Eagle's Descent

The words

1. Bingo

   A fuel-reserve threshold used in landing-or-abort decisions.

   Houston sent fuel countdowns as Armstrong brought Eagle down. They warned of an approaching decision about landing or aborting, while propellant remained for the final descent.

   NASA journal: the final landing minutes (opens a new tab)

2. Boulder Field

   Eagle approached an area strewn with rocks near West Crater. Armstrong took control and flew beyond the rough ground to find a clearer place for the landing.

   NASA: Eagle’s descent and landing (opens a new tab)

3. Charlie Duke

   Astronaut Charlie Duke was the capsule communicator in Houston during the landing. He relayed Mission Control’s assessments to Armstrong and Aldrin, including permission to continue after the computer alarms.

   NASA: Eagle’s descent and landing (opens a new tab)

4. Contact Light

   Aldrin called out when a probe beneath one of Eagle’s landing pads touched the Moon. The light signaled probe contact while the spacecraft was still settling onto the surface.

   Did you know?

   Eagle had surface probes beneath three landing pads. The leg with the ladder had none; Aldrin said the crew had asked for that probe to be removed.

   NASA journal: the final landing minutes (opens a new tab)

5. Data Dropout

   Eagle’s radio link to Earth was interrupted during early powered descent. Controllers temporarily lost spacecraft data, making it harder to follow the landing from Houston.

   NASA mission report, pp. 114–115, 189 · NASA report: Eagle’s descent systems (opens a new tab)

6. Descent Engine

   Eagle’s lower stage carried an engine whose thrust could be varied during landing. It slowed the spacecraft toward the surface; a separate engine later lifted the astronauts back into orbit.

   NSSDCA: Eagle’s two stages (opens a new tab)

7. Fuel Gauge

   Eagle’s instruments showed the propellant remaining, and a separate low-level light warned as the supply fell. These indications helped the crew and Houston judge the landing margin.

   NASA mission report, p. 118 · NASA report: Eagle’s descent systems (opens a new tab)

8. Landing Radar

   Eagle’s landing radar measured its height and motion relative to the Moon. It supplied altitude and velocity information to the guidance computer as the spacecraft approached the surface.

   Apollo 11 press kit, p. 105 · NASA press kit: Eagle’s guidance (opens a new tab)

9. Low Gate

   An aviation term marking the start of the final landing phase.

   Eagle’s descent was planned in braking, approach and landing phases. Near low gate, the design allowed continued inspection of the terrain and pilot takeover for the final touchdown.

   Bennett, lunar trajectories, pp. 3, 10 · Bennett: the descent’s three phases (opens a new tab)

10. Luminary

    Luminary IA was the guidance software carried by Eagle. It processed landing radar information for the descent; Apollo 10’s earlier software had not included the final landing phase.

    Apollo 11 press kit, p. 105 · NASA press kit: Eagle’s guidance (opens a new tab)

11. Pitchover

    Eagle tilted toward an upright attitude as it approached the landing area. The maneuver brought the ground ahead into Armstrong’s view through the forward window.

    NASA: Eagle’s descent and landing (opens a new tab)

12. Program Alarm

    The 1201 and 1202 alarms warned that Eagle’s computer could not finish all the requested work. Its guidance functions continued while the crew and Houston assessed the warnings.

    NASA mission report, pp. 33, 190–191 · NASA report: Eagle’s descent systems (opens a new tab)

13. Steve Bales

    Steve Bales was the guidance officer in Mission Control. With support from computer specialist Jack Garman in the back room, he assessed the alarms and recommended continuing Eagle’s descent.

    Did you know?

    After the mission, Bales accepted a NASA Group Achievement Award for the flight operations team. The astronauts received Presidential Medals of Freedom at the same dinner.

    NASA history: Bales and Garman (opens a new tab) · NASA: the flight team’s award (opens a new tab)

14. West Crater

    West Crater and its surrounding rocks lay near Eagle’s initial landing path. Armstrong flew beyond them; this was a different crater from Little West, near the final landing spot.

    NASA journal: the final landing minutes (opens a new tab)

15. White Team

    Flight director Gene Kranz led the White Team in Houston for Eagle’s landing. The controllers monitored spacecraft systems and supported decisions while Duke handled radio exchanges with the crew.

    Did you know?

    People on Earth followed the landing by radio, without live pictures from Eagle. The onboard film became available only after the astronauts returned it to Earth.

    NASA: Eagle’s descent and landing (opens a new tab)