20 July 1969


102:42:08 Duke: Roger. Copy. (Pause) Eagle, Houston. You’re Go for landing. Over.
102:42:13 Armstrong (on-board): Okay. 3000 at 70.
102:42:17 Aldrin: Roger. Understand. Go for landing. 3000 feet.
102:42:19 Duke: Copy.

102:42:19 Aldrin: Program Alarm. (Pause) 1201
102:42:24 Armstrong: 1201. (Pause) (On-board) Okay, 2000 at 50.
102:42:25 Duke: Roger. 1201 alarm. (Pause) We’re Go. Same type. We’re Go.
102:42:31 Aldrin: 2000 feet. 2000 feet.
102:42:33 Armstrong: (On-board) (With some urgency in his voice, possibly as he sees West Crater) Give me an LPD (angle).
102:42:34 Aldrin: Into the AGS, 47 degrees.
102:42:35 Duke: Roger. 
102:42:37 Armstrong (on-board): (Confirming Buzz’s LPD readout) 47. That’s not a bad looking area. (Garbled) Okay. (Pause) 1000 at 30 is good. What’s LPD?
102:42:41 Duke: Eagle, looking great. You’re Go. (Long Pause) Roger. 1202. We copy it.
102:43:01 Aldrin: 35 degrees. 35 degrees. 750. Coming down at 23 (feet per second).
102:43:07 Armstrong (on-board): Okay.
102:43:07 Aldrin: 700 feet, 21 (feet per second) down, 33 degrees.
102:43:10 Armstrong (on-board): Pretty rocky area.
102:43:11 Aldrin: 600 feet, down at 19.
102:43:15 Armstrong (on-board): I’m going to… 
102:43:16 Aldrin: 540 feet, down at…(LPD angle is) 30. Down at 15. (Pause)
102:43:26 Aldrin: Okay, 400 feet, down at 9 (feet per second). 58 (feet per second) forward.
102:43:32 Armstrong (on-board): No problem. 
102:43:33 Aldrin: 350 feet, down at 4. 
102:43:35 Aldrin: 330, three and a half down. (Pause)
102:43:42 Aldrin: Okay, you’re pegged on horizontal velocity. 
102:43:46 Aldrin: 300 feet (altitude), down 3 1/2 (feet per second), 47 (feet per second) forward. Slow it up.
102:43:52 Aldrin: 1 1/2 down. Ease her down. 270. 
102:43:58 Armstrong: Okay, how’s the fuel?
102:44:00 Aldrin: Eight percent. 
102:44:02 Armstrong (on-board): Okay. Here’s a…Looks like a good area here.
102:44:04 Aldrin: I got the shadow out there. 
102:44:07 Aldrin: 250 (feet altitude), down at 2 1/2, 19 forward. (Pause)
102:44:13 Aldrin: Altitude-velocity lights. 
102:44:16 Aldrin: 3 1/2 down, 220 feet, 13 forward. (Pause)
102:44:23 Aldrin: 11 forward. Coming down nicely.
102:44:25 Armstrong (on-board): Gonna be right over that crater. 
102:44:24 Aldrin: 200 feet, 4 1/2 down.
102:44:26 Aldrin: 5 1/2 down.
102:44:29 Armstrong (on-board): I got a good spot (garbled).
102:44:31 Aldrin: 160 feet, 6 1/2 down.
102:44:33 Aldrin: 5 1/2 down, 9 forward. You’re looking good.
102:44:40 Aldrin: 120 feet.
102:44:45 Aldrin: 100 feet, 3 1/2 down, 9 forward. Five percent (fuel remaining). Quantity light. 
102:44:54 Aldrin: Okay. 75 feet. And it’s looking good. Down a half, 6 forward.
102:45:02 Duke: 60 seconds (of fuel left before the ‘Bingo’ call). 
102:45:04 Aldrin: (Velocity) light’s on. 
102:45:08 Aldrin: 60 feet, down 2 1/2. (Pause) 2 forward. 2 forward. That’s good.
102:45:17 Aldrin: 40 feet, down 2 1/2. Picking up some dust. 
102:45:21 Aldrin: 30 feet, 2 1/2 down. (Garbled) shadow. 
102:45:25 Aldrin: 4 forward. 4 forward. Drifting to the right a little. 20 feet, down a half.
102:45:31 Duke: 30 seconds (until the ‘Bingo’ call).
102:45:32 Aldrin: Drifting forward just a little bit; that’s good. (Garbled) (Pause) 
102:45:40  Aldrin: Contact Light. 
102:45:43 Armstrong (on-board): Shutdown
102:45:44 Aldrin: Okay. Engine Stop. 
102:45:45 Aldrin: ACA out of Detent.
102:45:46 Armstrong: Out of Detent. Auto. 
102:45:47 Aldrin: Mode Control, both Auto. Descent Engine Command Override, Off. Engine Arm, Off. 413 is in. 
102:45:57 Duke: We copy you down, Eagle.
102:45:58 Armstrong (on-board): Engine arm is off. (Pause) Houston, Tranquility Base here. The Eagle has landed.
102:46:06 Duke: (Momentarily tongue-tied) Roger, Twan…(correcting himself) Tranquility. We copy you on the ground. You got a bunch of guys about to turn blue. We’re breathing again. Thanks a lot. (Source: NASA Official Transcript)



It began life as a rough model constructed of paperclips and wood. It was the first true spaceship, designed for operations exclusively outside the Earth’s atmosphere. It had a 100% mission completion rate and on one flight, was the slender thread that brought three astronauts back safe to Earth. It was built by the legendary Grumman Ironworks at Bethpage New York. It was the Lunar Excursion Module (LEM) later known as just the Lunar Module or LM. And thirty-eight years ago today, it was the vehicle that put the first men on the Moon.



Early in the decision-making process of how to get to the moon, two concepts were being considered – direct ascent to the moon or Earth-Orbit Rendezvous (EOR). In the first case, the moon landing would be accomplished by a single vehicle, shedding stages along the way. This would have required enormous lift capability (the Nova rocket) for launch from Earth and still have considerable mass for the return launch from the Moon. Alternately, EOR would launch components into Earth orbit where they would be assembled into a single vehicle which again, would land on the Moon. Like direct ascent, it would also have a substantial mass to both safely land on the Moon and launch to return to Earth. A guerilla-approach by supporters of the Lunar Orbit Rendezvous (LOR) eventually gained acceptance. One Saturn V would launch a spacecraft that was composed of modular parts. A command module would remain in orbit around the moon, while a lunar module would descend to the moon and then return to dock with the command module while still in lunar orbit. In contrast with the other plans, LOR required only a small part of the spacecraft to land on the Moon, thereby minimizing the mass to be launched from the Moon’s surface for the return trip. Now it was just a matter of designing the lunar lander…

The LEM contract was given to Grumman Aircraft Engineering and a number of subcontractors. Grumman had begun lunar orbit rendezvous studies in late 1950s and again in 1962. In July 1962 eleven firms were invited to submit proposals for the LEM. Nine did so in September, and Grumman was awarded the contract that same month. The contract cost was expected to be around $350 million. There were initially four major subcontractors — Bell Aerosystems (ascent engine), Hamilton Standard (environmental control systems), Marquardt (reaction control system) and Rocketdyne (descent engine).


The primary guidance, navigation and control system (PGNCS) on the LM was developed by the MIT Instrumentation Laboratory. The Apollo Guidance Computer was manufactured by Raytheon. A similar guidance system was used in the Command Module. A backup navigation tool, the Abort Guidance System (AGS), was developed by TRW.

Early configurations of the LEM included a forward docking port as it was believed the LEM crew would be active in docking with the Command /Service Module. Early designs included large curved windows. Configuration freeze did not start until April 1963 when the ascent and descent engine design was decided. In addition to Rocketdyne a parallel program for the descent engine was ordered from Space Technology Laboratories in July 1963, and by January 1965 the Rocketdyne contract was cancelled. As the program continued there were numerous redesigns to save weight (including "Operation Scrape"), improve safety, and fix problems. For example initially the module was to be powered by fuel cells, built by Pratt and Whitney but in March 1965 they were paid off in favor of an all battery design. The initial design had the LEM with three landing legs. Three legs, though the lightest configuration was the least stable if one of the legs were damaged during landing and the most stable, 5, was too heavy. The compromise was four landing legs. As features were dropped for weight consideration, the shape became more angular until it emerged as the LEM we all have come to know and love.

Development of the LM was problematic and by 1966 it was becoming clear to NASA that Grumman was going to have trouble making the very tight delivery timelines to ensure a lunar landing sometime in early 1968 (recall this was before the tragic Apollo 1 fire). Control of in-house costs was fairly efficient, estimates were, however, that by the end of June Grumman would spend $24 million more than its allotted funds. Moreover, since late 1965 Grumman’s scheduling position had been shaky, with delays indicated virtually across the board. In light of these severe overruns, Houston sent representatives to Bethpage to discuss cost-reduction measures. The reviews, lasting a month and a half, culminated in tightened test procedures and performance requirements. To make sure that cost-reduction measures were enforced, Grumman switched from quarterly to monthly meetings with its subcontractors, inviting the appropriate Houston subsystem manager to attend.

Despite these actions, lunar module costs had not leveled off by late spring. In-house cost control and forecasting had also begun to deteriorate, aggravating the problems already encountered. After a ten-day review, a review team reported its findings to company corporate officers and NASA officials with substantial recommendations on program management, costs, subcontractor control, and ground support equipment. To bring about the kind of cost forecasting and control that NASA wanted, Grumman adopted "work packages" – breaking the program down into manageable segments, with strict cost budgets, and assigning managers to ride herd on each package. By linking tasks to manpower, program managers could better judge and control work in progress. This approach was a real departure from the commodity-oriented approach used by Grumman until that time.

On top of the contracting difficulties, the LEM was running into technical and engineering difficulties with the navigation system, the rendezvous radar and the ascent  engines. The former were the source of considerable weight gain and yielded questionable performance and reliability. The latter, however, was causing grave concern as test runs had shown tendencies to rough running and excessive nozzle erosion. The problem was eventually solved though by combining efforts by Rocketdyne and Bell into a new engine which subsequently ran exceptionally well. Other challenges were likewise overcome.


The first LM flight was on January 22, 1968 when the unmanned LM-1 was launched on a Saturn IB for testing of propulsion systems in orbit. The next LM flight was aboard Apollo 9 using LM-3 on March 3, 1969 as a manned flight (McDivitt, Scott and Schweickart) to test a number of systems in Earth orbit including LM and CSM crew transit, LM propulsion, separation and docking. Apollo 10, launched on May 18, 1969, was another series of tests, this time in lunar orbit with the LM separating and descending to within 10 km of the surface.   The next flight would be the most famous – Apollo 11.

July 19, 1969.  Apollo 11 passes behind the Moon and fires its Service propulsion engine in order to enter lunar orbit. In the several orbits that followed, the crew got passing views of their landing site, the southern Sea of Tranquility about 20 km (12 mi) southwest of the crater Sabine D. The landing site was selected in part, because it had been characterized as relatively flat and smooth by the automated Ranger 8 and Surveyor 5 landers, as well as by Lunar Orbiter mapping spacecraft. It was therefore unlikely to present major landing or extra-vehicular activity (EVA) challenges.

July 20, 1969.  The lunar module (Eagle), separated from the Command Module (Columbia). Collins, alone aboard Columbia, inspected Eagle as it maneuvered before him to ensure the craft was not damaged. Armstrong and Aldrin used Eagle’s descent engine to right themselves and descend to the lunar surface.
As the landing began, Armstrong reported they were "running long" — Eagle was 4 seconds further along its descent trajectory than planned, and would land miles west of the intended site. The LM navigation and guidance computer reported several unusual "program alarms" as it guided the LM’s descent, taking the crew’s attention from the scene outside as the descent proceeded. In NASA’s Mission Control Center in Houston, Texas, controller Steve Bales told the flight director that it was safe to continue the descent in spite of the alarms; the computer was merely reporting it was over tasked and that nothing was wrong with the spacecraft. Once Armstrong returned his attention to the view outside it was apparent that the computer was guiding them toward a large crater with rocks scattered around it. Armstrong took manual control of the lunar module at that point, and with Aldrin’s assistance, calling out data from the radar and computer, guided it to a landing at 20:17 UTC on July 20 with about 30 seconds of fuel left. Armstrong’s first words after landing: "Houston, Tranquility Base here. The Eagle has landed."


 The one of the two remaining flight article LMs is LM-2, found today in the Smithsonian:

Oh, and the Soviets also had their design:

but it went nowhere…

  • Specifications: (Baseline LM)
    • Ascent Stage:
      • Crew: 2
      • Crew cabin volume: 6.65 m³ (235 ft3)
      • Height: 3.76 m (12.34 ft)
      • Diameter: 4.2 m (13.78 ft)
      • Mass including fuel: 4,670 kg (10,300 lb)
      • Atmosphere: 100% oxygen at 33 kPa (4.8 lb/in2)
      • Water: two 19.3 kg (42.5 lb) storage tanks
      • Coolant: 11.3 kg (25 lb) of ethylene glycol/water solution
      • RCS (Reaction Control System) Propellant mass: 287 kg (633 lb)
      • RCS thrusters: 16 x 445 N; four quads
      • RCS propellants: N2O4/UDMH
      • RCS specific impulse: 2.84 kN·s/kg
      • APS Propellant mass: 2,353 kg (5,187 lb)
      • APS thrust: 15.6 kN (3,500 lbf)
      • APS propellants: N2O4/Aerozine 50 (UDMH/N2H4)
      • APS pressurant: 2 x 2.9 kg helium tanks at 21 MPa
      • Engine specific impulse: 3.05 kN·s/kg
      • Thrust-to-weight ratio: 0.34 (in Earth gravity – The thrust was less than the weight on Earth, but enough on the Moon)
      • Ascent stage delta V: 2,220 m/s (7,280 ft/s)
      • Batteries: 2 x 296 Ah silver-zinc batteries
      • Power: 28 V DC, 115 V 400 Hz AC
    • Descent Stage:
      • Height: 3.2 m (10.5 ft)
      • Diameter: 4.2 m (13.8 ft)
      • Landing gear diameter: 9.4 m (30.8 ft)
      • Mass including fuel: 10,334 kg (22,783 lb)
      • Water: 1 x 151 kg storage tank
      • Power: 2 x 296 Ah silver-zinc batteries (secondary system)
      • Propellants mass: 8,165 kg (18,000 lb)
      • DPS thrust: 45.04 kN (10,125 lbf), throttleable to 4.56 kN (1025 lbf)
      • DPS propellants: N2O4/Aerozine 50 (UDMH/N2H4)
      • DPS pressurant: 1 x 22 kg supercritical helium tank at 10.72 kPa.
      • Engine specific impulse: 3050 N·s/kg
      • Descent stage delta V: 2,470 m/s (8,100 ft/s)
      • Batteries: 4 x 400 A·h silver-zinc batteries

Don’t forget to stop by the Tailhook Daily Briefing — today’s subject is

the YF4H-1 Phantom & Operation SAGEBURNER


  1. Great post! I was…not too old when this happened, but I remember it on TV. Years later, in grade school, I built a plastic model of the LEM.
    Amazing what America has done…

  2. Can it really have been that long ago? I was 14 that year, away at summer camp in northern Ontario, and with no TV we were all huddled around an old short-wave radio eagerly listening to every word. We had been following all of the communications between NASA and the Apollo astronauts from the launch, the landing on the moon, the walk, and right the way through to their being back home. Every evening the entire camp would gather down by the lake, wait for the moon to rise, and try to imagine what it must be like up there for the crew. You bet it was amazing…then and now! Thank you, sir!

    Veritas et Fidelis Semper

  3. Jeopardy

    One of the remaining Saturn V rockets (the one in Houston) was recently restored and the grand opening was today

  4. And to think some wackos think it was all a hoax!
    I like your website, I’ll bookmark you and I shall return.

  5. I was in Wakkanai, Japan on that day. I watched the landing in the wee, wee hours of the morning at one of those hole in the wall, “after-hours” places (commonly called a “snack”) after a night of socializing drinking with a bunch of Ops and maintenance types. We, including all the Japanese folks behind and in front of the bar, sat and watched in near silence and absolute, total, utter amazement. Words fail me as to the emotions that ran through that small group at that one particular small point in time. Keep in mind: the Viet Nam war was raging, protesters were in the streets, and the political climate was as bad, if not worse than it is now. We…Americans…desperately needed something great and good. And we got it.

    Perhaps the singular accomplishment of the generation that immediately preceded mine.

  6. Nose

    Great post,

    I always thought the most interesting part was the alarms. In your transcript, they repeatedly say “1201″ which was the alarm on the computer. The Radar Altimeter was feeding info too fast to the computer (we call it a computer, but it had less computing power than modern wristwatches). If that Bales guy weren’t so sharp – one book I read said he took apart the computer code and predicted the 1201 alarms, they might have had to scrub the Apollo 11 landing. As it was, they used a lot more fuel than planned.

    If you gave NASA an unlimited budget today it would take them 20 years to make it back to the moon and we would kill 20 people on the way.


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