21 November 2015

Space Station Resupply: The 1963 Plan to Turn the Apollo Spacecraft Into a Space Freighter

President John F. Kennedy messes up NASA's carefully wrought long-range plans, 25 May 1961. Image credit: NASA
When first proposed in 1959, the spacecraft that would come to be known as the Apollo Command and Service Module (CSM) was envisioned as an Earth-orbital "advanced manned spacecraft" capable of being uprated for circumlunar or lunar-orbital flights. On 15 November 1960, NASA awarded six-month feasibility study contracts for just such an Apollo spacecraft to three contractors: the Martin Company; the Convair Division of General Dynamics; and the General Electric Company Defense Electronics Division, Missile and Space Vehicle Department.

In 1960, the three-man Apollo spacecraft was expected to be the second U.S. piloted spacecraft after the Mercury capsule. It would include a Command Module (CM), a Service Module (SM), and an Orbital Module; the last of these would augment the work and living space available to the crew, in effect making the spacecraft into a mini-space station.

NASA expected that its piloted program in the 1960s would proceed down one or both of two "logical" paths, and that Apollo would be crucial for both. The first path would have Apollo spacecraft transport crews to a temporary "orbiting laboratory." The Orbital Module would be used to transport supplies to the lab in space. The other path would see an Apollo perform a piloted flight around the moon. What might come after 1970 was anybody's guess, though NASA expected that the orbiting lab path would lead to a permanent Earth-orbiting space station and the circumlunar path would lead to a piloted moon landing, piloted Mars and Venus flybys, and a piloted Mars landing.

Apollo as a fork in the road: NASA's plans for piloted spaceflight in 1959. Image credit: NASA
Martin, General Dynamics, and General Electric submitted their final study reports to NASA on 15 May 1961. Ten days later, new President John F. Kennedy wreaked havoc on NASA's logical plans when he opted to proceed directly to a lunar landing before 1970.

Stinging from the failed Bay of Pigs invasion of Cuba and the first piloted spaceflight by Soviet cosmonaut Yuri Gagarin (12 April 1961), Kennedy had asked Lyndon Baines Johnson, his Vice President and National Space Council chair, to propose a space goal that the U.S. might reach ahead of the Soviet Union. The apparent Soviet advantage in launch vehicle capability would, it was believed, give communist rocketeers a head-start if the goal was anything as modest as the establishment of an Earth-orbiting space station. Landing a man on the moon, on the other hand, was a goal audacious enough that the U.S. and Soviet Union would start out more or less evenly matched.

Model of the Apollo Command and Service Module atop a conceptual Landing Propulsion Module. Image credit: NASA
On 28 November 1961, NASA awarded North American Aviation (NAA) the contract to build the Apollo CSM, the design of which included two modules: the conical CM and the drum-shaped SM. The method by which NASA would carry out President Kennedy's bold lunar mandate remained uncertain, though it was widely assumed that the space agency would soon award a contract for a third Apollo spacecraft module: a Landing Propulsion Module for lowering the CSM to a gentle touchdown on the moon. NAA went so far as to specify in its April 1962 subcontract with Aerojet General Corporation that the CSM's Service Propulsion System (SPS) main engine be capable of generating enough thrust to launch the CSM off of the lunar surface and place it on course for Earth.

As it turned out, however, the Apollo CSM would never land on the moon. On 11 July 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 Aircraft Engineering Corporation, 7 November 1962), but it was for the Lunar Excursion Module (LEM), a bug-like two-man spacecraft that would undock from the CSM in lunar orbit and lower to a landing on the moon. The Apollo CSM thus became the mother ship for delivering astronauts and LEM to lunar orbit and returning astronauts and moon rocks to Earth.

Despite President Kennedy's new high-priority moon landing goal, space station studies within NASA did not cease. In fact, some believed that NASA might launch its first station into Earth orbit before an astronaut stepped onto the moon. They reasoned that lunar landing program development costs would peak two or three years before NASA launched its first lunar landing attempt (as in fact they did). If NASA's portion of the Federal purse remained near its peak as moon program costs declined, then funds might become available for a station in Earth orbit as early as 1968.

At the newly established NASA Manned Spacecraft Center (MSC) in Houston, Texas. engineer Edward Olling headed up space station planning. He informally named MSC's first proposed station program Project Olympus.

In April 1962, Olling circulated a draft planning document within MSC for comment; then, on 16 July 1962, he unveiled to top-level MSC managers his "Summary Project Development Plan" for the Project Olympus space station program. Olling envisioned a series of four 24-man stations launched and continuously staffed over a period of from five to seven years.

Olling explained that the Project Olympus space stations would provide NASA with enough astronauts, scientific equipment, pressurized volume, and electrical power to carry out wide-ranging basic and applied science research in space. Early station research would, however, seek to answer important questions about the efficacy of humans in space; for example, could astronauts work safely and effectively in orbit for long periods?

Each 138,600-pound Project Olympus station would consist of a 15,000-cubic-foot central hub from which would radiate three evenly spaced arms with a total of about 35,000 cubic feet of volume. The hub would include a hangar for crew and supply spacecraft. Each arm would include a pressurized crew module of oval cross-section with two cylindrical access tunnels. The Project Olympus station would launch atop a two-stage Saturn V rocket with its hub on top and its three radial arms folded below. Once in orbit, the station would separate from the Saturn V second stage and the three arms would hinge upward and lock into place. Pressurized tunnels would link each arm to the station hub.

Small rocket motors at the ends of the arms would ignite to spin the station. The 150-foot-wide Project Olympus station would revolve four times per minute to create acceleration in its arms which the crew inside would feel as gravity. "Down" would be away from the hub. The crew decks farthest from the hub would experience the greatest acceleration: the equivalent of one-quarter of Earth's gravitational pull, or about midway between lunar and martian surface gravity. Decks closer to the hub would experience less acceleration, so might be used mainly for storage. Olling hinted that the different levels of acceleration experienced at varying distances from the hub might be useful for scientific research, but he provided no specifics as to how.

Cutaway drawing of a Project Olympus-type space station. The centrifuge in lower part of the hub would support variable gravity experiments. Not shown is a station power system; NASA MSC proposed both solar- and nuclear-powered station designs. Image credit: North American Aviation/NASA
New research objectives would be added over time as old stations were retired and new ones launched. The Project Olympus stations would become space-environment research facilities, "national laboratories" for research into meteorology, geophysics, radio communications, navigation, and astronomy, as well as "orbital operations" platforms (that is, shipyards for preparing spacecraft bound for points beyond space station orbit).

Olling advised MSC management that Project Olympus stations should operate in circular 300-nautical-mile-high orbits inclined 28.5° relative to Earth's equator - what he called a "Mercury orbit" because it matched the orbital inclination of the one-man Mercury capsules. Astronaut Scott Carpenter orbited Earth for nearly five hours in the Aurora 7 capsule on 24 May 1962, while Olling prepared his project plan. Olling later lowered his recommended altitude to 260 nautical miles.

The 28.5° latitude of the launch pads at Cape Canaveral, Florida, determined the orbital inclination of the Project Olympus stations. Matching launch-site latitude and station orbital inclination would maximize both station mass and the mass of the payload that could be delivered to the station. Olling also mentioned (albeit briefly) the possibility of a polar-orbiting Project Olympus station that would pass over all points on Earth.

In April 1963, MSC awarded NAA a contract for a seven-month study of a Modified Apollo (MODAP) logistics spacecraft for delivering astronauts and cargo to Project Olympus space stations. The Apollo CSM design 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. The overall CSM layout was, however, firmly in place, giving NAA a meaningful point of departure for its MODAP study.

Apollo 15 Command and Service Module Endeavor in lunar orbit. Image credit: NASA
The Apollo CM included three astronaut couches, control consoles, small windows at strategic locations, a side-mounted hatch with a window, a docking tunnel and parachutes in its nose, thrusters for orienting it for atmosphere reentry, and, at its base, a bowl-shaped reentry heat shield. Umbilicals and cables in a hinged housing linked the CM to the SM.

The Apollo SM included seven major internal bays. A central cylindrical bay housed tanks of helium pressurant for pushing rocket propellants into the SPS main engine. Arrayed around the central compartment were six triangular bays containing tanks of fuel and oxidizer for the SPS and for four attitude-control thruster quads, electricity- and water-making fuel cells, and tanks of liquid oxygen and liquid hydrogen reactants for supplying the fuel cells.

The MODAP CSM would comprise a stripped-down SM and a beefed-up CM. Because it would spend a limited amount of time in free flight before it docked with an Earth-orbiting station, the MODAP SM could dispense with or minimize many Apollo lunar SM systems. Batteries would replace fuel cells, for example, and a compact LEM descent engine could replace the SPS. The LEM engine would draw its propellants from a pair of spherical tanks in the MODAP SM's central cylindrical compartment. These deletions and additions would free up four of the MODAP SM's triangular bays for cargo transport.

The Apollo SM had six roughly triangular bays arrayed around a cylindrical core. The bays contained propellants, fuel cells, and liquid hydrogen and liquid oxygen tanks, among other systems necessary for a lunar mission. For its Earth-orbital station logistics missions, the MODAP SM needed fewer systems and tanks, so could devote four of the six triangular bays to cargo. The section image at right displays the cargo and equipment bays and a possible arrangement for four cargo doors. Image credit: North American Aviation/NASA
A two-stage Saturn IB rocket capable of placing 32,500 pounds into a 105-nautical-mile circular parking orbit at 28.5° of inclination would launch the MODAP CSM. Pre-launch preparation, launch operations, and ascent to parking orbit would need from five to 10 days, from five to eight hours, and 11 minutes, respectively.

The MODAP CSM would remain in parking orbit for less than five hours before its crew ignited its LEM descent engine to place it into an elliptical transfer orbit with a 260-mile apogee (highest point above the Earth). Upon reaching apogee 45 minutes later, its crew would again ignite the engine to circularize its orbit. Subsequent station rendezvous and docking maneuvers might need up to 17.5 hours.

The company calculated that a 24-man station with crew stays lasting six months would need to receive a MODAP CSM bearing six astronauts and 5855 pounds of supplies eight times per year - that is, every 45 days. The typical cargo manifest would include 1620 pounds of food, 1035 pounds of oxygen, 505 pounds of nitrogen, 1450 pounds of propellants, and 1245 pounds of spare parts. The Project Olympus station would recover and reuse all water launched with it, so would have no need of water resupply.

These cutaway drawings of the Project Olympus hangar display internal (right) and external palletized cargo transfer methods. The internal method assumes that the entire MODAP CSM can fit into the hangar. The drawing at left shows how the protruding MODAP SM would separate from the MODAP CM and pivot into cargo-unloading position. MODAP CMs for Earth-return are docked radially on the dome-shaped docking hub near the floor of the hangar. Image credit: North American Aviation/NASA
Supplies would reach the Project Olympus station in drum-shaped Cargo Modules, or CAMs, packed in the four empty triangular MODAP SM bays. The mass of the empty CAMs would total 1970 pounds. Liquid and gaseous cargo would fill small CAMs, while solid cargoes would ride on disc-shaped pallets in large CAMs. In all, a MODAP CSM could transport 9127 pounds of cargo and CAMs.

The MODAP CSM would dock with the Project Olympus station via an axial docking unit at the bottom of the station hangar. NAA envisioned that the station would include either a tall hangar for the entire MODAP CSM or a short hangar for the MODAP CM alone (in which case the MODAP SM would protrude into space). If the former, then CAM transfer could occur entirely within the hangar. If the latter, then CAM transfer would occur external to the station. In both cases, after all cargo was transferred, the MODAP SM would be cast off and the hangar closed to protect the MODAP CM.

These cutaway drawings of the Project Olympus station hangar show CAM internal (right) and external transfer methods. Compare with palletized transfer drawings above. Image credit: North American Aviation/NASA
To free up the single axial docking port for the next MODAP CSM, a manipulator arm inside the hangar would pivot the MODAP CM to one of three radial berthing ports. It would remained parked there, undergoing periodic inspection and maintenance but otherwise dormant, for up to six months.

Discarding the MODAP SM with its LEM descent engine meant that the MODAP CM would need to carry a separate de-orbit propulsion module. NAA proposed a cluster of six solid-propellant retrorockets, any five of which could deorbit the MODAP CM. The retro package would include batteries for powering the MODAP CM during free-flight prior to reentry. NAA expected that, in normal circumstances, the MODAP CM would need 30 minutes for checkout and undocking. The MODAP CM's crew would ignite its retrorockets immediately after it maneuvered clear of the hangar.

The MODAP CM with solid-propellant retropack. Image credit: North American Aviation/NASA
Twenty-five minutes after retrofire and shortly after retropack separation, the MODAP CM would reenter Earth's atmosphere. Because the MODAP CM would encounter the atmosphere moving at about half the speed of the Apollo lunar CM, its heat shield could be about half as thick. Descent and splashdown would need 11 minutes. With six astronauts on board, 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, so 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 inclined orbit and Earth's rotation put it on course for reentry and splashdown at any of three sites. These were the prime site in the Gulf of Mexico, a site near Okinawa in the western Pacific Ocean, and one near Hawaii. To trim costs, fleets of recovery ships would not remain on standby at the landing sites; because of this, the astronauts might need to wait for up to 24 hours for rescue following an emergency splashdown near Okinawa or Hawaii.

An abort during ascent to Earth orbit could cause the Apollo and MODAP CMs to land in southern Africa; that is, to touch down 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.

A tight fit: six-man MODAP Command Module seating arrangement. Image credit: North American Aviation/NASA
Because the MODAP CM would carry six men arrayed in two rows of three couches each, with one row above the other, NAA found that vertical couch movement would not be an option. The three-man lunar CM would also rely on crushable material behind its heat shield to absorb the force of land impact; this would be inadequate for the greater mass of the six astronauts in the MODAP CM.

NAA proposed to solve the emergency land-landing problem by in effect moving the shock absorbers from the seat struts to the MODAP CM's heat shield and by adding four solid-propellant landing rockets. In the event of a land landing, the bowl-shaped heat shield would deploy downward on shock-absorbing struts and the landing rockets would ignite and pivot out from behind the shield.

NAA envisioned a MODAP CSM design & test program spanning from early 1964 to mid-1968. Operational MODAP CSMs would deliver crews and supplies to 24-man Project Olympus stations between mid-1968 and the end of 1973. The company anticipated that five MODAP CSMs would be used in ground tests and unmanned test flights, and that 40 MODAP CSMs would support the station program. Of these, perhaps two would fail, requiring assembly of at least two backup MODAP CSMs. NAA placed the total cost of the MODAP CSM program including $861 million for Saturn IB rockets at $1.881 billion.

A significant outcome of Olling's Project Development Plan and NAA's MODAP study was the realization that space station crew rotation and resupply would dominate total space station program cost. Summing up his findings, Olling wrote that a "reusable launch vehicle could contribute large economies" (that is, ensure large cost savings) for the station program. Even if four space stations were launched on expendable Saturn V rockets during the Project Olympus program, station cost would total only $1.273 billion; that is, about $600 million less than the MODAP CSM flights.

The Project Olympus and MODAP CSM study teams were not alone in reaching these conclusions; thus, as early as 1963, a reusable logistics spacecraft came to be seen as a desirable component of a large space station program. By 1968, this led to calls by high-level NASA management for a 1970s Space Station/Space Shuttle program.


Final Technical Presentation: Modified Apollo Logistics Spacecraft, Contract NAS 9-1506, North American Aviation, Inc., Space and Information Systems Division, November 1963

"Project Olympus: Proposed Space Station Program," Edward H. Olling, NASA Manned Spacecraft Center, 16 July 1962

More Information

A Bridge from Skylab to Station-Shuttle: Interim Space Station Program (1971)

One Space Shuttle, Two Cargo Volumes: Martian Marietta's Aft Cargo Carrier (1982)

After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)

No comments:

Post a Comment

I like hearing from my readers. No rules except the obvious ones - please keep it civil and on topic.