The Apollo astronauts who ‘landed’ on the Moon, between 1969 and 1972, used the Lunar Excursion Module – later called the LM. I would like you to read the Wikipedia article below and then move on to the article on Problems with the LM. The discussion here is not whether a space craft landed on the Moon or not, but rather, did men land on the Moon using the Lunar Excursion Module?
Apollo 16 LM Orion on the lunar surface
|Designer||Thomas J. Kelly|
|Country of origin||United States|
|Applications||Manned lunar landing|
|Design life||75 hours (Extended)|
|Launch mass||33,500 pounds (15,200 kg) initial
36,200 pounds (16,400 kg) Extended
|Dimensions||23 feet 1 inch (7.04 m) high
13 feet (3.9 m) wide
13 feet (3.9 m) deep
overall, landing gear deployed
|Habitable Volume||113 cubic feet (3.19 m3)|
|Power||Batteries (28 volts)|
|First launch||January 22, 1968|
|Last launch||December 7, 1972|
|Last retirement||December 14, 1972|
Apollo LM diagram
[Information not in the list above: Cabin pressure 4.8 ±. 0.2 psia; Cabin temperature 75° F (23.8 C)]
The Apollo Lunar Module (LM), originally designated the Lunar Excursion Module (LEM), was the lander portion of the Apollo spacecraft built for the US Apollo program by Grumman Aircraft to carry a crew of two from lunar orbit to the surface and back. Designed for lunar orbit rendezvous, it consisted of an ascent stage and descent stage, and was ferried to lunar orbit by its companion Command/Service Module (CSM), a separate spacecraft of approximately twice its mass, which also took the astronauts home to Earth. After completing its mission, the LM was discarded. It was capable of operation only in outer space; structurally and aerodynamically it was incapable of flight through the Earth’s atmosphere. The Lunar Module was the first manned spacecraft to operate exclusively in the airless vacuum of space. It was the first, and to date only, crewed vehicle to land on a natural object in the solar system other than the Earth.
Six such craft successfully landed on the Moon between 1969 and 1972. A seventh provided propulsion and life support for the crew of Apollo 13 when their CSM was disabled by an oxygen tank explosion en route to the Moon.
The LM’s development was plagued with problems which delayed its first unmanned flight by about ten months, and its first manned flight by about three months. Despite this, the LM eventually became the most reliable component of the Apollo/Saturn space vehicle, the only component never to suffer a failure that significantly affected a mission.
The total cost of the LM for development and the units produced was $21.3B in 2016 dollars, adjusting from a nominal total of $2.2B using the NASA New Start Inflation Indices.
At launch, the Lunar Module sat directly beneath the Command/Service Module (CSM) with legs folded, inside the Spacecraft-to-LM Adapter (SLA) attached to the S-IVB third stage of the Saturn V rocket. There it remained through Earth parking orbit and the Trans Lunar Injection (TLI) rocket burn to send the craft toward the Moon.
Soon after TLI, the SLA opened and the CSM separated, turned around, came back to dock with the Lunar Module, and extracted it from the S-IVB. During the flight to the Moon, the docking hatches were opened and the LM Pilot entered the LM to temporarily power up and test its systems (except for propulsion). Throughout the flight, he performed the role of an engineering officer, responsible for monitoring the systems of both spacecraft.
After achieving a lunar parking orbit, the Commander and LM Pilot entered and powered up the LM, replaced the hatches and docking equipment, unfolded and locked its landing legs, and separated from the CSM, flying independently. The Commander operated the flight controls and engine throttle, while the Lunar Module Pilot operated other spacecraft systems and kept the Commander informed on systems status and navigational information. After visual inspection of the landing gear by the Command Module Pilot, the LM was withdrawn to a safe distance, then the descent engine was pointed forward into the direction of travel to perform the 30 second Descent Orbit Insertion burn to reduce speed and drop the LM’s perilune to within approximately 50,000 feet (15 km) of the surface, about 260 nautical miles (480 km) uprange of the landing site.
At this point, the engine was started again for Powered Descent Initiation. During this time the crew flew on their backs, depending on the computer to slow the craft’s forward and vertical velocity to near zero. Control was exercised with a combination of engine throttling and attitude thrusters, guided by the computer with the aid of landing radar. During the braking phase altitude decreased to approximately 10,000 feet (3.0 km), then the final approach phase went to approximately 700 feet (210 m). During final approach, the vehicle pitched over to a near-vertical position, allowing the crew to look forward and down to see the lunar surface for the first time. Finally the landing phase began, approximately 2,000 feet (0.61 km) uprange of the targeted landing site. At this point manual control was enabled for the Commander, and enough fuel reserve was allocated to allow approximately two minutes of hover time to survey where the computer was taking the craft and make any necessary corrections. (If necessary, landing could have been aborted at almost any time by jettisoning the descent stage and firing the ascent engine to climb back into orbit for an emergency return to the CSM.) Finally, 66 inch (1676 mm) long probes extending from three footpads of the lander touched the surface, activating the contact indicator light which signaled time for descent engine cutoff, allowing the LM to settle on the surface.
Beginning with Apollo 14, increased LM fuel was made available for the powered descent and landing, by using the CSM engine to achieve the 50,000-foot (15 km) perilune. After the spacecraft undocked, the CSM raised and circularized its orbit for the remainder of the mission.
When ready to leave the Moon, the LM would separate the descent stage and fire the ascent engine to climb back into orbit, using the descent stage as a launch platform. After a few course correction burns, the LM would rendezvous with the CSM and dock for transfer of the crew and rock samples. Having completed its job, the LM was separated and sent into solar orbit or to crash into the Moon.
The Lunar Module (originally designated the Lunar Excursion Module, known by the acronym LEM) was designed after NASA chose to reach the Moon via Lunar Orbit Rendezvous(LOR) instead of the direct ascent or Earth Orbit Rendezvous (EOR) methods. Both direct ascent and EOR would have involved landing a much heavier, complete Apollo spacecraft on the Moon. Once the decision had been made to proceed using LOR, it became necessary to produce a separate craft capable of reaching the lunar surface and ascending back to lunar orbit.
In July 1962, eleven firms were invited to submit proposals for the LEM. Nine companies responded in September, answering 20 specific questions posed by the NASA RFP in a 60-page limited technical proposal. Grumman Aircraft was awarded the contract two months later. Grumman had begun lunar orbit rendezvous studies in the late 1950s and again in 1961. 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 TRW’s Space Technology Laboratories (descent engine).
The Primary Guidance, Navigation and Control System (PGNCS) 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.
The Lunar Module was chiefly designed by Grumman aerospace engineer Thomas J. Kelly. The first LEM design looked like a smaller version of the Apollo Command/Service Module (a cone-shaped cabin atop a cylindrical propulsion section) with folding legs. The second design invoked the idea of a helicopter cockpit with large curved windows and seats, to improve the astronauts’ visibility for hover and landing. This also included a second, forward docking port, allowing the LEM crew to take an active role in docking with the CSM.
As the program continued, there were numerous redesigns to save weight, improve safety, and fix problems. First to go were the heavy cockpit windows, and the seats; the astronauts would stand while flying the LEM, supported by a cable and pulley system, with smaller triangular windows giving them sufficient visibility of the landing site. Later, the redundant forward docking port was removed, which meant the Command Pilot gave up active control of the docking to the Command Module Pilot; he could still see the approaching CSM through a small overhead window. These changes resulted in significant weight savings. Egress while wearing bulky Extra-Vehicular Activity (EVA) spacesuits was also facilitated by a simpler-opening forward hatch (32 x 32 inches).
A configuration freeze did not start until April 1963, when the ascent and descent engine designs were decided. In addition to Rocketdyne, a parallel program for the descent engine was ordered from Space Technology Laboratories (TRW) in July 1963, and by January 1965 the Rocketdyne contract was canceled.
Power was initially to be produced by fuel cells built by Pratt and Whitney similar to the CSM, but in March 1965 these were discarded in favor of an all-battery design.
The initial design had three landing legs. As any particular leg would have to carry the weight of the vehicle if it lands at any significant angle, three legs was the lightest configuration. However, it would be the least stable if one of the legs were damaged during landing. The next landing gear design iteration had five legs and was the most stable configuration for landing on an unknown terrain. That configuration, however, was too heavy and the designers compromised on four landing legs.
In June 1966, the name was changed to Lunar Module (LM), eliminating the word “excursion”. According to George Low, Manager of the Apollo Spacecraft Program Office, this was because NASA was afraid that the word “excursion” might lend a frivolous note to Apollo. After the name change from “LEM” to “LM”, the pronunciation of the abbreviation did not change, as the habit became ingrained among engineers, the astronauts, and the media to universally pronounce “LM” as “lem” which is easier than saying the letters individually.
To allow astronauts to learn lunar landing techniques, NASA contracted Bell Aerosystems in 1964 to build the Lunar Landing Research Vehicle (LLRV), otherwise known as “The Flying Bedstead,” which used a gimbal-mounted vertical jet engine to counter 5/6 of its weight to simulate the Moon’s gravity, in addition to its own hydrogen peroxide thrusters to simulate the LM’s descent engine and attitude control. Successful testing of two LLRV prototypes at the Dryden Flight Research Center led in 1966 to three production Lunar Landing Training Vehicles (LLTV) which along with the LLRV’s were used to train the astronauts at the Houston Manned Spacecraft Center. This aircraft proved fairly dangerous to fly, as three of the five were destroyed in crashes. It was equipped with a rocket-powered ejection seat, so in each case the pilot survived, including the first man to walk on the Moon, Neil Armstrong.
LM-1 was built to make the first unmanned flight for propulsion systems testing, launched into low Earth orbit atop a Saturn IB. This was originally planned for April 1967, to be followed by the first manned flight later that year. But the LM’s development problems had been underestimated, and LM-1’s flight was delayed until January 22, 1968, as Apollo 5. At that time, LM-2 was held in reserve in case the LM-1 flight failed, which did not happen.
LM-3 now became the first manned LM, again to be flown in low Earth orbit to test all the systems, and practice the separation, rendezvous, and docking planned for Apollo 8 in December 1968. But again, last-minute problems delayed its flight until Apollo 9 on March 3, 1969. A second, higher Earth orbit manned practice flight had been planned to follow LM-3, but this was canceled to keep the program timeline on track.
Apollo 10 launched on May 18, 1969, using LM-4 for a “dress rehearsal” for the lunar landing, practicing all phases of the mission except powered descent initiation through takeoff. The LM descended to 47,400 feet (14.4 km) above the lunar surface, then jettisoned the descent stage and used its ascent engine to return to the CSM.
The first manned lunar landing occurred on July 20, 1969 with the Apollo 11 LM Eagle. Four days later, the Apollo 11 crew in the Command Module Columbia splashed down in the Pacific Ocean, completing President John F. Kennedy’s goal of “landing a man on the Moon and returning him safely to the Earth.”
This was followed by precision landings on Apollo 12 (Intrepid) and Apollo 14 (Antares).
In April 1970, the Apollo 13 Lunar Module Aquarius played an unexpected role in saving the lives of the three astronauts after an oxygen tank in the Service Module ruptured, disabling the CSM. Aquarius served as a “lifeboat” for the astronauts during their return to Earth. Its descent stage engine was used to replace the crippled CSM Service Propulsion System engine, and its batteries supplied power for the trip home and recharged the Command Module’s batteries critical for re-entry. The astronauts splashed down safely on April 17, 1970. The LM’s systems, designed to support two astronauts for 45 hours (including twice depressurization and repressurization causing loss of oxygen supply), actually stretched to support three astronauts for 90 hours (without depressurization and repressurization and loss of oxygen supply).
Hover times were maximized on the last four landing missions by using the Service Module engine to perform the initial Descent Orbit Insertion burn 22 hours before the LM separated from the CSM, a practice begun on Apollo 14. This meant that the complete spacecraft, including the CSM, orbited the Moon with a 9.1-nautical-mile (16.9 km) perilune, enabling the LM to begin its powered descent from that altitude with a full load of descent stage fuel, leaving more reserve fuel for the final approach. The CSM would then raise its perilune back to the normal 60 nautical miles (110 km).
Extended J-class missions
The Extended Lunar Modules (ELM) used on the final three “J-class missions”, Apollo 15, 16 and 17, were significantly upgraded to allow for greater landing payload weights and longer lunar surface stay times. The descent engine power was improved by the addition of a 10-inch (250 mm) extension to the engine bell, and the descent fuel tanks were increased in size. A waste storage tank was added to the descent stage, with plumbing from the ascent stage. These upgrades allowed stay times of up to 75 hours on the Moon.
The Lunar Roving Vehicle was carried folded up outside Quadrant 1 of the ELM descent stage and deployed by the astronauts after landing. This allowed them to explore large areas and return a greater variety of lunar samples.
Note that weights varied from mission to mission; those given here are an average for the non-ELM class vehicles. See the individual mission articles for each LM’s weight.
The Ascent stage contained the crew cabin with instrument panels and flight controls. It contained its own Ascent Propulsion System (APS) engine and two hypergolic propellanttanks for return to lunar orbit and rendezvous with the Apollo Command/Service Module. It also contained a Reaction Control System (RCS) for attitude and translation control, which consisted of sixteen hypergolic thrusters similar to those used on the Service Module, mounted in four quads, with their own propellant supply. A forward EVA hatch provided access to and from the lunar surface, while an overhead hatch and docking port provided access to and from the Command Module.
Internal equipment included an environmental control (life support) system; a VHF communications system with two antennas for communication with the Command Module; a unified S-band system and steerable parabolic dish antenna for communication with Earth; an EVA antenna resembling a miniature parasol which relayed communications from antennas on the astronauts’ Portable Life Support Systems through the LM; primary (PGNCS) and backup (AGS) guidance and navigation systems; an Alignment Optical Telescope for visually determining the spacecraft orientation; rendezvous radar with its own steerable dish antenna; and an ice sublimation system for active thermal control. Electrical storage batteries, cooling water, and breathing oxygen were stored in amounts sufficient for a lunar surface stay of 48 hours initially, extended to 75 hours for the later missions.
During rest periods while parked on the Moon, the crew would sleep on hammocks slung crosswise in the cabin.
The return payload included the lunar rock and soil samples collected by the crew (as much as 238 pounds (108 kg) on Apollo 17), plus their exposed photographic film.
- Crew: 2
- Crew cabin volume: 235 cu ft (6.7 m3)
- Habitable volume: 113 cubic feet (3.19 m3)
- Crew compartment height: 7 ft 8 in (2.34 m)
- Crew compartment depth: 3 ft 6 in (1.07 m)
- Height: 9 ft 3.5 in (2.832 m)
- Width: 13 feet (3.9 m) wide
- Depth: 13 feet (3.9 m) wide
- Mass, dry: 4,740 lb (2,150 kg)
- Mass, gross: 10,300 lb (4,700 kg)
- Atmosphere: 100% oxygen at 4.8 psi (33 kPa)
- Water: two 42.5 lb (19.3 kg) storage tanks
- Coolant: 25 pounds (11 kg) of ethylene glycol / water solution
- Thermal Control: one active water-ice sublimator
- RCS propellant mass: 633 lb (287 kg)
- RCS thrusters: sixteen x 100 lbf (440 N) in four quads
- RCS propellants: Aerozine 50 fuel / nitrogen tetroxide (N2O4) oxidizer
- RCS specific impulse: 290 s (2,840 N·s/kg)
- APS propellant mass: 5,187 lb (2,353 kg)
- APS engine: Bell Aerospace LM Ascent Engine (LMAE) & Rocketdyne LMAE Injectors
- APS thrust: 3,500 lbf (16,000 N)
- APS propellants: Aerozine 50 fuel / nitrogen tetroxide oxidizer
- APS pressurant: two 6.4 lb (2.9 kg) helium tanks at 3,000 pounds per square inch (21 MPa)
- APS specific impulse: 311 s (3,050 N·s/kg)
- APS delta-V: 7,280 ft/s (2,220 m/s)
- Thrust-to-weight ratio at liftoff: 2.124 (in lunar gravity)
- Batteries: two 28–32 volt, 296 ampere-hour silver-zinc batteries; 125 lb (57 kg) each
- Power: 28 V DC, 115 V 400 Hz AC
The Descent stage’s primary job was to support a powered landing and surface extravehicular activity. When the excursion was over, it served as the launch pad for the ascent stage. Octagon-shaped, it was supported by four folding landing gear legs, and contained a throttleable Descent Propulsion System (DPS) engine with four hypergolic propellant tanks. A continuous-waveDoppler radar antenna was mounted by the engine heat shield on the bottom surface, to send altitude and rate of descent data to the guidance system and pilot display during the landing. Almost all external surfaces, except for the top, platform, ladder, descent engine and heat shield, were covered in amber, dark (reddish) amber, black, silver, and yellow aluminized Kapton foil blankets for thermal insulation. The number 1 (front) landing leg had an attached platform (informally known as the “porch”) in front of the ascent stage’s EVA hatch and a ladder, which the astronauts used to ascend and descend between the cabin to the surface. The footpad of each landing gear contained a 67-inch (170 cm)-long surface contact sensor probe, which signaled the commander to switch off the descent engine. (The probe was omitted from the number 1 leg of every landing mission, to avoid a suit-puncture hazard to the astronauts, as the probes tended to break off and protrude upwards from the surface.)
Equipment for the lunar exploration was carried in the Modular Equipment Stowage Assembly (MESA), a drawer mounted on a hinged panel dropping out of the lefthand forward compartment. Besides the astronaut’s surface excavation tools and sample collection boxes, the MESA contained a television camera with a tripod; as the commander opened the MESA by pulling on a lanyard while descending the ladder, the camera was automatically activated to send the first pictures of the astronauts on the surface back to Earth. A United States flag for the astronauts to erect on the surface was carried in a container mounted on the ladder of each landing mission.
The Early Apollo Surface Experiment Package (EASEP) (later the Apollo Lunar Surface Experiment Package (ALSEP)), was carried in the opposite compartment behind the LM. An external compartment on the right front panel carried a deployable S-band antenna which, when opened looked like an inverted umbrella on a tripod. This was not used on the first landing due to time constraints, and the fact that acceptable communications were being received using the LM’s S-band antenna, but was used on Apollo 12 and 14. A hand-pulled Modular Equipment Transporter (MET), similar in appearance to a golf cart, was carried on Apollo 13 and 14 to facilitate carrying the tools and samples on extended moonwalks. On the extended missions (Apollo 15 and later), the antenna and TV camera were mounted on the Lunar Roving Vehicle, which was carried folded up and mounted on an external panel. Compartments also contained replacement Portable Life Support System (PLSS) batteries and extra lithium hydroxide canisters on the extended missions.
- Height: 10 ft 7.2 in (3.231 m) (plus 5 ft 7.2 in (1.707 m) landing probes)
- Width/depth, minus landing gear: 13 ft 10 in (4.22 m)
- Width/depth, landing gear extended: 31.0 ft (9.4 m)
- Mass including fuel: 22,783 lb (10,334 kg)
- Water: one 151 kg (333 lb) storage tank
- DPS propellant mass: 18,000 lb (8,200 kg)
- DPS engine: TRW LM Descent Engine (LMDE)
- DPS thrust: 10,125 lbf (45,040 N), throttleable between 10% and 60% of full thrust
- DPS propellants: Aerozine 50 fuel / nitrogen tetroxide oxidizer
- DPS pressurant: one 49-pound (22 kg) supercritical helium tank at 1,555 psi (10.72 MPa)
- DPS specific impulse: 311 s (3,050 N·s/kg)
- DPS delta-V: 8,100 ft/s (2,500 m/s)
- Batteries: four (Apollo 9-14) or five (Apollo 15-17) 28–32 V, 415 A·h silver-zinc batteries; 135 lb (61 kg) each
Lunar Modules produced
|Serial number||Name||Use||Launch date||Current location||Image|
|LM-1||Apollo 5||January 22, 1968||Reentered Earth’s atmosphere|
|LM-2||Intended for second unmanned flight; used instead for ground testing. Landing gear added for drop testing. Does not have optical alignment telescope and flight computer||On display at the National Air and Space Museum, Washington, DC|
|LM-3||Spider||Apollo 9||March 3, 1969||Descent and ascent stages reentered Earth’s atmosphere separately|
|LM-4||Snoopy||Apollo 10||May 18, 1969||Descent stage impacted Moon; Ascent stage in solar orbit. Snoopy is the only surviving flown LM ascent stage.|
|LM-5||Eagle||Apollo 11||July 16, 1969||Descent stage on lunar surface; Ascent stage left in lunar orbit (orbit decayed: impact location on Moon unknown)|
|LM-6||Intrepid||Apollo 12||November 14, 1969||Descent stage on lunar surface; Ascent stage deliberately crashed into Moon|
|LM-7||Aquarius||Apollo 13||April 11, 1970||Reentered Earth’s atmosphere|
|LM-8||Antares||Apollo 14||January 31, 1971||Descent stage on lunar surface; Ascent stage deliberately crashed into Moon|
|LM-9||Not flown (originally intended as Apollo 15, last H-class mission)||On display at the Kennedy Space Center (Apollo/Saturn V Center)|
|LM-10||Falcon||Apollo 15, first ELM||July 26, 1971||Descent stage on lunar surface; Ascent stage deliberately crashed into Moon|
|LM-11||Orion||Apollo 16||April 16, 1972||Descent stage on lunar surface; Ascent stage left in lunar orbit, eventually crashed on Moon|
|LM-12||Challenger||Apollo 17||December 7, 1972||Descent stage on lunar surface; Ascent stage deliberately crashed into Moon|
|LM-13||Not flown (originally intended as Apollo 18)||Partially completed by Grumman; restored and on display at Cradle of Aviation Museum, Long Island, New York. Also used during HBO’s 1998 mini-series From the Earth to the Moon.|
|LM-14||Not flown (originally intended as Apollo 19)||Never completed; unconfirmed reports claim that some parts (in addition to parts from test vehicle LTA-3) are included in LM on display at the Franklin Institute, Philadelphia.)|
|LM-15||Not flown (might have been Apollo Telescope Mount)||Scrapped|
|* For the location of LMs left on the Lunar surface, see the list of man-made objects on the Moon.|
Apollo Telescope Mount
One proposed Apollo Application was an orbital solar telescope constructed from a surplus LM with its descent engine replaced with a telescope controlled from the ascent stage cabin, the landing legs removed and four “windmill” solar panels extending from the descent stage quadrants. This would have been launched on an unmanned Saturn 1B, and docked with a manned Command/Service Module, named the Apollo Telescope Mission (ATM).
This idea was later transferred to the original wet workshop design for the Skylab orbital workshop and renamed the Apollo Telescope Mount to be docked on a side port of the workshop’s Multiple Docking Adapter (MDA). When Skylab changed to a “dry workshop” design pre-fabricated on the ground and launched on a Saturn V, the telescope was mounted on a hinged arm and controlled from inside the MDA. Only the octagonal shape of the telescope container, solar panels and the Apollo Telescope Mount name were kept, though there was no longer any association with the LM.
The Apollo LM Truck (also known as Lunar Payload Module) was a stand-alone LM descent stage intended to deliver up to 11,000 pounds (5.0 t) of payload to the Moon for an unmanned landing. This technique was intended to deliver equipment and supplies to a permanent manned lunar base. As originally proposed, it would be launched on a Saturn V with a full Apollo crew to accompany it to lunar orbit and guide it to a landing next to the base; then the base crew would unload the “truck” while the orbiting crew returned to Earth. In later AAP plans, the LPM would have been delivered by an unmanned lunar ferry vehicle.
Equipment location plans (1 of 2)
Equipment location plans (2 of 2)
Landing Gear plans
Apollo 15 landing on the Moon seen from the perspective of the Lunar Module Pilot. Starts at about 5000 feet.
Apollo 15 Lunar Module lifts off the Moon. View from TV camera on the Lunar Roving Vehicle.
Apollo 15 Lunar Module liftoff. View from inside LM.
Apollo 17 Lunar Module liftoff. View from TV camera on the lunar rover.[Wikipedia]
Problems with the LM
Some years ago I owned an old Volkswagen Kombi. It broke down a lot. When someone asked my wife why it broke down so often, she replied, “It’s a Volkswagen.” She would have got on well with Gus Grissom.
[Matt Groening]“Tis a fine barn, but sure ’tis no pool, English.”[Matt Groening]
Replace the word pool with spaceship and you get the message.
Take a good long look at the image above of one of the LMs. It’s a sorry sight. Why is it so battered? I certainly would be anxious about travelling to the Moon’s surface in that thing. It is little wonder that Virgil “Gus” Grissom hung a lemond on the LM that he and Chaffy and Robertson were going to use. Some-one once said to me, referring to another artist’s work, Í just can’t take it seriously’, and that is how I feel about the Landing Module.
Let’s look at some of the issues.
1. I realise that movement in a vacuum does not require aerodynamics. So they are off the hook there.
2. Vibration: When the LM is landing it is subject to the vibrational forces created by the 10,00lbs thrust descent engine. And when it is in takeoff, it still has the vibrations from its ascent engine. Astronauts have commented about the large amount of shaking felt during lift-off from Earth. Some of this shaking or vibrations will be from the effects of the Earth’s atmosphere. However it is ridiculous in the extreme to rule out altogether, the forces applied to the LM as it is in descent and ascent. The forces of vibrations would be shaking the astronauts so much, that when they were taking their voices would sound like a wobble. Try talking when you are in a car traveling over very rough ground. Voice communications from the LM to Earth would be difficult to understand. Yet in all the Apollo moon landings, the astronauts voices were smooth and quiet. Just like they were standing on a solid surface that was motionless.
3. Instability: When traveling in a vacuum, any light thrust will alter speed and or direction. As the LM is moving closer to the surface of the Moon, it is also being adjusted via maneuvering rockets located on the ascent module second. Because I cannot recreate this event, I have to use thought experiments. And in that I can see problems when the main thrust is being slowly reduced, the craft is still in some sort of órbit mode’ and astronauts are ‘driving’ their LMs horizontally. The practice landing module used at Houston, was never made stable. In fact Neil Armstrong on one of his training session with the practice craft almost lost his life when the vehicle became violently unstable and he ejected second before it smashed into the ground. When practicing in the LM simulator, no astronaut made a perfect soft landing. Yet later, 250,000 miles out in space 6 LMs were faultlessly piloted. That in itself is hard to believe. Even in our modern times, NASA has lost spacecraft.
4. Lack of Room:
Above we see Neil Armstrong inside the Lunar lander. There is precious little room for maneuvering. Put Aldrin in there as well suited up and how did they move around?
In this photograph Aldrin is in his spaceship ‘casual-wear’. You can see how little space there is if he was suited up like Amstrong. Now some people have said that they could have suited up separately. The first one egressing before the next gets into his spacesuit. But that would mean the second astronaut had to do it himself. No-one to help with the cumbersome suit. Also, for each egress the LM had to be depressurised so the astronaut could egress to space vacuum. That means the second guy, not suited up, would die.
Apollo Guidance Computer
The Apollo Guidance Computer (AGC) was a digital computer produced for the Apollo program that was installed on board each Apollo Command Module (CM) and Lunar Module (LM). The AGC provided computation and electronic interfaces for guidance, navigation, and control of the spacecraft. The AGC had a 16-bit word length, with 15 data bits and one parity bit. Most of the software on the AGC was stored in a special read only memory known as core rope memory, fashioned by weaving wires through magnetic cores, though a small amount of read-write core memory was provided.
Astronauts communicated with the AGC using a numeric display and keyboard called the DSKY (DiSplay&KeYboard, pronounced ‘DISS-key’). The AGC and its DSKY user interface were developed in the early 1960s for the Apollo program by the MIT Instrumentation Laboratory and first flew in 1966. The AGC is notable for being one of the first integrated circuit-based computers. The computer had a performance somewhere around that of the first generation of personal home computers like the Apple II, TRS-80, Commodore PET, which arrived in 1977.
Each flight to the Moon had two AGCs, one each in the Command Module and the Lunar Module, with the exception of Apollo 8 which did not take a Lunar Module on its lunar orbit mission. The AGC in the Command Module was at the center of that spacecraft’s guidance, navigation and control (GNC) system. The AGC in the Lunar Module ran its Apollo PGNCS (Primary Guidance, Navigation and Control System), with the acronym pronounced as pings.
Each lunar mission had two additional computers:
- The Launch Vehicle Digital Computer (LVDC) on the Saturn V booster instrumentation ring
- the Abort Guidance System (AGS, acronym pronounced as ‘ags’) of the Lunar Module, to be used in the event of failure of the LM PGNCS. The AGS could be used to take off from the Moon, and to rendezvous with the Command Module, but not to land.
The AGC was designed at the MIT Instrumentation Laboratory under Charles Stark Draper, with hardware design led by Eldon C. Hall. Early architectural work came from J.H. Laning Jr., Albert Hopkins, Richard Battin, Ramon Alonso,  and Hugh Blair-Smith. The flight hardware was fabricated by Raytheon, whose Herb Thaler was also on the architectural team.
The Apollo flight computer was the first computer to use integrated circuits (ICs). While the Block I version used 4,100 ICs, each containing a single three-input NOR gate, the later Block II version (used in the crewed flights) used 2,800 ICs, each with dual three-input NOR gates.:34 The ICs, from Fairchild Semiconductor, were implemented using resistor-transistor logic (RTL) in a flat-pack. They were connected via wire wrap, and the wiring was then embedded in cast epoxy plastic. The use of a single type of IC (the dual NOR3) throughout the AGC avoided problems that plagued another early IC computer design, the Minuteman II guidance computer, which used a mix of diode-transistor logicand diode logic gates.
The computer had 2048 words of erasable magnetic core memory and 36 kilowords of read-only core rope memory. Both had cycle times of 11.72 microseconds. The memory word length was 16 bits: 15 bits of data and one odd-parity bit. The CPU-internal 16-bit word format was 14 bits of data, one overflow bit, and one sign bit (ones’ complement representation).
The user interface to the AGC was the DSKY, standing for display and keyboard and usually pronounced dis-key. It had an array of indicator lights, numeric displays and a calculator-style keyboard. Commands were entered numerically, as two-digit numbers: Verb, and Noun. Verb described the type of action to be performed and Noun specified which data was affected by the action specified by the Verb command.
The numerals were displayed via green high-voltage electroluminescent seven-segment displays. The segments were driven by electromechanical relays, which limited the display update rate. Three five-digit signed numbers could also be displayed in octal or decimal, and were typically used to display vectors such as space craft attitude or a required velocity change (delta-V). Although data was stored internally in metric units, they were displayed as United States customary units. This calculator-style interface[nb 1] was the first of its kind, the prototype for all similar digital control panel interfaces.
The Command Module had two DSKYs connected to its AGC: one located on the main instrument panel and a second located in the lower equipment bay near a sextantused for aligning the inertial guidance platform. The Lunar Module had a single DSKY for its AGC. A flight director attitude indicator (FDAI), controlled by the AGC, was located above the DSKY on the commander’s console and on the LM.
In 2009, a DSKY was sold in a public auction held by Heritage Auctions for $50,788.
The AGC timing reference came from a 2.048 MHz crystal clock. The clock was divided by two to produce a four-phase 1.024 MHz clock which the AGC used to perform internal operations. The 1.024 MHz clock was also divided by two to produce a 512 kHz signal called the master frequency; this signal was used to synchronize external Apollo spacecraft systems.
The master frequency was further divided through a scaler, first by five using a ring counter to produce a 102.4 kHz signal. This was then divided by two through 17 successive stages called F1 (51.2 kHz) through F17 (0.78125 Hz). The F10 stage (100 Hz) was fed back into the AGC to increment the real-time clock and other involuntary counters using Pinc (discussed below). The F17 stage was used to intermittently run the AGC when it was operating in the standby mode.
The AGC had four 16-bit registers for general computational use, called the central registers:
A : The accumulator, for general computation Z : The program counter – the address of the next instruction to be executed Q : The remainder from the
DVinstruction, and the return address after
LP : The lower product after
There were also four locations in core memory, at addresses 20-23, dubbed editing locations because whatever was stored there would emerge shifted or rotated by one bit position, except for one that shifted right seven bit positions, to extract one of the seven-bit interpretive op. codes that were packed two to a word. This was common to Block I and Block II AGCs.
The AGC had additional registers that were used internally in the course of operation:
S : 12-bit memory address register, the lower portion of the memory address Bank/Fbank : 4-bit ROM bank register, to select the 1 kiloword ROM bank when addressing in the fixed-switchable mode Ebank : 3-bit RAM bank register, to select the 256-word RAM bank when addressing in the erasable-switchable mode Sbank(super-bank) : 1-bit extension to Fbank, required because the last 4 kilowords of the 36-kiloword ROM was not reachable using Fbank alone SQ : 4-bit sequence register; the current instruction G : 16-bit memory buffer register, to hold data words moving to and from memory X : The ‘x’ input to the adder (the adder was used to perform all 1’s complement arithmetic) or the increment to the program counter (Z register) Y : The other (‘y’) input to the adder U : Not really a register, but the output of the adder (the 1’s complement sum of the contents of registers X and Y) B : General-purpose buffer register, also used to pre-fetch the next instruction. At the start of the next instruction, the upper bits of B (containing the next op. code) were copied to SQ, and the lower bits (the address) were copied to S. C : Not a separate register, but the 1’s complement of the B register IN : Four 16-bit input registers OUT : Five 16-bit output registers
The instruction format used 3 bits for opcode, and 12 bits for address. Block I had 11 instructions:
DV(extra). The first eight, called basic instructions, were directly accessed by the 3-bit op. code. The final three were denoted as extracode instructions because they were accessed by performing a special type of
EXTEND) immediately before the instruction.
The Block I AGC instructions consisted of the following:
- An unconditional branch to the address specified by the instruction. The return address was automatically stored in the Q register, so the
TCinstruction could be used for subroutine calls.
CCS(count, compare, and skip)
- A complex conditional branch instruction. The A register was loaded with data retrieved from the address specified by the instruction. (Because the AGC uses ones’ complement notation, there are two representations of zero. When all bits are set to zero, this is called plus zero. If all bits are set to one, this is called minus zero.) The diminished absolute value (DABS) of the data was then computed and stored in the A register. If the number was greater than zero, the DABS decrements the value by 1; if the number was negative, it is complemented before the decrement is applied—this is the absolute value. Diminished means “decremented but not below zero”. Therefore, when the AGC performs the DABS function, positive numbers will head toward plus zero, and so will negative numbers but first revealing their negativity via the four-way skip below. The final step in
CCSis a four-way skip, depending upon the data in register A before the DABS. If register A was greater than 0,
CCSskips to the first instruction immediately after
CCS. If register A contained plus zero,
CCSskips to the second instruction after
CCS. Less than zero causes a skip to the third instruction after
CCS, and minus zero skips to the fourth instruction after
CCS. The primary purpose of the count was to allow an ordinary loop, controlled by a positive counter, to end in a
TCto the beginning of the loop, equivalent to an IBM 360’s
BCT. The absolute value function was deemed important enough to be built into this instruction; when used for only this purpose, the sequence after the
ADONE. A curious side effect was the creation and use of
CCS-holes when the value being tested was known to be never positive, which occurred more often than one might suppose. That left two whole words unoccupied, and a special committee was responsible for assigning data constants to these holes.
- Add the data retrieved at the address specified by the instruction to the next instruction.
INDEXcan be used to add or subtract an index value to the base address specified by the operand of the instruction that follows
INDEX. This method is used to implement arrays and table look-ups; since the addition was done on both whole words, it was also used to modify the op. code in a following (extracode) instruction, and on rare occasions both functions at once.
- A special instance of
INDEX25). This is the instruction used to return from interrupts. It causes execution to resume at the interrupted location.
- Exchange the contents of memory with the contents of the A register. If the specified memory address is in fixed (read-only) memory, the memory contents are not affected, and this instruction simply loads register A. If it is in erasable memory, overflow “correction” is achieved by storing the leftmost of the 16 bits in A as the sign bit in memory, but there is no exceptional behavior like that of
CS(clear and subtract)
- Load register A with the one’s complement of the data referenced by the specified memory address.
TS(transfer to storage)
- Store register A at the specified memory address.
TSalso detects, and corrects for, overflows in such a way as to propagate a carry for multi-precision add/subtract. If the result has no overflow (leftmost 2 bits of A the same), nothing special happens; if there is overflow (those 2 bits differ), the leftmost one goes the memory as the sign bit, register A is changed to +1 or −1 accordingly, and control skips to the second instruction following the
TS. Whenever overflow is a possible but abnormal event, the
TSwas followed by a
TCto the no-overflow logic; when it is a normal possibility (as in multi-precision add/subtract), the
TSis followed by
XCHto fixed memory) to complete the formation of the carry (+1, 0, or −1) into the next higher-precision word. Angles were kept in single precision, distances and velocities in double precision, and elapsed time in triple precision.
- Add the contents of memory to register A and store the result in A. The 2 leftmost bits of A may be different (overflow state) before and/or after the
AD. The fact that overflow is a state rather than an event forgives limited extents of overflow when adding more than two numbers, as long as none of the intermediate totals exceed twice the capacity of a word.
- Perform a bit-wise (boolean) and of memory with register A and store the result in register A.
- Multiply the contents of register A by the data at the referenced memory address and store the high-order product in register A and the low-order product in register LP. The parts of the product agree in sign.
- Divide the contents of register A by the data at the referenced memory address. Store the quotient in register A and the absolute value of the remainder in register Q. Unlike modern machines, fixed-point numbers were treated as fractions (notional decimal point just to right of the sign bit), so you could produce garbage if the divisor was not larger than the dividend; there was no protection against that situation. In the Block II AGC, a double-precision dividend started in A and L (the Block II LP), and the correctly signed remainder was delivered in L. That considerably simplified the subroutine for double precision division.
- Subtract (one’s complement) the data at the referenced memory address from the contents of register A and store the result in A.
Instructions were implemented in groups of 12 steps, called timing pulses. The timing pulses were named TP1 through TP12. Each set of 12 timing pulses was called an instruction subsequence. Simple instructions, such as TC, executed in a single subsequence of 12 pulses. More complex instructions required several subsequences. The multiply instruction (
MP) used 8 subsequences: an initial one called
MP0, followed by an
MP1subsequence which was repeated 6 times, and then terminated by an
MP3subsequence. This was reduced to 3 subsequences in Block II.
Each timing pulse in a subsequence could trigger up to 5 control pulses. The control pulses were the signals which did the actual work of the instruction, such as reading the contents of a register onto the bus, or writing data from the bus into a register.
Block I AGC memory was organized into 1 kiloword banks. The lowest bank (bank 0) was erasable memory (RAM). All banks above bank 0 were fixed memory (ROM). Each AGC instruction had a 12-bit address field. The lower bits (1-10) addressed the memory inside each bank. Bits 11 and 12 selected the bank: 00 selected the erasable memory bank; 01 selected the lowest bank (bank 1) of fixed memory; 10 selected the next one (bank 2); and 11 selected the Bank register that could be used to select any bank above 2. Banks 1 and 2 were called fixed-fixed memory, because they were always available, regardless of the contents of the Bank register. Banks 3 and above were called fixed-switchable because the selected bank was determined by the bank register.
The Block I AGC initially had 12 kilowords of fixed memory, but this was later increased to 24 kilowords. Block II had 32 kilowords of fixed memory and 4 kilowords of erasable memory.
The AGC transferred data to and from memory through the G register in a process called the memory cycle. The memory cycle took 12 timing pulses (11.72 μs). The cycle began at timing pulse 1 (TP1) when the AGC loaded the memory address to be fetched into the S register. The memory hardware retrieved the data word from memory at the address specified by the S register. Words from erasable memory were deposited into the G register by timing pulse 6 (TP6); words from fixed memory were available by timing pulse 7. The retrieved memory word was then available in the G register for AGC access during timing pulses 7 through 10. After timing pulse 10, the data in the G register was written back to memory.
The AGC memory cycle occurred continuously during AGC operation. Instructions needing memory data had to access it during timing pulses 7-10. If the AGC changed the memory word in the G register, the changed word was written back to memory after timing pulse 10. In this way, data words cycled continuously from memory to the G register and then back again to memory.
The lower 15 bits of each memory word held AGC instructions or data, with each word being protected by a 16th odd parity bit. This bit was set to 1 or 0 by a parity generator circuit so a count of the 1s in each memory word would always produce an odd number. A parity checking circuit tested the parity bit during each memory cycle; if the bit didn’t match the expected value, the memory word was assumed to be corrupted and a parity alarm panel light was illuminated.
Interrupts and involuntary counters
The AGC had five vectored interrupts:
- Dsrupt was triggered at regular intervals to update the user display (DSKY).
- Erupt was generated by various hardware failures or alarms.
- Keyrupt signaled a key press from the user’s keyboard.
- T3Rrupt was generated at regular intervals from a hardware timer to update the AGC’s real-time clock.
- Uprupt was generated each time a 16-bit word of uplink data was loaded into the AGC.
The AGC responded to each interrupt by temporarily suspending the current program, executing a short interrupt service routine, and then resuming the interrupted program.
The AGC also had 20 involuntary counters. These were memory locations which functioned as up/down counters, or shift registers. The counters would increment, decrement, or shift in response to internal inputs. The increment (Pinc), decrement (Minc), or shift (Shinc) was handled by one subsequence of microinstructions inserted between any two regular instructions.
Interrupts could be triggered when the counters overflowed. The T3rupt and Dsrupt interrupts were produced when their counters, driven by a 100 Hz hardware clock, overflowed after executing many Pinc subsequences. The Uprupt interrupt was triggered after its counter, executing the Shinc subsequence, had shifted 16 bits of uplink data into the AGC.
The AGC had a power-saving mode controlled by a standby allowed switch. This mode turned off the AGC power, except for the 2.048 MHz clock and the scaler. The F17 signal from the scaler turned the AGC power and the AGC back on at 1.28 second intervals. In this mode, the AGC performed essential functions, checked the standby allowed switch, and, if still enabled, turned off the power and went back to sleep until the next F17 signal.
In the standby mode, the AGC slept most of the time; therefore it was not awake to perform the Pinc instruction needed to update the AGC’s real time clock at 10 ms intervals. To compensate, one of the functions performed by the AGC each time it awoke in the standby mode was to update the real time clock by 1.28 seconds.
The standby mode was designed to reduce power by 5 to 10 W (from 70 W) during midcourse flight when the AGC was not needed. However, in practice, the AGC was left on during all phases of the mission and this feature was never used.
The AGC had a 16-bit read bus and a 16-bit write bus. Data from central registers (A, Q, Z, or LP), or other internal registers could be gated onto the read bus with a control signal. The read bus connected to the write bus through a non-inverting buffer, so any data appearing on the read bus also appeared on the write bus. Other control signals could copy write bus data back into the registers.
Data transfers worked like this: To move the address of the next instruction from the B register to the S register, an RB (read B) control signal was issued; this caused the address to move from register B to the read bus, and then to the write bus. A WS (write S) control signal moved the address from the write bus into the S register.
Several registers could be read onto the read bus simultaneously. When this occurred, data from each register was inclusive-ORed onto the bus. This inclusive-OR feature was used to implement the Mask instruction, which was a logical AND operation. Because the AGC had no native ability to do a logical AND, but could do a logical OR through the bus and could complement (invert) data through the C register, De Morgan’s theorem was used to implement the equivalent of a logical AND. This was accomplished by inverting both operands, performing a logical OR through the bus, and then inverting the result.
AGC software was written in AGC assembly language and stored on rope memory. The bulk of the software was on read-only rope memory and thus couldn’t be changed in operation, but some key parts of the software were stored in standard read-write magnetic-core memory and could be overwritten by the astronauts using the DSKY interface, as was done on Apollo 14.
The design principles developed for the AGC by MIT Instrumentation Laboratory, directed in late 1960s by Charles Draper, became foundational to software engineering—particularly for the design of more reliable systems that relied on asynchronous software, priority scheduling, testing, and human-in-the-loop decision capability. When the design requirements for the AGC were defined, necessary software and programming techniques did not exist so it had to be designed from scratch.
There was a simple real-time operating system designed by J. Halcombe Laning, consisting of the Exec, a batch job-scheduling using cooperative multi-tasking and an interrupt-driven pre-emptive schedulercalled the Waitlist which could schedule multiple timer-driven ‘tasks’. The tasks were short threads of execution which could reschedule themselves for re-execution on the Waitlist, or could kick off a longer operation by starting a ‘job’ with the Exec.
The AGC also had a sophisticated software interpreter, developed by the MIT Instrumentation Laboratory, that implemented a virtual machine with more complex and capable pseudo-instructions than the native AGC. These instructions simplified the navigational programs. Interpreted code, which featured double precision trigonometric, scalar and vector arithmetic (16 and 24-bit), even an
MXV(matrix × vector) instruction, could be mixed with native AGC code. While the execution time of the pseudo-instructions was increased (due to the need to interpret these instructions at runtime) the interpreter provided many more instructions than AGC natively supported and the memory requirements were much lower than in the case of adding these instructions to the AGC native language which would require additional memory built into the computer (at that time the memory capacity was very expensive). The average pseudo-instruction required about 24 ms to execute. The assembler and version control system, named YUL for an early prototype Christmas Computer, enforced proper transitions between native and interpreted code.
A set of interrupt-driven user interface routines called Pinball provided keyboard and display services for the jobs and tasks running on the AGC. A rich set of user-accessible routines were provided to let the operator (astronaut) display the contents of various memory locations in octal or decimal in groups of 1, 2, or 3 registers at a time. Monitor routines were provided so the operator could initiate a task to periodically redisplay the contents of certain memory locations. Jobs could be initiated. The Pinball routines performed the (very rough) equivalent of the UNIX shell.
Many of the trajectory and guidance algorithms used were based on earlier work by Richard Battin. The first command module flight was controlled by a software package called CORONA whose development was led by Alex Kosmala. Software for lunar missions consisted of COLOSSUS for the command module, whose development was led by Frederic Martin, and LUMINARY on the lunar module led by George Cherry. Details of these programs were implemented by a team under the direction of Margaret Hamilton. In total, software development on the project comprised 1400 person-years of effort, with a peak workforce of 350 people. In 2016, Hamilton received the Presidential Medal of Freedom for her role in creating the flight software.
The Apollo Guidance Computer software influenced the design of Skylab, Space Shuttle and early fly-by-wire fighter aircraft systems. The AGC code was uploaded to the internet in 2003, and the software itself was uploaded by a former NASA intern to GitHub on July 7, 2016.
A Block II version of the AGC was designed in 1966. It retained the basic Block I architecture, but increased erasable memory from 1 to 2 kilowords. Fixed memory was expanded from 24 to 36 kilowords. Instructions were expanded from 11 to 34 and I/O channels were implemented to replace the I/O registers on Block I. The Block II version is the one that actually flew to the moon. Block I was used during the unmanned Apollo 4 and 6 flights, and was on board the ill-fated Apollo I.
The decision to expand the memory and instruction set for Block II, but to retain the Block I’s restrictive three-bit op. code and 12-bit address had interesting design consequences. Various tricks were employed to squeeze in additional instructions, such as having special memory addresses which, when referenced, would implement a certain function. For instance, an
INDEXto address 25 triggered the
RESUMEinstruction to return from an interrupt. Likewise,
INDEX17 performed an
INHINTinstruction (inhibit interrupts), while
INDEX16 reenabled them (
RELINT). Other instructions were implemented by preceding them with a special version of
EXTEND. The address spaces were extended by employing the Bank (fixed) and Ebank (erasable) registers, so the only memory of either type that could be addressed at any given time was the current bank, plus the small amount of fixed-fixed memory and the erasable memory. In addition, the bank register could address a maximum of 32 kilowords, so an Sbank (super-bank) register was required to access the last 4 kilowords. All across-bank subroutine calls had to be initiated from fixed-fixed memory through special functions to restore the original bank during the return: essentially a system of far pointers.
The Block II AGC also has the mysterious and poorly documented
EDRUPTinstruction (the name may be a contraction of Ed’s Interrupt, after Ed Smally, the programmer who requested it) which is used a total of once in the Apollo software: in the Digital Autopilot of the Lunar Module. At this time, while the general operation of the instruction is understood, the precise details are still hazy, and it is believed to be responsible for problems emulating the LEM AGC Luminary software.
PGNCS generated unanticipated warnings during Apollo 11’s lunar descent, with the AGC showing a 1201 alarm (“Executive overflow – no vacant areas“) and a 1202 alarm (“Executive overflow – no core sets”). The cause was a rapid, steady stream of spurious cycle steals from the rendezvous radar (tracking the orbiting Command Module), intentionally left on standby during the descent in case it was needed for an abort.
During this part of the approach, the processor would normally be almost 85% loaded. The extra 6,400 cycle steals per second added the equivalent of 13% load, leaving just enough time for all scheduled tasks to run to completion. Five minutes into the descent, Buzz Aldrin gave the computer the command 1668 which instructed it to calculate and display DELTAH (the difference between altitude sensed by the radar and the computed altitude). This added an additional 10% to the processor workload, causing executive overflow and a 1202 alarm. After being given the “GO” from Houston, Aldrin entered 1668 again and another 1202 alarm occurred. When reporting the second alarm, Aldrin added the comment “It appears to come up when we have a 1668 up”. The AGC software had been designed with priority scheduling, and automatically recovered, deleting lower priority tasks including the 1668 display task, to complete its critical guidance and control tasks. Guidance controller Steve Bales and his support team that included Jack Garman issued several “GO” calls and the landing was successful. For his role, Bales received the US Presidential Medal of Freedom on behalf of the entire control center team and the three Apollo astronauts.
The problem was not a programming error in the AGC, nor was it pilot error. It was a peripheral hardware design bug that was already known and documented by Apollo 5 engineers. However, because the problem had only occurred once during testing, they concluded that it was safer to fly with the existing hardware that they had already tested, than to fly with a newer but largely untested radar system. In the actual hardware, the position of the rendezvous radar was encoded with synchros excited by a different source of 800 Hz AC than the one used by the computer as a timing reference. The two 800 Hz sources were frequency locked but not phase locked, and the small random phase variations made it appear as though the antenna was rapidly “dithering” in position, even though it was completely stationary. These phantom movements generated the rapid series of cycle steals.
J. Halcombe Laning’s software and computer design saved the Apollo 11 landing mission. Had it not been for Laning’s design, the landing would have been aborted for lack of a stable guidance computer.
These are the challenges we have here at the MoonHoax investigation program.
The lack of a landing crater and the lift-off investigation are in separate articles.
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