The Skylab and Salyut missions firmly established the feasibility of extended stays in orbit and of performing fundamental—if rudimentary—research. In order to move beyond their limitations, a quantum leap forward in technology, something truly revolutionary, would be required. As former Houston Skylab program manager Robert F. Thompson observed, Skylab was a
beautiful tactical program that had numerous shortcomings as a strategic program. Skylab was not designed for in-flight repair, re-supply with air and water, refurbishment with improved technology, re-visitation for re-boost to a higher orbit, or restructuring as part of a larger station. Consequently it could not, and did not, lead to a strategic, sustained human presence in space. 7
Although America's space agency, the National Aeronautics and Space Administration (NASA), chose not to follow up on its limited space station success, opting instead to develop a reusable space vehicle, the shuttle, the Soviets opted for a different course. Despite a horrific beginning for their Salyut program back in 1971, many successes followed. By the time the Salyut 6 and Salyut 7 projects had ended in the late 1980s, the Soviets' many discoveries decisively eclipsed their failures while at the same time eclipsing the more modest successes of Skylab.
The Salyut program's many accomplishments opened the way to the creation of the Soviets' Mir space station; this constituted the quantum leap aerospace engineers such as Thompson had asserted would be necessary if a sustained human presence in space was to be possible.
During the late 1970s, the Soviet Union committed itself full-bore to placing a space station in orbit that would vastly surpass the Salyut and Skylab
Many improvements would be needed to meet Mir's ambitious objectives. Highest on the list was a significantly larger interior space consisting of multiple compartments in which many different types of experiments could be conducted simultaneously. Also high on the list were improvements to the docking mechanisms so transport vehicles could more readily resupply the crews, improvements to the electrical systems, more sophisticated equipment that allowed for lengthier space walks, and more sophisticated optical equipment for viewing Earth and galaxies beyond the Milky Way.
Soviet scientists knew that a larger space station would make extended stays in orbit practical. The problem, though, was that a space station of the size they envisioned exceeded the weight and volume limits imposed by the Soviets' Proton rocket. In response, engineers designed Mir in six separate modules, each of which would be flown to orbit separately and then joined 250 miles above Earth. Some engineers describe this sort of module construction as "tinker toy" construction, but others liken it to snapping together Lego blocks.
Taken together, Mir's six modules would be roughly twice the size of Skylab and would collectively function as crew quarters, a computerized brain and communications center, and research facilities. The first of the six modules sent up, the Mir Core, was launched on February 20, 1986. As its name implied, the Core was engineered with six docking ports to which the other modules later would be attached. The Core was also aptly named in that it contained both the basic living quarters and research laboratories. The basic living quarters included individual crew quarters, a bathroom, shower facilities, and a small galley with cooking facilities and a table. The Core, therefore, was capable of functioning as a stand-alone space station until the additional modules could be sent up.
Following the successful deployment of the Mir Core, the remaining five modules were sent up and locked into place over a four-year period. In all cases, each module was loaded into the transfer vehicle, Soyuz, which was in turn loaded onto the Proton rocket and was launched into space. Once in space, the Proton rocket separated from Soyuz, which was then able to rendezvous with Mir by firing its thrust rockets. Once docked with the Core, cosmonauts were then able to remove each module and send Soyuz back to Earth for future reuse.
Coupling each module to the Core's docking ports required space walks on the part of the cosmonauts to secure the locking mechanisms, pressure seals, and electrical wiring. Despite many mechanical improvements, coupling the modules proved more complicated than anticipated. For example, when the Kvant module, which provided data and observations of active galaxies, quasars, and neutron stars as well as some biotechnology experiments, approached the Mir Core in 1987, something very wrong occurred. As it set up to rendezvous with its dock, the horrified crew on the Core watched in disbelief as the twenty-ton module floated past too high to lock. Four days later, a second approach went according to plan, but the final locking mechanism jammed. Forced to take another space walk to investigate the problem, the cosmonauts discovered a plastic trash bag lodged in the locking collar. Once removed, the Kvant module successfully locked in place.
Once all modules were properly locked onto the Core, Mir weighed about 150 tons, with dimensions of roughly 115 feet by 98 feet and an inner volume of about 14,100 cubic feet, significantly larger than Skylab had been. Orbiting high above Earth, the fully assembled Mir was the biggest man-made object in space.
Another of Mir's revolutionary improvements over previous space stations was its ability to support crews for long periods by allowing for delivery of fresh supplies. When the Soviets developed Mir, they also developed for it an unmanned supply vehicle named "Progress." To accommodate Progress for quick and reliable docking, Mir's docking port was redesigned with an improved locking assembly and with a computer program to automate docking.
The new locking assembly was a set of four hydraulic grappling hooks capable of extending ten inches to capture Progress's port and then retracting to pull Progress directly into Mir's docking port. Assisting in this mechanical ballet was a computer program on board Mir capable of sensing the position of Progress and Mir and then adjusting the orientation of each for flawless dockings.
Progress was basically a cylinder with an interior storage volume of twenty-five hundred cubic feet, enough to carry sixteen thousand pounds of supplies. Since Progress was relatively small, one small rocket could propel one supply vehicle to Mir; alternatively, a larger Soyuz SL-4 rocket could propel several supply vehicles. Because of this ability to resupply Mir, the Soviets would later set the record for the longest stay by a human in space, 438 days.
Progress delivered everything needed aboard Mir for experiments and for the crew's use. Most of Progress's cargo consisted of propellants and gases such as hydrogen, helium, argon, and oxygen, needed for experiments. In addition to propellants and gases, Progress ferried numerous housekeeping items to the station. The most vital part of this package for the crew was life-support hardware and supplies, such as chemicals that release oxygen and others that remove carbon dioxide from Mir's atmosphere. Other items included such necessities as computers, communication equipment, and expendable hardware such as bolts and electrical wire. Of even greater interest to the crew were personal items such as toothbrushes, toothpaste, combs, brushes, medical kits, laptop computers, and pens and pencils. Food and water were, of course, necessities, but unlike in the case of Salyut, Russian officials made certain that the food was not just nutritious but also palatable. According to David M. Harland, author of The Mir Space Station: A Precursor to Space Colonization , "Much of the food was fresh, and specialties such as apples, onions, garlic, and caviar were very much appreciated." 8
Mir fulfilled all of its expectations. It would remain in orbit for fifteen years, during which time it was never unoccupied. Four different individuals would each spend more than twelve months on Mir. Harland notes, "The Mir complex is a tentative first step towards an orbital habitat. This, along with the evaluation of the human organism in a weightless state, is Mir's raison d'être [reason for being]. Mir has succeeded in its mission." 9
As Mir began to age, a debate arose among Soviet scientists over refurbishing it or scrapping it in favor of a new-generation space station. Finding the money for such a project was a problem, however, so the Soviet Union explored enlisting the financial and engineering assistance of other nations. During the late 1980s and early 1990s, an easing of geopolitical tensions between the Soviet Union and the United States and its allies made this idea practical. Furthermore, unlike the 1950s, 1960s, and 1970s, when space was exclusively the competitive arena of the United States and the Soviet Union, now other technologically advanced nations were willing to participate in and benefit from an orbiting outpost.
American space scientists had opted to develop the space shuttle rather than compete with Mir by developing another space station. Still, in 1993 President Bill Clinton proposed to Russia and several other nations a cooperative effort to place the next generation of space stations in orbit. This novel and timely idea of sharing the costs, the risks, the technology, and the results of research spurred ambitious designs for the International Space Station (ISS). If all went well, the first of more than one hundred components of the ISS would be in orbit in 1998. Plans
Relegating space stations to the junk heap is both a tricky and complicated proposition. All space stations will eventually fall out of orbit and plummet back to Earth—unless regularly propelled back into orbit—as their speed and altitude drop due to Earth's gravitational pull. In 1991 Russian aerospace engineers finally allowed Salyut 7 to fall out of orbit and plummet to Earth. Unfortunately, Russian space engineers had no idea where it would hit the earth, and even after disintegrating as it plunged through the atmosphere, several tons of debris eventually scattered across the Andes mountains, much to the anger of many people.
Hoping to avoid another international incident, the Russians planned better when the time came to bring Mir out of orbit. In March 2001 the world was notified that the 130-ton Mir would be brought down somewhere over the Pacific Ocean, the largest unpopulated region on Earth. As the space station gradually lost altitude, the date of splashdown in the Pacific was announced as March 21. Soviet engineers announced that as it passed through the atmosphere at initial speeds of seventeen thousand miles per hour, 110 tons of the 130-ton craft would burn up from friction; the surviving 20 tons would scatter into thousands of small pieces that would splash into the ocean.
Hitting the Pacific on a particular day would require control. Soviet engineers conceived the idea of actually accelerating Mir's descent through the atmosphere to control the time and place of disintegration. To accomplish this objective, a Progress cargo ship was attached to the station, which had a rocket propulsion system. When Mir fell to about 136 miles, the rocket engines on Progress would be fired to accelerate Mir downward into the thicker layers of the atmosphere, where it would quickly break apart and burn.
The controlled reentry was projected to bring the craft down in a 380,000-square-mile swath of the Pacific between New Zealand and Chile, away from major air and sea routes. Tiny nations throughout the South Pacific were alerted to watch for the chunks of Mir, and dozens of island authorities warned their people not to go out March 21 and to stay off boats to avoid being hit by any parts.
In a trip condemned as suicidal by Russia's space agency, a California-based public relations firm chartered an airplane for a group of space enthusiasts and television crews to fly to the site. They hoped to photograph the blazing reentry, but NASA authorities estimated their chances of being hit as about 1 in 2 billion. Fortunately for everyone, the plan worked and the blazing scraps of Mir plunged harmlessly into the Pacific.
called for the locking of the remaining modules by the end of 2003, with experiments beginning immediately and running continuously until at least 2013.
Everyone involved in the project understood that the ISS would be the culmination of thirty years of research and experimentation on Salyut, Skylab, and Mir. Far from being just the next iteration of space stations, aeronautical engineers worked to make the ISS a second quantum leap in the wake of its predecessor, Mir. According to Daniel Goldin, the head of NASA, the ISS would push space station technology far beyond Mir:
The International Space Station (ISS) will change the course of human history. The ISS is certainly an ambitious idea. It is probably the largest international scientific and technological project ever undertaken. The goal is to establish and maintain a permanent presence in space and to provide a testbed for new technologies, medical research, and the development of advanced industrial materials. 10
The design of the ISS would be on a scale that would dwarf Mir. Rather than the total of five modules that Mir had, designers planned for six primary modules used exclusively as laboratories in addition to additional modules for crew quarters, storage facilities, docks for transport vehicles, and airlocks needed for space walks. All of these modules, when coupled with six pairs of solar panels and external apparatuses such as telescopes and communications antennae would give the ISS the look of an oversized spider moving through space.
Significantly larger than Mir, the ISS structure would have an overall length of 262 feet, a width of 365 feet, and a total weight of a massive 500 tons, nearly four times the weight of Mir. NASA engineers liken the total exterior space to the dimensions of two football fields and the interior space to that of the passenger cabin of a Boeing 747. Equally remarkable will be the ability of the ISS to accommodate a crew of seven—more than twice the capacity of Mir.
The first step toward building the ISS was assigning responsibilities and costs to each of the charter nations. In 1993 most of the details of the joint space contract were ironed out and agreed upon. In his book Living in Space: From Science Fiction to the International Space Station , space writer Giovanni Caprara comments on this agreement:
The signing of the joint space agreement marked the end of an era of antagonism [between Americans and Russians] and the beginning of a new phase of cooperation. . . . Until now, space programs had been viewed as an ideal means of demonstrating the superiority of a political system. Now they became a proving ground for experiments in cooperative agreements that could be usefully applied to other fields. 11
The United States and Russia were joined in the construction effort by a consortium of ten European nations—called the European Space Agency (ESA)—as well as by Canada and Japan. Engineers realized that overcoming the forty years of competition between the United States and Russia would be an asset to the new space station. Canada declared its intention to construct the robotic arm that would be used for assembly of the ISS modules and for placement and retrieval of a variety of equipment for experiments. Fifty-seven feet long, 15 inches in diameter, and weighing 911 pounds, the robotic arm derives its flexibility from six revolving joints and its grasping ability from pincers designed to maneuver a 266-ton object while in orbit. Since the robotic arm would be an essential component for assembly of the ISS, it would be one of the first items flown to the station.
Japan announced its interest in building a module called the Japanese Experiment Module (JEM), intended to be a multipurpose facility for a variety of space science and technology studies. Nicknamed "Kibo," the JEM is a cylinder thirty-seven feet long and ten feet in diameter. Attached to Kibo is an external platform similar to a back deck, called the Exposed Facility, available as a storage unit and laboratory for conducting experiments intended to be performed in a vacuum.
The ESA, which consisted of three major contributors—France, Germany, and Italy—and seven minor ones, agreed to contribute a research module called the Columbus Orbital Facility and a transfer vehicle that would be used to transport supplies to the ISS and to boost the orbit of the station to a higher altitude if needed.
Russia, the country with the most experience in long-term missions on space stations, was called upon to make a considerable contribution to the ISS. Russia agreed to build the first module that would go into orbit, the FGB, which is the Russian acronym for Functional Cargo Block. It would function as the control center for the ISS, providing docking ports, fuel tanks, and solar panels. Weighing nineteen tons, this forty-foot-by-twelve-foot cylinder would be the largest of the ISS modules. The Russians also agreed to supply at least two science modules, additional solar panels, resupply vehicles, and, of critical importance, an escape vehicle to be used in the event of some catastrophe on the ISS that would necessitate the crew's evacuation. Russia's one last major contribution, the Proton rocket, would muscle the main pieces into space, requiring an estimated ninety launches.
America's role began with building Node 1, named "Unity," which would function as conduit for power, liquids, gases, and communications needed by all the other modules. Next, the United States built the American Laboratory, which was intended to be used for a variety of experiments; the United States would also supply eight solar panels. America agreed to provide the space shuttle, which, along with the Proton rockets, would fly the ISS modules into orbit and provision them over the life of the space station.
ISS engineers applied the latest leading-edge technologies to create a safe interior work space for the crew. Each module has an outer shell of lightweight aluminum. This shell has an additional protective layer of four-inch-thick impact-resistant Kevlar and ceramic material. This layer functions as a bulletproof vest to provide extra protection from impacts by micrometeoroids and tiny grains of grit that punctured previous space stations, causing air leaks.
Another significant departure from Mir's design is the high degree of specialization of each ISS module. This specialization of function necessitates a great deal of interdependence with other modules. Unlike Mir, on which each module could function independently of the others, none of the ISS modules can survive in space without the assistance of the others. In this regard, aerospace engineers liken the ISS design to the human body, in which each of the body's systems has a distinct and highly specialized function yet each is dependent upon the proper functioning of all others.
Such a design will make possible more complex experiments that will answer more questions about
The engineering of each of the ISS modules is remarkably complex. An example is the eighteen-by-fifteen-foot cylinder built by the United States called Node 1, or the Unity Node, which functions as a conduit for all the essential elements of the ISS.
The aluminum walls of Unity are made of high-strength aluminum to withstand the impacts of delivery vehicles docking with it and the stress and torque of six other modules attaching to its six ports. To accomplish all of the requirements imposed on Unity by aerospace engineers, the American-made module contains more than fifty thousand mechanical items mounted in a maze of racks and tresses. This dazzling array of parts provides essential space station resources such as fluids, environmental control and life support systems, and electrical and data systems to the work and living modules.
To provide essential life support resources, Unity is packed with 216 pressurized conduits that carry fluids and gases. Since the weightless environment does not have natural air currents or liquid flow, gases, including oxygen, along with many liquids must be pumped throughout all human-occupied areas. And even more remarkable, this eighteen-foot-long module threads 121 separate internal and external electrical cables, which collectively consist of six miles of electrical and data wires.
the nature of physics and living in a weightless environment. According to Mary F. Musgrave, the associate dean of the College of Natural Sciences and Mathematics and a professor of biology at the University of Massachusetts, "The Mir and Skylab programs provided only a glimpse [of a space station's potential]. The International Space Station offers the opportunity to conduct research 24 hours a day, 365 days a year." 12 This view is echoed by many, including Al Feinberg, NASA public affairs officer at the Office of Space Flight, who added, "ISS is a radical departure from Mir." 13
The orbital assembly of the ISS began a new era of hands-on work in space. Although Mir was also a modular space station requiring orbital assembly, its design made the task quick and simple, involving not much more than clamps and cable hookups. The ISS would not be so simple. Because of the number of modules, their different configurations, and the unique requirements for scientific research, securing each one was a concern to designers from the start.
ISS engineers rejected the idea of clamps and cables in favor of mounting a large robotic arm, remotely controlled by crews inside the ISS, capable of seizing modules and coupling them with surgical precision. Built by the Canadians, the fifty-seven-foot-long robotic arm was one of the first components flown to and placed on the ISS. This arm, controlled by astronauts, will eventually assemble the full complement of the ISS modules. Once all modules are in place, the arm will also play a major role in supplying the space station, effecting repairs, and assisting in many experiments conducted outside of the pressurized environment of the station's modules.
What makes the arm work so effectively are seven motorized joints. These joints function much like wrists and elbows, only better. They are capable of revolving 360 degrees while arm segments extend in multiple directions. This arm is capable of handling large payloads and assisting with docking the space shuttle. To access all parts of the space station, the arm moves along rails running the length of the station and bolted to the truss framework.
Grasping is performed by an ingenious robotic "hand" called the Special Purpose Dexterous Manipulator, or Dextre for short. This device is capable of handling the delicate assembly tasks previously performed by astronauts during space walks. Equipped with lights, cameras, and tool packs, Dextre is capable of installing and removing small external payloads such as batteries, power supplies, and computers as well as manipulating, installing, removing, and inspecting scientific payloads. A typical task for Dextre is to replace a depleted 220 pound battery that involves bolting and unbolting operations as well as precision positioning to properly align and insert the spare battery within its work space and properly reattach all connectors.
Frightening moments on Salyut and Mir created life-threatening situations for cosmonauts on more than one occasion. Delicate mixtures of gases and chemicals needed for life support and scientific experiments created explosive situations from time to time. Added to this were fears of fire and catastrophic loss of atmospheric pressure should the skin of a module be punctured. To lessen the chances of a disaster on the ISS killing all on board, planners and engineers included in the design a permanent module that would function as an escape vehicle if needed.
Engineers designed the ISS to accommodate an escape vehicle permanently docked while astronauts worked in the station. The only available vehicle able to fulfill the requirements was the Russians' Soyuz transport vehicle that was designed to deliver cosmonauts to Mir and return them home. Unlike all other modules, Soyuz could be boarded and quickly released from the ISS in less than ten minutes.
Astronaut Buzz Aldrin, however, in an interview in Popular Mechanics magazine in 2003, pointed out one shortcoming of Soyuz as an escape vehicle, noting, "Currently the station [ISS] is limited to three, the number of people that can escape in the Soyuz capsule." 14 If the ISS is to increase its crew complement to the anticipated maximum of seven members, a larger escape vehicle is needed.
In response to the need for a modern escape vehicle capable of transporting all seven crew members, NASA is close to completing the development of a $4 billion escape vehicle called the X-38 that will replace the smaller Soyuz. The X-38, a twenty-nine-foot-long triangular pod, would use its body like a wing to glide back to Earth. Engineers have already tested two versions of the craft by dropping them from a B-52 aircraft over the California desert. The final version is anticipated for delivery in 2004. According to John Muratore, project manager for the X-38 project at Johnson Space Center in Houston:
It's an all-electric vehicle that uses high-tech lasers and fiber optics to initiate many of the on-board sequences. Although it utilizes cutting-edge technology, it gets its roots from science we've already successfully used for many years. It's a great blend of both old and new knowledge. 15
The architects of all space stations focused their time and energy on creating the best possible living environment in space. None of their ingenious inventions, from robotic arms to escape vehicles, would have value if the environment in which astronauts worked and lived were not optimized to allow for prolonged visits.