When first proposed in 1959, the spacecraft that would eventually become known as the Apollo Command and Service Module (CSM) was envisioned as a three-man Earth-orbital vehicle upgradable to lunar-orbital capability. On November 15, 1960, NASA awarded six-month feasibility study contracts for just such an Apollo spacecraft to the Martin Company, the Convair Division of General Dynamics, and the General Electric (GE) Company Defense Electronic Division, Missile and Space Vehicle Department. The CSM at that time was to include a Command Module (CM), a Service Module (SM), and an orbital module, a kind of mini-space station. The three companies submitted their final study reports on May 15, 1961.
Ten days later, President John F. Kennedy redirected Apollo - and, indeed, the entire U.S. civilian space program - toward the goal of landing a man on the moon by the end of the 1960s. On November 28, 1961, NASA awarded North American Aviation (NAA) the contract to build the Apollo CSM, the initial design of which included two modules: the conical CM and the drum-shaped SM. At the time, the method by which NASA would carry out the President's mandate remained uncertain, though it was widely assumed that it would soon award a contract for a third Apollo spacecraft module: a landing propulsion module for lowering the CSM to the lunar surface. NAA went so far as to design the Service Propulsion System (SPS) main engine, mounted at the base of the SM, with enough thrust to launch the CSM off the moon using the propulsion module as a launch pad.
The Apollo CSM would never land on the moon, however. On July 11, 1962, as part of an ongoing debate that was not finally settled until November of that year, NASA selected the Lunar-Orbit Rendezous (LOR) mode for accomplishing the Apollo mission. A contract for a third Apollo module was indeed awarded (to Grumman, on November 7, 1962), but it was for the Lunar Excursion Module (LEM), a bug-like two-man lander that would detach from the CSM in lunar orbit and land. The Apollo CSM thus became the mother ship for delivering astronauts and LEM to lunar orbit and returning astronauts and moon rocks to Earth.
If some within NASA had had their way, then the Apollo CSM would also have become the primary crew and cargo delivery vehicle for a 24-man Earth-orbiting space station beginning as early as 1968. In April 1963, NASA's Manned Spacecraft Center (MSC) awarded NAA a contract for a seven-month, two-phase study of a Modified Apollo (MODAP) Logistics Spacecraft. At the time, MSC personnel, who had moved from NASA's Langley Research Center in Virginia beginning in early 1962, were housed in temporary offices scattered across Houston, Texas. By the time NAA completed the MODAP study in November 1963, MSC had officially opened its new facilities on Houston's southern outskirts.
Not surprisingly, the Apollo CSM design in 1963 had yet to reach its final form. No docking unit design had been selected, for example, though the probe-and-drogue system eventually chosen was already the leading candidate. A peculiar phased-array high-gain antenna had yet to be replaced by the familiar four-dish Apollo high-gain. The overall layout and many other details were, however, firmly in place, giving NAA a meaningful point of departure for its MODAP design.
The Apollo CSM's crew-carrying CM included three astronaut couches, a control panel, small windows at strategic locations, a side-mounted hatch, a docking tunnel and parachutes in its nose, and a bowl-shaped heatshield and thrusters for orienting it for atmosphere reentry at its base. An umbilical linked the CM to the SM. The SM included seven major internal compartments. A central cylindrical compartment housed helium pressurant tanks for pushing rocket propellants to the SPS main engine. Arrayed around the central compartment were six triangular compartments containing tanks of fuel and oxidizer for the SPS and four attitude-control thruster quads, fuel cells for making electricity and water, and tanks of liquid oxygen and liquid hydrogen for supplying the fuel cells.
The MODAP CSM would have a stripped-down SM and a beefed-up CM. Because it would spend a limited amount of time in free flight before docking with an Earth-orbiting space station that could supply it with air, electricity, and cooling, it could dispense with or downgrade many lunar mission SM systems. Batteries would replace the lunar SM's fuel cells, for example, and a compact, less powerful LEM descent engine would replace the SPS. The LEM engine would draw propellants from a pair of spherical tanks in the central cylindrical compartment. This would free up the triangular compartments for cargo containers.
NAA assumed that the MODAP CSM would launch on a two-stage Saturn IB rocket capable of placing 32,500 pounds into a 105-nautical-mile-high circular parking orbit (NAA also looked at launching the MODAP CSM on a four-stage Titan-IIIC). Pre-launch preparations, launch operations, and ascent to parking orbit would need from five to 10 days, from five to eight hours, and 11 minutes, respectively. The spacecraft would remain in parking orbit for less than five hours before igniting the LEM descent engine to place itself into an elliptical transfer orbit with a 260-mile apogee (highest point above the Earth). Upon reaching this apogee 45 minutes later, it would again ignite its engine to circularize its orbit. Rendezvous and docking with the space station in 260-mile-high orbit would need up to 17.5 hours.
Though MSC was on the move throughout the MODAP study and busy with Apollo moon program preparations, its engineers had already found time to design the 24-man space station to which the MODAP CSM would deliver crews and cargo. Designed for launch on a single two-stage Saturn V rocket, MSC's station would reach orbit unmanned and unfold three "arms" from a central hub. The hub would included a docking port for MODAP CSM spacecraft and three berthing ports for MODAP CMs without their SMs.
NAA calculated that a 24-man space station with full crew rotation every six months would need to receive a MODAP CSM bearing six astronauts and 5855 pounds of cargo eight times per year, or once every 45 days. The cargo manifest would include 1620 pounds of food, 1035 pounds of breathing oxygen, 505 pounds of buffering nitrogen, 1450 pounds of propellants, and 1245 pounds of spare parts. Water would not be carried because the space station was expected to recycle all of its water.
The company estimated that containers for solid and liquid cargo - which it called Cargo Modules, or CAMs - would have a combined empty mass of 1970 pounds. The volume required to accommodate the cargo and containers would total 202.4 cubic feet, meaning that all necessary cargo could be carried in four of the SM's six triangular compartments. NAA noted that the MODAP CSM launched on a Saturn IB would have surplus cargo capacity equal to 1302 pounds of mass and 52 cubic feet of volume that might be applied to additional cargo, such as science instruments. In all, one MODAP CSM could transport 9127 pounds of cargo and CAMs.
NAA proposed that the MODAP SM include hinged doors for unloading cargo at the space station, a process that would have to be completed in 44 days or less to make way for the next MODAP CSM to dock. Small doors near the top of the SM, where it joined the CM, would provide access to four CAMs holding liquid cargo, while large doors below those would expose four solid-cargo CAMs.
NAA envisioned that the three-armed MSC space station would include a hangar for either the MODAP CM alone or for the entire MODAP CSM. If the hangar housed the CM alone, then the SM would protrude into open space following docking. A robot arm on the station would grip each CAM in turn and transfer it to a pipe-like loading chute on the station's exterior. After all cargo was transferred, the MODAP SM would be cast off and the hangar closed to protect the MODAP CM, which would remain attached to the station for up to six months. If, on the other hand, the hangar accommodated the entire MODAP CSM, then cargo transfer would occur within the hangar. The SM would still be cast off within 44 days of docking to make room for the next MODAP CSM.
After the MODAP SM was discarded, the MODAP CM would be pivoted using a manipulator arm to a berthing port to free up the main docking port. It would remained parked there, undergoing periodic inspection and maintenance but otherwise dormant, for up to six months.
Discarding the MODAP SM meant that the MODAP CM would need to carry a separate de-orbit propulsion module. NAA proposed a cluster of six solid-propellant retrorocket motors, any five of which would be adequate to deorbit the MODAP CM. The retro package would also include batteries for powering the MODAP CM during free flight prior to reentry. NAA expected that, under normal conditions, the MODAP CM would need 30 minutes for checkout and undocking, after which the retro motors would fire immediately. Twenty-five minutes later, shortly after de-orbit module separation, it would reenter Earth's atmosphere. Because the MODAP CM would encounter the atmosphere moving at about half the speed of the lunar CM, its heat shield could be about half as thick. Descent and splashdown would need 11 minutes. The MODAP CM would be heavier than the lunar CM, so would lower on four parachutes; that is, one more than the lunar CM. Its crew could splash down safely if one parachute failed.
Under normal circumstances, the MODAP CM would splash down in the Gulf of Mexico, not far from Houston, and crew recovery would take place within a few hours. NAA acknowledged, however, that emergencies might occur. Because of this, the MODAP CM could fly free of the space station for up to 10.5 hours while its orbit carried it into position for reentry and splashdown at any of three landing sites. These were the prime site in the Gulf of Mexico, a site near Okinawa in the western Pacific Ocean, and a site near Hawaii. To cut costs, fleets of recovery ships would not remain on standby at the landing sites; because of this, recovery might be delayed for up to 24 hours following an emergency splashdown near Okinawa or Hawaii.
An abort during ascent to orbit could cause the MODAP CM to land in southern Africa; that is, on land. To protect its three-man crew during a land landing, the lunar CM would include shock absorbers in its supporting seat struts. These would enable the crew couches to move vertically up to five inches to dissipate the force of impact.
Because the MODAP CM would carry six men arrayed in two rows of three couches, one row above the other, vertical couch movement was not an option. Insufficient room would exist within the MODAP CM to permit vertical movement totaling at least 10 inches (five inches per row). The lunar CM would also rely on crushable material in the CM heatshield; this would be inadequate to soften the blow for the greater mass of six men.
NAA proposed to solve this problem by, in effect, moving the shock absorbers from the seat supports to the MODAP CM's heat shield and by adding four solid-propellant landing rockets. In the event of a land landing, the heat shield would deploy downward on shock absorbing struts and the landing rockets would ignite and pivot out from behind the shield.
NAA assumed a MODAP CSM design and test program spanning from early 1964 to mid-1968, and that operational MODAP CSMs would deliver crews and cargoes to the 24-man space station from mid-1968 through 1973. The company anticipated that five MODAP CSMs would be used in ground tests and unmanned test flights, and that 40 MODAP CSMs would fly during the five-year space station program. Of these, perhaps two would fail, requiring assembly of at least two backup spacecraft. NAA placed the total cost of the MODAP CSM program (including $861 million for Saturn IB rockets) at $1,881,350,000.
Reference:
Final Technical Presentation: Modified Apollo Logistics Spacecraft, Contract NAS 9-1506, North American Aviation, Inc., Space and Information Systems Division, November 1963.
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