The Apollo programme

Neil Armstrong, the first person to set foot on the moon, died on 25 August. We take a look back at the Apollo programme that put him there.

Buzz Aldrin on the moon

Neil Armstrong spearheaded the greatest achievement in human history when, on 21 July 1969, he became the first of 12 people to set foot on the surface of the moon.

However the space programme that would ultimately take him there had begun several years earlier…

Small steps
The first mission of the Apollo lunar-landing programme was intended to be a test flight putting the the Command/Service module – the part designed to remain in orbit around the moon while the lander visits its surface – into Earth orbit.

However, during a test of the module’s power systems in January 1967, a number of design problems led to a fire in the cabin – killing its three crew, Gus Grissom, Edward White and Roger Chaffee.

The spacecraft underwent a major safety overhaul, particularly in the redesign of the inward-opening escape hatch, which the crew had not been able to open as the pressure in the cabin was higher than that of the outside atmosphere.

Although unmanned tests would continue, there would not be a manned test flight until that of Apollo 7 in October 1968.

The large Saturn V rockets needed to launch a spacecraft onto a lunar trajectory were not yet ready, and Apollo 7 was was taken into space by a smaller launch vehicle. The command module completed 163 orbits of the Earth in just under 11 days. The mission is perhaps most notable for the rejection of all its crew for any future space missions after the commander, Walter Schirra, developed a head cold, got irritable and began to ‘talk back’ to mission control and disobey instructions.

The Saturn V  rocket was ready for Apollo 8 in December 1968. Still the most powerful rocket ever built, it was made up of three expendable stages, each using up its fuel and then being jettisoned in order to shed most of the rocket’s substantial mass on the journey – on the launch pad, it weighed nearly three million kilogrammes.

The rocket propelled the mission’s command module into lunar orbit. Its crew of Frank Borman, Jim Lovell and William Anders were the first humans to see the Earth as a whole planet spinning through space, and to see the far side of the moon. Over the course of their six-day journey they completed 10 orbits of the moon.

Apollo 9 was the first flight with the lunar module attached to the command module, and Apollo 10 was a “dry run” of the epoch-making first successful mission to the surface of the moon.

Giant leap
A Saturn V rocket launched Neil Armstrong, lunar module pilot Buzz Aldrin and command module pilot Michael Collins from Florida on the morning of 16 July 1969.

After one and a half orbits of the Earth, the rocket’s third stage ignited to put the trio on course for the moon.

The spacecraft was now directly orbiting the Sun, and would require another rocket burn to put it in lunar orbit. Apollo 11’s engines fired on 19 July to leave it circling the moon.

The lunar module, Eagle,  detached the following day, with Armstrong and Aldrin descending towards the surface, touching down in the Sea of Tranquillity – but several miles west of the intended spot.

On the morning of 21 July, in a moment broadcast to television screens worldwide, Armstrong climbed down the Eagle’s ladder to the surface of the moon, uttering the famous first words to be spoken from the surface another world: “That’s one small step for [a] man, one giant leap for mankind.”

The crew collected samples of soil and rock, and left behind a commemorative plaque, a seismometer, a retroreflector to measure the distance to the moon using laser light beamed from Earth, and an American flag with a rod inside to keep it flying despite the absence of wind – which was knocked over by the Eagle’s exhaust gases when it returned to the command module on the evening of 21 July.

The command module splashed down in the Pacific Ocean on 24 July, and, after 18 days in quarantine, the crew received a hero’s welcome and extensively toured the world.

Unlucky 13
Apollo 12 repeated the achievement of its trailblazing predecessor without major setbacks, but the programme’s next mission is notable for being a “successful failure” – despite the moon landing being aborted, the crew made it safely back to Earth after an explosion in the oxygen tanks.

With the spacecraft about 200,000 miles from Earth, mission control gave the order to “stir” the tanks of hydrogen and oxygen – a regular procedure that helps keep quantity readings accurate. However an uncovered wire short-circuited the electronic systems and the tanks’ insulation caught fire.

Because Apollo 13 ran on fuel cells that converted hydrogen and oxygen to electricity and water, the loss of the tanks meant that the astronauts were short of both – and of air. Landing on the moon became impossible, and the astronauts’ priority was to make it back to Earth.

They succeeded by using the lunar module as a “lifeboat”, and swinging around the moon and making course-corrections manually – the commander Jim Lovell had to time the duration of rocket burns using his wristwatch. (Having previously commanded Apollo 8, Lovell is the only person to travel to the moon twice but never land there.)

Down to Earth
Apollo 14–17 achieved their objectives without further disasters, spending increasing amounts time on the surface and carrying out more and more scientific experiments there.

Apollo 14 commander Alan Shepard hit two golf balls there, with his second drive travelling for almost 400 m with no air resistance. Apollo 15 was the first moon mission to make use of the Lunar Rover, a buggy-like vehicle intended to give the astronauts greater mobility on the surface.

Apollo 16 visited the moon’s highland areas, whereas the others had landed in or near its “seas”.

After Apollo 17 landed, commander Eugene Cernan and lunar module pilot Harrison Schmitt spent a total of 22 hours exploring the surface. Cernan set a lunar landspeed record of 11.2 miles per hour in a Rover, just as he’d previously set a record for the fastest-travelling human ever when piloting the (non-landing) lunar module during Apollo 10, at 24 791 mph. Schmitt took the iconic “blue marble” photograph of the Earth.

Missions 18–20 of the programme were cancelled so that NASA’s Saturn V rockets could instead be used to launch the Skylab space station.

With the death of Neil Armstrong there are now only eight living men who’ve walked on the surface of the moon, and the youngest of them, Charles Duke, is 76 years old. No manned spaceflight has gone further than low Earth orbit since 1972.



Other IOP websites


Your guide to physics on the web