Page 43 - Apollo Moonships

The apollo moTher ship 41
THERMAL PROTECTION
The heat shields, responsible for protecting the CM from the extreme temperatures that it faced during space missions, were built of stainless steel brazed honeycomb filled with epoxy resin (a type of reinforced plastic) that works as an ablative material. The heat shields varied in thickness from 1⁄2 inch to 21⁄2 inches and safeguarded the inner structure from the cold
of space and the heat of the sun (280°F above zero
on the side facing the sun and 280°F below zero on the other side). The thermal shields also protected
the capsule from the fiery heat caused by air friction when the CM—the only part of the Apollo spacecraft recovered at the end of the mission—returned home and reentered into the Earth’s atmosphere. The reentry heat was so intense (5 000 °F) that it charred and melted away the ablative material, but it did it in such a way that the heat was rejected and did not penetrate into the CM inner compartments.
THE FORWARD COMPARTMENT
The CM forward compartment was divided into four
90° sections, which contained the Earth Landing
System (ELS), composed of three 83-foot-diameter
main parachutes, two 16-foot drogue chutes, three pilot mortar chutes, two reaction control engines, rescue antennas, a beacon light, and a sea recovery sling, among other components. The forward section was separated from the crew cabin by a bulkhead and was covered by
a heat shield. This thermal wrap—safeguarded from the heat of liftoff (1200°F) by the boost protective cover
(a fiberglass cone that fits over the CM like a glove)— contained four recessed fittings into which the legs of the Launch Escape Tower were attached to the CM inner structure. During the reentry to the Earth’s atmosphere, the forward heat shield was jettisoned by four pressurized-gas thrusters about 25 000 feet in altitude to expose the mortar assembly that permitted the deployment of the pilot, drogue, and main parachutes.
THE AFT COMPARTMENT
This section encompassed the area around the base
of CM—the widest part of the capsule—and was protected by the thickest thermal wrap: the aft heat shield, built with the same materials as the rest of
the heat shields but coated by a 21⁄2 inch layer of ablative material to dissipate heat more efficiently during the reentry to the Earth’s atmosphere. The CM aft compartment was divided by structural frames
into 24 bays, which housed ten reaction control thrusters, fresh water tanks, propellant tanks for the reaction control system (fuel, oxidizer, and helium as pressurant), crushable ribs to absorb the energy and reduce the shock force that astronauts suffered during the splashdown (external impact attenuation structure), and numerous instruments, cables, and pipes. The aft compartment also had the umbilical point where the wiring and plumbing ran from the Command Module to the Service Module and vice versa, connecting both space vehicles.
Yaw engines
Helium tank
Propellant tank
Crushable rib