The Brazilian Space Agency (AEB, Brazil) participates through a separate contract with NASA. The Italian Space Agency similarly has separate contracts for various activities not done in the framework of ESA's ISS works (where Italy also fully participates).

The ISS is a continuation of what began as the U.S. Space Station Freedom, the funding for which was cut back severely. It represents a merger of Freedom with several other previously planned space stations: Russia's Mir 2, the planned European Columbus and the Japanese Experiment Module. Construction of the station is currently underway, with a projected completion date of 2010, but ISS is already larger than any previous space station.

The ISS has been continuously inhabited since the first resident crew entered the station on November 2, 2000, thereby providing a permanent human presence in space. The station is serviced primarily by Russian Soyuz and Progress spacecraft and by U.S. Space Shuttle orbiters. At present the station has a capacity for a crew of three. Early crewmembers all came from the Russian or U.S. space programs. German ESA astronaut Thomas Reiter joined the Expedition 13 crew in July 2006, becoming the first crewmember from another space agency. The station has however been visited by astronauts from 14 countries, and the Expedition 16 crew will include members from all five space agencies forming the ISS partnership. ISS was also the destination of the first four space tourists.

In the early 1980s, NASA planned Space Station Freedom as a counterpart to the Soviet Salyut and Mir space stations. It never left the drawing board, and with the end of the Soviet Union and the Cold War it was cancelled. The end of the Space race prompted the U.S. administration officials to start negotiations with international partners Europe, Russia, Japan and Canada in the early 1990s, in order to build a truly international space station. This project was first announced in 1993 and was called Space Station Alpha.^[3] It was planned to combine the proposed space stations of all participating space agencies: NASA's Space Station Freedom, Russia's Mir-2 (the successor to the Mir space station, the core of which is now ISS Zvezda) and ESA's Columbus that was planned to be a stand-alone spacelab.

Throughout the 1990s, construction delays hit the project, budget projections were heavily revised and the ISS structure was modified frequently. 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 2016 to be in the region of €100 billion.^[4]

The first section, the Zarya Functional Cargo Block, 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, Expedition 1, was sent. Expedition 1 docked to the ISS on November 2, 2000, and consisted of U.S. astronaut William Shepherd and two Russian cosmonauts, Yuri Gidzenko, and Sergei Krikalev.

Columbia disaster and consequences

After the breakup of Columbia 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.

The Space Shuttle Program resumed flight on July 26, 2005 with the STS-114 mission of Discovery. This mission to the ISS was intended both to test new safety measures implemented since the Columbia disaster, and to deliver supplies to the station. Although the mission succeeded safely, it was not without risk; foam was shed by the external tank, leading NASA to announce future missions would be grounded until this issue was resolved.

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, instead of the previous 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.

Changes in construction plans

Present configuration of the ISS

ISS construction is now far behind the original planned schedule for completion in 2004 or 2005. This is mainly due to the halting of all NASA Shuttle flights following the Columbia disaster in early 2003 (although there had been prior delays due partly to Shuttle problems, and partly to delays stemming from the Russian space agency's budget constraints). During the shuttle standdown construction of the ISS was halted and the science conducted aboard was limited due to the crew size of two.

As of the beginning of 2006 many changes have been made to the originally planned ISS, even before the Columbia disaster. Modules and other structures have been cancelled or replaced and the number of Shuttle flights to the ISS has been reduced from previously planned numbers. Still, the newest ISS Shuttle launch manifest and the current ISS design scheme reveal that more than 80% of the hardware planned to be part of the ISS in the late 90s, is still planned to be orbited to the ISS by its scheduled completion date in 2010.

In March 2006 a meeting of the heads of the five participating space agencies accepted the new ISS construction schedule that plans to complete the ISS by 2010.^[5] A crew of six is expected to be established in 2009, after the Shuttle's next 12 construction flights following the second Return to Flight mission STS-121. Requirements for stepping up the crew size include enhanced environmental support on the ISS, a second Soyuz permanently docked on the station to function as a second 'lifeboat', more frequent Progress flights to provide double the amount of consumables, more fuel for orbit raising maneuvers, and a sufficient supply line of experimental equipment.

[edit] Current status

The second Return to Flight mission, STS-121, was delayed and did not launch until July 4, 2006. After the successful completion of that mission, ISS assembly resumed with the launch of STS-115 on September 9, 2006. On December 9, 2006 STS-116 lifted off for the second Space Shuttle assembly mission since the Columbia disaster. It took with it the first Swedish astronaut, Christer Fuglesang. EVAs conducted by Fuglesang and other members of the STS-116 crew upgraded the electrical system of the space station. Station power is now supplied for the first time from solar arrays attached to the permanent truss structure.

Structures and design

International Space Station mockup at Johnson Space Center in Houston, Texas

See also: ISS assembly sequence

The space station is located in orbit around the Earth at an altitude of approximately 360 km (220 miles), a type of orbit usually termed low Earth orbit (The actual height varies over time by several kilometres due to atmospheric drag and reboosts). It orbits Earth in a period of about 92 minutes; by June 2005 it had completed more than 37,500 orbits since launch of the Zarya module on November 20, 1998.

The ISS, when completed, will be essentially made of a set of communicating pressurized modules connected to a truss, on which are attached four large pairs of photovoltaic modules. The pressurized modules and the truss will be perpendicular: the truss spanning from starboard to port and the habitable zone extending on the aft-forward axis. Although during the construction the station attitude may vary, when all four photovoltaic modules are in their definitive position the aft-forward axis will be parallel to the velocity vector.^[6]

A total of 10 main pressurized modules (Zarya, Zvezda, Destiny, Unity Module -also called Node 1-, Node 2, Node 3, Columbus, Kibo, MLM and the RM) are currently scheduled to be part of the ISS by its completion date in 2010.^[7] A number of smaller pressurized sections will be adjunct to them (Soyuz spacecrafts (permanently 2 as lifeboats - 6 months rotations), Progress transporters (2 or more), the Quest and Pirs Airlocks, as well as periodically the MPLM, the ATV and the HT-V).

Power supply

Main article: Electrical system of the International Space Station

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.^[8]

Environmental Control and Life Support System (ECLSS)

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

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 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.^[9]

Pressurized modules already launched

Cosmonaut Sergei Krikalev inside the Zvezda Service Module, November 2000

March 10, 2001 - The Leonardo Multi-Purpose Logistics Module rests in Discovery's payload bay during STS-102.

Currently, the ISS consists of only four main pressurized modules; two Russian modules Zarya and Zvezda and two US modules Destiny and Node 1. Zarya was the first module launched by a Proton rocket in November 1998, followed by a shuttle mission that connected Zarya with Node 1, the first of three node modules, 2 weeks after Zarya had been launched. This bare 2-module core of the ISS remained unmanned for the next one and a half years, until in July 2000 the Russian module Zvezda was added, allowing a minimum crew of two astronauts or cosmonauts to be on the ISS permanently.

Since 2000, the only main pressurized module delivered to the ISS was the Destiny Laboratory Module by STS-98 in 2001. The US Lab was also the first science module delivered to the ISS, whereas Zarya provides electrical power, storage, propulsion, and guidance functions and Zvezda provides living quarters, a life support system, a communication system, electrical power distribution, a data processing system, a flight control system, and a propulsion system. Node 1's primary function is to link different modules together, however fluids, environmental control and life support systems, electrical and data systems are also routed through Node 1 to supply work and living areas of the station.

Other pressurized sections of the current configuration of the ISS are the Quest Airlock and the Pirs Airlock. Soyuz spacecraft and Progress spacecraft docked to the ISS also extend the pressurized volume. At least one Soyuz spacecraft has to stay docked permanently as a 'lifeboat' and is replaced every six months by a new Soyuz as part of crew rotation.

Although not permanently docked with the ISS, the Multi-Purpose Logistics Module (MPLM) forms part of the ISS during Shuttle missions that include the MPLM. The MPLM is attached to Node 1 and is used for resupply and logistics flights. Speculation that the last Space Shuttle flight involving an MPLM could leave one MPLM permanently docked with the Station are fueled by the MPLM's potential capacity for a long-term stay in orbit. Modifications would need to be made, including power support and checks on whether the MPLM would influence the ISS overall structure. As of 2006, it is not planned to integrate the MPLM permanently into the ISS structure.

Pressurized modules to be launched

Node 2

Columbus Laboratory Module

Japanese Experiment Module, aka Kibō module

Cupola

Node 2 — 2007

As of March 2006, nearly all already built pressurized modules are planned to be launched by the Space Shuttle after return to flight with STS-121 in July 2006. If the current Shuttle launch sequence is not disrupted materially, Node 2 will be launched in the second quarter of 2007 by STS-120. Node 2 was built by the Italian Space Agency, however its ownership has been already transferred to NASA as part of a bartering agreement between NASA and ESA.^[10] Node 2 will contain eight racks that provide air, electrical power, water and other systems essential to support life on the spacecraft and is scheduled to be the hub for the Columbus module and Kibo.

Columbus Laboratory Module — 2007

The next Shuttle flight after Node 2 is scheduled to bring the European module Columbus to the ISS. Columbus will be the second module mainly dedicated to science on the ISS, including the Fluid Science Laboratory (FSL), the European Physiology Modules (EPM), the Biolab, the European Drawer Rack (EDR) and various storage racks.

Japanese Experiment Module — 2008/2009

The Japanese Experiment Module (also known as JEM or "Kibo") is the next pressurized module on the schedule. It consists of two pressurized sections and one exposed facility. Three shuttle flights are needed to bring the Kibo laboratory into orbit. The pressurized sections are scheduled to fly in the second half of 2008 and in the first half of 2009. Kibo will be mounted on the Node 2, on the opposite side to the Columbus module.

Multipurpose Laboratory Module — 2009

The Russian space agency has announced that the Multipurpose Laboratory Module (MLM) is scheduled to be launched by a Proton rocket in 2009. The MLM is the main Russian science module, and depending on its actual launch date the third or fourth science module to be launched to the ISS. It will be equipped with an altitude control system that can be used as a backup by the ISS and will be docked onto either the Zarya control module side docking port or the Zvezda docking port. The European Robotic Arm will be launched together with MLM, mated on its surface for a later deployment in space, according to an agreement signed in October 2005 between ESA and Roskosmos.

Node 3 and Cupola — 2010

Node 3 is currently scheduled for the beginning of 2010 on the next to last Shuttle flight. Like Node 2, Node 3 was built in Italy by the Italian Space Agency, but is owned by NASA. It will be used as a storage compartment as its original purpose, to be a hub for the Habitation Module as well as the Crew Return Vehicle, is no longer relevant - both items were cancelled in 2001. One of the curiosities of the ISS, the Cupola 'space window' is currently scheduled to be flown together with Node 3. ESA has finished construction and is storing the Cupola until its flight with Node 3.

Russian Research Module — 2010 or later

NASA's ISS schedule still includes one Russian Research Module (RM) as part of the ISS that may be docked to either Zvezda or Zarya and is rumoured to fly to the ISS at some point after 2010 or later on a Russian Proton rocket. Construction on this module has not yet begun, which casts doubt on its actual delivery to the ISS.

Unpressurized elements

There is also a large unpressurized truss system partially in place that will eventually support the prominent solar arrays, as well as external experiments like the Alpha Magnetic Spectrometer.

Cancelled elements

• Centrifuge Accommodations Module - would have been attached to Node 2
• Universal Docking Module - replaced by Multipurpose Laboratory Module
• Docking and Stowage Module - replaced by Multipurpose Laboratory Module
• Habitation Module -^[11]
• 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

 Visiting Craft

• Space Shuttle - resupply vehicle, assembly and logistics flights and crew rotation
• 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 Nov 2007)
• Planned: Japanese (JAXA) H-II Transfer Vehicle (HTV) resupply vehicle for Kibo module (scheduled for 2008)
• Proposed: SpaceX Dragon for NASA Commercial Orbital Transportation Services (Scheduled for 2009)
• Proposed: Rocketplane Kistler K-1 Vehicle for NASA Commercial Orbital Transportation Services (Scheduled for 2009)
• Proposed: Russian Space Shuttle Kliper for possible crew rotation and as resupply transporter (scheduled for 2012)
• Proposed: Crew Exploration Vehicle possible crew rotation and as resupply transporter (officially scheduled for 2014)
• Proposed: Advanced Crew Transportation System Soyuz-derived European-Russian crew rotation and resupply spacecraft (scheduled for 2014)

 Current assembled components

Building the ISS requires more than 40 assembly and utilization flights. Of these flights, currently 33 are planned to be Space Shuttle flights, with 20 ISS-shuttle flights currently flown and 13 more planned between 2007 and 2010. Other assembly flights consist of modules lifted by the Russian Proton rocket or in the case of the Pirs Airlock by a Soyuz rocket.

In addition to the assembly and utilization flights, approximately 30 Progress spacecraft flights are required to provide logistics until 2010. Experimental equipment, fuel and consumables are and will be delivered by all vehicles visiting the ISS: the Shuttle, the Russian Progress, the European ATV (prospectively from May 2007 onwards) and the Japanese HTV.

When assembly is complete, the ISS will have a pressurized volume of approximately 1,000 cubic meters, a mass of approximately 400,000 kilograms, approximately 100 kilowatts of power output, a truss 108.4 meters long, modules 74 meters long, and a crew of six.

As of December 2006 the station consists of several modules and elements:

Legal Aspects

Agreement

Cover page of the Space Station Intergovernmental Agreement signed on January 28, 1998

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 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.^[12]

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.^[13]

Utilization

The nadir window in the Destiny lab - the Destiny lab is 100% owned by NASA

The Zarya module was built in Russia but is 100% owned by NASA

There is a 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.^[12] 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 most cited figure of an estimate of overall costs of the ISS is 100 billion (very often cited as USD; ESA, the only agency actually stating potential overall costs on its website, estimates €100 billion^[4]). 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.

NASA

Overview

NASA's budget projections currently see an end to ISS funding in 2017 in order to free funds for the Vision for Space Exploration

The overall majority of costs for NASA are incurred by flight operations and expenses for the overall management of the ISS. Costs for initially building the U.S. portion of the ISS modules and external structure on the ground and construction in space as well as crew and supply flights to the ISS do account for far less than the general operating costs (see annual budget allocation below).

NASA does not include the basic Space Shuttle program costs in the expenses incurred for the ISS program, despite the fact that the Space Shuttle has been nearly exclusively used for ISS construction and supply flights since December 1998.

NASA's 2007 budget request^[14] lists costs for the ISS (without Shuttle costs) as $25.6 billion for the years 1994 to 2005. For each of 2005 and 2006 about $1.7 to 1.8 billion are allocated to the ISS program. The annual expenses will increase until 2010 when they will reach $2.3 billion and should then stay at the same level, however inflation-adjusted, until 2016, the defined end of the program. NASA has allocated between $300 and 500 million for program shutdown costs in 2017.

2005 ISS budget allocation

NASA allocates about 125 million US dollars annually to EVAs

The $1.8 billion expensed in 2005 consisted of:^[15]

• Development of new hardware: $70 million were allocated to core development, for instance development of systems like navigation, data support or environmental.
• Spacecraft Operations: $800 million consisting of $125 million for each of software, extravehicular activity systems, and logistics and maintenance. An additional $150 million is spent on flight, avionics and crew systems. The rest of $250 million goes to overall ISS management.
• Launch and Mission operations: Although the Shuttle launch costs are not considered part of the ISS budget, mission and mission integration ($300 million), medical support ($25 million) and Shuttle launch site processing ($125 million) is within the ISS budget.
• Operations Program Integration: $350 million was spent on maintaining and sustaining U.S. flight and ground hardware and software to ensure integrity of the ISS design and the continuous, safe operability.
• ISS cargo/crew: $140 million was spent for purchase of supplies, cargo and crew capability for Progress and Soyuz flights.

Shuttle costs as part of ISS costs?

The only non-ISS related Shuttle flight between 2006 and 2010 will be a Hubble Space Telescope servicing mission in 2008

Only costs for mission and mission integration and launch site processing for the 33 ISS-related Shuttle flights are included in NASA's ISS program costs. Basic costs of the Shuttle program are, as mentioned above, not considered part of the overall ISS costs by NASA, because the Shuttle program is considered an independent program aside from the ISS. Since December 1998 the Shuttle has however been used nearly exclusively for ISS flights (since the first ISS flight in December 1998 until December 2006 only 5 flights out of 25 flights have not been to the ISS and only the planned Hubble Space Telescope servicing mission (see STS-125) in 2008 will not be ISS-related out of 14 planned missions until the end of the Space Shuttle program in 2010).

Shuttle program costs during ISS operations from 1999 to 2005 (disregarding the first ISS flight in December 1998) have amounted to approximately $24 billion (1999: $3,028.0 million, 2000: $3,011.2 million, 2001: $3,125.7 million, 2002: $3,278.8 million, 2003: $3,252.8 million, 2004: $3,945.0 million, 2005: $4,319.2 million). In order to derive the ISS-related costs, expenses for non-ISS flights need to be substracted, which amount to 20% of the total or about $5 billion. For the years 2006-2011 NASA projects another $20.5 billion in Space Shuttle program costs (2006: $4,777.5 million, 2007: $4,056.7 million, 2008: $4,087.3 million, 2009: $3,794.8 million, 2010: $3,651.1 million and 2011: $146.7 million). If the Hubble servicing mission is excluded from those costs, ISS-related costs will be approximately $19 billion for Shuttle flights from 2006 until 2011. In total, ISS-related Space Shuttle program costs will therefore be approximately $38 billion.

Overall ISS costs for NASA

Assuming NASA's projections of average costs of $2.5 billion from 2011 to 2016 and the end of spending money on the ISS in 2017 (about $300-500 million) after shutdown in 2016 are correct, the overall ISS project costs for NASA from the announcement of the program in 1993 to its end will be about $53 billion (25.6 billion for the years 1994-2005 and about 27 to 28 billion for the years 2006-2017).

There have also been considerable costs for designing Space Station Freedom in the 1980s and early 1990s, before the ISS program started in 1993. Plans of Space Station Freedom were reused for the International Space Station.

To sum up, although the actual costs NASA views as connected to the ISS are only half of the $100 billion figure often cited in the media, if combined with basic program costs for the Shuttle and the design of the ISS' precursor project Space Station Freedom, the costs reach $100 billion for NASA alone.

ESA

ESA calculates that its contribution over the 30 year lifetime of the project will be €8 billion ^[16]. The costs for the Columbus Laboratory total more than €1 billion already, costs for ATV development total several hundred million and considering that each Ariane 5 launch costs around €150 million, each ATV launch will incur considerable costs as well. In addition ESA has constructed a ground control station in the South of Germany in order to control the Columbus Laboratory.

JAXA

The development of the Kibo Laboratory, JAXA's main contribution to the ISS, has cost about 325 billion yen (about $2.8 billion) ^[17] In the year 2005, JAXA allocated about 40 billion yen (about 350 million USD) to the ISS program ^[18]. The annual running costs for Kibo will total around $350 to 400 million. In addition JAXA has committed itself to develop and launch the HTV-Transporter, for which development costs total nearly $1 billion. In total, over the 24 year lifespan of the ISS program JAXA will contribute well over $10 billion to the ISS program.

Roskosmos

A considerable part of the Russian Space Agency's budget is used for the ISS. Since 1998 there have been over two dozen Soyuz and Progress flights, the primary crew and cargo transporters since 2003. The question, how much Russia spends on the station, measured in USD, is, however, not easy to answer. The two modules currently in orbit are derivatives of the Mir program and therefore development costs are much lower than for other modules; in addition, the exchange rate between ruble and USD is not adequately giving a real comparison to what the costs for Russia really are.

The $20 million each space tourist has paid for an available seat on a Soyuz to the ISS is only offsetting a very small part of Russia's financial contribution to the ISS.

CSA

Canada, whose main contribution to the ISS is the Canadarm2, is estimating that through the last 20 years it has contributed about C$1.4 billion to the ISS.^[19]

• Wikipedia: The free encyclopedia. (2007, January 6). FL: Wikipedia Foundation, Inc. Retrieved January 6, 2007, from http://www.wikipedia.org