Saturn V/ Apollo Command module (MIX FILE) (REF#msfc-68-MS-G-1335)
An early depiction of the Apollo Command Module, Block I. Note the missing docking tunnel of Block II vehicles. (NASA)

Creating the Apollo Command Module thermal protection system was a labor of love. This video is from Textron Systems, once Avco Corporation (a conglomerate that has connections close to home, in the Midwest, to TV programs and stations it once owned).

This NASA film details how the CM’s ablative heat shielding was made. Fiberglass honeycomb was placed all around the spacecraft, top to bottom, custom fitted over every window, thruster, hatch and access port. Workers filled over 370,000 cells. Not a single cell was allowed to be imperfect. All of the ablative thermal-protection was cured and then machine-honed to thickness based on heating.

This film shows Avco’s work on the Block I Command Modules. These never flew manned as planned, of course. The Apollo 1 fire occurred inside the vehicle, killing its crew in a pad test, where Avco’s work could not aid them.

Spacecraft CM-012, before the Fire. (NASA)

After the Fire, with little time to play with the Block I (the original Apollo designs had no Lunar Module and, thus, no docking tunnel), the remaining Block I vehicles were used in unmanned tests (often with Block II components for testing) and later scrapped or sent away eventually to museums.

While researching, I wondered why Block I CM was simply painted, but the Block II had that particular silver skin.

As it turns out, the paint was simply the initial Block I default covering.

Close-up of the base of Apollo 4’s heat shield edge, looking from underneath. You can see the honeycomb that makes up the thermal protection throughout. The wedge-like section is the old-style Service Module umbilical connection used on the Block I spacecraft

Later improvements to save weight and help with thermal projection after lessons learned from the returned unmanned CM launch tests would remove the paint (as well as removing some excess internal insulation). Then, some Kapton coated with aluminum and silicon monoxide were laid in strips over the CM to provide improved thermal control while in space for the Block II vehicles.

Some of the last Skylab-bound Command Modules were painted white on its sunward side to aid in thermal control while docked for extended periods to the space station.

Enjoy the video.