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)

18 November 2015

Series Development: A 1969 Plan to Merge Shuttle and Saturn V to Spread Out Space Program Cost

Apollo 4, the first Saturn V rocket to fly, departs the Vertical Assembly Building bound for Pad 39A, 26 August 1967. LUT 1 rides beside the rocket on a crawler-transporter; a second LUT in the background awaits its first launch. Image credit: NASA
A red-painted Launch Umbilical Tower (LUT) was the Saturn V's constant companion from the moment technicians lowered the rocket's 138-foot-tall S-IC first stage into place beside it within a Vertical Assembly Building (VAB) high bay until shortly after the S-IC's engines ignited on one of the twin Launch Complex (LC) 39 pads. At the moment of liftoff, the nine servicing arms linking the 398-foot-tall LUT to the 363-foot-tall Saturn V would retract or swing out of the way; then, between 1.4 and 9.4 seconds after liftoff, the rocket would perform a LUT clearance yaw maneuver, its five F-1 engines bathing the launch pad in flame. After that, the LUT would stand alone, awaiting transport back to the VAB atop one of Kennedy Space Center's two enormous crawler-transporters and assembly of a new Saturn V.

By late 1969, with the Apollo 11 and 12 lunar landing missions successfully accomplished, it had become clear that only a few more Saturn V rockets would depart LC 39 for the moon. The $25-billion Apollo Program had achieved its goal of humbling the Soviet Union, and many outside of space industry and the fledgling planetary science community saw little cause to continue it.

Meanwhile, NASA Administrator Thomas Paine aspired to replace the moon program with a large Earth-orbiting Space Station serviced by a fully reusable crew rotation and logistics resupply spacecraft (a "Space Shuttle"). A fully functional 6-man or 12-man core station would reach Earth orbit on a Saturn V rocket; later, Saturn V rockets would launch multiple large Space Station modules which would be brought together to form a 50- or 100-man "Space Base." By the beginning of the 1980s these would, it was hoped, become elements in an Integrated Program Plan that would lead to a manned lunar surface base and men on Mars by 1990.

The Nixon White House and the Congress would have none of it, however. By the time Congress passed the $3.75-billion Fiscal Year 1970 NASA budget - the lowest since 1962, the first year of the Apollo Program build-up - space planners had begun to seek tactics that they could use to achieve ambitious goals while spreading out costs. One of those tactics was "series development."

Booster-first development: in this artist concept, a reusable Space Shuttle Booster carries an expendable Saturn S-IVB stage and payload to the edge of space. Image credit: NASA
As applied to the Space Shuttle, series development could take either of two forms. In the first, the Space Shuttle's fully reusable piloted Booster would be developed and brought into service, then development work would begin on its fully reusable piloted Orbiter.

Until the Orbiter became available, the suborbital Booster would lift off from Cape Kennedy, Florida, carrying on its back an unmanned payload attached to an expendable upper stage based on an existing stage design - the Saturn V S-IVB third stage was one attractive candidate. The upper stage would ignite high over the Atlantic, boosting the payload to Earth orbit - or beyond. The astronauts, meanwhile, would pilot the Booster back to a runway at Cape Kennedy, where it would be refurbished, mated with a new upper stage and payload, and flown again.

Three-stage Saturn V rocket with Apollo spacecraft payload on top, Orbiter with Saturn S-IC first stage, and LUT with nine Apollo Saturn V servicing arms. Image credit: Bellcomm/NASA
More attractive to space planners eager to see astronauts continue to fly into orbit (that is, almost all of them) was development of the Shuttle Orbiter followed by development of the Booster. In this "Orbiter-first" scenario, an expendable Saturn V S-IC would stand in for the Booster during the first few years of Shuttle flights.

On the last day of 1969, C. Eley, an engineer with Bellcomm, NASA's Washington, DC-based planning contractor, published a memorandum in which he examined how the Orbiter/S-IC combination might be serviced and launched using a LUT "without extensive [and expensive] modifications." Eley assumed that the S-IC would fly virtually unmodified (apart from a 10-foot-long streamlined shroud linking its dome-shaped top to the Orbiter's tail) and that the Orbiter would measure 183 feet long. This would make the combination 331 feet tall, or 32 feet shorter than the Apollo Saturn V.

Eley found that LUT servicing arms 1, 2, 4, 8, and 9 would remain useful for Orbiter/S-IC pre-launch servicing. He recommended that arms 3, 5, 6, and 7 be removed and stored to prevent them from becoming damaged (implying, perhaps, that the LUT might be restored to its original form and purpose - that is, launching Saturn V rockets - at some point). Arms 1 and 2, which would service the S-IC stage, would remain completely unchanged in form and function.

Orbiter-first development: a reusable Shuttle Orbiter with an expendable Saturn S-IC first stage stands beside a modified LUT. Image credit: Bellcomm/NASA
All Orbiter servicing - for example, propellants loading - would employ arm 4, close by the Orbiter's tail. Arm 8 would provide services - for example, cooling - to the payload in the Orbiter's payload bay, but would not enable access to the payload because the Orbiter's top side, where its payload bay doors would be located, would face away from the LUT on the pad. Eley assumed that the Mobile Servicing Structure used during Apollo to reach parts of the Saturn V located out of reach of the LUT arms would not be used with the Orbiter/S-IC. He suggested that a special arm be added to the LUT if payload access on the launch pad were judged to be necessary. Arm 9 would reach out from the LUT to cap the Orbiter's nose, permitting access to its crew cabin.

Eley then examined the probable launch rate of the Orbiter/S-IC stage Space Shuttle. He made three assumptions about the Orbiter and the LUT: that the Orbiter would include an "autonomous checkout capability" that would help to reduce to from five to 10 days time spent on the launch pad prior to launch; that all three Apollo LUTs would be modified for Orbiter/S-IC launches; and that experience would prove that a LUT could be fully refurbished within 15 days of taking part in a launch.

If these assumptions were shown to be correct, Eley found, then more than 40 Orbiter/S-IC launches could take place in a year. If, on the other hand, only a single modified LUT, a 30-day LUT refurbishment period, and an on-pad preparation time no less than 30 days were assumed, then only six or seven Orbiter/S-IC flights could occur per year.

A little more than two years after Eley completed his memorandum, budget shortfalls forced NASA to postpone Space Station development until after the Shuttle flew - another example of series development. Shuttle Orbiters, not Saturn V rockets, would launch NASA's future Space Station. The Station would be launched in pieces in the Shuttle Orbiter payload bay and assembled in Earth orbit.

Two of the Apollo LUTs were put to use in the Space Shuttle Program, though not as Eley envisioned. NASA partially dismantled them, reducing their height to 247 feet (not counting a new 80-foot-tall lightning mast), then permanently mounted them on the two LC 39 pads. The third LUT was dismantled sometime after 1982 and scrapped in 2004 after its peeling red paint was judged to be an environmental hazard.


"Feasibility of Shuttle (Orbiter)/S-IC Launches at LC-39 - Case 320," C. Eley, Bellcomm, Inc., 31 December 1969

Welcome to the Save the LUT Campaign - http://www.savethelut.org/ (link accessed 19 November 2015)

More Information

What if an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

An Alternate Station-Shuttle Evolution: The Spirit of '76 (1970)

McDonnell Douglas Phase B Space Station (1970)

Where to Launch and Land the Space Shuttle? (1971-1972)

14 November 2015

Reviving & Reusing Skylab in the Shuttle Era: NASA Marshall's November 1977 Pitch to NASA Headquarters

The Skylab Orbital Workshop as seen by the Skylab 4 crew, the last astronauts to live on the station. Image credit: NASA
On 14 May 1973, the last Saturn V rocket to fly, designated SA-513, launched the Skylab Orbital Workshop (OWS) space station into a 435-kilometer-high orbit about the Earth. Flight controllers soon realized that the 85-ton space laboratory was in trouble. Although they did not know it at the time - Skylab climbed rapidly into dense clouds, so could not be imaged during most of its ascent - 63 seconds after liftoff a design flaw caused Skylab's meteoroid shield to rip away. Shield debris jammed one of the workshop's two main electricity-producing solar arrays. The other array remained attached to Skylab's side only at its hinge (forward) end.

Shield debris also pummeled SA-513, tearing at least one hole in the tapered interstage adapter that linked its S-II second stage with the Skylab station. Debris also apparently damaged the system for separating the cylindrical adapter that linked the S-II to the S-IC first stage. The adapter, meant to separate shortly after the spent S-IC, remained stubbornly attached to the S-II all the way to orbit.

Skylab 1 launch, 14 May 1973. Image credit: NASA
After the S-II's five J-2 engines shut down, forward-facing solid-propellant rockets ignited to push the spent stage away from Skylab. Their plumes blasted open and tore away the loose solar array. Ironically, the jammed array probably survived because it was tied down by meteoroid shield debris.

Without the protection of the reflective meteoroid shield, temperatures within Skylab's 11,303-cubic-foot pressurized volume soon soared, raising fears that its air would become tainted by outgassing from materials on board, film would be ruined, and food and medicines spoiled. Flight controllers soon found to their dismay that maneuvers designed to cool Skylab's interior tended to starve it of electricity, for they turned away from the Sun the four "windmill" solar arrays on the Apollo Telescope Mount (ATM), the beleaguered space laboratory's only functioning sources of electricity.

NASA immediately began a Skylab salvage effort. Engineers developed deployable sunshields and tools for freeing the stuck main solar array, flight controllers carefully maneuvered Skylab to maximize the amount of electricity the ATM arrays could produce while reducing temperatures on board as much as possible, and the first crew meant to board Skylab (their mission was designated Skylab 2) hurriedly trained to become the world's first orbital repairmen.

Skylab 2 astronauts Joseph Kerwin, Charles "Pete" Conrad, and Paul Weitz. Image credit: NASA
On 25 May, the Skylab 2 crew of Pete Conrad, Paul Weitz, and Joe Kerwin lifted off in an Apollo Command and Service Module (CSM) atop a Saturn IB rocket. After a failed attempt to pull open the one remaining main solar array with a hook extended from the open CSM hatch, they docked with and entered Skylab, then deployed a sunshield through an experiment airlock. Temperatures began to fall, but the Orbital Workshop remained starved for electricity. On 7 June, Conrad and Kerwin succeeded in forcing open the surviving main solar array, saving not only their own 28-day mission but also the planned Skylab 3 and Skylab 4 missions.

The Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off on 28 July. During their 6 August spacewalk, Lousma and Garriott deployed an improved sunshield. The lived and worked on board the station for 59 days.

The Skylab 4 crew of Jerry Carr, William Pogue, and Ed Gibson boarded Skylab on 16 November. Carr and Gibson mounted a meteoroid collector on an ATM strut during their spacewalk on 3 February 1974, in the hope that a Space Shuttle crew might retrieve it as early as 1979. When the Skylab 4 crew undocked on 8 February 1974 after a record-breaking 84 days in space, Skylab was expected to remain aloft until 1983, when atmospheric drag would cause it to reenter Earth's atmosphere. They left Skylab's airlock hatch closed but not latched so that it could provide entry for future visitors.

This pre-launch cutaway illustration of Skylab shows the station as it would have appeared if it had reached Earth orbit undamaged. In addition to two large main solar array, it includes the micrometeoroid shield which tore free during Skylab's ascent through the atmosphere. Image credit: NASA
During the solar-minimum years of the mid-1970s, the Sun was more active than had been anticipated at the time of Skylab's launch. Solar activity heated and expanded Earth's upper atmosphere, subjecting the first U.S. space station to more aerodynamic drag than had been expected. In March 1977, the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, lead center for the Skylab station, asked NASA Headquarters to grant it permission by mid-1977 to begin work on a mission to raise Skylab's orbital altitude.

On 10 June 1977, former Skylab Deputy Director John Disher, by then NASA's Director of Advanced Programs, requested that MSFC conduct a preliminary in-house study of the feasibility of reusing Skylab in the Space Shuttle era. At about the same time, NASA Headquarters directed NASA Johnson Space Center (JSC), lead center for the Space Shuttle, to study an early Shuttle mission to either boost Skylab to a higher, longer-lived orbit or cause it to safely reenter over an unpopulated area.

In September 1977, JSC informed NASA Headquarters and MSFC that the earliest it could reboost or deboost Skylab was September 1979, as part of the fifth Orbital Flight Test (OFT) Shuttle mission. At the time, NASA envisioned a total of six OFT missions before the Shuttle was declared operational. NASA Headquarters then gave the go-ahead for MSFC and JSC to begin work toward a September 1979 Skylab reboost/deboost mission.

On 16 November 1977, MSFC engineers J. Murphy, B. Chubb, and H. Gierow presented to NASA Associate Administrator for Space Flight John Yardley results of the study they had begun in June. They were speaking to a Skylab expert: before coming to NASA in 1974, Yardley had managed Skylab work at McDonnell Douglas, the prime contractor for the OWS.

The MSFC engineers first described Skylab's condition. They reported that when the Skylab 4 crew returned to Earth, the Orbital Workshop's water system contained 1930 pounds of water (enough to supply three men for 60 days). The water, they said, probably remained potable, but might have developed a bad taste. If it was no longer potable, then it might be used for bathing. In any case, the Skylab water system included resupply points, so a Space Shuttle crew could refill it with fresh water if water transfer equipment were developed.

The oxygen/nitrogen supply remaining on Skylab was probably sufficient to supply three men for 140 days at Skylab's standard operating pressure of five pounds per square inch, the MSFC engineers estimated. The station's ventilation and carbon dioxide-removal systems were almost certainly functional. Even if they were not, their most important components were designed to be replaceable in space.

The MSFC engineers also assessed Skylab's electrical power system. They estimated that the main solar array Conrad and Kerwin had freed could still generate between 1.5 and 2.5 kilowatts of electricity, and that the batteries it had charged, located in Skylab's Airlock Module, were probably still usable. The batteries for the four ATM arrays, located inside the ATM, were, on the other hand, almost certainly frozen. The team recommended that controllers reactivate the main array electrical system from the ground before the first Shuttle visit, and that any effort to revive the ATM electrical system be left for a later time.

More problematic than the electrical system was Skylab's attitude control system, which relied on a trio of Control Moment Gyros (CMGs) to turn Skylab so that, among other things, it could reliably point its solar arrays at the Sun. At the time the Skylab 4 crew departed, one CMG had already failed and another showed signs of impending failure. In addition, Skylab's guidance computer was probably dead after being subjected to "extreme thermal cycling" as Skylab passed between daylight and night. The Orbital Workshop's thruster system, on the other hand, was probably operational with about 30 days of propellant remaining.

Finally, the MSFC team looked at Skylab's cooling system, which had leaked while the astronauts were on board and had probably frozen and ruptured since the last crew returned to Earth. They called "serviceability of [the] cooling system. . .the most questionable area" as far as Skylab's reusability was concerned, but added that "any inflight 'fixes' should be well within the scope of crew capability."

The MSFC engineers then proposed a four-phase plan for reactivating and reusing Skylab. The target date for their first Phase I milestone had already passed by the time they briefed Yardley: though it was already mid-November, they made a point of calling for an October 1977 decision on whether Skylab should be reboosted to a higher orbit, extending its orbital lifetime until about 1990, or deboosted so that it could reenter safely over an unpopulated area.

Assuming that NASA decided to reboost Skylab, then a ground-controlled Skylab reactivation test would occur between June 1978 and March 1979. If the test was successful, then the fifth OFT Space Shuttle mission would rendezvous with Skylab. As already mentioned, in September 1977 JSC estimated that the fifth OFT would fly in September 1979. Two months later, when the MSFC team briefed Yardley, the mission had already slipped to February 1980.

Artist concept of Teleoperator spacecraft. Image credit: NASA
The MSFC team anticipated that the Space Shuttle crew would conduct an inspection fly-around of Skylab, then would deploy an unmanned Teleoperator spacecraft from the Shuttle Orbiter's payload bay. Using a control panel on the Orbiter flight deck, the astronauts would guide the Teleoperator, which would carry an Apollo probe-type docking unit, to a docking with the drogue-type docking unit on the front of Skylab's Multiple Docking Adapter. The Teleoperator would fire its thrusters to raise Skylab's orbit; then, its work completed, it would detach, freeing up Skylab's front docking port for Phase II of MSFC's plan.

Astronauts in a nearby Space Shuttle Orbiter stand by as the Teleoperator ignites its thrusters to raise Skylab's orbit and extend its orbital lifetime. Image credit: NASA
Phase II would begin in March 1980, when NASA would initiate development of Skylab refurbishment kits, a 10-foot-long Docking Adapter (DA) module, and a 25-kilowatt Power Module (PM). The DA would include at one end an Apollo-type probe docking unit for attaching it to Skylab's front port and at the other end an Apollo-Soyuz-type androgynous unit with which Shuttle Orbiters and the PM could dock.

The first refurbishment kit and the DA would reach Skylab on board a Shuttle Orbiter in January 1982, almost two years after the reboost mission. During the 1982 mission, spacewalking astronauts would fold two of the four ATM solar arrays out of the way to improve clearance for visiting Orbiters and would retrieve the meteoroid experiment the Skylab 4 astronauts had left on the ATM. As time allowed, this and other Phase II crews would perform unspecified "simple passive experiments" on board Skylab and would collect samples of its structure for engineering analysis on Earth.

The third Shuttle visit to Skylab would not take place until August 1983. The astronauts would install additional refurbishment kits and would tackle the daunting job of repairing Skylab's damaged cooling system.

The refurbished Skylab station after the start of Phase III of the NASA MSFC reactivation program. The Power Module, Docking Adapter, and Shuttle-carried Spacelab are clearly visible. Image credit: Junior Miranda
The MSFC engineers told Yardley that Phase III of the Skylab reactivation program would begin in March 1984 with delivery of the PM and any remaining refurbishment kits. Using the Shuttle's Remote Manipulator System robot arm, astronauts would lift the PM from the Orbiter's payload bay and turn it 180° so that it protruded forward well beyond the Orbiter's nose. They would then dock one of the PM's three androgynous docking units to an identical unit at the front of the Orbiter's payload bay. The Shuttle would use another of the PM's docking units to dock with the DA on Skylab.

Following docking with Skylab, the astronauts would deploy the PM's twin solar arrays and thermal radiators, link the PM to Skylab's systems using cables extended through open hatchways or installed on the hull during spacewalks, and power up the PM's three CMGs to replace Skylab's crippled attitude control system. The Orbiter would then undock from the PM, leaving it attached permanently to Skylab. Shortly thereafter, NASA would declare the revived and expanded Orbital Workshop to be fully habitable.

Phase III would continue with the first in a series of 30-to-90-day missions aboard Skylab. During these, a Shuttle Orbiter carrying a Spacelab module in its cargo bay would remain docked with the Orbital Workshop. The astronauts would work in the Spacelab module, take advantage of Skylab's large pressurized volume to perform "simple experiments" requiring more room than Shuttle and Spacelab could provide (for example, preliminary trials of space construction methods), and begin building up stockpiles of food, film, clothing, and other supplies on the revived station.

Another 30-to-90-day mission would see the astronauts refurbish and use selected Skylab science equipment, install new experiments based on Spacelab experiment designs, and stockpile more supplies. Between these missions, the new and improved Skylab would fly unmanned under control from the ground.

The view from the Sun: all of the solar arrays deployed for Phase III of the Skylab reactivation program are visible in this image by Junior Miranda
The MSFC engineers told Yardley that the volume available to a crew on board a Shuttle Orbiter without a Spacelab module in its payload bay would total only 1110 cubic feet. Adding a Spacelab would increase that to about 5100 cubic feet. This would, however, amount to less than half the pressurized volume of Skylab. For a mission including a Shuttle Orbiter, Spacelab module, and Skylab, the total volume available to the crew would exceed 16,400 cubic feet.

They were not specific about what Skylab would be used for when Phase IV of their program began in mid-1986, though they did offer several intriguing possibilities. Shuttle Orbiters might, for example, attach modified Spacelab modules and experiment pallets to the third docking port on the PM.

A Shuttle External Tank might be joined to Skylab to serve as a strongback for large-scale space construction experiments using a mobile "space crane." These experiments might include construction of a large space solar power module or a multiple beam antenna.

A new "floor" might be assembled within Skylab, enabling it to house up to nine astronauts. As NASA developed confidence in the revived space laboratory's health, manned missions on board Skylab without a Shuttle Orbiter present might commence, leading to permanent manning and "support [of] major space operations."

The MSFC engineers did not estimate the cost of Phases I and IV of their plan, though they did provide (perhaps optimistic) cost estimates for Phases II and III. Their estimates did not include Space Shuttle transportation and contractor study costs.

In Fiscal Year (FY) 1980, NASA would spend $2 million each on Phases II and III. This would increase to $5 million for Phase II and $3.4 million for Phase III in FY 1981. FY 1982, their plan's peak funding year, would see $4.5 million spent on Phase II and $10.2 million spent on Phase III. In FY 1983, NASA would spend $2.5 million to close out Phase II and $12 million to continue Phase III. The following year it would spend $9.1 million on Phase III. Phase III closeout in FY 1985 would cost $4.5 million. Phase II would cost a total of $14 million, while the more ambitious Phase III would total $41.2 million.

In November 1977, the month the MSFC engineers briefed Yardley on their study, NASA awarded Martin Marietta Corporation a small ($1.75-million) contract to begin development of the Teleoperator. The remote-controlled spacecraft was envisioned as a small space tug made up of modular components.

No decision was taken at that time as to whether the Teleoperator would reboost Skylab to make it available for possible future use or would deorbit it in a controlled manner; that decision would await assessment of Skylab's condition and additional study of potential applications. McDonnell Douglas and Martin Marietta subsequently commenced more detailed and extensive Skylab reuse studies under supervision of JSC and MSFC, respectively.


Skylab 1 Investigation Report, Hearing Before the Subcommittee on Manned Space Flight of the Committee on Science and Astronautics, US House of Representatives, Ninety-Third Congress, First Session, 1 August 1973

"Skylab Reuse Study Presented to Mr. Yardley by MSFC," 16 November 1977

Living and Working in Space: A History of Skylab, NASA SP-4208, W. David Compton & Charles D. Benson, 1983, pp. 361-372

More Information

What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

Evolution vs. Revolution: The 1970s Battle for NASA's Future

What Shuttle Should Have Been: NASA's October 1977 Space Shuttle Flight Manifest

08 November 2015

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

Skylab liftoff on a two-stage Saturn V rocket, 14 May 1973. Had the ISS Program gone ahead as planned, its four station launches in 1976, 1978, 1981, and 1983 would have closely resembled this one. Image credit: NASA
On 6 April 1971, eight engineers in the Advanced Concepts & Missions Division, NASA Headquarters Office of Advanced Research and Technology (OART), completed a blueprint of NASA's future. Their detailed report was strictly internal and of limited circulation.

Had the OART team's plan become more widely known, it would surely have generated controversy. This was because it proposed to end U.S. lunar exploration with Apollo 15 so that the Saturn V rockets earmarked for missions 16, 17, 18, and 19 could be used to launch into Earth orbit a series of four "interim" space stations, each more capable than the last, between early 1976 and late 1983.

Although the OART plan sounds like an Apollo massacre, it would in fact have deprived the U.S. of two manned moon missions, not four. By the time the OART team proposed its program, NASA had already cancelled three Apollos. First was Apollo 20, nixed in January 1970 so that its Saturn V rocket could launch 85-ton Skylab, a temporary space station, into low-Earth orbit (LEO).

Next to go were Apollo 15 and Apollo 19 in September 1970. NASA Administrator Thomas Paine scrapped the two lunar landing missions - an H-class walking mission and a J-class rover mission, respectively - to free up funds for NASA's hoped-for 12-man permanent Space Station and the fully reusable winged Space Shuttle intended to deliver its crews, supplies, and experiment equipment. NASA subsequently renumbered its remaining Apollo missions, so the cancelled missions are more commonly known today as Apollo 18 and Apollo 19.

The Interim Space Station (ISS) Program would have played much the same role for NASA in the mid-1970s/early 1980s as Gemini played in the 1960s. Soon after President John F. Kennedy's 21 May 1961 call for an American on the moon by the end of the 1960s decade, aerospace engineers realized that they needed an experience-building "bridge" program to link simple Mercury suborbital and LEO missions with complex Apollo lunar orbiter and landing missions. Gemini evolved from Mercury - it was initially called "Mercury Mark II" - to fulfill that role.

The Saturn IB stage served as the Apollo moon rocket's third stage, the Saturn IB rocket's second stage, and the structural basis of the Skylab station. Image credit: NASA
OART's ISS Program was envisioned as an evolutionary extension of the Skylab Program. Skylab A and its backup, Skylab B, employed 22-foot-diameter Saturn S-IVB rocket stages as their basic structure. The S-IVB was the third stage of the three-stage Saturn V moon rocket and the second stage of the two-stage Saturn IB rocket. From top to bottom, the stage comprised the ring-shaped Instrument Unit (the "electronic brain" of the Saturn V or Saturn IB rocket of which the S-IVB stage was part), a large tank for low-density liquid hydrogen fuel, a small tank for higher-density liquid oxygen oxidizer, and a restartable J-2 rocket engine.

Through the addition of metal-grid decks, life-support equipment and consumables, lights and air ducts, a film vault, living quarters, and experiment apparatus, the S-IVB hydrogen tank became the Orbital Workshop (OWS), Skylab A's main habitable volume. The empty S-IVB liquid oxygen tank served as a dumpster, and a radiator replaced its J-2 engine.

The OWS hydrogen tank had bolted to its top the Airlock Module (AM), which in turn linked to the Multiple Docking Adapter (MDA) at Skylab A's front. The AM included a surplus Gemini hatch for spacewalks. The MDA included a main axial (front) docking port and a back-up radial port.

Besides the OWS, MDA, and AM, Skylab A included the Apollo Telescope Mount (ATM), an unpressurized compartment containing instruments for viewing the Sun. The ATM, mounted on a truss attached to the side of the MDA, included four electricity-generating solar arrays arranged in "windmill" fashion. These augmented two large solar-array "wings" on Skylab A's sides.

The Skylab space station as envisioned in 1970. Image credit: NASA
Skylab A was commonly referred to simply as Skylab, since no firm plan existed to actually launch Skylab B. When the OART engineers completed their report, NASA planned to launch Skylab in late 1972; then, over a period of about nine months, the U.S. civilian space agency would launch to the station three crews in Apollo Command and Service Module (CSM) spacecraft atop Saturn IB rockets. The three-man crews would live and work on board Skylab for up to 56 days. While unoccupied - months might pass between one crew's departure and the next crew's arrival - Skylab would operate under ground control.

The OART engineers applied the term "interim" to their eight-and-half-year program because they intended that it should lead from the Skylab Program to a permanent Space Station through "evolutionary, gradual, and step-wise spacecraft systems development." Beginning about three years after the third and final Skylab crew returned to Earth, a new ISS would reach LEO every two and a half years. Each would be staffed continuously for from 360 to 420 days.

NASA planning was in flux at the time the OART team prepared its report, and would remain so even after President Richard Nixon approved development of a semi-reusable Space Shuttle in January 1972. The ISS Program would span most of a decade, and NASA had in its dozen-year history experienced program instability on the scale of months. These factors caused the OART engineers to avoid making assumptions about the nature of NASA's eventual permanent Space Station when they planned their ISS Program.

They went so far as to suggest, in fact, that the Station/Shuttle Program might be delayed or abandoned in favor of some new space goal before the ISS Program ran its course. For planning purposes, however, they adhered to a timeline which saw NASA's permanent Space Station become operational in late 1987, about six years after the date they gave for the Shuttle's maiden flight and a little more than three years after the last ISS crew returned to Earth.

In keeping with the $3.3-billion Fiscal Year 1972 NASA budget Nixon's Office and Management and Budget had sought from Congress in January 1971, the OART engineers optimistically assumed a steady NASA annual funding stream of $3.3 billion throughout the ISS Program. They estimated that each interim station would cost $2 billion, of which about $330 million would be spent on hardware development, $500 million on experiments, and $1.6 billion on spacecraft hardware. Their program would, they calculated, cost on average about $500 million per year, leaving $2.8 billion for other NASA projects, including Station/Shuttle development.

Interestingly, just 13 days after the OART team completed its report, the Soviet Union launched 20-ton Salyut 1, the world's first space station. The Soviets had during the 1969-1970 period made it known publicly - most prominently in an October 1969 speech by Soviet leader Leonid Brezhnev - that they intended to establish Earth-orbiting stations, so it is tempting to suppose that OART's study was at least in part motivated by Soviet statements.

In January 1970, in fact, the U.S. Central Intelligence Agency had completed a report, classified "SECRET," in which it suggested that the Soviets might construct a series of stations, each larger and more capable than the last, culminating, perhaps, in a $5-billion, 150-ton station between 1976 and 1980. The OART engineers did not, however, mention Soviet space plans in their report.

Interim Space Station design. Image credit: NASA
Like Skylab, the interim stations would reach LEO atop two-stage Saturn V rockets. The first station in the series, designated Interim Space Station-A (ISS-A), would be mainly outfitted for biotechnology research. It would operate in a a 245-nautical-mile (nm) orbit inclined 28.5° relative to Earth's equator. The OART team envisioned that ISS-A would be built from Skylab B. Like the other three stations in its series, ISS-A would lack an ATM.

Based on Skylab experience, the OART engineers calculated that ISS-A would at launch weigh at least 57.25 tons. They then assumed a 30-ton "growth allowance" which could be wholly or partly used during development and assembly. This meant that ISS-A might weigh as much as 87.25 tons at launch.

NASA would launch the first three-man ISS-A crew - indeed, the first crew of the ISS Program - in a modified CSM within a day or two of the station's launch. No more than 16 hours after they reached LEO, the astronauts would pilot their spacecraft to a docking at one of ISS-A's two MDA docking ports.

The CSMs that delivered astronauts to the interim stations would differ significantly from their Apollo/Skylab predecessors. The most obvious change would be a new-design launch vehicle. The OART engineers considered using either the Saturn IB or the Titan-IIIM to launch ISS CSMs before they settled on a hybrid of the two.

Dubbed the SRM-S-IVB, the new rocket's first stage would comprise a cluster of three 10-foot-diameter, seven-segment Titan-IIIM solid-propellant rocket motors. The Titan-IIIM, never flown, had been meant to launch the U.S. Air Force Manned Orbiting Laboratory, which was cancelled in February 1969. As its name implies, the SRM-S-IVB launch vehicle's second stage would be a lightly modified Saturn S-IVB stage.

The SRM-S-IVB would be capable of launching a 28.7-ton payload from Kennedy Space Center, Florida, to a 245-nm orbit at 28.5° of inclination. For comparison, the Saturn IB could launch about 17.5 tons to the same orbit.

The ISS CSM, like its Apollo and Skylab predecessors, would be a two-part spacecraft. The smaller of the two parts was the conical Command Module (CM), a three-man crew capsule with a reentry heat shield on its broad aft end and an active probe docking unit on its nose. It would lower on parachutes to a splashdown at mission's end. The drum-shaped Service Module (SM) had a Service Propulsion System main engine bell protruding from its aft end.

The 6.3-ton ISS CM would closely resemble its Apollo and Skylab counterparts. The ISS SM, on the other hand, would undergo many changes. Because it would need to carry only enough propellants for Earth-orbital rendezvous and docking maneuvers plus an end-of-mission de-orbit burn, OART proposed to replace its propellant tanks, which were sized for a voyage to lunar orbit and back, with smaller tanks derived from those in the Apollo Lunar Module. Because the ISS CSM would fly independently for a total of less than a day, rechargeable batteries in the ISS SM would stand in for the Apollo SM's trio of fuel cells and tanks of fuel-cell reactants.

These changes would free up for conversion into cargo holds four of the six 175-cubic-foot bays clustered around the SM's cylindrical core bay. The four bays would transport a total of about 10 tons of supplies and equipment. Minus cargo, the ISS SM would weigh 8.6 tons.

The Apollo Command and Service Module (CSM) spacecraft would undergo considerable modification for the ISS Program. Image credit: NASA
Water, oxygen, and nitrogen stored in tanks in the ISS SM cargo bays would pass through umbilicals to nozzles in the ISS CM. The astronauts would attach hoses to the nozzles to transfer the water, oxygen, and nitrogen to storage tanks inside the ISS.

Solid cargo, on the other hand, could only be transferred from the ISS SM to the ISS by spacewalks. The OART team noted that the spacewalking astronauts would have to travel only about 15 feet to reach the ISS SM from the ISS AM.

The astronauts would hinge open panels in the ISS SM's sides and transfer cargo items to the open ISS AM hatch by attaching them to a clothesline-like "endless line" similar, perhaps, to that used on the moon to convey sample boxes and film from the base of the LM ladder to the LM ascent stage hatchway. Cargo items as large as 3.5 feet wide by 12 feet long could be removed from the ISS SM cargo bays and transferred through the Gemini-type hatch into the ISS AM, the OART team estimated.

Because it would be cast off to burn up in Earth's atmosphere after it performed the deorbit burn, the ISS SM could transport only "up" cargo. "Down" cargo - for example, biological samples and exposed film - would reach Earth within the relatively small volume of the ISS CM. The OART engineers estimated that, by removing all lunar mission equipment and supplies from the ISS CM, enough room would be freed up to enable it to convey to Earth all experiment cargo a three-man crew was likely to generate during a 90-day stint on board an ISS.

Converting the Apollo CSM into the ISS CSM would cost $100 million, the OART engineers estimated. This price-tag would not include the $80-million cost of developing the SRM-S-IVB launcher.

The Saturn S-IVB rocket stage would form the largest habitable component of Skylab and the ISS stations. Spacious with a Skylab or ISS-A crew of three, it would become increasingly crowded as the ISS Program evolved. Image credit: NASA
Astronauts would occupy ISS-A continuously for 360 days. Four three-man crews would live and work on board for 90 days each. During crew rotations, the replacement crew would dock at the vacant MDA port and six men would temporarily inhabit ISS-A.

OART made biotechnology ISS-A's main research emphasis because its crews would need to demonstrate that astronauts could remain fit and competent throughout a 90-day stay in space. In addition, it would seek to advance medicine on Earth through the study of the human organism in novel conditions. Most of the experiments performed in the ISS series would have a similar dual purpose: that is, to advance the cause of spaceflight and to provide tangible benefits to people on Earth.

ISS-A's mission, the OART team explained, would continue and expand the biomedical research program begun on board Skylab. In addition to copies of Skylab experiment apparatus, experiment equipment launched on board ISS-A would include a 1750-pound "Manned Onboard Centrifuge" - a centrifuge large enough to spin a human - and a 1300-pound Integrated Medical and Behavioral Laboratory Measurement System (IMBLMS). The IMBLMS would be linked to operational control systems throughout ISS-A to monitor crew performance. Centrifuge, IMBLMS, and "peripheral equipment" such as a bicycle ergometer, an experiment airlock, and a sound-proofed work area would together cost $72 million.

Astronauts on board the interim stations would work 10 hours per day, six days per week. At any one time, two-thirds of the crew on an ISS would be focused on its experiment programs, while the rest would maintain systems and perform housekeeping chores. For ISS-A, this meant that, during any particular working day, two of the three astronauts on board would focus on experiments while the third served as space handyman.

Forty-five man-hours per week would be spent on IMBLMS experiments and 55 man-hours per week on centrifuge experiments. Other experiments - for example, assessment of techniques for weightless maintenance of life-support equipment intended for more than a year of continuous use - would require a total of 30 man-hours per week.

The OART team estimated that Skylab's six solar arrays and the batteries it carried for storing electricity for the night part of its orbit would produce about six kilowatts of continuous power and have a total mass of 7.5 tons. The ATM arrays and OWS arrays would each produce about half of Skylab's electricity. The team assumed that ISS-A's arrays and batteries would weigh the same as Skylab's, but would produce between six and 10 kilowatts of continuous electricity. In the absence of an ATM, the ISS-A solar array configuration would necessarily differ from that of Skylab.

Of the stations in its series, ISS-A would most resemble Skylab. Beginning with ISS-B, larger crews and more complex experiment programs would drive evolutionary modifications to the ISS design, though all would retain the basic MDA-AM-OWS layout.

The AM would have undergone little modification from its first flight as part of Skylab to its last as part of ISS-D. Image credit: NASA
The first three-man ISS-B crew would arrive for a 90-day stint beginning in July 1978, one-and-a-half years after ISS-A's last crew returned to Earth. A second three-man crew would reach the station a month later. The resulting six-man crew would work together for 60 days, then the first three-man crew would return to Earth. A third three-man crew would arrive almost immediately to replace them. Thirty days later, the second ISS-B crew would return to Earth and a fourth crew would replace them. The seventh three-man ISS-B crew would return to Earth in July 1979 and not be replaced, and the eighth and last three-man crew would splash down a month later, about 390 days after ISS-B reached LEO.

ISS-B's main mission would be to perform experimental Earth surveys, which the OART team placed into five multi-part categories. These were: agriculture/forestry/geography; geology/mineralogy; hydrology/water resources; oceanography; and meteorology. The station would revolve around the Earth in an orbit inclined 50° relative to the equator, so that it would pass over the "most populace [sic] and agriculturally productive areas of the Earth."

ISS-B astronauts would spend 90 man-hours per week testing, calibrating, and modifying a $40-million, 4700-pound suite of 19 experiment sensors covering the spectrum from ultraviolet through visible light to infrared and microwave. They would also continue biotechnology experiments; for example, the OART team allotted 70 man-hours per week to continuation of the IMBLMS program begun on board ISS-A.

ISS-B solar arrays and batteries would produce between seven and 15 kilowatts of continuous electricity for experiments and station operations. As with ISS-A, the OART engineers did not specify ISS-B's solar array configuration, though they implied that it would have a collecting area larger than the ISS-A configuration.

The MDA flown as part of Skylab was more more cluttered than it appears in this NASA cutaway. Skylab crews did not feel comfortable within the MDA because it lacked an obvious "up-down" orientation; no doubt the ISS MDAs would have been modified to take this into account. EREP = Earth Resources Experiment Package. ATM = Apollo Telescope Mount
ISS-C, scheduled for launch in January 1981, and ISS-D, scheduled for launch on NASA's last Saturn V rocket in July 1983, would have many similarities. Each would have a crew complement of nine, making NASA's reliance on the three-man ISS CSM for crew rotation and resupply somewhat problematic. Somewhat surprisingly, though the OART engineers acknowledged that, based on their own NASA flight schedule, the reusable Space Shuttle would have begun flights in late 1981, they elected (for the sake of "simplicity") not to use it for ISS-C and ISS-D crew rotation and resupply.

ISS CSM launches in January, February, and March 1981 would launch ISS-C's initial nine-person crew. Only a month after its third crew arrived, its first crew would complete its 90-day stint on board the station and would return to Earth. NASA would immediately launch a fourth crew to replace them.

ISS-C and ISS-D would each receive 12 three-man crews. Each station would support nine men for 360 of the 420 days it was occupied. Flights to ISS-C and ISS-D would bring to 36 the total number of ISS CSMs and SRM-S-IVB boosters required for the program.

ISS-C astronauts would "evaluate in terms of direct Earth economic benefits the use of the space environment for materials processing and manufacture." Taking advantage of weightlessness and nearly pure vacuum, the astronauts would devote 95 man-hours per week to manufacturing large crystals, exotic composite materials, and biological compounds impossible (or at least very difficult) to create under terrestrial conditions. Manufactured materials and compounds would splash down with returning astronauts as "down" cargo in the ISS-C CMs.

The Saturn V S-IC second stage would have served as a counterweight for the ISS-C artificial-gravity experiment. Image credit: NASA
ISS-C would also see a 45-day artificial-gravity experiment that would preempt the space exploitation experiments. The OART engineers provided few details of the experiment, though they did explain that the spent S-II second stage of the Saturn V that launched ISS-C into orbit would serve as an artificial-gravity counterweight. Probably cables would have linked the interim station and the spent stage; as the cables were slowly reeled out, thrusters on ISS-C would have fired to spin the assemblage end-over-end and keep the cables under tension. As the cables reached maximum extension, thrusters would have carefully trimmed the spin rate to ensure the desired acceleration - which the crew would feel as gravity - on board the ISS-C station.

The ISS-C/ISS-D solar array configuration would be identical to that of ISS-B; technological advancements would, however, enable their power systems to provide no less than 15 kilowatts of continuous electricity. The ISS-C and ISS-D astronauts would also evaluate Isotope Brayton nuclear power units for use on NASA's permanent Space Station.

The Isotope Brayton units would not reach space attached to ISS-C and ISS-D; rather, they would be launched separately, possibly atop Titan rockets. The OART engineers did not describe how they would rendezvous and dock with ISS-C and ISS-D. The five-ton ISS-C Isotope Brayton unit would generate six kilowatts of electricity; the more advanced six-and-a-half-ton ISS-D unit would produce 15 kilowatts, doubling that station's electrical supply.

Biotechnology experiments would continue during the ISS-C and ISS-D missions. The ISS-C biotechnology program would, of course, include assessment of the effects of spin-induced artificial gravity. With their nine-person crews, the third and fourth stations of the ISS program would be more crowded than their predecessors, offering an opportunity for study of complex human interactions aboard spacecraft.

ISS-D would include three free-flying astronomy modules in addition to astronomy instruments on the station. How the free-flyers would reach LEO was not made clear. The $50-million Cosmic Ray Physics Laboratory would weigh in at a whopping 26,700 pounds. The $125-million, 6195-pound Solar Astronomy Module would include "larger versions" of the Sun-observing instruments in the Skylab ATM. The $130-million, 6000-pound Stellar Astronomy Module would carry a telescope with a three-meter mirror. For comparison, the Hubble Space Telescope primary mirror is 2.4 meters across. Astronauts would regularly collect exposed film from the free-flying modules, though how they would reach them was not explained.

The OART engineers estimated that, by the time the last ISS-D crew returned to Earth, NASA would have accrued the equivalent of more than two years of permanent Space Station biomedical data and operations experience from its four interim stations. This would, they concluded, constitute the ISS Program's chief benefit to U.S. spaceflight; specifically, it would
enable the [permanent] Space Station to start its effective experimental usefulness almost at initial manning. . . [because] most of the human and operational uncertainties of long duration spaceflight would have been removed by. . .results [from the] four earlier interim space station flights.

Study of an Evolutionary Interim Earth Orbit Program, Memorandum Report MS-1, J. Anderson, L. Alton, R. Arno, J. Deerwester, L. Edsinger, K. Sinclair, W. Tindle, and R. Wood, Advanced Concepts and Missions Division, Office of Advanced Research and Technology, NASA Headquarters, 6 April 1971

"Intelligence Report: Aims and Costs of the Soviet Space Station Program," SR IR 70-1-S, Directorate of Intelligence, Central Intelligence Agency, January 1970

More Information

An Alternate Station Shuttle Evolution: The Spirit of '76 (1970)

Evolution vs. Revolution: The 1970s Battle for NASA's Future

Skylab-Salyut Space Laboratory (1972)

Dreaming a Different Apollo, Part One

03 November 2015

Dreaming a Different Apollo, Part Three: Circumnavigation

Image credit: NASA
Had anyone told him on 4 January 1964 that he'd be standing on the moon on 4 January 1974, he'd probably have punched whoever that was in the nose. That was the day Al burned and they lost the race. They'd stumbled, taken too long to get up again, and so had emboldened their adversary.

The Soviets had taken a different approach to piloted moon-flight; one less costly, safer, and more likely to succeed than the American Apollo plan. They never tired of saying that. They had used their converted R-7 missiles, the same rockets that had launched Sputnik and Laika and Gagarin and Leonov. They had ignored their captured Germans, they said, had gone with native Russian wisdom.

Five launches, five pieces orbiting Earth, with the last one carrying two men. They had chased down the other four, docked with them. Those four payloads turned out to be rocket stages; by the time the next-to-last exhausted its propellants and was cast off, the two cosmonauts were on course for the moon.

No one expected them to land. Everyone thought it was a fly-around circumlunar mission - which would have been bad enough, as far as American prestige was concerned. Yet land they did. 8 October 1968 - the date that men, products of the superior Soviet system, stood for the first time on another world. Even after almost six years, he could not quite believe that it had happened.

The two cosmonauts spent their last rocket stage and most of the propellants in their tiny lander to set down not far from a robot lander launched a month before. They hadn't said much about that lander after they launched it, so everyone thought it had crashed. Suddenly, though, its purpose became clear: besides providing a landing beacon for the manned lander, it was tanker.

After they'd planted and saluted their flag, the first thing they did was drive the tubby tanker, with its eight little wheels, to within hose length of their lander. Then they fastened on the hoses and pumped across the propellants.

The Russians called the place they landed Tranquility Base. Of course it wasn't a real "base" - that came later. They picked up a few rocks and saluted their flag a second time for the camera. Then, five hours after they landed, they blasted off for home.

"Charlie, you daydreaming over there?" The voice from his headphones gave him a start. He cleared his throat. "No, boss. Keepin' an eye on things." He heard Young chuckle, then his commander appeared out of the long shadow Lander-2 cast on the stark gray plain.

Beyond stood three more landers, L-1, L-3, and L-4, scattered off into the distance. L-1 was short, empty, abandoned. L-3 and L-4, with their pointy Earth-Return Vehicles on top, were the tallest things for a hundred miles around.

Native Russian wisdom, Duke thought, snorting. No way the Russians could do what they were about to do, even with the Proton and Salyut rockets they had used to win the second moon race, the race to establish a permanent lunar outpost.

The pressurized rover Endurance was already unloaded from L-1, powered up, and checked out. Argo, its near-twin, still stood atop L-2, its front windows pointed at the sky. Argo's four cleated wheels glinted in stark sunlight; its roof was in shadow, but visible by light reflected from the lunar surface. The wheels were locked onto the ramp Argo would roll down to reach the ground.

Now the ramp and Argo's rounded nose began to tip slowly - ever so slowly - off vertical, toward the rising lunar Sun. "Gene-o," Duke said, "tip start looks good from this side. Do you copy?" Cernan, commander of Endurance, spoke up after a moment. "Yeah, Charlie - looks nice and straight here, too. Over."

"Good resistance on the motors," said Evans, Cernan's pilot. He stood close by L-2, reading the lighted display on the flip-down rover-release control panel. Argo was now tilted about 30 degrees from vertical. "Stand by for the drop," Evans said.

Argo continued to tip, passing horizontal. As its nose began to angle downward, the ladder-like lower ramp slid out and touched the surface in two puffs of dust. "Ramp is locked," Evans reported.

Duke moved forward to watch the wheel locks disengage. "Ready for wheel lock release," said Evans. "Go ahead, Ron," said Young. Duke saw the three locking mechanisms disengage and tip out of the way. On Earth, there'd been three rapid loud bangs - pyros cutting the locks. Here, in lunar vacuum, utter silence.

Argo rolled the last yard to the surface, bounced a little on its suspension and stirred up some dust. As it rolled to a stop, the umbilical linking it to L-2 pulled free and, after a moment, the rover's low-gain antenna tilted and slewed automatically and found Earth.

"Rover boys, this is Houston." That was Ken Mattingly on Capcom. Mission Control shift had changed from White to Maroon. A long, crackling pause. "We are receiving Argo telemetry. Looks good."

"Whew-ee! That's two for two," said Cernan.

"Can't wait to get behind the wheel," said Young as he circled Argo, video recording its exterior for the engineers back on Earth. "Ken - how are we on the timeline? Over."

A pause. "John, you're about 10 minutes behind. Not yet into your PLSS reserve. No one is worried here. Over." "Roger that," said Young, as he stowed his recorder in his hip bag.

Mattingly spoke again after a moment. "Rover control says - he says, 'no racing once you're behind the wheel.' He keeps saying that. He's worried about you hotshots. Over." Young and Cernan both chuckled.

Cernan spoke. "John, Charlie, Ken - Ron and me, we're headed back to Endurance. We're hungry. Over."

"Go ahead, get your dinner," Young said, hopping past Duke, toward their lander. "Charlie and I will return to L-4 in a coupla minutes. That OK, Ken?"

A pause. "Gene, John - you are go to close out EVA-1. Over."

Duke hopped over to Young. He turned, minding his footing, and looked back at Argo, glittering on the surface of the moon, and at the retreating PLSS backpacks of Cernan and Evans, who followed the trail of footprints leading to Endurance. Argo had light blue painted highlights and Endurance had red ones. They matched the red stripes on Cernan's suit and the blue stripes on Young's.

"All right, Charlie, let's get inside," Young said. "Tomorrow we test-drive our new ride. Can you believe it?"

Duke felt a lump in his throat. They had come so far, and now they were ready to make history. The first lunar surface circumnavigation. They'd follow the route the engineers and scientists had so carefully plotted for them using the high-res images from the Apollo 12 and Apollo 14 lunar polar orbiters. They'd cross the north pole and drive south over the high center of Farside, then cross the south pole and drive north. They'd rendezvous with Surveyor-derived cargo landers every couple hundred miles or so to take on supplies and refuel.

If all came off as planned, in two months they'd all be back here, in Sinus Medii, ready to power up L-3 and L-4 and return to Earth. And it would all come off as planned, Duke was sure of it. It was time America scored a victory on the moon.

After that, other astronauts - most likely Jack and Karl doing science, plus Dick and Ken in command - would drive around the moon along its equator. If all went as planned, the second circumnavigation would be under way during the U. S. Bicentennial.

"We're on our way, John," said Duke, as he hopped toward L-4's ladder. "It feels real good."