International Space Station

The ISS insignia.

(PD) Photo: NASA
The ISS on July 19, 2011, photographed from the space shuttle Atlantis.

(PD) Photo: NASA
The ISS, photographed in December 2009 by the STS-129 crew of the Space Shuttle Atlantis shortly after undocking to return to Earth. Visible on the ISS are numerous modules, trusses, and long wing-like solar panels.

The International Space Station (ISS) is a research facility currently in low earth orbit. It is being assembled with international cooperation between the United States of America (NASA), Russia (RKA), Japan (JAXA), Canada (CSA) and several European countries (ESA). The ISS is the largest space station ever assembled, and has been continuously inhabited since November 2, 2000. At present the it has a capacity for a crew of three, which will be expanded to six when construction is complete in 2012. It is planned to remain operational through 2016.

History

As the the Cold War and the space race came to a close the United States approached foreign partners in order to collaborate on an international space station. Announced in 1993, the project was initially called Space Station Alpha. It was designed to combine elements from various planned space stations of the participating space agencies: NASA's Space Station Freedom, Russia's Mir-2, ESA's Columbus, and the Japanese Experiment Module.

The first section, Zarya, was put in orbit in November 1998 on a Russian Proton rocket. Two further pieces, the Unity Module and Zvezda service module, were added before the first crew arrived on November 2, 2000. It consisted of U.S. astronaut William Shepherd and two Russian cosmonauts, Yuri Gidzenko and Sergei Krikalev. The Destiny Laboratory Module, the most recent pressurized module, was delivered to the station in 2001.

The future of the ISS was uncertain after the Space Shuttle Columbia was destroyed in 2003 and the shuttle program was suspended for two and a half years. During this time crew exchanges were carried out solely using the Russian Soyuz spacecraft. Beginning with Expedition 7, station crews consisted of only two astronauts. Construction has resumed, but is far behind the original schedule, planned for completion in 2004 or 2005. Modules and other structures have been canceled or replaced and the number of scheduled construction flights were reduced. The schedule called to expand the station crew to six in 2009, and the completion of all construction by 2010. 2012 is the earliest expected completion date.

Components to be launched

By the time the ISS is completed, it will have, in addition to the modules already in orbit:

• A Node Module;
• Another laboratory module (Multipurpose Laboratory Module).

Components

There is a large unpressurized truss system in place that support the prominent solar arrays, as well as external experiments like the Alpha Magnetic Spectrometer and the Plasma Contactor Unit [1]. An addition to unpressurized experiment accommodations on ISS is being developed by the Goddard Space Flight Center, called EXPRESS Logistics Carrier, or ELC (formerly EXPRESS Pallet). "EXPRESS" stands for "EXpedite the PRocessing of Experiments to the Space Station". Several ELC units will be installed on the exterior of ISS to provide a home for space science experiments. ELC units provide not just a berth for experiments, but also provide power, heat, and command & telemetry links to experiments.

Cancelled modules

• Centrifuge Accommodations Module - would have been attached to Node 2, now named Harmony
• Universal Docking Module - replaced by Multipurpose Laboratory Module
• Docking and Stowage Module - replaced by Multipurpose Laboratory Module
• Habitation Module
• Crew Return Vehicle (CRV)
• Interim Control Module - no need to replace Zvezda (in storage ready to launch at short notice if required)
• ISS Propulsion Module - no need to replace Zvezda
• Science Power Platform - power will be provided to the Russian segments partly by the US solar cell platforms
• Russian Research Module - Replaced by Docking Cargo Module (DCM)

Major ISS Systems

Power supply

The source of electrical power for the ISS is the sun: light is converted into electricity through the use of solar panels. Before assembly flight 4A (shuttle mission STS-97, November 30, 2000) the only power source was the Russian solar panels attached to the Zarya and Zvezda modules: the Russian segment of the station uses 28 volts dc (like the Shuttle). In the rest of the station, electricity is provided by the solar panels attached to the truss at a voltage ranging from 130 to 180 volts dc. The power is then stabilized and distributed at 160 volts dc and then converted to the user-required 124 volts dc. Power can be shared between the two segments of the station using converters, and this feature is essential since the cancellation of the Russian Science Power Platform: the Russian segment will depend on the U.S. built solar arrays for power supply.

Using a high-voltage (130 to 160 volts) distribution line in the so-called U.S. part of the station led to smaller power lines and thus weight savings.

Life support

(PD) Photo: Tracy Caldwell Dyson/NASA
Astronaut Tracy Caldwell Dyson in the cupola of the ISS, September 11th, 2010. This section is the station's main observatory.

The ISS Environmental Control and Life Support System provides or controls elements such as atmospheric pressure, oxygen levels, water, and fire extinguishing, among other things. The Elektron system generates oxygen aboard the station. The highest priority for the life support system is the ISS atmosphere, but the system also collects processes and stores water and waste used and produced by the crew. For example, the system recycles fluid from the sink, shower, urine, and condensation. Activated charcoal filters are the primary method for removing byproducts of human metabolism from the air.

Attitude control

The attitude (orientation) of the station is maintained by either of two mechanisms. Normally, a system using several control moment gyroscopes (CMGs) keeps the station oriented, i.e. with Destiny forward of Unity, the P truss on the port side and Pirs on the earth-facing (nadir) side. When the CMG system becomes saturated, it can lose its ability to control station attitude. If this happens, the Russian Attitude Control System can take over, using thrusters to maintain station attitude and allowing the CMG system to desaturate. This has happened automatically as a safety measure, as happened for example during Expedition 10. When a shuttle orbiter is docked to the station, it can also be used to maintain station attitude. This procedure was used during STS-117 as the S3/S4 truss was being installed.

© Photo: Thierry Legault, www.astrophoto.fr
Image of the solar transit of the International Space Station and Space Shuttle Atlantis 50 minutes before docking, taken from the area of Madrid (Spain) on May 16th 2010 at 13h 28min 55s UT.

Scientific research

One of the main goals of the ISS is to provide a place to conduct experiments that require one or more of the unusual conditions present on the station. The main fields of research include biology (including biomedical research and biotechnology), physics (including fluid physics, materials science, and quantum physics), astronomy (including cosmology), and meteorology. As of 2007, little experimentation other than the study of the long-term effects of microgravity on humans has taken place. With four new research modules set to arrive at the ISS by 2010, however, more specialized research is expected to begin.

Scientific ISS modules

The Destiny Laboratory Module is the main research facility currently aboard the ISS. Produced by NASA and launched in February 2001, it is a research facility for general experiments. The Columbus module is another research facility, though it was designed by the ESA for the ISS. Its purpose is to facilitate scientific experiments and is set to be launched into space with the STS-122 shuttle launch on December 6, 2007. It should provide a generic laboratory as well as ones specifically designed for biology, biomedical research, and fluid physics. There are also a number of planned expansions that will be implemented to study quantum physics and cosmology. The Japanese Experiment Module, also known as Kibō, is scheduled to be in space after the STS-127 launch in or around January, 2009. It is being developed by JAXA in order to function as an observatory and to measure various astronomical data. The ExPRESS Logistics Carrier, developed by NASA, is set to be launched for the ISS with the STS-129 mission, which is expected to take place no earlier than September 11, 2009. It will allow experiments to be deployed and conducted in the vacuum of space and will provide the necessary electricity and computing to locally process data from experiments. The Multipurpose Laboratory Module, created by the RKA, is expected to launch for the ISS in late 2009. It will supply the proper resources for general microgravity experiments.

A couple of planned research modules have been cancelled, including the Centrifuge Accommodations Module (used to produce varying levels of artificial gravity) and the Russian Research Module (used for general experimentation). Several planned experiments, such as the Alpha Magnetic Spectrometer, have been cancelled as well.

Areas of research

There are a number of plans to study biology on the ISS. One goal is to improve our understanding of the effect of long-term space exposure on the human body. Subjects such as muscle atrophy, bone loss, and fluid shifts are studied with the intention to utilize this data so space colonization and lengthy space travel can become feasible. The effect of near-weightlessness on evolution, development and growth, and the internal processes of plants and animals are also studied. In response to recent data suggesting that microgravity enables the growth of three-dimensional human body-like tissues and that unusual protein crystals can be formed in space, NASA has indicated a desire to investigate these phenomena.

NASA would also like to study prominent problems in physics. The physics of fluids in microgravity are not completely understood, and researchers would like to be able to accurately model fluids in the future. Additionally, since fluids in space can be combined nearly completely regardless of their relative weights, there is some interest in investigating the combination of fluids that would not mix well on Earth. By examining reactions that are slowed down by low gravity and temperatures, scientists also hope to gain new insight concerning states of matter (specifically in regards to superconductivity).

Additionally, researchers hope to examine combustion in the presence of less gravity than on Earth. Any findings involving the efficiency of the burning or the creation of byproducts could improve the process of energy production, which would be of economic and environmental interest. Scientists plan to use the ISS to examine aerosols, ozone, water vapor, and oxides in Earth's atmosphere as well as cosmic rays, cosmic dust, anti-matter, and dark matter in the Universe.

The long-term goals of this research are to develop the technology necessary for human-based space and planetary exploration and colonization (including life support systems, safety precautions, environmental monitoring in space, etc.), new ways to treat diseases, more efficient methods of producing materials, accurate measurements with a precision impossible if done on Earth, a fuller concept of the Universe, and a new understanding from all experiments undertaken.

Major incidents

2003 Columbia disaster

After the Space Shuttle Columbia disaster on February 1, 2003, and the subsequent two and a half year suspension of the U.S. Space Shuttle program, followed by problems with resuming flight operations in 2005, there was some uncertainty over the future of the ISS until 2006. Between the Columbia disaster and the resumption of Shuttle launches, crew exchanges were carried out solely using the Russian Soyuz spacecraft. Starting with Expedition 7, two-astronaut caretaker crews were launched in contrast to the previously launched crews of three. Because the ISS had not been visited by a shuttle for an extended period, a larger than planned amount of waste accumulated, temporarily hindering station operations in 2004. However Progress transports and the STS-114 shuttle flight took care of this problem.

2006 Smoke problem

On September 18, 2006, the Expedition 13 crew activated a smoke alarm in the Russian segment of the International Space Station when fumes from one of three oxygen generator triggered momentary fear about a possible fire. Flight engineer Jeffrey Williams reported an unusual smell, but officials said there was no fire and the crew was not in any danger.

The crew reported at first smoke in the cabin and a smell. It turns out what was happening was a leak of potassium hydroxide from an oxygen vent. The equipment was turned off. Potassium hydroxide is odorless and the smell reported by Williams more likely was associated with an overheated rubber gasket in the Elektron system.

In any case, the station's ventilation system was shut down to prevent the spread of smoke or contaminants through the rest of the lab complex. A charcoal air filter was put in place to help scrub the atmosphere of any lingering potassium hydroxide fumes. The space station's program manager said the crew never donned gas masks, but as a precaution puts on surgical gloves and masks to prevent contact with any contaminants.

On November 02, 2006 the payload brought by the Russian Progress M-58 allow the crew to repair the Elektron using spare parts.

2007 computer failure

On 14 June 2007 during Expedition 15 and on flight day 7 of STS-117's visit to ISS, a computer malfunction on the Russian segments at 06:30 UTC left the station without thrusters, oxygen generation, carbon dioxide scrubber, and other environmental control systems, which caused temperatures to rise. A successful restart of the computers resulted in a false fire alarm which awakened the crew at 11:43 UTC. The two computer systems (command and navigation) are each composed of three computers. Each computer is referred to as a Lane.

By 15 June the primary Russian computers were back online and talking to the US side of the station by bypassing a circuit. Secondary systems were still offline and work would be needed. NASA had options to extend STS-117 if the issues could not be resolved and stated there was an "option to depart" if at least one of the station's stabilizing computers could not be fixed and the three member crew that is currently there, would have to be taken back to Earth aboard Atlantis. Without the computer that controls the oxygen levels, the station had only 56 days of oxygen available.

By the afternoon of 16 June, ISS's program manager Michael Suffredini confirmed that all six computers governing command and navigation systems, including two thought to have failed, for Russian segments of the station were back online and will be tested within the next day or two. The cooling system was the first system brought back online. NASA believes the overcurrent protection circuits designed to safeguard each computer from power spikes were at fault and that the leading theory is that they were tripped due to increased interference, or "noise," from the station's plasma environment related to the addition of massive new starboard trusses and solar arrays. Analysis of the failure continues for both the Station itself and by ESA for the Columbus Laboratory Module and the Automated Transfer Vehicle, which use the same computer systems that were supplied by EADS Astrium Space Transportation. According to NASA's Michael Suffredini, evidence suggests the plasma field shifted when the station's shape changed with the addition of the new truss segment and that "As the station gets bigger, this potential will continue to grow" and that "the Russians have noted some changes in their systems as we have grown."

Visiting spacecraft

• Space Shuttle - resupply vehicle, assembly and logistics flights and crew rotation (to be retired in 2010)
• Soyuz spacecraft - crew rotation and emergency evacuation, replaced every 6 months
• Progress spacecraft - resupply vehicle

Planned

• European (ESA) Automated Transfer Vehicle (ATV) ISS resupply spacecraft (scheduled for January 2008)
• Japanese (JAXA) H-II Transfer Vehicle (HTV) resupply vehicle for Kibo module (scheduled for 2009)
• Orion possible crew rotation and as resupply transporter (officially scheduled for 2014)

Proposed

• SpaceX Dragon for NASA Commercial Orbital Transportation Services (Scheduled for 2009)
• Rocketplane Kistler K-1 Vehicle for NASA Commercial Orbital Transportation Services (Scheduled for 2009)
• Russian Space Shuttle Kliper for possible crew rotation and as resupply transporter (scheduled for 2012)
• Crew Space Transportation System Soyuz-derived European-Russian crew rotation and resupply spacecraft (scheduled for 2014)

Expeditions

The ISS in its formation as of mid 2007. Photo made on June, 2007. Credits: STS-117 Crew, NASA

All permanent station crews are named "Expedition N", where N is sequentially increased after each expedition. Expeditions (aka Increments) have an average duration of half a year.

The International Space Station is the most-visited spacecraft in the history of space flight. As of September 11, 2006, it has had 159 (non-distinct) visitors. Mir had 137 (non-distinct) visitors (See Space station). The number of distinct visitors of the ISS is 124 (see list of International Space Station visitors).

Legal aspects

Agreement

The legal structure that regulates the space station is multi-layered. The primary layer establishing obligations and rights between the ISS partners is the Space Station Intergovernmental Agreement (IGA), an international treaty signed on January 28, 1998 by fifteen governments involved in the Space Station project. The ISS consists of the United States, Canada, Japan, the Russian Federation, and eleven Member States of the European Space Agency (Belgium, Denmark, France, Germany, Italy, The Netherlands, Norway, Spain, Sweden, Switzerland and the United Kingdom). Article 1 outlines its purpose:

This Agreement is a long term international co-operative framework on the basis of genuine partnership, for the detailed design, development, operation, and utilisation of a permanently inhabited civil Space Station for peaceful purposes, in accordance with international law.

The IGA sets the stage for a second layer of agreements between the partners referred to as 'Memoranda of Understanding' (MOUs), of which four exist between NASA and each of the four other partners. There are no MOUs between ESA, Roskosmos, CSA and JAXA due to the fact that NASA is the designated manager of the ISS. The MOUs are used to describe the roles and responsibilities of the partners in more detail.

A third layer consists of bartered contractual agreements or the trading of the partners' rights and duties, including the 2005 commercial framework agreement between NASA and Roskosmos that sets forth the terms and conditions under which NASA purchases seats on Soyuz crew transporters and cargo capacity on unmanned Progress transporters.

A fourth legal layer of agreements implements and supplements the four MOUs further. Notably among them is the ISS code of conduct, setting out criminal jurisdiction, anti-harassment and certain other behavior rules for ISS crewmembers.

Utilization

There is no fixed percentage of ownership for the whole space station. Rather Article 5 of the IGA sets forth that each partner shall retain jurisdiction and control over the elements it registers and over personnel in or on the Space Station who are its nationals. Therefore, for each ISS module only one partner retains sole ownership. Still, the agreements to use the space station facilities are more complex.

The three planned Russian segments Zvezda, the Multipurpose Laboratory Module and the Russian Research Modules are made and owned by Russia, which, as of today, also retains its current and prospective usage (Zarya, although constructed and launched by Russia, has been paid for and is officially owned by NASA). In order to use the Russian parts of the station, the partners use bilateral agreements (third and fourth layer of the above outlined legal structure). The rest of the station, (the U.S., the European and Japanese pressurized modules as well as the truss and solar panel structure and the two robotic arms) has been agreed to be utilized as follows (% refers to time that each structure may be used by each partner):

1. Columbus: 51% for ESA, 49% for NASA and CSA (CSA has agreed with NASA to use 2.3% of all non-Russian ISS structure)
2. Kibo: 51% for JAXA, 49% for NASA and CSA (2.3%)
3. Destiny Lab: 100% for NASA and CSA (2.3%) as well as 100% of the truss payload accommodation
4. Crew time and power from the solar panel structure, as well as rights to purchase supporting services (upload/download and communication services) 76.6% for NASA, 12.8% for JAXA, 8.3% for ESA and 2.3% for CSA

Costs

The ISS has been, as of today, far more expensive than originally anticipated. The ESA estimates the overall cost from the start of the project in the late 1980s to the prospective end in 2010 to be in the region of $130 billion (€100 billion).

Giving a precise cost estimate for the ISS is, however, not straightforward; it is, for instance, hard to determine which costs should actually be contributed to the ISS program or how the Russian contribution should be measured, as the Russian space agency runs at considerably lower USD costs than the other partners.

Criticism

The ISS and NASA have been the targets of varied criticism over the years. Critics believe that the time and money spent on the ISS could be better spent on other projects -- whether they be robotic spacecraft missions, space exploration, investigations of problems here on Earth, or just tax savings. Some critics, like Bob Park, argue that very little scientific research was convincingly planned for the ISS in the first place. They also argue that the primary feature of a space-based laboratory is its microgravity environment, which can usually be more-cheaply studied with a vomit comet -- that is, an aircraft which flies in parabolic arcs. Two of the most ambitious ISS projects to date -- the Alpha Magnetic Spectrometer and the Centrifuge Accommodations Module, have both been cancelled due to the prohibitive costs NASA faces in simply completing the ISS. As a result, the research done on the ISS is generally limited to experiments which don't have a specialized apparatus. For example, in the first half of 2007, ISS research dealt primarily with human biological responses to being in space, covering topics like kidney stones^[2], circadian rhythm^[3], and the effects of cosmic rays on the nervous system^[4]. Critics tend to believe that this sort of research is of little pragmatic value, since space exploration is today almost universally done by robots.

Other critics have attacked the ISS on some technical design grounds:

1. Jeff Foust argued that the ISS requires too much maintenance, especially by risky, expensive EVAs;
2. The Astronomical Society of the Pacific has mentioned that its orbit is rather highly inclined, which makes Russian launches cheaper, but US launches more expensive. This was intended as a design point, to encourage Russian involvement with the ISS -- and Russian involvement saved the project from abandonment in the wake of the Space Shuttle Columbia disaster -- but the choice may have increased the costs of completing the ISS substantially.

In response to some of these criticisms, advocates of manned space exploration say that criticism of the ISS project is short-sighted, and that manned space research and exploration have produced billions of dollars' worth of tangible benefits to people on Earth. Jerome Schnee estimates that the indirect economic return from spin-offs of human space exploration has been many times the initial public investment. However, this can be a rather contentious point: a review of the claims by the Federation of American Scientists argued that NASA's rate of return from spinoffs is actually very low, except for aeronautics work that has led to aircraft sales.

Critics also say that NASA is often casually credited with "spin-offs" (such as Velcro and portable computers) that were developed independently for other reasons. NASA maintains a list of spin-offs from the construction of the ISS, as well as from work performed on the ISS. However, NASA's official list is much narrower and more arcane than dramatic narratives of billions of dollars of spin-offs.

It is therefore debatable whether the ISS, as distinct from the wider space program, will be a major contributor to society. Some advocates argue that apart from its scientific value (or lack thereof), it is an important example of international cooperation. Others claim that the ISS is an asset that, if properly leveraged, could allow more economical manned Lunar and Mars missions. Either way, advocates argue that it misses the point to expect a hard financial return from the ISS; rather, it is intended as part of a general expansion of spaceflight capabilities.

Sightings

Due to the size of the International Space Station, and particularly the large reflective area offered by its solar panels, ground based observation of the station is possible with the naked eye; indeed, it is one of the brightest naked-eye objects in the sky on such occasions. Since the station is in low earth orbit, and the sun angle and observer locations also need to coincide, it is only visible for brief periods of time.

NASA provides data on forthcoming opportunities for viewing the ISS (and other objects) via their Sightings web page, and so does the European Space Agency [5].

Miscellaneous

Space tourism and weddings

As of 2007 there have been five space tourists to the ISS, each spending around US$25 million; they all went there aboard Russian supply missions. There has also been a space wedding when cosmonaut Yuri Malenchenko on the station married Ekaterina Dmitrieva, who was in Texas.

Golf Shot Around The World was an event in which, on an EVA, a special golf ball, equipped with a tracking device, was hit from the station and sent into its own low Earth orbit for a fee paid by a Canadian golf equipment manufacturer to the Russian Space Agency. The task was supposed to be performed on Expedition 13, but the event was postponed, and took place on Expedition 14.

Microgravity

At the ISS altitude, the gravity from the Earth is still 88% of that at sea level. The state of weightlessness is a result of the fact that the ISS is in constant free fall, which according to the equivalence principle is indiscernible from being in a state where all forces, including gravity, are absent. However, due to (1) the drag resulting from the residual atmosphere, (2) vibratory acceleration due to mechanical systems and the crew on board the ISS, (3) orbital corrections by the on-board gyroscopes or thrusters, and (4) the spatial separation from the real centre of mass of the ISS, the environment on the station is often described as microgravity, with a level of gravity on the order of 2 to 1000 millionths of g (the value varies with the frequency of the disturbance; the low value occurs at frequencies below 0.1 Hz, the higher value at frequencies of 100 Hz or more).