After ten orbits Armstrong and Aldrin entered the lunar module, Eagle, to prepare for separation from the command and service module, Columbia. Eagle was named after the bald eagle, the American national bird; Columbia was named in honour of the famous explorer and national figure, and with a nod in the direction of the fictional giant cannon, the Columbiad in Jules Vernes book From the Earth to the Moon. Co-incidentally, in the book, the Columbiad was situated near Tampa in Florida, only a hundred miles or so from Kennedy Space Center. It had been thought prudent to use less flippant call signs than those chosen by previous crews, which would be regarded as more appropriate for historical purposes if the landing was successful.

The mission patch on crew uniforms had been designed by Michael Collins, and originally depicted a bald eagle over a moonscape with wings spread, talons extended, and an olive branch in its beak. The outstretched claws were thought by the approval committee to be too menacing; and the design was modified to show the olive branch in its talons. Collins observed dryly that he '...hoped it dropped the olive branch before landing'.

Inside Eagle, Aldrin began to test the Primary Guidance Navigation and Control System, PGNCS or 'pings', as it was generally referred to. The task of pings was to fly Eagle down a predetermined flight path to the landing site. Armstrong could take over control if necessary with the aid of the Abort Guidance System (AGS or 'aggs') and fly the craft manually. Aggs, a second on-board computer, would run a similar program consecutively with pings and comparison between the two checked out and backed up the primary system.

Aldrin checked the alignment of the LM's Internal Measurement Unit (IMU), which supplied orientation data to the 'aggs and pings' system. The IMU sensed changes in the lander's orientation in relation to a theoretical flight path programmed into the computer. Gyroscopes and inertia sensors in the IMU registered Eagle's movements in the three planes of pitch, roll, and yaw, and fed the information to the computers for comparison. Once below 30,000 feet the computer would also have data from the landing radar; and pings could make corrections to the actual flight path by gimballing the descent engine and firing the attitude thrusters to keep the craft on course.

Once their pressure suits were connected into the LM's environmental system, Aldrin aligned the S-band antennae with the earth tracking station, while Armstrong checked out the VHF radio communication with Collins in the CSM. They completed their checks on all the LM's subsystems and, by the thirteenth orbit, were strapped into the restraining harness and ready for undocking.

GET 99:22 - Columbia and Eagle are about to pass around to the rear of the moon, where the craft undock; and Collins will visually check out Eagle to see that its landing legs are fully extended. The Capcom for the landing is astronaut Charlie Duke.

MCC: 'Apollo eleven, Houston. We're go for undocking, over.'

Armstrong: 'Roger, understand.'

Apollo 11 passed out of sight and communication with earth. Mission control transmitted their exchanges with Apollo 11 to an estimated one third of the world's population:

This is Apollo control at 100 hours and 14 minutes. We are now less than two minutes from re-acquiring the spacecraft on the 13th revolution... We're presently 25 minutes from the separation burn that will be performed by Mike Collins in the command module to give the lem and the CSM a separation of about two miles... We'll stand by now to re-acquire the spacecraft...

Columbia and Eagle undocked; and Armstrong pirouetted Eagle to allow Collins to check that the landing gear was down and locked. Collins observed, 'You've got a fine looking flying machine there, Eagle, despite the fact you're upside down.' Undocked and with their individual call signs, the two craft reappear from behind the moon keeping station with one another separated by about 1,000 feet.

MCC: 'Hello Eagle, Houston. We're standing by...'

Armstrong: 'Roger Houston... The Eagle has wings.'

GET 101:27 - Eagle and Columbia pass behind the moon again; and the LM's descent engine is started for a 30 second burn for the Descent Orbit Insertion (DOI) manoeuvre. This is to create a new elliptical orbit for Eagle with a low point ten miles above the lunar surface east of Apollo Landing Site 2, from where they can initiate the final phase of the landing. The second burn is the Powered Descent Initiation (PDI) burn, which will slow Eagle sufficiently to drop out of orbit and descend to the landing site.

GET 102:27 - Communication is breaking up between Eagle and Houston. The computer program controlling the High Gain aerial alignment is having difficulty tracking earth, as it is on the limit of its adjustment. Transmission between them has to be relayed to Eagle by Collins in Columbia. Houston recommends a ten degree yaw manoeuvre to align Eagle's aerial with earth. They are only five and a half minutes from beginning the powered descent. 'Eagle, Houston, if you read you're go for powered descent.' Collins relays the message on.

GET 102:33 - Eagle reaches the lowest point of its new elliptical orbit, 300 miles up range of the landing site, 50,000 feet over the western edge of the Mare Fecunditatis (Sea of Fertility). Flying face down and landing legs first, Armstrong now has to decide whether to commit to the landing. He starts the computers programmed flight plan and the engine restarts at 10 per cent power to initiate the PDI burn, then builds to its full thrust of 9,800 pounds, slowing Eagle's orbital speed so that its rate of descent increases and the craft begins its long drop towards the lunar surface.

Armstrong and Aldrin checked off landmarks on 'US 1', the unofficial name given to the landing site approach path. As they overflew the edge of the Sea of Tranquillity and the crater Maskelyne, Armstrong realized that, although their altitude and rate of descent are correct, they were arriving over their check positions about three seconds early. This meant that they were going to overshoot their target by about a mile for every second.

Eagle passed Maskelyne and three minutes into the burn Armstrong rolled the lander 180 degrees into a face up attitude to find themselves looking at the lunar sky with the earth framed in their windows. Eagle's ground ranging radar locked on and began feeding altitude readings back to the computer and the crews display panel.

GET 102:38 - Descending through 34,000 feet, an amber coloured alarm light comes on for the first time.

Armstrong: 'Program alarm... It's a 1202.'

The alarm warned that the onboard computer was showing a '1202 executive overload.' Neither of the crew could immediately recognize the coded alarm but programmer-engineer Steven Bales in MCC, acting as flight controller monitoring computer activity, recognized the signal and was able to advise them that there was no serious cause for concern. Mission control informed the crew, 'Roger, we got you, we're go on that alarm.'

The computer was trying to advise the crew that it was overloading and was diverting excess information from the ground ranging radar. Aldrin cancelled the alarm, but it continued to re-occur as they descended at a rate of 132 feet per second. On their return to earth, Steve Bales stood beside Armstrong and Aldrin in the White House Rose Garden and received the 'Medal of Freedom' in recognition of his decision to continue the mission.

GET 102:39 - At 25,000 feet pings cuts the engines to 60 per cent power and begins to pitch Eagle up so that the crew can begin to see the moonscape in the direction of the landing site through their observation windows. The alarm starts to flash again. Mission control reported:

Seven minutes thirty seconds into the burn... Altitude 16,300 feet.

Eagle, ten miles up range from the landing site was being taken by pings to a point in the descent flight plan 7,500 feet high and five miles up range, where it would fire Eagle's thrusters in a 'pitchover manoeuvre' to bring the spacecraft from its near horizontal attitude to 45 degrees off the vertical, allowing the crew to see the approaching landing site.

We are now in the approach phase...everything looking good. Altitude 5,200 feet.

Eagle continued to kill off its vertical descent rate, but still had forward speed. Armstrong took control of the attitude thrusters as Aldrin read off rate of descent and horizontal ground speed figures from the computer display. Armstrong called for the Landing Point Designator (LPD) readings, which he could align with two scales scribed on the LM's window to give him a line of sight to the precise point on the ground to which pings predicted the landing point would be. By blipping the hand controller Armstrong could command the computer to move the projected landing spot, which would alter the spacecraft's attitude, flying the craft to the re-designated site.

Altitude forty-two hundred feet.

At 3000 feet the alarm went off again. Aldrin reported: 'Program alarm... 1201.' Mission control gave the go-ahead to continue the descent.

Eagle approached its landing site with minimal forward and descent speeds, but it had already overshot the original target site by nearly four miles. As it descended through 600 feet towards the surface, Armstrong could see that they were heading towards the edge of a crater, West crater, which was surrounded by large boulders. He switched the guidance system to aggs, allowing him to take full manual control and fly Eagle directly through the hand controller in the manner of a helicopter.

Aldrin reported:

...400 feet (altitude), down at 9... 8 forward... (feet per second)... You're pegged on horizontal velocity...

Controlling the engine thrust with his left hand and the attitude thrusters with his right Armstrong increased the forward speed, overflying the crater and the boulder field while searching for a suitable place to set down. Mission control read out the estimated remaining fuel reserve as Aldrin continued to call out the instrument readings:

300 feet down at three and a half... 47 forward, slow it up... That's it's (LM's) shadow out there...

Armstrong and Aldrin could now see the shadow of the LM on the surface in front of them.

Altitude velocity light, three and a half down, 220 feet.. Coming down nicely, 200 feet, four and a half down... 100 feet three and a half down, nine forward.. 5 per cent [fuel remaining]... quantity light.. Okay 75 feet, things looking good...

Mission control reported that there was only 60 seconds worth of fuel remaining.

Lights on... sixty feet... down two and half... forward... forward... that's good... forty feet, down two and a half... picking up some dust...

As they approached the surface the crew's sight of the ground was being obscured by surface dust blown across it from the engine's efflux.

30 feet, two and a half down.. faint shadow.. four forward, four forward...drifting to the right a little...

Armstrong tried to correct Eagle's sideways drift and keep the craft's forward movement, so that touchdown would occur on ground he has just passed over, reducing the risk of putting a landing pad in an unseen crater. Mission control reported 30 seconds of fuel left.

Contact light

One of the three, five foot long probes extended under the landing gear pads touched the lunar surface and triggered a blue warning light on the dash display. Armstrong punched the engine stop button and Eagle settled onto the moons surface.

In a flurry of activity Aldrin disarmed the power circuits to the engine and called up the computer program 413 that stored the spacecraft's orientation at landing. This would serve as a base navigational reference which would have to be used by the abort guidance computer if they needed to make an immediate take-off.

Neil Armstrong reported:

Houston, Tranquillity base here. The Eagle has landed.

Mission supervisors and technicians in the control centre erupted in a spontaneous burst of applause and cheering as Armstrong's words came through.

Roger Tranq... Tranquillity, we copy you on the ground. You've got a bunch of guys about to turn blue, we're breathing again, thanks a lot.

GET 102:45:43 - Touchdown on the Sea of Tranquillity at 0.71 degrees North, 23.63 degrees East was at 3.17pm Houston time, 8.17pm GMT 20 July, 1969, with less than thirty seconds of fuel remaining.

The First Lunar EVA

One minute after touchdown, there was another decision for Armstrong to make: T1, stay/no stay. Was it safe to remain, or should they abort the mission and take off if the craft was in a precarious position? They began a countdown to prepare for an immediate take off, as they assessed their situation. The T1 extension would last only 4 minutes, the time during which they could take off, catch, and rendezvous with Collins in Columbia, who had passed overhead during the final minutes of Eagle's descent. Four minutes later with the landing established, mission control advised them that they were OK to stay until T2. This extended the stay time to at least two hours, the duration of Columbia's next orbit when it would have circled the moon and returned to a point where Eagle could launch to meet up. Meanwhile, mission control had also been busy,

This is Apollo control at 103 hours 44 minutes. We have some updated information on the landing point. It appears that the spacecraft Eagle touched down just about on the lunar equator at 23.46 degrees longitude, which would put it about four miles from the targeted landing point down range. At this point all LM systems seem to look very good.

T2 passed and Eagle was committed to stay. Armstrong and Aldrin abandoned the countdown and began to power down the lander. They described the view from the observation windows while configuring the lander to stay. Aldrin commented on their surroundings,

Ah, we'll get to the details of what's around here, but it looks like a collection of just about every variety of shape, angularity, granularity, about every variety of rock you could find. The colours are, well pretty much depending on how you're looking relative to the zero phase point. There doesn't appear to be too much of a general colour at all, however it looks as though some of the rocks and boulders, of which there are quite a few in the near area, it looks as though they're going to have some interesting colours to them over.

Armstrong added,

[The view from] the window is a relatively level plain cratered with a fairly large number of craters of the five to fifty foot variety and some ridges, small twenty, thirty feet high, I would guess, and literally thousands of little one and two foot craters around the area, we see some angular blocks out several hundred feet in front of us that are probably two feet in size and have angular edges. There is a hill in view, just about on the ground track ahead of us, difficult to estimate but might be half a mile, or a mile.

GET 105:00 - The crew take a meal and are scheduled to start a four hour rest period, prior to commencing the first Extra Vehicular Activity (EVA).

The mission planner's expectation that the crew would be able to sleep immediately after completing the first moon landing, during which Armstrong had registered a heart rate of 156 and Aldrin 125, was somewhat optimistic. They were about to step out onto another world and mission control concurred with the crew's plan to bring the moonwalk forward in the schedule. They began their preparations to go outside by donning their EVA Personal Life Support equipment.

The EVA suit, known as the Integrated Thermal Meteoroid Garment (ITMG), worn throughout the landing consisted of a multi layered garment costing over $100,000. Manufactured by the International Latex Corporation of Delaware, the outer layers were made from Mylar, an aluminiumised material which was designed to reflect direct sunlight and ward off possible hits from micro meteorites.

The innermost layer worn next to the skin, was a cotton, long john like, comfort garment called the Liquid Cooled Garment (LCG), which was equipped with a network of plastic tubes, through which cooling water was circulated next to the astronauts' skin to remove excess body heat within the suit. The next layer was a one piece, pressure bladder, made of thin neoprene rubber, to retain the inner oxygen pressure. To prevent this bladder ballooning when inflated, a restraint layer of stiff fabric, articulated joints and wire cables retained the suit's shape while allowing flexibility. Separate integrated gloves locked onto the pressure suit's metal cuff rings; and supplementary over-boots and gloves for use during the EVA went over them.

The suit was articulated at the ankles, knees, hips, elbows and shoulders to facilitate movement. Umbilical tubes connected the suit to the spacecraft's environmental system during the landing, but were connected to a Personal Life Support System (PLSS) backpack for the EVA. The inner pressure helmet consisted of a 0.25 inch thick 'Lexan' plastic globe that locked onto a neck ring on the pressure suit; and an outer plastic helmet incorporating two visors, one with a polarising finish and the second coated with a reflective metallic oxide to guard against direct sunlight.

The PLSS backpack unit was essentially a portable environmental unit which provided the oxygen, temperature regulation, and communication services to the suit. Manufactured by Hamilton Standard, the PLSS fed oxygen to the suit at a pressure of 3.8 pounds per square inch, circulating it by a fan through the suit and a lithium hydroxide filter to remove exhaled carbon dioxide. The cooling water from the inner LCG garment was circulated by a pump in the PLSS through the backpack and the suit in a closed loop. A secondary, expendable water supply from a header tank in the PLSS, removed the heat in the primary circuit through a heat exchanger coil. The secondary water circuit sublimated the heated water to the vacuum of space thereby removing the excess heat from the suit.

The PLSS also contained batteries and radio for communications on the lunar surface with the other astronaut and back to earth via a relay through the LM. Carried on top of the PLSS was an Oxygen Purge System (OPS) for use in an emergency, if either the PLSS or the suit failed. Operation of a toggle on the suits control panel could maintain suit oxygen pressure from a reserve oxygen bottle for up to an hour in the event of failure of either the suit or the PLSS, giving the astronaut time to return to the LM and plug into its environmental system. In all, the complete suite and PLSS backpack combination, referred to as Extra vehicular Mobility Unit (EMU), weighed more than the astronaut, but its use in weightless or one-sixth lunar gravity made it manageable.

GET 109:04 - The crew decompressed the LM, venting its oxygen into space and, with a little difficulty, pried the hatch open. Assisted by Aldrin, Armstrong backed through the hatch and out onto a porch at the top of the lander's ladder. By pulling a lanyard at the top of the access ladder he deployed the Modularised Equipment Stowage Assembly (MESA), which included a monochrome TV camera focussed on the ladder. As the camera came into operation, the first stark, grainy television pictures from the surface of the moon were transmitted back to earth; and an earth wide audience was able to see the figure of Armstrong descending the ladder to the lunar surface. He paused on the footpad of the lander.

I'm at the foot of the ladder. The lem footpads are only depressed in the surface about one or two inches, although the surface appears to be very, very fine grained, as you get close to it, it's almost like a powder. Now and then it's very fine... I'm going to step off the lem now...

From the landing pad Armstrong moved his left foot out and placed it on the surface of the moon.

That's one small step for man... one giant leap for mankind.

GET 109:24:26 - Armstrong stepped with his left foot onto the moon at 9.56pm Houston time, 20 July 1969. In London, England, it was 2.56am GMT 21 July, 1969; and in Canberra Australia 12.56pm AEST 21 July, 1969.

On the surface Armstrong described the lunar surface surrounding the craft and his footprint in the dust. He clipped a Hasselblad camera to the front of his suit and photographed the area under the lander and the footpads. He stepped back from Eagle's shadow into the sunlight to take more photographs of the LM and a panoramic view of the surrounding moonscape. Mission control meanwhile was becoming concerned that he should collect a 'contingency sample', one of the prime objectives of the mission, a sample of moon rock. In the event of having to abort the EVA at this early stage they wanted to be sure that they had a sample to return to earth.

Using a scoop with an extendible handle he scraped a sample from the surface and tried to put it into a pocket in his suits legging. Hampered by the suit it required Aldrin's guidance from the LM to get the pocket flap open and the sample into the pocket. Back on earth scientists breathed a sigh of relief as their object of the mission was secured.

Armstrong guided Aldrin out of the LM's hatch and down the ladder taking a photograph of him as he descended. Aldrin later remembered 'making sure not to lock it on the way out'. He stepped out onto the surface some 18 minutes 12 seconds behind Armstrong and described his surroundings as 'Magnificent desolation'. Aldrin had set a 16mm camera in the LM's window running exposures at one frame per second to record their movements around the spacecraft. They adjusted the TV camera lens to show themselves as they uncovered a plaque on the lander. It showed the two hemispheres of the earth with a message below:

Here Men from the Planet Earth First set Foot Upon the Moon.
JULY 1969, AD.
We Came in Peace for All Mankind.

Below the inscription it bore the signatures of the three crewmen and President of the United States, Richard Nixon.

Moving around on the surface did not prove difficult; but the astronauts were still hampered by the space suits, despite the low gravity. Various means of locomotion were tried and the one easiest to maintain was a bouncing walk dubbed the 'kangaroo hop', although their ability to stop or change direction required care due to their high centre of mass. Armstrong then relocated the TV camera to a point north of the LM showing the lander and its surrounding moonscape. They continued with a number of scheduled tasks and setting up experiments to be left behind on the surface.

The priority of the Apollo 11 mission was to establish a landing and, due to weight and time constraints, it carried only a limited scientific package. The Early Apollo Surface Experiment Package (EASEP) contained only two experiments to be left behind on the surface, a solar powered Passive Seismic Experiment (PSE) and a Laser Ranging Retro Reflector (LRRR). Aldrin deployed the PSE, a passive seismometer, the purpose of which was to measure seismic activity or 'moon quakes'. The instrument contained a weight which remained immobile while the remainder of the casing responded to tremors from the lunar landscape; and the relative motion between the weight and casing, converted to an electrical signal, was beamed back to earth. Power for the instrument came from two attached solar panels, converting sunlight to electricity. Accompanying the seismometer, the LRRR received a laser beam fired from earth and reflected it back, so that the exact distance from the earth to the moon could be measured from the returned beam.

Aldrin erected the Stars and Stripes flag, but he had difficulty getting the frame on which it was mounted to fully unfold; he also had problems getting the support pole far enough into the surface to stay upright. He then set out a Solar Wind Experiment (SWE). The SWE was a panel of thin sheet aluminium on a frame set to face the sun to record the passage of any free particles such as helium, neon, krypton, or xenon through the foil.

Armstrong meanwhile, carried on collecting for the bulk sample and using the Hasselblad camera. He also carried a second 'Gold' camera, named after radio-astronomer Thomas Gold. It was used for close-up stereoscopic surface photography to investigate Gold's theories on lunar surface composition. Gold had postulated that the lunar surface would be covered in a deep layer of loose dust, into which the spacecraft could sink without trace.

Aldrin only used the Hasselblad for a short period during the EVA, taking panoramic photographs around the lander and of the lander itself during his inspection of the craft. Consequently few photographs taken with the Hasselblad are of Armstrong on the lunar surface. Post flight analysis of the photo's revealed difficulties in identifying individual astronauts and lead to the introduction of 'commanders stripes', on later crew's suits and helmets to make individual identification in photographs easier.

Aldrin then carried out a number of mobility experiments, evaluating the ease with which they were able to move around in the one sixth gravity. With movement curtailed in the stiff suit he experimented with running, changes of direction, and stopping. Their perambulations were interrupted by mission control to bring them into the TV camera's field of view together to be addressed by the United States President, Richard Nixon from the White House's Oval Office.

Hello Neil and Buzz, I am talking to you by telephone from the Oval Room at the White House and this certainly has to be the most historic telephone call ever made. I just can't tell you how proud we all are of what you... For every American, this has to be the proudest day of our lives, and for people all over the world, I am sure they too join with America in recognizing what an immense feat this is. Because of what you have done, the heavens have become a part of man's world, and as you talk to us from the Sea of Tranquillity it inspires us to redouble our efforts to bring peace and tranquillity to earth. For one priceless moment, in the whole history of man, all the people on this earth are truly one. One in their pride in what you have done, and one in our prayers that you will return safely to earth.

Aldrin later recalled that among all the talk of peace and tranquillity he was concerned that the flag would not fall over in front of the television cameras. The proceedings were relayed to Collins circling above who was 'probably the only person around without television coverage'. In fact only four nations on earth, China, Albania, North Korea, and North Vietnam did not inform their populations of the landing, while the USSR made the announcement on a television broadcast some six hours after the event.

Armstrong continued to take the main bulk of rock samples, while Aldrin took core samples from the surface. He experienced extreme difficulty in driving the sampler tube into the surface more than a few inches; and with time running out, despite an extension of the EVA by 15 minutes, he was unable to complete all the scheduled sampling tasks.

At this point in the EVA, Armstrong had decided to carry out a small, unscheduled excursion of his own. During the landing he had overflown the large 'West Crater', into which pings had been directing the craft, and then a 30 yard wide 'Little West crater', some 50 yards from the landing point, which is the closest feature to Tranquillity Base on the otherwise flat mare. Unannounced, and out of sight of the television camera, Armstrong ran out to Little West Crater to take a panoramic photo of the crater, but didn't have time to take a sample from its interior. His trip used the last few minutes available to him before the astronauts began to close up the EVA.

Buzz, this is Houston. You have approximately three minutes until you must commence EVA termination activities, over. Neil, this is Houston. Anything else you can throw into the box would be acceptable.

Aldrin returned to the LM; and Armstrong hoisted the sample boxes, camera, and solar wind experiment using the Lunar Equipment Conveyor (LEC), which essentially was an endless looped lanyard and pulley, to transfer the samples up to the Aldrin on the LM's porch. Armstrong recorded his highest heart rate of 160 while using the LEC, which he had dubbed the 'Brooklyn Clothesline'. Aldrin's highest rate during the EVA had reached 125. With both astronauts inside the LM they depressurised the cabin and removed the PLSS packs, outer boots, and gloves. Connected back up to the LM's systems by umbilical they later depressurised the cabin again and jettisoned the backpacks and now redundant overgarments to compensate for the weight of rock samples.

The EVA had lasted for 2 hours 31 minutes, during which they collected a total of 44 pounds of lunar rock and dust. After answering a number of questions on various aspects of the EVA they finally settled down to a rest period of eight hours fitful sleep, during which Aldrin slept on the LM's floor while Armstrong laid across the engine cover with the aid of a jury rigged strap hammock for his legs. Neither of the crew slept well in the cramped conditions, both were cold and the environmental system pumps were noisy, preventing either of them resting. They were awake when the following morning's wake-up call from mission control came through to begin breakfast and the countdown to launch from the lunar surface.

Further Reading

• Apollo 11
• Apollo 11 - Return to Orbit
• The Apollo Missions, The Beginnings
• Project Apollo, Mission Planning
• Apollo Missions, Landing Site Selection
• Apollo Missions Earthbound Support Systems
• Apollo Missions - Astronaut Selection and Training
• The Saturn/Apollo Stack
• Apollo Pathfinders
• The Early Missions
• The Intermediate Missions
• Apollo 15 Exploration
• Apollo 16 Exploration
• Apollo 17 Exploration
• Skylab and Apollo-Soyuz
• Apollo Conclusion