Introduction
Over the past two years the U.S. space station program has evolved to a three-phased international program, with the first phase consisting of the use of the U.S. Space Shuttle and the upgrading and use of the Russian Mir Space Station, and the second and third phases consisting of the assembly and use of the new International Space Station. Projected capabilities for research, and plans for utilization, have also evolved and it has been difficult for those not directly involved in the design and engineering of these space stations to learn and understand their technical details. The Committee on the Space Station of the National Research Council, with the concurrence of the National Aeronautics and Space Administration, undertook to write this short report in order to provide concise and objective information on space stations and platforms with emphasis on the Mir Space Station and International Space Station and to supply a summary of the capabilities of previous, existing, and planned space stations.
In keeping with the committee charter and with the task statement for this report, the committee has summarized the capabilities of five major space platforms. By providing the summary, together with brief descriptions of the platforms, the committee hoped to assist interested readers, including scientists and engineers, government officials, and the general public, in evaluating the utility of each system to meet perceived user needs. Since to date no agreed-on definitive set of requirements for a space station exists, the ability to evaluate existing or proposed capabilities against a complex and evolving set of user expectations may be useful in defining research projects. The committee has not made any judgments on the relative merits of research projects proposed or on the abilities of each space platform to support specific research projects
This chapter introduces the space stations and platforms considered in the report: International Space Station, the Mir Space Station, the Space Shuttle (with a Spacelab or Spacehab module in its cargo bay), the Space Station Freedom (which was redesigned to become the International Space Station in 1993 and 1994), and Skylab. Skylab, as the only U.S. space station to date, is included because the operational experience gained from this program is relevant, as are the Space Shuttle program and the Space Station Freedom design effort, to NASA's ability to design and develop the International Space Station. Chapter 2 discusses space station research with emphasis on the anticipated research planned for the International Space Station. Chapter 3 provides data and information on the various space stations and platforms introduced in this chapter and defines the parameters used to describe them. Chapter 4 describes the Mir Space Station and the research that has been performed on board Mir since its launch in 1986. The previous Soviet experience with the Salyut space stations has been superseded by over nine operational years of Mir. Chapter 5 describes the basic aspects of the design and research program planned for the International Space Station. Chapter 6 highlights the differences among the space stations and platforms described in the report, with an emphasis on the differences between International Space Station and its predecessors. The Appendix provides the statements of task for this study and for the Committee on the Space Station.
The International Space Station (ISS) has evolved from the space station program of the United States and from the Mir Space Station program of the former Soviet Union and the current Russian Federation. The U.S. program responded to direction from President Reagan in 1984 that called for a space station to be built within a decade. This initial program, which in 1988 was named Space Station Freedom (SSF), was led by the Headquarters of the National Aeronautics and Space Administration (NASA), with design and development separated into four "work packages" awarded to four separate contractor teams managed by four NASA centers. The program has been redesigned and reorganized several times since its inception. The SSF program was a collaborative effort of the United States, the member nations of the European Space Agency (ESA), Japan, and Canada. The Mir program has evolved over a 24-year Soviet and Russian history of supporting long-duration manned presence in low Earth orbit
In March 1993, congressional and administration responses to projected cost overruns in the SSF program, combined with increased pressures on the federal budget, forced another redesign to cut the cost and reduce the complexity of that design and program. This redesign resulted in Space Station Alpha in September 1993. More Russian components were added to the design, and in late 1993 Space Station Alpha became the International Space Station Alpha. In recent months "Alpha" has been dropped and the program and design are now referred to as the International Space Station. This program is led by a Program Director at NASA Headquarters, Washington, D.C., and carried out by a special NASA program office and a prime contractor, Boeing, located at NASA's Johnson Space Center, Houston, Texas
The Russian Space Agency will provide the baseline modules for the initial assembly of ISS, the Functional Cargo Block (FGB) module, and a service module similar to the core of the current Mir Space Station, as well as a life-support module, three research modules, a docking and stowage module, a science power platform with solar arrays, and the Soyuz crew transfer and Progress cargo transport vehicles. The FGB is to be purchased from Russia by Boeing for NASA, and it will be U.S.-owned. NASA will provide the elements of the central truss with hardware for distributed systems providing functions including thermal control and electric power distribution, as well as the large photovoltaic (PV) arrays that will track the Sun as ISS orbits the Earth. NASA will complete the space station configuration with habitation and laboratory modules containing hardware for support of the crew and much of the program's research objectives. Additional laboratory modules will be provided by the ESA and the National Space Development Agency of Japan (NASDA), and Canada will supply a robotic mobile servicing system.
NASA separates the current International Space Station program into three phases. Phase 1, which is primarily the joint use of the Mir Space Station by Russia and the United States, began in 1994 with the flight of the first cosmonaut on the Space Shuttle. Phase 1 has continued during 1995 with the addition of the Spektr module (equipped with some U.S. hardware for research) to Mir and the first docking of the Space Shuttle at Mir. Phase 1 is scheduled to continue through September 1997 with a series of six more Space Shuttle missions to Mir. Phase 2 is to begin in November 1997 with the launch of the first element of the ISS, the FGB. Phase 3 is to begin in 1999, when the U.S. Laboratory Module is scheduled to be fully equipped and able to be used for research. Figure 1 shows ISS in its assembly-complete configuration, and the data in Table 1 in Chapter 3 describe ISS at the end of this phase (scheduled for June 2002). NASA states that ISS will be operable for at least 10 years after its assembly is completed. ISS will be the largest space vehicle ever constructed as well as an unprecedented example of international cooperation on a highly complex project. Construction of ISS's major elements is currently underway.
Mir is the last of 10 space stations built and launched by the Soviet Union, beginning in 1971. It is composed of a core module that was launched in 1986 and several smaller modules that were launched subsequently. Currently, it is operated by the Russian government and the Russian industrial enterprise, RKK (Rocket Space Corporation) Energia. The late-1995 parameters described in Table 1 in Chapter 3, and the configuration shown in Figure 2, are based on the U.S.-Russian program for cooperation in human space missions, which includes improvements of Mir as a precursor to the ISS. The first phase of cooperation between Russia and NASA adds two more Russian-made modules, Spektr and Priroda, equipped with U.S. and Russian payloads as well as new PV arrays providing increased electric power to the Mir. The first of these modules, Spektr, docked with Mir in June 1995. The first of seven planned Space Shuttle missions to dock with Mir, STS-71, took place in June and July of 1995. These missions are to continue through late 1997, just prior to the launch of the first component of ISS. The information in Table 1 in Chapter 3 describes Mir as it is projected to be after the Priroda module is attached, and Chapter 4 describes the Mir Space Station in detail.
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Figure 1 The International Space Station (assembly complete), shown as described at the March 1995 Incremental Design Review. Source: NASA.
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Figure 2 The Mir Space Station (tentative 1996 configuration).
Courtesy of Daniel James Gauthier.
In operation since 1981, the Space Shuttle is the only operating reusable piloted space vehicle. (The Russian Buran vehicle was designed to be reusable and operated with a human crew, but was flown only once without a crew in 1988.) The Space Shuttle information in Table 1 in Chapter 3 describes the existing operational Space Shuttle equipped with a Spacelab module (built by the ESA), or a Spacehab module (built by a private U.S. company), in its payload bay. Both modules are currently used by NASA and will be involved in aspects of the ISS program. The Spacelab and Spacehab modules cannot be deployed free of the Space Shuttle. Illustrations of the Space Shuttle with a Spacelab module and with a Spacehab module are provided in Figures 3 and 4. Although both of these modules greatly expand the research capability of the Space Shuttle, even with a Spacelab or Spacehab in its cargo bay the Space Shuttle does not constitute a true space station (the Space Shuttle cannot stay on orbit indefinitely or provide a site for the permanent presence of humans).
The Spacelab was first flown in 1983, and over 20 Spacelab missions have been completed through late 1995. The Spacelab is modular and configured to meet specific mission requirements. Its four principal components are a module, which is equipped with laboratory equipment for each individual mission and provides a shirt-sleeve working environment; one or more open pallets that expose(s) instruments and materials to space; a tunnel to gain access to the module from the Space Shuttle mid-deck; and an instrument pointing subsystem to enable instruments to be pointed with high accuracy and stability at astronomical targets or the Earth. Twelve Space Shuttle missions have carried the Spacelab Module. In various configurations, Spacelab equipment has been used to conduct research in life and microgravity sciences (using the module), as well as for space science, earth observing science, and commercial research (using a pallet and mission-specific equipment).
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Figure 3 The Space Shuttle with a Spacelab module in its payload bay.
Source: NASA.
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Figure 4 The Space Shuttle with a Spacehab module in its payload bay.
Source: Spacehab, Inc.
A Spacehab module is about 40 percent the size of a Spacelab module and has flown on the Space Shuttle three times: in June 1993, February 1994, and February 1995. The next flight is scheduled for April 1996. It is connected to the Space Shuttle mid-deck through a modified Spacelab tunnel, and the module accommodates various quantities, sizes, and locations of hardware for experiments. Standard experiment accommodations include lockers and racks similar to those used to place experiments in the Space Shuttle mid-deck. The Spacehab module also has an optical viewport, and there is the capability to attach equipment on the exterior of the module. As with Spacelab, provisions exist to deliver power, cooling, and command and data resources to payloads attached inside and outside the module.
NASA plans to use the Spacelab and Spacehab modules to augment the use of Mir and ISS. The Spacelab module has been the site of much of the life and microgravity sciences research performed thus far using the Space Shuttle. If cooperation with Russia on Mir had not been initiated and if ISS were not to be built, the Spacelab or Spacehab would most likely have continued to be used as the primary locales for U.S. research in space using the Space Shuttle. After ISS is completed, the Spacelab and Spacehab modules may be used to perform missions in which a long-term stay in space is not necessary, to carry some pressurized payloads to ISS, or to return samples or materials from ISS to Earth. The capabilities of these modules are also of interest if one seeks to compare current U.S. capabilities with projected future capabilities that will come with ISS
As stated above, elements of the SSF and Russian plans for a next-generation Mir Space Station were incorporated to create the design for ISS during 1993 and 1994. The U.S.-led space station design was named Space Station Freedom in 1988, and the configuration shown in Figure 5 and described in Table 1 in Chapter 3 is the one that underwent a Critical Design Review (Program Incremental Design Review) in mid-1993. Most of the major components of the SSF design are still planned for implementation on ISS. The SSF program was led by NASA and was a collaborative effort of the United States, the ESA, Japan, and Canada. At the end of the program, in late 1993, there was little Russian involvement envisioned other than the possibility of using Russian Soyuz vehicles for assured crew return.
The four major modules planned for SSF will be included on ISS, although the U.S. Laboratory Module and Habitation Module and the European module have been modified from the SSF design. The Japanese Experiment Module is unchanged. SSF was to be assembled solely from payloads brought to orbit by the Space Shuttle at an orbital inclination of 28.5 degrees to maximize the mass of the payload that could be carried to orbit by the Space Shuttle. SSF had a design requirement to stay operational for 30 years.
Skylab was launched by the United States on May 14, 1973, and was inhabited for 28, 59, and 84 days by three different three-man crews. The last crew left Skylab and returned to Earth on February 8, 1974. During the three Skylab missions, research focused on investigations in solar astronomy, life sciences and human factors, Earth observations, astrophysics, and materials science. Before Skylab could be reboosted by a special propulsion module that might have been carried into orbit on an early Space Shuttle mission, Skylab's orbit decayed, and it fell to Earth on July 11, 1979.
Skylab had five major components: a pressurized module or "orbital workshop" that was the main habitable area, a telescope module, a docking adapter, an airlock, and an Apollo command module (for return to Earth). Except for the Apollo command module, Skylab was launched all at once using a Saturn V rocket, and the main module was adapted from the shell for the third-stage rockets and propellant used to propel earlier Apollo missions toward the moon. Skylab is shown in Figure 6, and the information representing Skylab in Table 1 in Chapter 3 describes the space station in its operational configuration. Skylab is the only U.S. space station built thus far. With its unique attributes it provides a basis for comparison for current and future space station designs.
The ability of the astronauts to make repairs during extra-vehicular activity was instrumental in ensuring that Skylab became a habitable and functional space station. Sixty-three seconds into the launch that carried Skylab to orbit without a crew, the meteoroid shield, that was to also shade Skylab's main module, deployed inadvertently and was torn off by atmospheric drag. The loss of the meteoroid shield during ascent led to the loss of one of Skylab's solar panels, and repairs and modification were conducted by spacewalking astronauts on the first crewed flight.
Figure 7 shows all of the space stations and platforms, described above, on the same linear scale for comparison of the physical dimensions of each space vehicle.
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Figure 5 Space Station Freedom (as described at the 1993 Critical Design Review).
Source: NASA.
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Figure 6 Skylab.
Source: Teledyne Brown Engineering, illustration by Robert A. Sweeney.
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Figure 7 Space stations and platforms to scale (1 cm equals approximately 10 m).