Apollo and America's Moon Landing Program: Command Module (CSM) Reference
National Aeronautics and Space Administration (NASA), World Spaceflight News
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APOLLO AND AMERICA'S MOON LANDING PROGRAM
COMMAND MODULE (CSM) REFERENCE
WORLD SPACEFLIGHT NEWS SPECIAL REPORT
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APOLLO SPACECRAFT
The Apollo spacecraft is the entire structure atop the launch vehicle. It is 82-feet tall and has five distinct parts: the command module, the service module, the lunar module, the launch escape system, and the spacecraft-lunar module adapter.
The three modules make up the basic spacecraft; the launch escape system and adapter are special-purpose units which are jettisoned early in the mission after they have fulfilled their function. The launch escape system is essentially a small rocket which will thrust the command module — with the astronauts inside — to safety in case of a malfunction in the launch vehicle on the pad or during the early part of boost. The spacecraft-lunar module adapter serves as a smooth aero-'dynamic enclosure for the lunar module during boost and as the connecting link between the spacecraft and the launch vehicle.
The spacecraft program has been divided into two parts, referred to as Block I (early earth-orbital test) and Block II (lunar mission version). The Block I program has been completed, and ail future Apollo spacecraft flights will be with the Block II lunar mission type.
The basic difference in the two versions was in the addition, in Block II, of some equipment and systems designed specifically for the lunar mission. NASA's purpose in dividing the program was to get basic structure and systems tested in space as quickly as possible, while providing the time and the flexibility to incorporate changes. Thus, in addition to lunar equipment, Block II contains a great number of refinements and improvements of equipment and systems, many the result of continuing research and many evolving from the Block I unmanned flight and ground tests.
The spacecraft and systems described in this book are Block II.
For brevity, abbreviations for a few basic items of the Apollo program will be used throughout the book. For the spacecraft, these are CM for command module, SM for the service module, LM for the lunar module, CSM for the command and service modules together, and SLA for the spacecraft-lunar module adapter.
Abbreviations and acronyms are a key part of the engineering jargon; thousands are used commonly in the Apollo program. Many of the major ones are listed at the end of the glossary. Otherwise, they appear in this book only on a few diagrams or schematics where it was impossible because of limited space to spell them out. If the text does not make it clear what item of equipment is being referred to, a check with the glossary should provide the answer.
COMMAND MODULE
This is the control center for the spacecraft; it provides living and working quarters for the three-man crew for the entire flight, except for the period when two men will be in the LM for the descent to the moon and return. The command module is the only part of the spacecraft that returns to earth from space.
The CM consists of two shells: an inner crew compartment (pressure vessel) and an outer heat shield. The outer shell is stainless steel honeycomb between stainless steel sheets, covered on the outside with ablative material (heat-dissipating material which chars and falls away during earth entry).
The inner shell is aluminum honeycomb between aluminum alloy sheets. A layer of insulation separates the two shells. This construction makes the CM light as possible yet rugged enough to stand the strain of acceleration during launch, the shock and heat of earth entry, the force of splashdown, and the possible impact of meteorites.
Inside, it is a compact but efficiently arranged combination cockpit, office, laboratory, radio station, kitchen, bedroom, bathroom, and den. Its walls are lined with instrument panels and consoles, and its cupboards (bays) contain a wide variety of equipment. In flight, the cabin is air conditioned to a comfortable 70 to 75 degrees. The atmosphere is 100-percent oxygen, and the pressure is about 5 pounds per square inch (a little better than one-third of sea-level pressure of 14.7 pounds per square inch).
The command module's controls enable the crew to guide it during flight. Test equipment permits checkout of malfunctions in spacecraft subsystems. Television, telemetry and tracking equipment, and two-way radio provide communication with earth and among the astronauts during moon exploration and the moon orbit rendezvous. These and other subsystems, such as the reaction control, guidance and navigation, earth landing, and parts of the environmental control and electrical power, occupy almost every inch of available space in the module.
Although crewmen can move about from one station to another, much of their time will be spent on their couches. The couches can be adjusted so the crew can stand or move around. Space by the center couch permits two men to stand at one time. The couches are made of steel framing and tubing and covered with a heavy, fireproof fiberglass cloth. They rest on eight crushable honeycomb shock struts which absorb the impact of landing. Control devices are attached to the armrests.
SERVICE MODULE
The service module's function, as its name implies, is to support the command module and its crew. It houses the electrical power subsystem, reaction control engines, part of the environmental control subsystem, and the service propulsion subsystem including the main propulsion engine for insertion into orbit around the moon, for return from the moon, and for course corrections.
The SM is constructed of aluminum alloy. Its outer skin is aluminum honeycomb between aluminum sheets. Propellants (a combination of hydrazine and unsymmetrical dimethylhydrazine as fuel and nitrogen tetroxide as oxidizer) and various subsystems are housed in six wedge-shaped segments surrounding the main engine.
The service module is attached to the command module until just before earth entry, when the SM is jettisoned.
LUNAR MODULE
The LM will carry two men from the orbiting CSM down to the surface of the moon, provide a base of operations on the moon, and return the two men to a rendezvous with the CSM in orbit. Its odd appearance results in part from the fact that there is no necessity for aerodynamic symmetry; the LM is enclosed during launch by the SLA and operates only in the space vacuum or the hard vacuum of the moon.
The LM structure is divided into two components: the ascent stage (on top) and the descent stage (at the bottom). The descent stage has a descent engine and propellant tanks, landing gear assembly, a section to house scientific equipment for use on the moon, and extra oxygen, water, and helium tanks.
The ascent stage houses the crew compartment (which is pressurized for a shirtsleeve environment like the command module), the ascent engine and its propellant tanks, and all LM controls. It has essentially the same kind of subsystems found in the command and service modules, including propulsion, environmental control, communications, and guidance and control.
Portable scientific equipment carried in the LM includes an atmosphere analyzer, instruments to measure the moon's gravity, magnetic field, and radiation, rock and soil analysis equipment, a seismograph, a soil temperature sensor, and cameras (including television).
APOLLO FLIGHT TESTS
The Apollo flight test program up to September 1968 included space tests of four command and service modules, one lunar module, and space and atmospheric tests of 10 boilerplate (test) command and service modules. These tests were conducted under the "all-up" philosophy of testing as many things simultaneously as possible and thus minimizing the number of launches, as well as cost and time.
The program is aimed at designing the spacecraft so that all launches contribute to its development. The command and service modules are being developed separately from the lunar module; this permits both modules to be tested on the smaller Saturn IB launch vehicle. The test program depends on the Saturn V only for missions that require its large payload.
Another test program goal has been maximum development on the ground; space flights have been undertaken only with spacecraft with almost all systems aboard and operating.
An example of this philosophy of combining many tests on one flight was the Apollo 6 mission on April 4, 1968. This mission included the second flight of a Saturn V launch vehicle as well as a number of important spacecraft tests.
Although launch vehicle problems caused selection of an alternate mission and prevented achievement of some major objectives, NASA termed the spacecraft's accomplishments impressive. These included the longest single burn in space of the service propulsion engine (7 minutes, 25 seconds), proper control of the engine during this burn by the guidance and navigation subsystem, proper maintenance of spacecraft attitude by the reaction control subsystem during the long cold soak period, and another successful test of the spacecraft's heat shield. This also was the first space test of the new unified crew hatch and seals and they withstood the mission in good condition.
The first flight of the Saturn V was on Nov. 9, 1967, in the Apollo 4 mission, which also was a major test of the CWI's heat shield, service propulsion subsystem, guidance and navigation equipment, and environmental control subsystem. The major objectives of Apollo 4, all fulfilled, were: the first launch of the Saturn V first stage, the first flight of the hydrogen-powered second stage, restart of the third stage in earth orbit, restart of the service propulsion engine in space and its record firing for nearly 5 minutes, a hot and cold soak of the spacecraft far out in space, and entry under the severest conditions yet encountered by a spacecraft (a velocity of 24,913 miles per hour and a heat shield temperature of about 5,000 degrees F).
The Apollo 4 results were impressive. There was no structural damage to the command module and no areas of burn-through on the heat shield. The environmental control subsystem kept the cabin temperature between 60 and 70 degrees even through the fiery entry. Cabin pressure remained between 5.6 and 5.8 psia during the entire mission, indicating negligible leakage rate. Fuel cells and subsystems using cryogenics operated satisfactorily, as did all other operating subsystems.
The first space test of the lunar module came Jan. 22, 1968, on the Apollo 5 mission. The LM was launched by a Saturn IB, with the apex of the vehicle covered by an aerodynamic shroud. The shroud was jettisoned and then-the spacecraft-LM adapter panels deployed as on a lunar mission. The lunar module's descent engine was burned three times and performed as expected. At the end of the third burn, a "fire-in-the-hole" abort—in which the LM's ascent and descent stages separate, the ascent engine begins to burn and simultaneously the descent engine stops firing—was performed successfully. A second ascent engine burn was performed later in the mission. Data telemetered to the ground indicated that all other subsystems of the module operated satisfactorily.
COMMAND MODULE
Dimensions
Height 10 feet 7 inches
Diameter 12 feet 10 inches
Weight (including crew) 13,000 lbs
Weight (splashdown) 11,700 lbs
Propellant
Reaction control subsystem 270 lbs
(fuel—monomethylhydrazine; oxidizer—nitrogen tetroxide)
Function
The command module is the control center and living quarters for most of the lunar mission; one man will spend the entire mission in it and the other two will leave it only during the lunar landing. It is the only part of the spacecraft recovered at the end of the mission.
Major Subsystems
Communications
Earth landing
Electrical power
Environmental control
Guidance and navigation
Launch escape
Reaction control
Service propulsion
Stabilization and control
Thermal protection (heat shields)
The CM is divided into three compartments: forward, crew, and aft. The forward compartment is the relatively small area at the apex of the module, the crew compartment occupies most of the center section of the structure, and the aft compartment is another relatively small area around the periphery of the module near the base.
During boost and entry the CM is oriented so that its aft section is down, like an automobile resting on its rear bumper. In this position the astronauts are on their backs; the couches are installed so that the astronauts face the apex of the module. In the weightlessness of space the orientation of the craft would make little difference except in maneuvers like docking, where the craft is moved forward so that the probe at the CM's apex engages the drogue on the LM. Generally, however, the module will be oriented in space so that its apex is forward.
Crewmen will spend much of their time on their couches, but they can leave them and move around. With the seat portion of the center couch folded, two astronauts can stand at the same time. The astronauts will sleep in two sleeping bags which are mounted beneath the left and right couches. The sleeping bags attach to the CM structure and have restraints so that a crewman can sleep either in or out of his space suit.
Food, water, clothing, waste management, and other equipment are packed into bays which line the walls of the craft. The cabin normally will be pressurized to about 5 pounds per square inch (about a third of sea level pressure) and the temperature will be controlled at about 75°F. The pressurization and controlled atmosphere will enable the three crewmen to spend much of their time out of their suits. They will be in their space suits, however, during critical phases of the mission such as launch, entry, docking, and crew transfer.
The astronaut in the left-hand couch is the spacecraft commander. In addition to the duties of command, he will normally operate the spacecraft's flight controls. The astronaut in the center couch is the CM pilot; his principal task is guidance and navigation, although he also will fly the spacecraft at times. On the lunar mission, he is the astronaut who will remain in the CM while the other two descend to the surface of the moon. The astronaut in the right-hand couch is the LM pilot and his principal task is management of spacecraft subsystems.
Although each has specific duties, any of the astronauts can take over the duties of another. The command module has been designed so that one astronaut can return it safely to earth.
STRUCTURE
The CM consists of two basic structures joined together: the inner structure (pressure shell) and the outer structure (heat shield).
The inner structure is of aluminum sandwich construction which consists of a welded aluminum inner skin, adhesively bonded aluminum honeycomb core and outer face sheet. The thickness of the honeycomb varies from about 1-/2 inches at the base to about % inch at the forward access tunnel. This inner structure — basically the crew compartment — is the part of the module that is pressurized and contains an atmosphere.
The outer structure is the heat shield and is made of stainless steel brazed honeycomb brazed between steel alloy face sheets. It varies in thickness from 1/2 inch to 2 inches.
Part of the area between the inner and outer shells is filled with a layer of fibrous insulation as additional heat protection.
THERMAL PROTECTION (HEAT SHIELDS)
The interior of the command module must be protected from the extremes of environment that will be encountered during a mission. These include the heat of boost (up to 1200°F), the cold of space and the heat of the direct rays of the sun (about 280° below zero on the side facing away from the sun and 280° above zero on the other side), and — most critical — the intense temperatures of entry (about 5000°F).
The heat of launch is absorbed principally through the boost protective cover, a fiberglass structure covered with cork which fits over the command module like a glove. The boost protective cover weighs about 700 pounds and varies in thickness from about 3/10 of an inch to about 7/8 of an inch (at the top). The cork is covered with a white reflective coating. The cover is permanently attached to the launch escape tower and is jettisoned with it at approximately 295,000 feet during a normal mission.
The insulation between the inner and outer shells, plus temperature control provided by the environmental control subsystem, protects the crew and sensitive equipment during the CM's long journey in space.
The principal task of the heat shield that forms the outer structure is to protect the crew from the fiery heat of entry—heat so intense that it melts most metals. The ablative material that does this job is a phenolic epoxy resin, a type of reinforced plastic.
This material turns white hot, chars, and then melts away, but it does it in such a way that the heat is rejected by the shield and does not penetrate to the surface of the spacecraft.
The ablative material controls the rate of heat absorption by charring or melting rapidly. This dissipates the heat and keeps it from reaching the inner structure.
The command module enters the atmosphere with its base down; this is covered by the aft heat shield which is the thickest portion.
The heat shield varies in thickness: the aft portion is 2 inches and the crew compartment and forward portions are Vi inch. Total weight of the shield is about 3,000 pounds. 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 panels are produced by Aeronca Manufacturing Co., Middletown, Ohio, and the ablative coating was developed and applied by Avco Corp., Lowell, Mass.
IMPACT ATTENUATION
During a water impact the CM deceleration force will vary from 12 to 40 G's, depending on the shape of the waves and the CM's rate of descent. A major portion of the energy (75 to 90 percent) is absorbed by the water and by deformation of the CM structure. The module's impact attenuation system reduces the forces acting on the crew to a tolerable level.
The impact attenuation system is part internal and part external. The external part consists of four crushable ribs (each about 4 inches thick and a foot in length) installed in the aft compartment. The ribs are made of bonded laminations of corrugated aluminum which absorb energy by collapsing upon themselves at impact. The main parachutes suspend the CM at such an angle that the ribs are the first point of the module that hits the water.
The internal portion of the system consists of eight struts which connect the crew couches to the CM structure. These struts (two each for the Y and Z axes and four for the X axis) absorb energy by deforming steel wire rings between an inner and an outer piston. The struts vary in length from 34 to 39 inches and have a diameter of about 214 inches.
The axes of the spacecraft are three straight lines, each at a right angle to the other two. They are used for reference and to describe the spacecraft's movements. The X axis is the line running from the apex of the command module through its base; the Y axis is the line running laterally, or from side to side through the couches; the Z axis is the line running up and down, or from the head to the feet of the astronauts in their couches. The command module's movement about the X axis is called roll, about the Y axis is called pitch, and about the Z axis is called yaw.
FORWARD COMPARTMENT
The forward compartment is the area around the forward (docking) tunnel. It is separated from the crew compartment by a bulkhead and covered by the forward heat shield. The compartment is divided into four 90-degree segments which contain earth landing equipment (all the parachutes, recovery antennas and beacon light, and sea recovery sling), two reaction control engines, and the forward heat shield release mechanism.
The forward heat shield contains four recessed fittings into which the legs of the launch escape tower are attached. The tower legs are connected to the CM structure by frangible (brittle) nuts which contain small explosive charges. When the launch escape subsystem is jettisoned, these charges are fired, breaking the nuts and separating the tower from the module.
At about 25,000 feet during entry, the forward heat shield is jettisoned to expose the earth landing equipment and permit deployment of the parachutes.
AFT COMPARTMENT
The aft compartment is located around the periphery of the command module at its widest part, just forward of (above) the aft heat shield. The compartment is divided into 24 bays by the 24 frames of the structure. In these bays are 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 runs from one module to the other-also is in the aft compartment. The panels of the heat shield around the aft compartment are removable for maintenance of the equipment before flight.
CREW COMPARTMENT
The crew compartment is a sealed cabin with a habitable volume of 210 cubic feet. Pressurization and temperature are maintained by the environmental control subsystem. In it are the controls and displays for operation of the spacecraft, crew couches, and all the other equipment needed by the crew. It contains two hatches, five windows, and a number of bays or cupboards packed with equipment.
HATCHES
The two CM hatches are the side hatch, used for getting in and out of the module, and the forward hatch, used to transfer to and from the lunar module when the two modules are docked.
The side hatch is a single integrated assembly which opens outward and has primary and secondary thermal seals. It is about 29 inches high and 34 inches wide: The hatch normally contains a small (about 9 inches in diameter) window, but has provisions for installation of an airlock. The hatch weighs about 225 pounds; with the airlock it weighs about 245 pounds.
The hatch normally is operated by a handle which the crewman pumps back and forth. The handle drives a ratchet mechanism which opens or closes the 12 latches around the periphery of the hatch. The latches are so designed that pressure exerted against the hatch serves only to increase the locking pressure of the latches. If the latch gear mechanism should fail, it can be disconnected and the latches opened or closed manually.
The hatch also can be opened from the outside by a tool that is part of the crew's tool set and is carried by ground personnel. The tool is the emergency wrench, essentially a modified allen head L-wrench. It is 6-1/4 inches long and has a 4-1/4-inch drive shaft.
The hatch handle mechanism also operates the mechanism which opens the access hatch in the boost protective cover. A counterbalance assembly enables the hatch and boost protective cover hatch to be opened easily. This consists of two nitrogen bottles and a piston assembly. Each nitrogen bottle contains about 5-1/2 cubic inches of gas under a pressure of 5,000 pounds per square inch. One of the bottles is punctured on the launch pad, permitting the gas to stroke the piston and force the door open when the latches are released. A pressure of about 2,200 pounds per square inch is needed to open the door.
The ground crew can easily close the hatch by pushing it. In the weightlessness of space, the crew can close the hatch from the inside by pulling on a handle near the lower hinge which swings the hatch inward. Another handle near the opposite edge of the door is provided primarily for the use of astronauts engaged in extravehicular activity.
The piston cylinder and nitrogen bottle can be vented after launch since the counter-balance assembly is not needed in space. If it is vented, the second nitrogen bottle can be used to open the hatch after landing. A knob on this bottle is used to puncture it and release the gas into the system.