|This NASA artwork from 1972 portrays the sheer volume of the Skylab Orbital Workshop, the first U.S. space station.|
Nearly three years earlier, budget cuts had halted Saturn V production, so NASA had been forced to abandon plans for a single-launch, 33-foot-diameter core station. The Space Shuttle, originally intended as a cost-saving fully reusable space station crew and cargo transport, was subsequently tapped to serve also as the sole launch vehicle for a multi-modular space station built up over the course of many flights. This meant that the Shuttle Orbiter's payload bay dimensions (15 feet in diameter by 60 feet long) and maximum payload mass (in theory, up to 32.5 tons) would dictate the size and mass of station modules and other components.
In the event, the first mission of the partially reusable Shuttle, STS-1, did not lift off until 12 April 1981, nearly two years after Skylab reentered and broke up over Australia (11 July 1979). The Orbiter Columbia remained aloft for two days before gliding to a landing on the dry lake-bed at Edwards Air Force Base (EAFB), California.
By then, engineers at NASA's Johnson Space Center had been at work for more than two years on a design for a Shuttle-launched station they dubbed the Space Operations Center (SOC). The SOC included a laboratory for experiments in microgravity, but was conceived mainly as a construction site for large structures, a servicing center for satellites, and a home port for a small fleet of space tugs. It was intended, in fact, to serve as a space shipyard, where would be assembled spacecraft for voyages beyond low-Earth orbit and large space structures such as Solar Power Satellites.
Reagan withheld his support for a further 18 months, until the beginning of the 1984 election year, when endorsing a space station - which was bound to create thousands of jobs - could provide maximum political advantage. During his 25 January 1984 State of the Union Address, he echoed President John F. Kennedy's May 1961 "Urgent National Needs" speech by calling on the U.S. civilian space agency "to develop a permanently manned space station and to do it within a decade." Reagan made mention only of the station's role as a laboratory. The station would, he said, "permit quantum leaps in our research in science, communications and in metals and life-saving medicines that can only be manufactured in space."
The Reagan White House disdained a space shipyard for two reasons. First, it was a relatively complicated design that could not be built for $8 billion spent over 10 years, the maximum price Administration budget watchdogs were willing to pay for a space station. The second reason was related to the first: a shipyard in space implied that things would be built there, and that in turn implied a commitment to new expenditures in the future.
From the Power Tower evolved the "Dual Keel" in late 1985. In May 1986, NASA released its Space Station "Baseline Configuration," a Dual-Keel station measuring 503 feet wide and 361 feet tall. The new design included about twice as many truss elements as the Power Tower, providing ample room for both space-facing and Earth-facing user payloads and eventual addition of space construction facilities. Assembly in orbit was to begin in 1992 and to be completed by Reagan's 1994 deadline.
|NASA's ambitious Dual-Keel Baseline Configuration of May 1986 was dead on arrival. Image credit: NASA|
The year 1990 saw new problems. Persistent hydrogen fuel leaks grounded the three-orbiter Shuttle fleet for nearly half the year, renewing doubts about the Shuttle's ability to reliably launch, assemble, resupply, and staff Freedom. Against this background, news emerged of a dispute within NASA over estimates of the number of spacewalks required to build and maintain the Space Station. The row triggered congressional hearings in May 1990.
In a report released on 20 July 1990, former astronaut and spacewalker William Fisher and JSC robotics engineer Charles Price, co-chairs of the Space Station Freedom External Maintenance Task Team, declared that Freedom would need four two-man spacewalks per week during its assembly and 6,000 hours of maintenance spacewalks per year after its completion. This amounted to 75% more spacewalks than the official NASA estimate, which was already considered excessive. Fisher called the spacewalk requirement "the greatest challenge facing the Space Station."
In November 1990, with new budget cuts in the offing, NASA began yet another Freedom redesign. At about the same time, Space Industries Incorporated (SII), a small engineering firm for which Maxime Faget, co-designer of the Mercury capsule, worked as Technical Advisor, began to examine a radical new approach to solving Freedom's persistent problems. SII performed its Orbiter-Derived Station (ODS) study on contract to Rockwell International, prime contractor for the Shuttle Orbiter.
SII noted that the U.S. House of Representatives Committee on Science, Space, and Technology wanted a "permanently manned Space Station, that meets our International Agreements, retains a capability for evolution, and has minimum annual and aggregate cost." At the same time, it explained, scientists and engineers of the space technology development and microgravity and life sciences research communities wanted NASA to provide an orbiting laboratory "without spending the entire available budget on the laboratory rather than on the experiments."
To satisfy these needs, SII proposed to draw upon Space Shuttle design heritage and operational experience. Specifically, the company proposed that NASA launch in 1996 an unmanned "stripped-down" Orbiter – one without wings, tail, landing gear, body flap, forward reaction control thrusters, and reentry thermal protection – to serve as Freedom's largest single element.
|Orbiter Derived Station in Man Tended Configuration after Mission Build-1. Image credit: SII/NASA|
What follows is a synthesis of information from two SII documents concerning the ODS. The first, a set of presentation slides, is not dated, though individual slides in the presentation carry July 1991 dates. The second document is SII's final report to Rockwell International dated September 1991. When the documents differ in significant ways, this is noted.
Copying NASA parlance, SII referred to the launch of the stripped-down Orbiter as Mission Build-1 (MB-1). Upon achieving a 220-nautical-mile-high orbit inclined 28.5° relative to Earth's equator, the ODS would turn its payload bay doors toward Earth, open them to expose the pressurized module and door-mounted radiators, and unroll its solar arrays to generate up to 120 kilowatts of electricity. At that point, the ODS would achieve Man-Tended Configuration (MTC). MTC meant that the station could be staffed while a Shuttle Orbiter was docked with it. According to SII, NASA's Freedom would not achieve MTC until MB-6, and its solar arrays would not generate 120 kilowatts of electrical power until MB-10.
|Orbiter Derived Station (top) and Shuttle Orbital Maneuvering System propulsion pod design differences. Image credit: SII/NASA|
SII proposed changes to the stripped-down Orbiter's OMS pods to increase reliability and enable long-duration use. A hydrazine monopropellant system would replace the baseline Orbiter bi-propellant system. The SSMEs would insert the stripped-down Orbiter directly into its initial elliptical orbit, then two sets of four 500-pound-thrust OMS engines – one set per OMS pod – would each draw on a pair of propellant tanks to perform the OMS-2 orbit-circularization burn at apogee. The roughly 13,000 pounds of propellant remaining after the OMS-2 burn would be sufficient to resist atmospheric drag and supply OMS pod attitude-control thrusters for two years.
SII suggested that the OMS tanks be refilled in orbit after they exhausted their initial load of hydrazine, but provided no details as to how this might be accomplished. Alternately, the company suggested, a new propulsion module might be docked with the ODS after the modified OMS pods ran out of propellant.
With MB-1 complete, SII's ODS would provide 11,000 cubic feet of pressurized volume containing 58 standardized payload racks. NASA’s Freedom, by comparison, would have no pressurized volume at all until the addition of the U.S. Lab during MB-6, and would not exceed 10,000 cubic feet of pressurized volume until MB-13. The U.S. Hab and Lab modules would together hold only 48 racks.
In SII's July 1991 ODS design, the large module launched in the stripped-down Orbiter payload bay on MB-1 included only Hab module functions, and MB-2 in 1997 would see a piloted Shuttle Orbiter deliver the U.S. Lab module. In its September 1991 final report, SII combined Lab and Hab in the stripped-down Orbiter payload bay and substituted a 47.5-foot-long "core module" for the Lab on MB-2. The cylindrical core would include eight docking ports on its sides and one at either end.
One of the core module end ports would be docked permanently with the port on the Hab/Lab module. Visiting Shuttle Orbiters would dock with the Earth-facing port at the core module's other end. Addition of the core module would increase ODS pressurized volume to 15,000 cubic feet. NASA's Freedom station would not exceed 15,000 cubic feet of volume until MB-16.
SII envisioned that ODS assembly flights would be interspersed with utilization flights beginning immediately after MB-1. The first ODS utilization mission would occur in 1996, and three would take place in 1997.
In addition to permitting early research on board the ODS, some utilization flights after MB-2 would deliver supplies and equipment in a drum-shaped Logistics/Life Support Module (LLSM). Astronauts would dock the LLSM to a core module side port using the visiting Orbiter's Canada-built Remote Manipulator System (RMS). Spent LLSMs would be returned to Earth for refurbishment and reuse. SII placed the ODS toilet and shower in the LLSM, arguing that servicing waste and water systems on the ground would be preferable to doing so in orbit.
SII noted that its Station would need very few assembly and maintenance spacewalks. It would, nevertheless, include a modified Shuttle Orbiter airlock attached to one of its core module side ports. The airlock would reach the ODS during an unspecified utilization flight after MB-2. Because ODS assembly would be relatively simple and assembly spacewalks minimal, SII assumed that the Station could do without its own Canada-built RMS. The company did not address how deletion of the Station RMS would affect U.S.-Canada relations.
The second assembly mission of 1997, MB-3, would see arrival of an Orbiter bearing in its payload bay an eight-man Assured Crew Return Vehicle (ACRV), a space station lifeboat. With the docking of the ACRV at a core module side port, the ODS could be staffed by eight astronauts with no Orbiter present. NASA called the ability to maintain a full crew with no Orbiter present "Permanent Manned Configuration" (PMC). NASA's Freedom Station would not achieve PMC until MB-16.
|Orbiter Derived Station in Assembly Complete configuration after Mission Build-6 in late 1998. The image displays an RMS robot arm, though SII stated that the stripped-down Orbiter would not carry one. Image credit: SII/NASA|
MB-4 would see an Orbiter deliver the pressurized part of the Japanese Experiment Module (JEM). Astronauts would use the Orbiter's RMS to dock it to a core module side port. During MB-5, astronauts would use the visiting Orbiter RMS to add the European Space Agency's Columbus laboratory module. With that, the SII's ODS would achieve its maximum pressurized volume: 24,000 cubic feet, or about 8,000 cubic feet more than planned for NASA's Freedom Station. MB-6 would add Logistics and unpressurized Exposure components to complete the JEM.
SII recommended that the core module's Earth-facing port be designed to rotate so that visiting Orbiters could optimally position themselves for assembly missions. During MB-5, for example, the visiting Orbiter's nose would face in the ODS's direction of flight so that its RMS could place the Columbus module at its designated core module side port. During MB-4 and MB-6, it would face in the opposite direction so that JEM components could be added.
MB-6, which would take place near the end of 1998, would mark the end of ODS assembly. By then, SII's station would have hosted seven utilization flights. For comparison, NASA's Freedom Space Station would host no utilization flights until 1998, when three would take place. Freedom would not reach "Assembly Complete" until 2000.
SII proposed ways that the baseline ODS might be upgraded. The company noted that, beginning with MB-10, NASA's Freedom would provide experimenters with more electricity (180 kilowatts) than would the ODS. If this power level were judged to be necessary for ODS operations, then a 60-kilowatt "power kit" could be added during a utilization flight. The company suggested that the kit's rolled solar arrays be attached to a special port installed in the stripped-down Orbiter's nose behind a streamlined faring.
The ODS included no provision for space-facing experiments; all of its modules were expected to be mounted on its Earth-facing payload bay side. This reflected the science and technology community's desire for a microgravity lab and the fact that highly capable automated space-facing satellites (for example, the Hubble Space Telescope) were available. If, however, space-facing experiments were desired on board the ODS, then it could be launched with a docking port on the Orbiter's space-facing belly. A tunnel through the ODS payload bay floor would link the port to the Hab/Lab module.
Probably the company's most controversial proposal was to accelerate ODS assembly by stripping down Columbia, NASA's oldest Orbiter. SII noted that Columbia was the heaviest Orbiter, so had the least payload capacity. It assumed that NASA would want to replace Columbia with a new, less heavy Orbiter, thus increasing the Shuttle fleet's overall lift capacity. SII called this "disposing of the worst and and replacing it with the best." Some components stripped from Columbia could, it suggested, be reused in the new Orbiter to save money.
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Space Station: Leadership for the Future, NASA PAM-509, F. Martin & T. Finn, NASA, August 1987
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McDonnell Douglas Phase B Space Station (1970)
Where to Launch and Land the Space Shuttle? (1971-1972)
Skylab-Salyut Space Laboratory (1972)
Evolution vs. Revolution: The 1970s Battle for NASA's Future
NASA's 1992 Plan to Land Soyuz Space Station Lifeboats in Australia