The first U.S. space station was Skylab, which NASA carefully dubbed an "Orbital Workshop" in order to distinguish it from the "real" space station it hoped to launch into low-Earth orbit (LEO) before the end of the 1970s. Skylab - a converted 22-foot-diameter Saturn S-IVB rocket stage - was launched on the last Saturn V rocket to fly. Three three-man crews lived and worked onboard the single-launch station for a total of 171 days between 26 May 1973 and 8 February 1974.
Nearly three years earlier, budget cuts had killed the Saturn V, so that NASA had been forced to abandon plans for a single-launch, 33-foot-diameter, multi-deck core space station. The Space Shuttle, originally intended as a cost-saving reusable space station crew and cargo transport, was tapped to serve also as the station's sole launch vehicle. This meant that the Shuttle Orbiter's payload bay dimensions (15 feet in diameter by 60 feet long) and maximum payload mass (in theory, about 32.5 tons) would dictate the size and mass of station modules and other components.
It also meant that NASA could not begin to launch its station until after Space Shuttle development and flight testing were completed. When the last crew left Skylab, the Shuttle's orbital maiden flight was set for early 1978. Operational flights were to start by 1980. In the event, the first Shuttle mission, STS-1, did not lift off until April 1981. The Shuttle Orbiter Columbia remained aloft for two days before gliding to a landing on the dry lakebed at Edwards Air Force Base (EAFB), California.
By then, engineers at NASA's Johnson Space Center had been at work for two years on a design for a Shuttle-launched space station that they dubbed the Space Operations Center. The SOC included a laboratory for experiments in microgravity, but it was conceived mainly as a construction site for large structures, a servicing center for satellites, and the home port of a small fleet of space tugs. It was intended, in fact, to serve as a space shipyard, the take-off point for voyages beyond LEO and the industrialization of space.
On 20 May 1982, a little more than a year after STS-1 and a little more than a month before STS-4 (27 June-4 July 1982), NASA Administrator James Beggs established the NASA-wide Space Station Task Force. President Ronald Reagan was on hand at EAFB Runway 22 that U.S. Independence Day to welcome Columbia home, and some within NASA hoped that he would use the occasion to declare his support for a permanent Earth-orbiting space station, "the next logical step" after Shuttle. Instead, Reagan declared only that the Shuttle was operational.
Reagan withheld his support for a further 18 months, until the beginning of the 1984 election year. 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. It 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."
Despite this clear message, NASA refused to abandon its plans for a shipyard in orbit. In August 1984, the space agency released a "reference configuration" intended to guide aerospace companies bidding on Space Station Program contracts. Called the "Power Tower," it included a 400-foot-long single main truss where SOC-like space construction hardware might eventually be mounted. In NASA artwork depicting the station, featureless boxes stand in for unspecified large user payloads and hoped-for shipyard elements.
NASA envisioned that spacewalking astronauts would bolt together the Power Tower truss in orbit piece by piece. During Shuttle mission STS-61B (26 November-3 December 1985), in fact, spacewalking astronauts successfully tested two truss-assembly methods in the payload bay of the Orbiter Atlantis.
From the Power Tower evolved the "Dual Keel" in late 1985. In May 1986, NASA released its Space Station "Baseline Configuration." It was a Dual-Keel station measuring 503 feet wide and 361 feet tall (image at top of post). 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 be completed by Reagan's 1994 deadline.
The Baseline Configuration was dead on arrival, however, because of the 28 January 1986 loss of the Shuttle Orbiter Challenger and its seven-member crew. By March 1986, NASA and its contractors had begun work to scale back the Space Station. At first it shrank but retained its Dual-Keel shape. After that, in the "revised baseline configuration" of 1987, it lost its keel trusses, becoming only a single truss with solar arrays at either end and laboratory and habitat modules at its center. NASA made sure, however, that the design included "hooks" and "scars" that would enable eventual expansion to the Dual-Keel design.
President Reagan christened the Space Station Freedom in 1988. The following year, with the Station expected to be over-budget, overweight, underpowered, and too demanding to build, NASA abandoned the Dual Keel configuration entirely. At the same time, planners proposed an advanced "transportation node" space station for the early 21st century. This proposed separation of functions was an acknowledgment that an orbital shipyard's jolts and vibrations would wreak havoc on microgravity experiments.
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 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, or reentry thermal protection - to serve as Freedom's largest single element. Removing systems with a total mass of 45,600 pounds would boost the Orbiter's payload capacity to 81,930 pounds, permitting it to transport a 56.5-foot-long pressurized module permanently mounted in its payload bay and four pairs of rolled-up 120-foot-long solar arrays under streamlined housings along its sides. The pressurized module would include a single docking port and a hatch linking it to the stripped-down Orbiter's two-deck crew compartment. In effect, SII's approach would briefly restore the space station launch capability lost when the U. S. abandoned the Saturn V rocket.
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 dates in July 1991. The second is the company's final report to Rockwell International dated September 1991. When the documents differ in significant ways, it 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 toward Earth, open its payload bay doors 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 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 until MB-10.
During a normal Space Shuttle mission, the twin 6,000-pound-thrust Orbital Maneuvering System (OMS) engines would ignite twice to complete orbital insertion after the Orbiter's three Space Shuttle Main Engines (SSMEs) shut down and and its External Tank separated. The OMS-1 burn would put the Orbiter into an elliptical orbit; then, at apogee (the high point of its orbit), OMS-2 would raise its perigee (the low point in its orbit) to make its orbit circular. Subsequently, the OMS engines would be used to perform major maneuvers and would slow the Orbiter at the end of its mission so that it could reenter the atmosphere. The OMS engines would burn hypergolic (ignite-on-contact) hydrazine/nitric acid propellants.
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 bipropellant 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 circularization burn at apogee. The propellant remaining after the OMS-2 burn (about 13,000 pounds) 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 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. It would include 58 standardized payload racks in its pressurized module. NASA's Freedom, by comparison, would have no habitable volume at all until the addition of the U.S. lab on 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 48 racks.
In SII's July 1991 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 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's 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 volume to 15,000 cubic feet. NASA's Freedom 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. One such mission would occur in 1996, and three would take place in 1997. In addition to enabling 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 a utilization flight after MB-2. Because assembly would be relatively simple and spacewalks minimal, SII assumed that the ODS could do without its own RMS. The company did not address how deletion of the station RMS would affect NASA-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), or space station lifeboat. With the docking of the ACRV at a core module side port, the ODS could be staffed by eight astronauts in the absence of a visiting Orbiter. NASA called the ability to maintain a full crew with no visiting Orbiter present "Permanent Manned Configuration" (PMC). NASA's Freedom would not achieve PMC until MB-16.
The year 1998 would see three assembly flights, all international in character, and three utilization flights. In his January 1984 State of the Union speech, Reagan had invited U.S. allies to lend a hand in building NASA's space station. MB-4 would see astronauts use the visiting Orbiter's RMS to dock the pressurized part of the Japanese Experiment Module (JEM) to a core module side port. On MB-5, they would add the European Space Agency's Columbus laboratory module. The ODS would thereby achieve its maximum volume: 24,000 cubic feet, or about 8,000 cubic feet more than planned for NASA's Freedom. M-6 would add Exposure and Logistics facilities to the JEM.
SII recommended that the core module Earth-facing port be capable of rotation to enable visiting Orbiters to position themselves in the manner most convenient for a given assembly mission. 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 would host no utilization flights until 1998, when three would take place, and would not be completed 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 would include no provisions for space-oriented experiments; all of its modules would 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 astronomy satellites (for example, the Hubble Space Telescope, launched 24 April 1990) were available. If, however, space-oriented experiments were desired, then the side of the hab/lab module facing the stripped-down Orbiter's payload bay floor could include a docking port identical to that on its Earth-facing side. A tunnel through the payload bay floor and Orbiter belly would provide access to the space-facing port.
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 with the least payload capacity. It assumed that NASA would replace Columbia with a new, lighter Orbiter, increasing the Shuttle fleet's overall capability. SII called this "disposing of the worst and and replacing it with the best." Some components stripped from Columbia could, it suggested, be used in the new Orbiter to save money.
By the time SII submitted its final report, NASA's latest Freedom configuration had been public for three months. The new design included truss segments that would be launched pre-assembled, shorter U.S. modules, and other changes meant to reduce the number of spacewalks and assembly flights required to build and maintain it. The Station would, however, lose yet more capability (notably in the area of electrical power, which was reduced to about 60 kilowatts at PMC). The April 1991 redesign set the stage for Freedom's near-cancellation in 1992 and its revival as the International Space Station beginning in 1993.
References:
Shuttle Derived Space Station Freedom, Space Industries International, Inc./Rockwell International Space Systems Division, presentation materials, n.d. (July 1991).
Expanded Orbiter Missions Final Report: Orbiter Derived Space Station Freedom Concept, prepared by Space Industries, Inc. (SII), Webster, Texas, for Rockwell International, Inc., Downey, California, September 1991.
"Operation Scale-Down," Tim Furniss, Flight International, 29 May-4 June 1991, pp. 76-78.
