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 their plan seems like an Apollo massacre, it would in fact have deprived the United States of two manned moon missions, not four. By the time the OART team proposed it, 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. These were scrapped to free up funds for NASA's hoped-for 12-man Space Station and the fully reusable winged Space Shuttle that would deliver its crews and supplies. NASA subsequently renumbered its surviving Apollo missions, so the cancelled missions are more commonly known as Apollo 18 and Apollo 19 today.
OART's proposed Interim Space Station (ISS) program was, in effect, 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 Instrument Unit (the "electronic brain" of the Saturn V or Saturn IB rocket of which the S-IVB was part), a large tank for liquid hydrogen fuel, a small tank for liquid oxygen oxidizer, and a restartable J-2 rocket engine.
Through the addition of decks, life-support equipment and consumables, and experiment apparatus, the S-IVB hydrogen tank became the Orbital Workshop (OWS), Skylab A’s main habitable volume. The OWS had bolted to its top the Airlock Module (AM), which was in turn linked to the Multiple Docking Adapter (MDA) at Skylab A's front. The MDA would include a main axial docking port and a back-up radial port. Besides the OWS, MDA, and AM, Skylab A had mounted on a truss attached to the MDA an Apollo Telescope Mount (ATM) with instruments for viewing the Sun. The ATM included four electricity-generating solar arrays arranged in “windmill” fashion. These augmented two large solar-array "wings" on Skylab A's sides. The empty liquid oxygen tank served as a dumpster, and a radiator replaced the J-2 engine.
Skylab A was commonly referred to simply as Skylab, since no firm plan existed to launch Skylab B. When the OART engineers completed their report, NASA planned to launch Skylab in late 1972 and then, over about nine months, launch three crews to it atop Saturn IB rockets in Apollo Command and Service Module (CSM) spacecraft. Each three-man crew would live and work on board Skylab for up to 56 days. Skylab would operate under ground control between crew visits.
The OART engineers applied the term “interim” to their eight-and-half-year program because they intended for it to lead from Skylab 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 interim station would reach LEO every two and a half years. Each would be staffed continuously for from 360 to 420 days.
Because NASA planning was in flux and their interim station program spanned the better part of a decade, the OART engineers sensibly made no assumptions about the precise form that NASA's eventual permanent Space Station might take. They went so far as to acknowledge that the Station/Shuttle Program might be delayed or abandoned in favor of some new space goal before the interim station program ran its course. For planning purposes, however, they offered a timeline in which NASA's permanent Station became operational in late 1987, about six years after the Shuttle's maiden flight and a little more than three years after the last interim station crew returned to Earth.
In keeping with the $3.31-billion Fiscal Year 1972 NASA budget President Nixon's Office and Management and Budget had requested from Congress in January 1971, the OART engineers assumed a steady NASA annual budget of $3.3 billion throughout the interim station 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 cost an average of about $500 million annually.
Interestingly, just 13 days after the OART team completed its report, the Soviet Union launched Salyut 1, the world's first space station. The Soviets had during 1969-1970 made known publicly - most notably in an October 1969 speech by Soviet leader Leonid Brezhnev - their intention to establish Earth-orbiting stations, so it is tempting to suppose that OART's study was in part motivated by Soviet statements. In fact, in January 1970, the U.S. Central Intelligence Agency 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 the Soviet space program in their report.
Like Skylab, the interim stations would reach LEO atop two-stage Saturn V rockets. The first, designated ISS-A, 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. The OART engineers calculated, based on Skylab experience, that ISS-A would at launch weigh at least 57.25 tons. To this would be added during development and assembly some or all of a 30-ton "growth allowance." This meant that ISS-A could in its final form weigh as much as 87.25 tons at launch from Earth and still attain its operational orbit.
NASA would launch the first three-man ISS-A crew in an Apollo CSM-derived spacecraft within a day or two of the station's launch. No more than 16 hours after liftoff, 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 in many ways from those of Apollo and Skylab. To begin with, they would employ a new-design launch vehicle. The OART engineers considered using either the Saturn IB or the Titan-IIIM developed for the canceled U.S. Air Force Manned Orbiting Laboratory before they settled on a hybrid of the two. Dubbed the "SRM-S-IVB," it would include a first stage comprising a cluster of three 10-foot-diameter, seven-segment Titan-type solid-propellant rocket motors and an S-IVB second stage. The SRM-S-IVB, which OART estimated would cost $80 million to develop, 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 interim station CSMs would, like their Apollo and Skylab counterparts, comprise a conical Command Module (CM) and a drum-shaped Service Module (SM). Their CMs would be upgraded to operate for 90 days in space while docked with an interim station, but otherwise would be very similar to their Apollo and Skylab counterparts. Each would carry three astronauts, weigh 6.3 tons, and splash down at sea at mission's end.
The SM, on the other hand, would undergo many alterations. OART proposed to replace the SM's propellant tanks, which were sized for a voyage to lunar orbit and back, with smaller Apollo Lunar Module tanks, because the SM needed to carry only enough propellants for rendezvous and docking maneuvers and an end-of-mission deorbit burn. The SM electrical system could also be simplified and reduced in size. These changes would free up four of the six 175-cubic-foot bays clustered around the SM's cylindrical core for conversion into cargo bays. The four bays would be capable of transporting a total of about 10 tons of supplies and equipment. The SM would weigh 8.6 tons without cargo.
In some respects, the interim station CSM design resembled the 1963 North American Aviation MODAP logistics spacecraft design. Converting the Apollo/Skylab CSM into the interim station CSM would cost $100 million, the OART team estimated.
Nozzles in the CM could supply water, oxygen, and nitrogen from tanks installed in the SM cargo bays to hoses linked to storage tanks inside the interim station, but solid cargo could be transferred only through spacewalks. The spacewalking astronauts would, however, have to travel only about 15 feet to reach the SM from the AM. They would open panels in the SM's sides and transfer cargo to the open AM hatch by affixing it to a clothesline-like "endless line" similar, perhaps, to one 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 SM bays and moved into the AM, the OART team estimated.
The SM could transport only "up" cargo, for it would be cast off to burn up in Earth's atmosphere after it performed the end-of-mission deorbit burn. "Down" cargo - for example, biological samples and film - could only reach Earth in the CM. The OART engineers estimated that, by removing all lunar mission equipment from the CM, enough return capacity could be created to enable it to transport to Earth all experiment results that a three-man crew was likely to generate during a 90-day stint on board an interim station.
Retooled to support "biotechnology" research, ISS-A would be continuously occupied 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.
Biotechnology would be ISS-A's research emphasis because its crews would need to demonstrate that astronauts could remain fit and competent throughout a 90-day stay in space, the standard crew stay-time on board the ISS stations. In addition, it would seek to advance medicine in general through 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 would, the OART team explained, continue and expand the biomedical research program begun on board Skylab. In addition to copies of Skylab experiment apparatus, experiments 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 for 10 hours per day, six days per week. At any one time, two-thirds of the crew on an interim station would focus 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 experiments involving the centrifuge. 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 batteries 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 solar 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 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 crew would return to Earth and a fourth 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 space.
ISS-B's main mission would be to perform experimental Earth surveys, which the OART team grouped into five 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 could 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 experimental sensors covering the spectrum from ultraviolet through visible light to infrared and microwave. They would also continue biomedical 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 team did not specify ISS-B's solar array configuration, though they implied that it would have a larger collecting area than the ISS-A configuration.
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 full crew complement of nine, making more challenging NASA's reliance on the three-man ISS CSM for crew rotation and resupply. Surprisingly, though the OART engineers acknowledged that, based on their own NASA flight schedule, the reusable Space Shuttle would begin flights in late 1981, they elected (for the sake of "simplicity") not to consider using it for ISS-C and ISS-D crew rotation and resupply.
Monthly ISS CSM launches in January, February, and March 1981 would bring ISS-C's population to nine. 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. The stations would support nine men for 360 of the 420 days each was occupied. Flights to ISS-C and ISS-D would bring to 36 the total number of ISS CSMs and SRM-S-IVB boosters launched in the interim station program.
The OART engineers explained that ISS-C astronauts would "evaluate in terms of direct Earth economic benefits the use of the space environment for materials processing and manufacture." Specifically, they would spend 95 man-hours per week performing "space exploitation" experiments in the space environment. Taking advantage of weightlessness and nearly pure vacuum, the astronauts would manufacture 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 CM.
ISS-C would, however, also see a 45-day artificial-gravity test that would preempt space exploitation experiments. The OART engineers provided few details of the artificial-gravity 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 a counterweight for the station. The linked spent stage and stage-based station would then be spun end over end to create acceleration which the astronauts in ISS-C would feel as gravity.
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 astronauts would also test Isotope Brayton nuclear power units in order to evaluate them 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 the interim stations. 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.
Biomedical experiments would continue during the ISS-C and ISS-D missions. The third and fourth stations of the ISS program would be more crowded than their predecessors, offering an opportunity for the study of complex human interactions on board spacecraft. The ISS-C biomedical program would also include assessment of the effects of spin-induced artificial gravity.
ISS-D would include three free-flying astronomy modules as well as instruments mounted on the station. 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 solar astronomy 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's mirror is one meter across. Astronauts would regularly collect exposed film from the free-flying modules, though how they would reach them was not explained. Some station-mounted astronomy instruments would make use of an experiment airlock.
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 interim station program's chief benefit to U.S. spaceflight; specifically, it would
References
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.
