Apollo safety requirements in space and on the ground required new hardware and procedures in Block II (lunar mission type) spacecraft. Major changes affect the command module's test and pre-launch atmosphere, the hatch, the use of nonmetalIic materials, cabin emergency oxygen and fire-fighting provisions, wiring protection, and monitoring of crew and command module interior during hazardous ground tests.GROUND ATMOSPHERE
The atmosphere in the cabin of the command module for tests on the launch pad and at launch will be 60- percent oxygen and 40-percent nitrogen (60/40) rather than pure (100-percent) oxygen. The new mixed-gas atmosphere is supplied by ground equipment. Astronauts breathe pure oxygen in their space suits from Apollo's on-board systems. After launch, the cabin atmosphere is vented at a controlled rate, then replenished with pure oxygen so that in 4 to 6 hours it is approximately 95-ercent oxygen. The safety of the modified spacecraft was judged acceptable in the 60/40 mixed-gas atmosphere of 16 psi, and in a pure oxygen atmosphere at the space pressure of about 6 psi after extensive tests at NASA's Manned Spacecraft Center.
SIDE HATCH
A one-piece door replaces the two-cover hatch system on the command module. The side hatch is made of aluminum with fiberglass and ablative material. The door deployment mechanism has a gas-operated counter- balancing device that offsets gravity and permits easy opening on the ground. The hatch can be unlatched and opened by the flight crew in less than seven seconds and by the ground crew in about 10 seconds.
On the ground and during the early part of boost, the command module is shielded from boost heating by the boost protective cover. This cover, which is attached to and jettisoned with the launch escape tower, also has a hatch. As the unified hatch is opened from the inside, it activates a release mechanism between it and the boost protective cover hatch. The mechanism releases the single latch of the cover hatch and the two hatches swing open together.
MATERIAL
All materials in the spacecraft command module have been re-evaluated. Non-metallic materials were subjected to a rigid series of flammability tests and were replaced as required.
Among the more important changes are the use of stainless steel tubing instead of aluminum for the astronauts' high-pressure oxygen system. Aluminum solder joints of lines carrying water-glycol liquid for cooling or heating have been reinforced with protective armor where necessary. Protective plates cover coolant lines and also protect wiring against wear or accidental damage. Stowage boxes are made of aluminum.
Flammable materials are stowed in fireproof containers (metal or polyimide fiberglass storage boxes and Beta Cloth stowage bags).
Nylon Velcro material, used to grip or hold objects in the weightlessness of space, has been replaced with a new Teflon and polyester Beta fiberglass product, and wherever practical, mechanical fasteners are used to "button down" or hold equipment. A new flame-resistant material called Ladicote has been introduced and is applied by brush to potted connections.
Significant material changes include:
OLD NEW Nylon Velcro Teflon Beta fiberglass (for the pile); polyester Beta fiberglass (for the hook) Polyurethane line insulation Molded glass fibers Nylon Raschell knit debris trap Aluminum coverings Silicone rubber wire bundle antichafe wrap Teflon sheet Nomex (nylon) wire bundle spot ties Teflon-coated Beta fiberglass Mylar window shades Aluminum sheeting (not roll-up type) Silicone heat-shrink wire insulation Teflon heat-shrink wire insulation Trilock couch padding New fabric couch pad made of Teflon-coated fiberglass Most plastic knobs and switch levers Aluminum Polyolefin coaxial cable Wrapped with aluminum foil tape; later spacecraft to have Teflon cable Plastic switches in main display panel Metal Silicone oxygen umbilical hose Covered with Fluorel Crewman's communications umbilical (silicone rubber) Molded Fluorel Epoxy laminate food boxes Polyimide laminate Silicone laminate panel scuff covers Polyimide laminate covers Electroluminescent panels Covered with copper overcoat Silicone rubber spacers Covered with Beta fabric Nylon zipper on space-suit bags Metal Circuit breakers of diallylphthalate (DAP) and Melamine, both resins Covered with Ladicote Epoxy laminated structures Polyimidestructures Postlanding vent duct (silicone laminate) Metal and Fluorel impregnated glass fabric Felt filters in lithium-hydroxide canisters Teflon felt Uralane foam (cushion material for mirrors, etc.) Fluorel foam Fiberglass tape Aluminized tape Nylon Webbing (such as hook on CO2 absorber) Beta webbing Dacron cloth in the environmental control system Armalon cloth Aluminum high-pressure oxygen lines of environmental control system Stainless steel CABIN PROVISIONS
An emergency oxygen system with three masks and an independent oxygen supply would protect the crew from toxic fumes. Special fire-fighting provisions include a portable fire extinguisher, protection panels to isolate a fire, and special ports where the extinguisher's nozzle is inserted to douse a flame behind a panel.
WIRING PROVISIONS
A number of changes makes the estimated 15 miles of wiring safer in Block 11 spacecraft. Some circuit breakers were added and others reduced in capacity to improve wiring protection. Teflon wrapping separates power wires from others in a bundle. Aluminum enclosures protect wire runs in the crew compartment. Ladicote, a special fire-resistant material which is applied by a brush, coats terminals, metallic elec- tronic components, and circuit breakers. Ladicote was developed by chemists at North American Rockwell's Los Angeles Division.
MONITORING
Hazardous ground tests are more closely con- trolled by monitoring of biomedical data from the three crew members and observation through closed-circuit television of the command module interior.
EARTH LANDlNG SUBSYSTEM
The earth landing parachute system has been modified to handle the increased weight of the command module. Its two drogue parachutes were expanded from 13.7 to 16.5 feet. A dual-reefing feature was added to permit the three main chutes to open more slowly.
Copyright 1997-2005 by John
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