The program was encoded by routing wires through or around magnetic cores. Rope is read-only storage, not the working memory.
EDUCATIONAL RECONSTRUCTION · NO AGC CPU EMULATION
EAGLE / COMMANDER’S WINDOW
P66LM-5 / SEA OF TRANQUILITYSIM T+00:00
FINAL APPROACHILLUSTRATIVE TERRAIN / SI PHYSICS
Positive tilt → right · All times here are simulation time.
02 / INSIDE THE APOLLO COMPUTER
The computer that knew what mattered.
The flight is paused. Operate the DSKY alongside the original source. Return to Land the Eagle to resume.
Block II · memory & interface
Ferrite-core working storage held changing navigation and program data. A word carried 15 data bits and a parity bit.
The DSKY was the crew interface, not the computer itself. The AGC connected inertial navigation, radar, guidance calculations and control outputs.
Explore the executive alarms ↓ · History, people and limits ↓
READY / Set approximately 27% thrust to hover; lower it gently to descend. Keep the target within 40 m.
Flight checklist · read before your first landing
START begins the clock. Set hover thrust to stop accelerating downward; existing descent does not stop immediately. Add thrust briefly to reduce the descent rate, then ease back. Tilt left/right to change horizontal acceleration; level out and counter-tilt to brake. Sliders and target selection take over manual control.
Success limits: vertical speed ≤ 2.5 m/s, horizontal speed ≤ 1.5 m/s, tilt ≤ 8°, within 40 m of the selected site. These are museum training limits, not certified LM operating limits. Outside the envelope the attempt fails. Try guided mode to watch a complete model descent; you may take over at any time.
Within the flight console: Up/Down change thrust by 1%, Left/Right change tilt by 1°, Space pauses/resumes. Shortcuts do not intercept selects, buttons or sliders. Hidden tabs and the computer view pause the flight; return and resume explicitly. Restart restores the selected scenario. No audio, uploads or external runtime services.
HISTORICAL MISSION RECORD
GET / 1969P63BRAKINGP64APPROACHP66FINAL DESCENT
P63 · Powered descent ignition
NASA mission report, Table 5-I. Historical clock: independent of your flight. Select events; this is not live telemetry.
HOUSTON / MISSION CONTROL
CAPCOMWe're Go on that alarm.
Contact Light.
Houston, Tranquility Base here. The Eagle has landed.
Historical quotations: NASA Lunar Surface Journal. Transcript call times can differ from measured event times.
Your flight log · generated by the model
LUMINARY 099 / ORIGINAL SOURCE
LMY99 R001Original source, not an execution trace.
Loading local source…
Select an instruction above to inspect its meaning.
1201 / 1202 · FAULT TOLERANCE
An alarm. A restart.
A mission that continued.
The executive could not allocate another work area. 1202 meant no core sets; 1201 meant no VAC areas for interpretive jobs. Restart protection restored essential work instead of trying to finish every queued task.
Unexpected rendezvous-radar counter activity stole computer cycles. Steve Bales and Jack Garman helped Houston assess the alarms. This was not a computer that simply ignored errors.
INTERACTIVE EXPLANATION / NOT A CPU LOAD METER
Guidance & controlPROTECTED
Navigation updatePROTECTED
Nonessential display jobQUEUED
Select an alarm to see why lower-priority work could be discarded while the guidance task recovered. This demonstration does not inject a failure into your flight.
ENGINEERING, HISTORY & HONEST LIMITS
Small computer. Extraordinary responsibility.
Built by people
Eagle carried a Block II Apollo Guidance Computer. MIT’s Instrumentation Laboratory developed the Apollo guidance system under Charles Stark Draper. Raytheon manufactured the AGC hardware. Margaret Hamilton led the onboard flight software division; Hal Laning’s executive and restart design made scheduling and recovery central to the system. Don Eyles worked on lunar landing software. The achievement belonged to a much larger team, including the people who fabricated and tested the rope modules.
P63 → P64 → P66
P63 braked the spacecraft during powered descent. P64 approached the landing site after pitchover made it visible. P66 allowed the commander to control the descent rate and attitude with computer assistance. It was not simply flying with the computer switched off. Our model changes phase at 1,800 m and 150 m; these are educational thresholds, not Luminary’s original transition logic.
What really runs here?
Independent JavaScript flight physics and a bounded DSKY interpreter. Original Luminary 1A build 099 / LMY99 revision 001 source is displayed locally, never executed. The source view does not follow an instruction pointer. Virtual AGC’s GPL emulator is linked as further reading and is not bundled. A CPU alone would still need spacecraft sensor, I/O and navigation models.
The physical model
A 2D local plane with constant lunar gravity (1.62 m/s²), 45,040 N maximum thrust, 311 s specific impulse and variable mass. Fuel flow is thrust ÷ (specific impulse × standard gravity). At 60 fixed steps per simulated second we integrate thrust, tilt, velocity and position. Dry mass is 6,800 kg; initial fuel is 600 kg for training or 4,500 kg for the guided scenario. These are chosen scenario values, not a reconstruction of Eagle’s full mass history.
A view, not a surveyed landing map
The procedural craters, shadow and cockpit view are original illustrations. Collision occurs on a flat datum; craters have no collision geometry. There is no orbit, 6-axis attitude dynamics, radar error model, propellant slosh, real RCS or ascent/abort simulation. Throttle is continuous from 0–100%; the real descent engine had operating restrictions. Guided mode is a feedback controller, not a recorded trajectory.
Source provenance
The original listing identifies “Assemble revision 001 of AGC program LMY99 by NASA 2021112-061”, 14 July 1969. Paul Fjeld digitized the MIT Museum pages, with arrangements by Deborah Douglas; Virtual AGC transcribed and checked the code. Local files retain their public-domain headers. The MIT license covers this exhibit’s new code only.
Complete historical event table · NASA Table 5-I
| GET | Documented event |
|---|---|
| 102:33:05 | P63 · Powered descent ignition |
| 102:37:51 | Landing radar data good |
| 102:38:22 | 1202 · Executive overflow |
| 102:38:45 | Radar updates enabled |
| 102:39:02 | 1202 · Second alarm |
| 102:41:32 | P64 · Approach phase |
| 102:42:18 | 1201 · No VAC areas |
| 102:42:43 | 1202 · Fourth alarm |
| 102:42:58 | 1202 · Fifth alarm |
| 102:43:09 | Landing-point redesignation |
| 102:43:22 | P66 · Rate-of-descent control |
| 102:44:28 | Low-level sensor indication |
| 102:45:40 | Landing / engine off (rounded) |
Table 5-I rounds landing and engine shutdown to the same second. The journal records the contact-light call at 102:45:40 and the shutdown call at 102:45:43. They are different observations. Some journal commentary transposes alarm times: we use the original mission-report table for all five alarm events.
Read the story behind this exhibit: the Apollo 11 Guidance Computer
Sources & further exploration
- NASA · Apollo 11 Mission Report (MSC-00171), §5, Table 5-I
- NASA · Apollo 11 Lunar Surface Journal · The First Lunar Landing
- NASA · Program Alarms · Jack Garman
- NASA · Computers in Spaceflight · Apollo Guidance Computer
- Virtual AGC · DSKY drawings and indicator arrangements
- Virtual AGC · Luminary software history
- Apollo-11 · Luminary099 public-domain transcription
- Virtual AGC · emulator project (not used here)
Earlier Apollo DSKY exhibit · IMSAI 8080 / WarGames · Technical notes & test commands
Independent educational exhibit. No NASA affiliation or endorsement. No historic photographs or mission audio are bundled.