Research Uses of a Space Station
From before the first launch of an artificial satellite, Sputnik 1 in 1957, many ideas have been put forward for potential uses of a space station. These ideas have included using a space station as an Earth and space observatory; a staging point for interplanetary or lunar missions; a laboratory for biomedical, materials science, or physicochemical research; as a center for testing or assembling spacecraft before they are released into Earth orbit; and even as a destination for tourists. For the ISS, NASA and its international partners propose areas of scientific and technological research that require the operational presence of humans and are practical in low Earth orbit. The primary areas for scientific research currently planned for ISS are in the space life sciences, including the study of human adaptation to long-duration space flight and the effect of space flight on the basic biology of plants and animals, and microgravity sciences, including materials science, fluid mechanics, and the study of physicochemical processes such as combustion. NASA and its partners also plan to use the ISS to facilitate engineering research, for example, to aid in the development and testing of new enabling technologies for space in areas such as communications, power generation, advanced life support, and robotic and teleoperated procedures. Space systems, whether manned or unmanned, historically have had a 5- to 10-year cycle from concept to launch and often incorporate technologies that are already nearing obsolescence at the time of launch. NASA intends to use ISS as a proving ground for technology evaluation and insertion, both for replacing systems on ISS and for future spacecraft and missions. Some traditional areas of space science research (e.g., astrophysics, geophysics, and Earth sciences) are not major emphases of current U.S. plans for the use of ISS. NASA envisions that promising commercial activities will be identified as candidates during ISS research and development programs.
This chapter focuses on NASA's work and plans for ISS. European, Japanese, and Canadian work to date on crewed missions has been performed on the Space Shuttle and on Soviet or Russian space stations; their research emphases for ISS are similar to NASA's. The Russian plans for ISS payloads are not available, but Russia has indicated that the research areas prominent aboard Mir will be continued on ISS. [1] Chapter 4 covers Russia's work on Mir over the last 9 years. The research described below pertains only to that performed on crewed space platforms, not on research performed using unmanned scientific spacecraft in Earth orbit or interplanetary space. Describing in detail what has been achieved on the various space platforms, including over 70 Space Shuttle missions and over 19 man-years on Mir, and other space platforms such as the Salyut space stations and Skylab, was outside the scope of the study.
Research opportunities planned for ISS are discussed briefly in the following sections. The bibliography at the end of the report contains references to detailed reports from the National Research Council on several of these topics and to other relevant reports and books detailing the breadth and scope of space research in low Earth orbit.
Life sciences research in space has had two thrusts: (1) the investigation of the influence of gravity on basic biological processes, and (2) assessment of the impact and limitation on space operations resulting from the physiological deconditioning associated with weightlessness. [2]
The first thrust, the basic study of gravitational biology, requires long-duration exposure of plants and animals, the ability to repeat experiments, a well-equipped space laboratory, and a specialized crew. Unexpected alterations in living organisms and biological samples, ranging from cell cultures and plants to the nervous systems of mammals, have been observed in short-duration flights. Very little work has been done with artificial gravity levels between 0 and 1 g, a capability that could be provided by an onboard centrifuge, or with multiple-generation studies on the effects of space flight on normal development using animals and plants that reproduce relatively quickly.
The second thrust, space operations medicine, may make progress through the use of ISS for long-duration missions with a large number of crew members. ISS will have a crew of six astronauts and cosmonauts. All crew members are likely to be available as subjects for some investigations, and this increased opportunity to gather data may provide the means for increased insight into the adequacy of proposed exercise protocols and other countermeasures to enable people to return to Earth in good condition after a prolonged mission. Experience on Mir has shown that crew members can withstand long-term space flights (including up to 14 months–longer than projected in the crew rotation plans for ISS) and return to Earth in generally good health. But the ISS, with its larger set of more advanced biomedical devices, will provide the opportunity to test new techniques to diminish the physiological adaptations to microgravity that prove deleterious upon return to Earth (e.g., reduced bone density) and enable increased insight into the body's overall adaptation to microgravity conditions. Results may eventually contribute to long-term goals related to human exploration of the solar system beyond Earth orbit, as well as to biomedical insights applicable to terrestrial applications in the treatment of disease.
In addition to the capabilities described above that contribute to the ability to perform life sciences research in space, other parameters that enable space life sciences research include adequate electrical power, specialized biomedical equipment and facilities, significant crew time for research, a crew including biomedical professionals, an ability to send data to and communicate with researchers on the ground and the ability to preserve biological specimens and return them to Earth on a regular basis.
Through thousands of years of observing physical phenomena and theorizing as to cause and 400 years of organizing data scientifically to explain observed facts, gravity has always been present. It has only been in the last 35 years that more than a few seconds of scientific observations in the absence of gravity have been possible and even fewer years since the first coordinated series of microgravity scientific experiments were carried out in space. Since some initial work on Apollo and Skylab missions, NASA has performed only relatively short-term research in microgravity on the Space Shuttle, placing payloads in the Spacelab module, cargo bay, and mid-deck lockers. Nevertheless, the field is still in its early phases of development. ISS will provide both the opportunity for longer-term (e.g., 15 days to several years) microgravity experimentation and the ability to rework and repeat experiments until consistent and reproducible results are received.
Through the use of ISS, opportunities will exist for microgravity experimentation in fluid mechanics and transport phenomena, combustion, biotechnology, materials science and processing, and microgravity physics. To sustain the development and utilization of inherently complex flight hardware and experiments capable of yielding high-quality data in both the space life sciences and microgravity sciences research, the following factors will be important: maintenance of the quality of the microgravity environment, early involvement of the scientific community in experiment planning, and shortening of the cycle from designation of a principal investigator to flight of a selected experiment. The general capabilities necessary for conducting microgravity research in space are similar to those necessary for life sciences research. However, microgravity research is considered to derive greater benefits from gravity or acceleration levels as near as possible to zero because the physicochemical processes studied are generally more sensitive to higher or fluctuating gravity levels than are biological systems (within the ranges seen on an orbiting space platform). [3]
The traditional space sciences pursued by NASA include astrophysics, planetary science, and space physics (primarily the study of the Sun, interplanetary space, and the magnetospheres and upper atmospheres of planets). At the present time, NASA has limited plans and funding for the use of ISS as a space sciences observation and data acquisition platform, but has selected one space science experiment to be conducted as an attached payload on ISS. NASA plans to continue to rely on dedicated unmanned spacecraft for detailed investigations of the solar system, near-Earth space, and the galaxy and universe beyond our solar system. The U.S. and Soviet Union have both developed technologies to enable observations from spacecraft in low Earth orbit, including crewed space stations. In the 1970s many observations of the Sun, other astronomical bodies, and the Earth were made from Skylab and during the 1980s and 1990s observations have been made from the Space Shuttle. As discussed in Chapter 4 of this report, the Mir Space Station has also been extensively utilized for such observations. The availability of ISS as a permanently manned spacecraft can be expected to provide opportunities for its use as a platform for the mounting of instruments or experiments to respond rapidly to unforeseen opportunities for space sciences observations. A precedent for this kind of potential utilization of ISS is the use of Skylab in 1973-1974 as a site for observations of the comet Kohoutek.
A low orbital inclination of 28.5o (which resulted in a restricted ability to view most of the temperate areas of the Earth), combined with funding problems, led to the elimination of the Earth observing payloads from the Space Station Freedom (SSF) design. With this low inclination orbit, none of the partner nations in SSF would have been able to see or study most of their countries from orbit. In the United States, only southern Florida, southern Texas and Hawaii would have been overflown, and none of Japan, Canada or Europe would have been overflown. Looking toward the horizon, data would have been able to be gathered somewhat north and south of the actual flight path, as far north as Georgia in the United States and southern Japan in Asia. An earlier version of the U.S. space station program included a separate unmanned space platform that would have been launched into a polar orbit in order to be able to observe all of the Earth's surface over time. This portion of the program was eliminated during a 1991 redesign of SSF.
Now that the orbital inclination of its successor, ISS, has been set at 51.6o, more of the Earth, including most of Asia and Europe and all of the United States except Alaska, will be in view. As described in Chapter 4, the Mir Space Station, at the same inclination, has been used and continues to be used to conduct a significant Earth observation research program. Although funding limitations preclude the initiation of a major NASA Earth sciences program from ISS, NASA has made some preliminary plans for such research. The Earth Observing System (EOS), a part of NASA's Mission to Planet Earth concept, consists of a series of polar-orbiting and low-inclination satellites intended to provide long-term global observations of land surface, biosphere, solid Earth, atmosphere, and oceans. As part of the Mission to Planet Earth, a single two-part experiment, the Stratospheric Aerosol and Gas Experiment (SAGE) III, will fly one part on ISS with a second part placed on a polar-orbiting spacecraft scheduled for launch in 1998.
Many technologies for space platforms have been developed and tested on the ground prior to launch. The availability of ISS as a long-term, permanently crewed, orbiting testbed will support the demonstration of subsystem modifications and new concepts and technologies. Technology tests on ISS may provide useful results without jeopardizing spacecraft performance, as might be the case if the first use of a new technology were in a critical application. Continuing engineering research on topics including materials exposure, fluid processes, on-orbit assembly, electric power generation and storage, debris protection, food and water supply and recycling, data management, crew-return and supply vehicles, and space systems operation has the potential to lead to more efficient and less-expensive operations in space. These research initiatives, together with rapid advances in the capabilities and availabilities of new commercial off-the-shelf technologies, may produce upgrades to subsystems of the initial ISS configuration, as well as new capabilities. For example, commercial computer hardware and software technology will support onboard sensor data processing, converting the sensor-provided bit stream into usable information and eliminating the requirement for high-capacity data downlinks.
Using ISS to prove new technology may help increase the use of new technology in unrelated space endeavors. An example of this kind of technology research concerns the high cost of command and control, including facilities and manpower. These could possibly be reduced by greater reliance on autonomous, onboard spacecraft operation, but there has been understandable reluctance on the part of the spacecraft controller to give up authority to an unproven onboard system while retaining responsibility for the health of a spacecraft. Functioning as a testbed, ISS could demonstrate autonomous operations at reduced risk. [4]
Many factors will determine the ability to pursue technology development research, including the ability to bring large payloads to orbit and to integrate as appropriate outside or inside the pressurized volume of a space station, the electrical power available, the size of the space station and facilities present onboard, a crew with appropriate expertise and time to conduct extended research programs, the ability to involve researchers from many countries, and the ability to communicate with researchers on the ground.
The projected commercial utility of a space station has varied widely over the last 10 years. It is now generally assumed that although some useful products (e.g., pharmaceuticals or thin-film materials for use in electronics) may be produced on a future space station, it is unlikely that any endeavor identified to date as a potential source of revenue could be cost-effectively pursued if the prorated cost of the resources and infrastructure employed were taken into account. High costs have made the commercialization of any enterprise involving humans in space an elusive goal.
The international character and openness of the ISS program may well foster an increase in the commercial relevance of the work performed onboard by making it easier for companies to fly their payloads in space. However, it is currently not possible to justify development of a space station by projecting financial return from commercial enterprises. The true utility of a space platform to support commercial use will only be understood after such a station is operational and a realistic assessment of potential can be made.
[2] For detailed information on space life sciences see the several relevant reports of the NRC's Space Studies Board and its Committee on Space Biology and Medicine from 1987 to 1994.
[3] Scientific and programmatic issues related to microgravity research are detailed in an NRC (1995) report entitled Microgravity Research Opportunities for the 1990s. Especially relevant is Chapter 8, "Flight Opportunities and Challenges."
[4] Identification of additional engineering and technology transfer opportunities in the ISS program has recently been addressed by the NRC Committee on the Use of the International Space Station for Engineering Research and Technology Development.