International Space Station

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International Space Station

The International Space Station (ISS), formally designated International Space Station Alpha, is a habitable (normally manned) orbital facility that has been under construction since 1998 and is scheduled for completion (as of October 2006) in 2010. About 40 assembly and utilization flights (in total) by the United States space shuttle fleet are required to assemble the ISS. In addition, the Russian space program will fly other necessary construction flights, along with Japanese and

ESA flights to add experimental equipment, fuel, consumable, and other necessary materials to ISS. The space station is a joint project of the United States (National Space and Aeronautics Administration, NASA), Russia (Russian Federal Space Agency, RKA), Japan (Japan Aerospace Exploration Agency, JAXA), Canada (Canadian Space Agency, CSA), and Europe (European Space Agency, ESA). (Brazil also participates through NASA, while Italy participates through ESA.) As of October 2006, participants from twelve countries have worked onboard ISS. When finished, it will contain about four times as much working space as the former Russian space station Mir (1986–2001), the former record holder, and will have a mass of about 881,800 lb (400,000 kg) and a pressurized volume of about 35,300 cu ft (1,000 cu m). The ISS orbits at an average altitude of 220 mi (360 km) and at an average speed of 17,200 mph (27,685 km/h).

A number of science experiments are to be conducted aboard the ISS in such fields as health effects of radiation, molecular and cell biology, earth science, fluid dynamics, astronomy, combustion physics, and crystal growth.

History and structure

The ISS was originally proposed by United States President Ronald Reagan (1911–2004) in 1984, and was slated to cost $8 billion. Originally, thirty-six U.S. shuttle flights plus nine Russian rocket launches were required for ISS construction. However, as of October 2006, fewer flights will be needed due to cutbacks on the number of sections to be installed on the structure. The project is about five years behind schedule due primarily to the two U.S. space shuttle disasters in January 1986 (Challenger ) and February 2003 (Columbia ). Since the 2003 loss of Columbia twelve construction flights will be used to finish the building of ISS. Today there are 15 major partners in the ISS effort, including the United States, Russia, Japan, Canada, and 11 of the member states of the European Space Agency. The U.S., through its National Aeronautics and Space Administration (NASA), is the largest single contributor, bearing most of the cost of building, launching, and operating ISS for at least a decade.

Assembly of the ISS commenced in 1998 with launch of the Russian control module Zarya on a proton rocket from Kazahkstan. The U.S. module Unity Node, a connecting segment, was carried into space on the shuttle Endeavor later in 1998. This unit is primarily a docking hub to which other sections join. In 2000, another Proton rocket lofted the Russian service module Zvezda, the main Russian contribution to the ISS. Zvezda provided living quarters and life support during the early phases of the ISS’s growth; it also provides steering rockets to control the ISS’s attitude (orientation in space) and to re-boost it to higher altitudes as its orbit decays due to friction with high-altitude traces of the Earth’s atmosphere.

The ISS is powered by photovoltaic electricity. The first of its four large solar arrays (112 by 39 ft [34.2 by 11.9 m]) was added in 2000. When completed, the ISS will receive about 260 kilowatts of power (peak) from an acre of sun-tracking solar panels. An energy-storage subsystem consisting of six large nickel-hydrogen (Ni-H2) batteries supplies electrical power to the ISS during its passage through Earth’s shadow, which lasts about 45 out of every 90 minutes.

In 2001, the U.S. laboratory module Destiny, the largest and most elaborate of the ISS components, was added using the robot arm of the space shuttle Atlantis. The United States lab module contains 13 equipment racks, on which various scientific experiments will be mounted, and a 20-in (0.5-m) window set in the Earthside wall.

Smaller components were added piecemeal in 2002 by several shuttle flights, and in 2001–2002 several Russian flights ferried passengers and supplies. The ISS’s final configuration will contain a European laboratory module, a Japanese laboratory module, three Russian laboratory modules, a Canadian robot arm to assist in assembly and maintenance, exterior racks for experiments requiring direct exposure to space, and an emergency Crew Return Vehicle on standby. The shuttle has been continuously inhabited since November 2, 2000, and under normal circumstances houses a full crew of six.

Science

The ISS is intended to serve as a platform for the performance of scientific experiments that can only be carried out in space. The presence of a crew allows more complex experiments to be performed with simpler equipment than would be possible using purely robotic space vehicles. On the other hand, human beings require much complex gear to survive in space. Further, the ISS is not a particularly efficient platform for astronomical experiments, as it is vulnerable to vibrations, and experiments that merely require a vacuum can be performed economically in vacuum chambers on Earth. Yet, the ISS does offer something that cannot be obtained for more than a few seconds at a time on earth: weightlessness, or, more precisely (since the components of the ISS itself create a slight gravitational field), microgravity.

Unlike traditional science-fiction space stations, the ISS does not rotate in order to provide a centrifugal equivalent of gravity to its inhabitants. Such an arrangement would require a much more expensive structure due to the stresses imposed by rotation; observational science experiments that need to point steadily at one part of the sky would be difficult to operate on a rapidly rotating platform; and rotation would destroy the very microgravitational conditions that make the ISS a unique place to conduct science.

Several of the experiments that have exploited (or will exploit) microgravity are the following:

Dendrite formation in solidifying metals. When metals solidify they tend, like snowflakes, to form branching or treelike crystalline structures termed dendrites (from the Greek word dendrites, meaning pertaining to a tree). Observing the growth of metallic dendrites that are not deformed by Earth’s gravity should help improve mathematical models of dendrite formation, which in turn may help in the design of stronger and more durable alloys.
Bone deterioration. As previous experience with long-term habitation of space has shown, persons living in weightlessness lose about 1% of their bone mass per month, even when performing bone-stressing exercises. Generations of small animals raised in space will enable biologists to study the effect of microgravity on genetic mechanisms of bone growth and resorbtion. Understanding these mechanisms may someday make long space voyages (e.g., to Mars) medically feasible.
Atomic clock. A French experiment will use micro-gravity to improve the accuracy of an atomic clock by a factor of ten by observing oscillations of cesium atoms in free fall.
Commercial research. Between 30 and 40% of the United States lab module resources are reserved for use by private corporations, who will pay for access to microgravity research conditions. A slightly lower percentage of lab resources are reserved for commercial buyers in the European laboratory module. However, few corporations have yet purchased lab time on the ISS.

Controversy

The ISS is enthusiastically supported by many people who are interested in space travel for its own sake and by those scientists who hope to fly their own experiments on the platform. However, it has long been heavily criticized by a majority of the scientific community for delivering too little science for the dollar. In other words, it diverts money from other research. Some scientists argue that the bulk of the research planned for the ISS addresses technical questions that are peripheral, rather than fundamental. For example, Science, the journal of the American Association for the Advancement of Science, complained in 1998 that the ISS’s “greatest impact will be felt in the small community already studying problems related to space flight—a vital research area only if we assume that increasing numbers of people will someday travel, or even live, outside of normal Earth gravity.” In other words, the ISS is an ultimately romantic project that puts astronauts in space in order to figure out how to put more astronauts in space.

The claim that the ISS has little to offer science was boosted by Russia’s conveyance to the ISS of two private space tourists—officially designated Space Flight Participants—in 2001 and 2002, over loud protests from other ISS participant nations. Two wealthy men, one American and the other South African, paid $20 million apiece to the cash-strapped Russian government in exchange for a trip to the ISS. As of 2006, four space tourists have gone to the ISS via Russian supply missions, at a cost of $20 million each.

Even before the loss of the space shuttle Columbia in February 2003, funding for completion of the ISS was in doubt. Both the United States Congress and the governments of the European Union have long been skeptical of the ISS’s costs, and NASA was under such political pressure that it admitted it could not guarantee that the station will ever be grown beyond the “core complete” stage, with long-term living quarters for only three astronauts. Three astronauts, however, are not enough to tend the scores of experiments for which the ISS’s racks have room, so if the ISS is not expanded much of the science potential already constructed will go to waste. Critics of the ISS argued that continued support for the ISS amounted to throwing good money after bad; supporters of the ISS counter-argued that ISS research is essential for make an eventual trip to Mars and that human space-travel projects generate valuable technological spinoffs.

The Columbia disaster of early 2003 has, has delayed the progression of ISS by numerous months. Although Russian rockets have supplied many of the ISS’s needs and ferried astronauts back and forth to it, only the space shuttle’s cargo hold is large enough to carry many of the components planned for the ISS. Another, more urgent factor is that the ISS loses orbital altitude steadily due to friction with the outer fringes of the Earth’s atmosphere. Small rockets attached to the station regularly restore its altitude. The fuel for these rockets has been delivered via space shuttle, but after the Columbia disaster, minimum needed deliveries of fuel has been provided by the Russians until the United States resumed fuel deliveries in 2006.

As of 2006, about 80% of the original hardware for the ISS will still be added to ISS. Between 2006 and 2010, 16 shuttle flights by the space shuttle fleet will deliver hardware to ISS. Two flights have already flown: Discovery (STS-114) launched on July 26, 2005, with the External Stowage Platform onboard, and Atlantis (STS-115) launched on September 9, 2006 with the P3/P4 Truss-Solar arrays onboard. STS-121 (Discovery ) also flew on July 4, 2006, but did not send any assembly structures to ISS.

If all goes on schedule, in 2007, the following will be delivered to the ISS: Node 2 (built by Italy) to provide air, electrical power, water, and other life support systems; and Columbus Laboratory Module (ESA) to provide science equipment such as the Fluid Science Laboratory, Biolab, and European Drawer Rack. In 2008: Multipurpose Laboratory Module (Russia) to provide Russian science equipment; and Japanese Experiment Module (Japan, on three shuttle flights) to provide two pressurized sections and one exposed facility. In 2009 and 2010: Node 3 and Cupola (Italy, may be cancelled) to provide storage space; and unpressurized elements to support solar arrays.

Budget

It is very difficult to pinpoint an exact figure for the cost of ISS because so many countries are contributing to the project. In addition, the annual U.S./NASA budget for the space shuttle program is not included in the cost of ISS, even though much of its expense involves serving the space station. However, the most quoted figure for all of the participants of the ISS, as of 2006, stands at about $100 billion. The ISS budget for NASA is listed as $25.6 billion for 1994 through 2005; $1.7 billion and $1.8 billion for 2005 and 2006, respectively; and a rising budget from 2007 to 2010, with an estimated budget in 2010 of $2.3 billion. The budget is expected to level off after 2010, with an expected end of the project in 2016.

The future of the ISS is highly dependent on the health of the space shuttle fleet. No other country except the United States can accomplish all the assembly flights necessary to complete the station. If NASA suffers another disaster or a serious problem with the shuttles, then the completion of the ISS is doubtful at best. NASA resumed flights on July 26, 2005, with the STS-114 mission of Discovery. The mission was successful; however, foam was again shed from the external tank. NASA officials grounded the fleet until the problem was identified and resolved. NASA resumed shuttle flights in July 2006. With two successful flights to the ISS, NASA is hopeful that the space station can be completed by 2010. NASA expects to retire the space shuttle fleet in 2010 and replace it with Orion, an Apollo-type vehicle that will take humans to the moon and Mars beginning in 2015.

Resources

BOOKS

Launius, Roger D. Space Stations: Base Camps to the Stars. Washington, DC: Smithsonian Books, 2003.

Rau, Dana Meachen. The International Space Station. Minneapolis, MN: Compass Point Books, 2005.

PERIODICALS

Lawler, Andrew, “Can Space Station Science Be Fixed?” Science. 5572 (May 24, 2002): 1387–1389.

Lawler, Andrew, “Space Station Research: Bigger Is Better for Science, Says Report.” Science. 5580 (July 19, 2002, 2002): 316–317.

Revkin, Andrew. “And Now, the Space Station: Grieving, Imperiled.” New York Times. February 4, 2003.

Young, Laurence, “The International Space Station at Risk.” Science. 5567 (April 19, 2002, 2002): 429.

OTHER

National Aeronautics and Space Administration. “Space Station.” <http://www.nasa.gov/mission_pages/station/main/index.html> (accessed October 13, 2006).

Larry Gilman

The Gale Encyclopedia of Science