NASA recordings of the final 13 minutes of the Apollo 11 Moon landing capture the tension and the triumph of Neil Armstrong, Buzz Aldrin and Michael Collins's historic mission. Follow the radio communications between the astronauts and Mission Control during the lunar module's descent.
When did Apollo 11 land on the Moon?
Those 13 minutes to the Moon had been meticulously planned in the years building up to the first lunar landing mission, but this was still an unprecedented challenge for the Apollo Program.
Intermittent radio signal, unfamiliar computer alarms and a rocky landing site all tested astronauts Neil Armstrong and Edwin 'Buzz' Aldrin to their limits during the descent to the Moon's surface. Hearing how the astronauts and Mission Control responded to these problems in real time remains one of the most extraordinary records of the Apollo 11 Moon landing.
What did the astronauts say during the Apollo 11 Moon landings?
Despite signal problems, Armstrong and Aldrin managed to remain in communication with both Mission Control and third Apollo 11 astronaut Michael Collins orbiting above them in the command module.
Below is a full account of what was said during the landing phase, from the moment the lunar module began its powered descent to Armstrong's historic declaration: "The Eagle has landed."
The transcript is based on NASA videos and audio recordings of radio communications between the Apollo 11 lunar module and Mission Control. Where a phrase or term is unclear, we have attempted to explain in italics what the astronauts or Mission Control were referring to.
Apollo 11 Moon landing: minute by minute
Buzz Aldrin: One, zero. Ignition. Ten per cent.
Aldrin is confirming that the lunar module’s engine has been fired at 10 per cent of maximum power. This firing, beginning gently, is designed to slow the Eagle down in preparation for landing. The sequence has been calculated by the Apollo Guidance Computer (AGC), which performs a series of calculations and operations designed to help guide the lunar module to its destination. Currently the computer is running Programme 63 (P63), which manages the braking phase of the lunar landing.
Mission Control (speaking to Michael Collins): Columbia, Houston. We’ve lost them. Tell them to go aft omni. Over.
Mission Control in Houston is struggling to establish communication with the lunar module. Without reliable data and radio communications from the lunar module, the landing may have to be aborted. Mission Control asks astronaut Michael Collins in the command module Columbia to relay a message to Neil Armstrong and Buzz Aldrin telling them to try a different aerial, the ‘aft omni-directional antenna’.
Michael Collins (to the lunar module): They’d like to use the omni.
Buzz Aldrin: OK, we’re reading you relayed to us, Mike.
Michael Collins: Say again, Neil?
Michael Collins incorrectly thinks he’s talking to Neil Armstrong.
Buzz Aldrin: I’ll leave it in Slew.
Neil Armstrong: Relay to us.
‘Slew’ essentially means that Buzz Aldrin is keeping the antenna in manual mode so he can angle the aerial himself and try to establish better communication.
Buzz Aldrin: See if they have got me now. I’ve got good signal strength in Slew.
Michael Collins: OK. You should have him now, Houston.
Mission Control: Eagle, we got you now. It’s looking good. Over.
Buzz Aldrin: OK, rate of descent looks good.
Mission Control: Eagle, Houston. Everything’s looking good here. Over.
Buzz Aldrin: Roger. Copy.
Mission Control: Eagle, Houston. After yaw-around, [use] angles S-band pitch -9, yaw +18.
These are the angles that Mission Control is suggesting Aldrin use for the antenna after ‘yaw-around’ - the moment the lunar module will rotate during the next landing phase.‘Yaw’ is the term for an aircraft’s vertical axis rotation.
Aldrin: AGS and PGNS agree very closely.
Mission Control: Roger.
Aldrin is comparing the measurements from the main guidance system PGNS (Primary Guidance and Navigation System) and the back-up system AGS (Abort Guidance System).
Aldrin: Data on. Altitude’s a little high.
Aldrin: Houston, I’m getting a little fluctuation in the AC voltage now.
Mission Control: Roger.
Aldrin: Could be our meter maybe, huh?
Mission Control: Stand by. Looking good to us. You’re still looking good at three… coming up three minutes.
Aldrin: Rate of descent looks real good. Altitude’s right about on.
Armstrong: Our position checks down range show us to be a little long.
Mission Control: Roger. Copy.
While Aldrin is piloting the lunar module, Armstrong is looking through the window directly down onto the lunar surface, noting key landmarks and comparing them with notes he has prepared ahead of the mission. This is how he is able to judge that they may land “a little long”: beyond the planned landing site.
Aldrin: AGS is showing about 2 feet per second greater rate of descent [than the PGNS].
Aldrin is once again comparing the two guidance systems available to him.
Armstrong: I show us to be about… Stand by…
Aldrin: Altitude rate looks right down the groove.
Armstrong: Roger. About three seconds long. Rolling over.
By marking the time certain landmarks pass by the window, Armstrong calculates that they are three seconds too long. This equates to about three miles too long when it comes to the landing site.
When Armstrong says, “Rolling over”, he is announcing that he is preparing to rotate the lunar module so that the legs are pointing directly down at the Moon's surface. The lunar module's landing radar is positioned on the bottom of the lunar module. After the Eagle has rotated, Armstrong, Aldrin and Mission Control should begin to receive a signal from the radar telling them how high and how fast they are travelling.
Aldrin: Well I think it’s going to drop.
Aldrin is replying to a comment from Armstrong on board to keep an eye on the signal strength for communications with Mission Control.
Mission Control: Eagle, Houston…
Aldrin: OK Houston, the ED Batts are Go at four minutes.
ED Batts are 'explosive device batteries', which supply power to the devices that help operate the descent engines. Aldrin and Mission Control accidentally talk over each other at this point in the transmission, which is why Mission Control’s all-important next instruction - to continue the mission - is repeated.
Mission Control: Roger. You are Go. You are Go to continue powered descent. You are Go to continue powered descent.
Mission Control: And Eagle, Houston, we’ve got data drop-out. You’re still looking good.
As the lunar module rotates, radio reception continues to be a problem, as the static heard during this part of the recording makes clear.
Aldrin: OK, we’ve got good lock on.
Once the lunar module has 'rolled over', the landing radar is able to "lock on" to the Moon’s surface.
Aldrin: Altitude light’s out. Delta-H is minus 2,900 [feet].
Delta-H compares the landing radar altitude reading with the Primary Guidance and Navigation System (PGNS). These numbers should ideally be closely aligned. According to Aldrin, the radar shows an altitude 2,900 feet lower than that shown on the PGNS. In a few moments Armstrong will ask Mission Control to try understand why these numbers don't correlate.
Mission Control: Roger, we copy.
Aldrin: Got the Earth straight out our front window.
Armstrong: Houston, you looking at our Delta-H?
Mission Control: That’s affirmative.
Armstrong: Programme alarm.
This is the beginning of one of the most nerve-wracking parts of the Moon landing, the infamous ‘1202’ programme alarm. Mission Control does not immediately appear to register the urgency in Armstrong’s voice, and instead answers his previous query about their Delta-H.
Mission Control: It’s looking good to us. Over.
Armstrong: It’s a 1202.
Neither Armstrong nor Aldrin are sure what the 1202 programme alarm means, and are asking Mission Control for guidance.
Armstrong to Aldrin: Let’s incorporate [the landing radar data.]
Armstrong to Mission Control: Give us a reading on the 1202 programme alarm.
Mission Control: Roger, we got you. We’re Go on that alarm.
Mission Control has made the decision to continue the mission, despite the potential danger highlighted by this alarm. The 1202 programme alarm was a warning from the Apollo Guidance Computer that its core processing system had been overloaded. However, the computer had been designed so that even if this occurred, mission critical programmes would take priority.
Thanks to the rapid response from Apollo Guidance Computer specialist Jack Garman in Mission Control, flight controllers understood that as long as the alarms did not come in rapid succession the mission could continue. In all, there were four 1202 alarms and one related 1201 alarm during the lunar descent.
Armstrong: Roger. 330.
Mission Control: 6 plus 25. Throttle down.
Mission Control is instructing that the engine be throttled down six minutes and 35 seconds into the burn.
Aldrin: OK, looks like about 820…
Aldrin is interrupted by Mission Control.
Mission Control: 6 plus 25, throttle down.
Aldrin: Roger. Copy.
Armstrong: 6 plus 25.
Aldrin: Same alarm, and it appears to come up when we have a 16/68 up.
Mission Control: Roger. Copy.
Aldrin is trying to work out what the 1202 programme alarm means, and tells Mission Control that it may be linked to when he requests a data display from the computer ('16/68'). Instead of overloading the computer further, Mission Control will monitor the Delta-H reading and feed it back to Aldrin.
Mission Control: Eagle, Houston. We’ll monitor your Delta-H.
Aldrin: Yes it’s coming down beautifully.
The difference between the two computer guidance systems, Delta-H, appears to be reducing.
Armstrong: Roger. It looks good now.
Mission Control: Roger. Delta-H is looking good to us.
Aldrin: Wow! Throttle down.
Armstrong: Throttle down on time.
Mission Control: Roger. We copy throttle down.
Aldrin: You can feel it in here when it throttles down. Better than the simulator.
Aldrin is surprised by the feeling in the lunar module compared to his experience in the simulator during training. The fact that the throttle down manoeuvre has initiated at the correct time also suggests that the 1202 programme alarm has not interrupted key guidance programmes.
Mission Control: Rog.
Aldrin: AGS and PGNS look real close.
Aldrin again compares the two computer guidance systems. Remember, the Abort Guidance System (AGS) is their back-up system, and the astronauts’ only way out should something go wrong with the primary system.
Mission Control: At seven minutes you’re still looking great to us Eagle.
Aldrin: OK, I’m still on Slew so we may tend to lose as we gradually pitch over. Let me try Auto again now and see what happens.
Mission Control: Roger.
Aldrin is trying to switch the radio antenna back to automatic mode and let the computer take care of the positioning as the lunar module rotates.
Aldrin: OK, looks like it’s holding.
Mission Control: Roger. We got good data.
Mission Control: Eagle, Houston. It’s Descent Two fuel to monitor. Over.
Mission Control is telling the lunar module which fuel monitoring system to look at.
Armstrong: Going to Two.
Aldrin: Give us an estimated switchover time please, Houston.
Mission Control: Roger. Standby. You’re looking great at eight minutes.
Aldrin is asking Mission Control when the computer will switch from programme P63 to P64, the final approach phase of the lunar landing.
Mission Control: Eagle, you’ve got 30 seconds to P64.
Mission Control: Eagle, Houston. Coming up on 8:30 you’re looking great.
Mission Control: We copy.
P64 has been initiated.
Mission Control: Eagle, you’re looking great. Coming up nine minutes.
Armstrong: Manual attitude control is good.
Mission Control: Roger. Copy.
Armstrong is testing the manual controls of the lunar module. In video footage from the landing, the module can be seen gently rocking and rotating.
Mission Control: Eagle, Houston. You’re Go for landing. Over.
Aldrin: Roger. Understand. Go for landing. 3,000 feet. Programme alarm. 1201.
Mission Control: Roger. 1201 alarm.
Aldrin and Armstrong are facing yet another programme alarm. Mission Control react quickly to reassure them.
Mission Control: We’re Go. Same type. We’re Go.
Aldrin: 2,000 feet. 2,000 feet. Into the AGS, 47 degrees.
Mission Control: Roger.
Aldrin: 47 degrees.
In the lunar module, Armstrong is asking Aldrin for an LPD (Landing Point Designator). This refers to a scale on the window, marked in degrees, that shows where the computer is aiming for on the lunar surface.
Mission Control: Eagle, looking great. You’re Go.
Mission Control: Roger. 1202, we copy it.
Mission Control is acknowledging yet another computer alarm code.
Aldrin: 35 degrees.
Again, Aldrin is reading out the angle for the Landing Point Designator (LPD). From here on in he will regularly call out both the altitude and speed of descent. Armstrong meanwhile is closely analysing the lunar surface, as the computer appears to be guiding them towards a rocky landing site around a spot called West Crater.
Aldrin: 35 degrees. 750 [feet]. Coming down at 23 [feet per second].
Aldrin: 700 feet, 21 [feet per second] down, 33 degrees.
Aldrin: 600 feet, down at 19 [feet per second].
At this stage Armstrong assumes manual control of the lunar module’s attitude, allowing him to pilot towards a clearer landing site.
Aldrin: 540 feet, down at… [LPD angle] 30. Down at 15 [feet per second].
Aldrin: 400 feet, down at 9 [feet per second]. 58 [feet per second] forward.
Aldrin: 350 feet, down at 4.
Aldrin: 330, 3.5 down.
Aldrin: You’re pegged on horizontal velocity.
Aldrin: 300 feet, down 3.5. 47 forward. Slow it up. 1.5 down.
Aldrin: I got the shadow out there.
Aldrin is seeing the shadow of the lunar module on the Moon’s surface.
Aldrin: 250, down at 2.5. 19 forward.
Aldrin: Altitude, velocity lights.
Aldrin is reporting warning lights in the lunar module. These are caused because the landing radar has lost its lock on the surface.
Aldrin: 3.5 down. 220 feet. 13 forward.
Aldrin: 11 forward. Coming down nicely. 200 feet. 4.5 down. 5.5 down.
Aldrin: 160 feet. 6.5 down. 5.5 down. 9 forward. You’re looking good. 120 feet.
Aldrin: 100 feet. 3.5 down. 9 forward. 5 per cent. Quantity light.
“5 per cent” relates to the amount of fuel left available for the landing stage. With the fuel at this level, Mission Control has initiated a timer counting down to the moment where the lunar module will either have to land immediately – or abort. This is known as a ‘bingo’ call.
Aldrin: OK, 75 feet and it’s looking good. Down a half. 6 forward.
Mission Control: 60 seconds.
This is the amount of time the Eagle has left before the ‘bingo’ call.
Aldrin: Lights on. 60 feet. Down 2.5. Forward. Forward.
Aldrin: 40 feet, down 2.5. Picking up some dust.
Aldrin: 30 feet, 2.5 down… shadow.
Aldrin: 4 forward. 4 forward. Drifting to the right a little. 20 feet. Down a half.
Mission Control: 30 seconds.
Aldrin: Drifting forward just a little bit. That’s good.
Aldrin: Contact light.
A sensor hanging from the feet of the Eagle has touched the surface, setting off a light inside the lunar module.
Aldrin: OK engine stop. ACA out of detent. Mode control: both Auto. Descent Engine Command override: off. Engine arm: off. 413 is in.
All these announcements are related to the Apollo Guidance System, confirming that the lunar module has landed.
Mission Control: We copy you down, Eagle.
Armstrong: Houston, er… Tranquility Base here. The Eagle has landed.