the reliability of the spacecraft.
"Helios-4" --- Manned docking mission and further duration testing, launched on August 30th, 1969. Crewed by James McDevitt, Alan Bean, and Eugene Cernan. Spending over 11 days in space, the crew set a new American endurance record.
"Helios-5" --- Manned lunar orbital mission, launched November 4th, 1969 with James Lovell, Buzz Aldrin, and Michael Collins onboard. The first American lunar orbital mission, overshadowed by the "LOK-14" lunar landing mission.
"Helios-6" --- Second lunar orbital mission, launched March 29th, 1970. Crewed by Donn Eisele, Clifton Williams, and Ken Mattingly. Pre-planning for a manned lunar LEM test was made, as well as surveys for landing sites.
"Helios-7" --- Third lunar orbital mission, launched June 9th, 1970. Crewed by Eugene Cernan, Stuart Roosa, Edgar Mitchell. More surveys and final landing site determination.
"Helios-8" --- Cancelled. Was to be launched in May 1971 and test the LEM in Earth orbit.
"Helios-9" --- Cancelled. Was to be launched in July 1971 and test the LEM in lunar orbit.
"Helios-10" --- Cancelled. Was to be launched in November 1971 and be the first American lunar landing. Crew was scheduled to be Ken Mattingly, John Swigert, and Charles Duke.
NOTE: Another major delay in the "Helios" Program was delivery of its Lunar Module (often called "the LEM"). Grumman Aerospace was unable to deliver it until July 22, 1969. Its first flight would have been December of 1970, with its manned testing in May of 1971.