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On the Apollo 11 Flight Journal Day 9: Re-entry and Splashdown, it says something about the "Constant g-phase". This is what the ALSJ says:

Planned drag level (deceleration) during the constant g phase: 4.00g.

An analysis of the Apollo 11 re-entry shows a graph of the g-forces experienced during re-entry (measured after entry interface). Here's the graph for reference:

enter image description here

The graph shows no flat line indicating a constant g-level. So what is this constant g-phase, and why did it not show up on the re-entry analysis? If this graph is incorrect, where can I find a correct version of the graph?

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Constant-g was used in backup manual control modes.

Note your quote says planned - the value of g the crew would fly was read up to them as part of the pad.

See the discussion in your link.

191:58:13 Evans: Okay, Mike. Of course, this is in the event the G&N and the EMS quits and you have to fly the constant-g;

Also APOLLO EXPERIENCE REPORT - MISSION PLANNING FOR APOLLO ENTRY

Two backup trajectory-control modes are used for the Apollo entry. Both these modes use manual CM attitude control and are based upon constant-aerodynamic-load-factor (constant-g) trajectories...

The basic control technique, using the EMS, is to control the entry trajectory to a load factor of 4g until the CM velocity is reduced below the circular orbital velocity...

In the event of a GNCS and EMS failure, the entry is controlled to a constant-g trajectory with manual attitude control by using the g-meter and backup attitude reference as the primary displays.

It wasn't actually used.

Acronymology

  • CM Command Module
  • EMS Entry Monitoring System
  • G&N Guidance and Navigation
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