pressurized crew compartment. The outer structure was made of stainless steel brazed-honeycomb brazed between steel alloy face sheets. It varied in thickness from 0.5 inch to 2.5 inches. Part of the area between the inner and outer shells was filled with a layer of fiberglass insulation as additional heat protection. Thermal protection (heat shield) An ablative heat shield on the outside of the CM protected the capsule from the heat of reentry, which is sufficient to melt most metals. This heat shield was composed of phenolic formaldehyde resin. During reentry, this material charred and melted away, absorbing and carrying away the intense heat in the process. The heat shield has several outer coverings: a pore seal, a moisture barrier (a white reflective coating), and a silver Mylar thermal coating that looks like aluminum foil. The heat shield varied in thickness from in the aft portion (the base of the capsule, which faced forward during reentry) to in the crew compartment and forward portions. The Total weight of the shield was about . Forward compartment The -tall forward compartment was the area outside the inner pressure shell in the nose of the capsule, located around the forward docking tunnel and covered by the forward heat shield. The compartment was divided into four 90-degree segments that contained Earth landing equipment (all the parachutes, recovery antennas and beacon light, and sea recovery sling), two reaction control thrusters, and the forward heat shield release mechanism. At about during reentry, the forward heat shield was jettisoned to expose the Earth landing equipment and permit deployment of the parachutes. Aft compartment The -tall aft compartment was located around the periphery of the command module at its widest part, just forward of (above) the aft heat shield. The compartment was divided into 24 bays containing 10 reaction control engines; the fuel, oxidizer, and helium tanks for the CM reaction control subsystem; water tanks; the crushable ribs of the impact attenuation system; and a number of instruments. The CM-SM umbilical, the point where wiring and plumbing ran from one module to the other, was also in the aft compartment. The panels of the heat shield covering the aft compartment were removable for maintenance of the equipment before flight. Earth landing system The components of the ELS were housed around the forward docking tunnel. The forward compartment was separated from the central by a bulkhead and was divided into