International Space Station

The International Space Station (ISS) is a research facility being assembled in space. Its on-orbit assembly began in 1998. The space station is in a low Earth orbit and can be seen from Earth with the naked eye: it has an altitude of about 350 km (217 mi)^[1] above the surface of the Earth, and travels at an average speed of 27,700 km (17,210 statute miles) per hour, completing 15.77 orbits per day.

The ISS is a joint project among the space agencies of the United States (NASA), Russia (RKA), Japan (JAXA), Canada (CSA) and eleven European countries (ESA).^[2] 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). China has reportedly expressed interest in the project,^[3] especially if it is able to work with the RKA,^[4] though it is not currently involved.^[3]

The ISS is a continuation of several other previously planned space stations: Russia's Mir 2, the U.S. Space Station Freedom, the European Columbus, and Kibo, the Japanese Experiment Module. The projected completion date is 2010, with the station remaining in operation at least until 2016. As of 2008, the ISS is larger than any previous space station.

The ISS has been continuously staffed since the first resident crew entered the station on November 2 2000, thereby providing a permanent human presence in space. The crew of Expedition 17 are currently aboard. At present the station has a capacity for a crew of three. In order to fulfill an active research program it will eventually hold 6 crew members.^[5] Early crew members all came from the Russian and U.S. space programs. German ESA astronaut Thomas Reiter joined the Expedition 13 crew in July 2006, becoming the first crew member from another space agency. The station has, however, been visited by astronauts from 16 countries. The ISS was also the destination of the first five space tourists.

Origins

Assembly

The assembly of the International Space Station is a major aerospace engineering endeavor. When assembly is complete the ISS will have a pressurized volume of approximately 1,000 cubic meters. Assembly began in November 1998 with the launch of Zarya – the first ISS module – on a Proton rocket, and as of July 2008 assembly is about 75% complete.

Two weeks after Zarya was launched, the STS-88 shuttle mission followed, bringing Unity, the first of three node modules, and connecting it to Zarya. 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 maximum crew of three astronauts or cosmonauts to be on the ISS permanently.

Pressurized modules

The ISS is currently under construction, and will eventually consist of fourteen pressurized modules with a combined volume of around 1,000 cubic metres. These modules include laboratories, docking compartments, airlocks, nodes and living quarters, nine of which are already in orbit, with the remaining five awaiting launch on the ground. Each module is launched either by Space Shuttle, Proton rocket or Soyuz rocket, and is listed below along with its purpose, launch date and mass.

Module	Launch date	Launch vehicle	Docking date	Mass	Assembly flight	Purpose
Zarya (FGB)	1998-11-20	Proton-K	N/A		1A/R	Provided electrical power, storage, propulsion, and guidance during initial assembly, now serves as a storage module (both inside the pressurized section and in the externally mounted fuel tanks).
Unity (Node 1)	1998-12-04	Space Shuttle Endeavour, STS-88	1998-12-07		2A	First American node, connecting the American section of the station to the Russian section (via PMA-1). Provides berthing locations for the Z1 truss, Quest airlock, Destiny laboratory and Node 3.
Zvezda (Service Module)	2000-07-12	Proton-K	2000-07-26		1R	Station service module, providing main living quarters for resident crews, environmental systems and attitude & orbit control, in addition to docking locations for Soyuz spacecraft, Progress spacecraft and the Automated Transfer Vehicle. The addition of the module rendered the ISS permanently habitable for the first time.
Destiny (US Laboratory)	2001-02-07	Space Shuttle Atlantis, STS-98	2001-02-10		5A	Primary research facility for American payloads aboard the ISS, also providing environmental systems and living quarters to the station.
Quest (Joint Airlock)	2001-07-12	Space Shuttle Atlantis, STS-104	2001-07-14		7A	Primary airlock for the ISS, hosting spacewalks with both American EMU and Russian Orlan spacesuits.
Pirs (Docking Compartment)	2001-09-14	Soyuz-U	2001-09-16		4R	Provides the ISS with additional docking ports for Soyuz & Progress spacecraft, and allows egress and ingress for spacewalks by cosmonauts using Russian Orlan spacesuits, in addition to providing storage space for these spacesuits.
Harmony (Node 2)	2007-10-23	Space Shuttle Discovery, STS-120	2007-11-14		10A	The "utility hub" of the ISS. Node 2 contains four racks that provide electrical power, bus electronic data, and act as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kib? laboratories are currently berthed to Harmony. In addition, the Harmony module serves as a berthing port for the Multi-Purpose Logistics Modules during space shuttle logistics flights.
Columbus (European Laboratory)	2008-02-07^[8]	Space Shuttle Atlantis, STS-122	2008-02-11		1E	Primary research facility for European payloads aboard the ISS, providing ten International Standard Payload Racks and mounting locations for external experiments.
Experiment Logistics Module (JEM-ELM)	2008-03-11	Space Shuttle Endeavour, STS-123	2008-03-12	^[9]	1J/A	Part of the Kib? Japanese Experiment Module laboratory, the ELM provides storage and transportation facilities to the laboratory, with a pressurized section to serve internal payloads and an unpressurized section to serve external payloads.
Japanese Pressurized Module (JEM-PM)	2008-05-31	Space Shuttle Discovery, STS-124	2008-06-03	^[10]	1J	Part of the Kib? Japanese Experiment Module laboratory, the PM is the core module of Kib? to which the ELM & Exposed Facility are berthed. The laboratory is the largest single ISS module, and contains ten International Standard Payload Racks.

Mini-Research Module 2	2009-08-15	Soyuz-U	TBD		5R	Not yet launched. The newest Russian component of the ISS, MRM2 will likely be used for docking and cargo storage aboard the station.
Node 3	2010-03-18	Space Shuttle Discovery, STS-132	TBD		20A	Not yet launched. The last of the station's US nodes, Node 3 will contain an advanced life support system to recycle waste water for crew use and generate oxygen for the crew to breathe. The node also provides four berthing locations for more attached pressurized modules or crew transportation vehicles, in addition to the permanent berthing location for the station's Cupola.
Cupola	2010-03-18	Space Shuttle Discovery, STS-132	TBD		20A	Not yet launched. The Cupola is an observatory module that will provide ISS crew members with a direct view of robotic operations and docked spacecraft, as well as an observation point for watching the Earth. The module will come equipped with robotic workstations for operating the SSRMS and shutters to prevent its windows from being damaged by micrometeorites.
Mini-Research Module 1	2010-03-18	Space Shuttle Atlantis, STS-131	TBD		ULF4	Not yet launched. MRM1 will be used for docking and cargo storage aboard the station.
Multipurpose Laboratory Module	December 2011^[11]	Proton-K	TBD		3R	Not yet launched. The MLM will be Russia's primary research module as part of the ISS, and will be used for experiments, docking and cargo logistics. It will also serve as a crew work and rest area, and will also be equipped with a backup attitude control system that can be used to control the station's attitude.

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 (as does the Shuttle). In the remainder of the station, electricity is provided by the solar cells 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.^[12]

Using a high-voltage (130 to 160 volts) distribution line in the U.S. part of the station allows smaller power lines and less weight.

The solar array normally tracks the Sun to maximize the amount of solar power. The array is about 375 m� in area and long. In the fully-complete configuration, the solar arrays track the sun in each orbit by rotating the alpha gimbal; while the beta gimbal adjusts for the angle of the sun from the orbital plane. (until the main truss structure arrived, the arrays were in a temporary position perpendicular to the final orientation, and in this configuration, as shown in the image to the right, the beta gimbal was used for the main solar tracking.) Another slightly different tracking option, Night Glider mode, can be used to reduce the drag slightly by orienting the solar arrays edgewise to the velocity vector.

Life support

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. In this event, the Russian Attitude Control System is designed to take over automatically, using thrusters to maintain station attitude and allowing the CMG system to desaturate. This happened during Expedition 10.^[14] 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.

Altitude control

The ISS is maintained at an orbit from a minimum altitude limit of 278 km to a maximum limit of 460 km. The normal maximum limit is 425 km to allow Soyuz rendezvous missions. Because ISS is constantly losing altitude due to minute atmospheric drag and gravity gradient effects, it needs to be boosted to a higher altitude several times each year.^[15] A graph of altitude over time shows that it drifts down almost 2.5 km per month.^[16] The boosting can be performed by two boosters on the Zvezda module, a docked Space Shuttle, a Progress resupply vessel or by ESA's ATV and takes approximately two orbits (three hours) in which it is boosted several kilometers higher.^[15] While it is being built the altitude is relatively low so that it is easier to fly the Space Shuttle with its big payloads to the space station.

Scientific research

Scientific ISS modules

Areas of research

There are a number of plans to study biology on the ISS. One goal is to improve 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.^[17]

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).^[17]

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.^[17]

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), new ways to treat diseases, more efficient methods of producing materials, more accurate measurements than would be impossible to achieve on Earth, and a more complete understanding of the Universe.^[17]^[18]

Future of the ISS

NASA Administrator Michael D. Griffin says the International Space Station has a role to play as NASA moves forward with a new focus for the manned space program, which is to go out beyond Earth orbit for purposes of human exploration and scientific discovery. "The International Space Station is now a stepping stone on the way," says Griffin, "rather than being the end of the line".^[22] He says ISS crews will not only continue to learn how to live and work in space but also will learn how to build hardware that can survive and function for the years required to make the round-trip voyage from Earth to Mars.

However, in an internal e-mail sent 18 August, 2008 to NASA managers (published 6 September, 2008 in the Orlando Sentinel^[23]), Griffin flatly stated his belief that the current US administration is has made no viable plan for US crews to participate in the ISS beyond 2011, and that OMB and OSTP are actually seeking its demise. Griffin believes the only reasonable solution is to extend the operation of the Space Shuttle beyond 2010, but notes that Executive Policy (ie, the White House) is firm that there will be no extension of the shuttle retirement date, and thus no US capability to launch crews into orbit until the Ares I/Orion system becomes operational in 2014 at the very earliest. He does not see purchase of Russian launches for NASA crews as politically viable following the 2008 South Ossetia war, and hopes the new US administration will resolve the issue in 2009 by extending shuttle operations beyond 2010.

Major incidents

2003 – Columbia disaster

The Space Shuttle Columbia disaster on February 1 2003, the following two-and-a-half-year suspension of the U.S. Space Shuttle program, followed in turn by another one-year suspension following STS-114, all resulted in some uncertainty about the future of the International Space Station. All crew exchanges between February 2003 and July 2006 were carried out solely using the Russian Soyuz spacecraft (STS-114 in July 2005 was a logistics-only visit). 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 had 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 the three oxygen generators 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 initially reported smoke in the cabin, as well as a smell. It was later found to be caused by 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 put on surgical gloves and masks to prevent contact with any contaminants.^[24]

On November 2 2006 the payload brought by the Russian Progress M-58 allowed the crew to repair the Elektron using spare parts.^[25]

2007 – Computer failure

On June 14 2007 during Expedition 15 and 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, and caused the temperature on the station to rise. A successful restart of the computers resulted in a false fire alarm that woke the crew at 11:43 UTC.^[26]^[27] The two computer systems (command and navigation) are each composed of three computers. Each computer is referred to as a "lane".^[27]

By June 15, 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 further work was needed.^[28] NASA reported that without the computer that controls the oxygen levels, the station had 56 days of oxygen available.^[29]

By the afternoon of June 16, ISS Program Manager Michael Suffredini confirmed that all six computers governing command and navigation systems for Russian segments of the station, including two thought to have failed, were back online, and would be tested over several days. The cooling system was the first system brought back online. NASA suggested that the overcurrent protection circuits designed to safeguard each computer from power spikes were at fault, and may have been tripped due to increased interference, or "noise," from the station's plasma environment related to the addition of the new starboard trusses and solar arrays.^[27] Troubleshooting of the failure by the ISS crew found that the root cause was condensation inside the electrical connectors, leading to a short-circuit that triggered the "power off" command line leading to all three of the redundant processing units.^[30] This was initially a concern, because the European Space Agency uses the same computer systems, supplied by EADS Astrium Space Transportation, for the Columbus Laboratory Module and the Automated Transfer Vehicle.^[31] Once the root cause was understood, plans were implemented to avoid the problem in the future.

2007 – Torn solar panel

On October 30, 2007 during Expedition 16 and flight day 7 of STS-120's visit to ISS, following the reposition of the P6 truss segment, ISS and Space Shuttle Discovery crew members began the deployment of the trusses' two solar arrays. The first array deployed without incident, and the second array deployed approximately 80% before astronauts noticed a tear. The arrays had been deployed in earlier phases of the space station's construction, and the retraction necessary to move the truss to its final position had gone less smoothly than planned.^[32]

A second, smaller tear was noticed upon further inspection, and the mission's planned spacewalks were completely replanned in mere days to devise a repair. On Saturday November 3, spacewalker Scott Parazynski assisted by Douglas Wheelock fixed the torn panels using makeshift "cufflinks" and riding on the end of the space shuttle's boom inspection arm; the first ever spacewalker to do so. The spacewalk was regarded as significantly more dangerous than most due to the possibility of shock from the electricity generating solar arrays, the unprecedented usage of the shuttle boom arm, and the lack of spacewalk planning and training for the impromptu procedure. Parazynski was, however, able to repair the damage as planned and the repaired array was fully deployed.^[33]

2007 – Damaged starboard Solar Alpha Rotary Joint

The starboard Solar Alpha Rotary Joint (SARJ) malfunctioned during the STS-120 mission. This and the port SARJ rotate the large solar arrays to keep them facing the Sun while the ISS's main body axis remains horizontal, pointing forward in the direction of orbital motion. Excessive vibration and high current spikes in the array drive motor resulted in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs showed extensive contamination from metallic shavings and debris in the large drive gear.^[34] More recent inspections confirmed damage to the large metallic race ring at the heart of the joint. Following the STS-123 mission, the cause of the problem was still not fully understood, and therefore no permanent fix was identified. The station appears to have sufficient operating power to carry out its near-term science program with only modest impact on operations.

On September 25, 2008, NASA announced significant progress in diagnosing the source of the starboard SARJ problem, and a program to repair it on orbit, beginning with the upcoming STS-126 (Endeavour ) flight^[35], currently expected no earlier than November 16, 2008^[36]^[37]. STS-126 will be a 15-day mission with four EVAs, largely dedicated to servicing and repair of the Solar Alpha Rotary Joints, plus station logistics and resupply. Both the starboard and port SARJs will be serviced.^[38] In addition to lubricating both bearings, the remaining 11 Trundle Bearings in the right SARJ will be replaced.^[39]

On January 30 2008, NASA announced that another problem, also on the starboard array side, is believed to have been rectified with the replacement of the Bearing Motor Roll Ring Module (BMRRM) in the Beta Gimbal Assembly (BGA) 1A.^[40]

Visiting spacecraft

Currently docked

Planned

Proposed

An additional spacecraft, the K-1 Vehicle manufactured by Rocketplane Kistler, was proposed as part of the NASA Commercial Orbital Transportation Services program, and was scheduled to fly in 2009. On October 18 2007, NASA discontinued its agreement with Rocketplane Kistler after the company couldn't secure further financing and didn't meet a critical design review for the pressurized cargo module.^[42] NASA then announced that the remaining $175 million commitment to the project would be made available to other companies.^[43] On 19 February 2008, NASA awarded Orbital Sciences Corporation with the remaining $170 million to develop its Cygnus spacecraft for the COTS program.^[44]

Expeditions

All permanent station crews are named , where n is sequentially increased after each expedition. Expeditions have an average duration of half a year and are often considered synonymous with "Increments." However, "Increments" are distinguished from Expeditions as the program planning period for activities that are to occur during a particular Expedition's residence on ISS. The start of both an Expedition and an Increment is defined by the departure of the previous Expedition crew on a Soyuz spacecraft. The definition of the Increment is in flux in preparation for 6-person crews that will be broken up into 3-person crews which overlap in their 6-month missions on ISS.

The International Space Station is the most-visited spacecraft in the history of space flight. As of April 11, 2008, it has had 213 (non-distinct) visitors. Mir had 137 (non-distinct) visitors (See Space station). The number of distinct visitors of the ISS is 158 (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 Canada, Japan, the Russian Federation, the United States, 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.^[45]

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.^[46]

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.^[45] 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 Docking and Cargo 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):

Costs

Given the complexity of the ISS, it is impossible to calculate an overall cost for the entire project. It is, for example, hard to determine which costs should actually be attributed 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 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 lists costs for the ISS (without Shuttle costs) as $25.6 billion for the years 1994 to 2005.^[47] 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

Shuttle costs as part of ISS costs

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 October 2007 only 5 flights out of 28 flights have not been to the ISS, and only the planned Hubble Space Telescope servicing mission in 2008 will not be ISS-related out of 13 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 subtracted, 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 15 year lifetime of the project will be ?9 billion.^[49] Just the costs for the Columbus Laboratory tops more than ?1.4 billion (about $2.1 billion), including the money spent on the ground control infrastructure known as Columbus Control Center to operate it. The total development costs for ATV amount to approximately ?1.35 billion^[50] and considering that each Ariane 5 launch costs around ?150 million, each ATV launch will incur considerable costs as well.

The ISS has been far more expensive than originally anticipated. The ESA estimates the overall cost from the start of the project in the early 1990s to the prospective end in 2017 to be in the region of ?100 billion ($157 billion or �65.3 billion).^[51]

JAXA

The development of the Japanese Experiment Module, JAXA's main contribution to the ISS, has cost about 325 billion yen (about $2.8 billion).^[52] In the year 2005, JAXA allocated about 40 billion yen (about 350 million USD) to the ISS program.^[53] The annual running costs for Japanese Experiment Module will total around $350 to 400 million. In addition JAXA has committed itself to develop and launch the H-II Transfer Vehicle, 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 of 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.

CSA

Canada, whose three main contributions to the ISS are the Canadarm2, the mobile base system, and Dextre (the Special Purpose Dexterous Manipulator, also known as the Canada Hand), estimates that through the last 20 years it has contributed about C$1.4 billion to the ISS. Canada has continued to be a vital member of ISS through the past ten years and continues to play a major role in the ISS.^[54]

Criticism

Two of the most ambitious ISS projects to date—the Alpha Magnetic Spectrometer and the Centrifuge Accommodations Module—have been cancelled or delayed 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 do not require any 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, circadian rhythm, and the effects of cosmic rays on the nervous system.^[58]^[59]^[60] Critics argue that this research has little practical value, since space exploration is today almost universally done by robots.

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 estimated that the indirect economic return from spin-offs of human space exploration has been many times the initial public investment.^[64] A review of the claims by the Federation of American Scientists argued that NASA's rate of return from spin-offs is actually very low, except for aeronautics work that has led to aircraft sales.^[65]

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.^[66] NASA maintains a list of spin-offs from the construction of the ISS, as well as from work performed on the ISS.^[67]^[68] 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, it is an important example of international cooperation.^[69] Others claim that the ISS is an asset that, if properly leveraged, could allow more economical manned Lunar and Mars missions.^[70] 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, which is the size of an American football field, and particularly due to the large reflective area offered by its solar panels, ground based observation of the station is possible with the naked eye if one is within 63 degrees latitude. In many cases the station is one of the brightest naked-eye objects in the sky, though it is only visible for brief periods of time. This is because the station is in low earth orbit, and the sun angle and observer locations need to coincide.^[71]

Miscellany

Space tourism

As of 2007 there have been five space tourists to the ISS, each paying 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.

ISS golf event

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.^[73]

Microgravity

At the station's orbital altitude, the gravity from the Earth is 88% of that at sea level. The state of weightlessness is due to the constant free fall of the ISS, which according to the equivalence principle, is indiscernible from being in a state of zero gravity. The environment on the station is often described instead as microgravity, due to four effects:

Time zone

The ISS uses Coordinated Universal Time (UTC, sometimes informally called GMT) to regulate its onboard day. This is roughly equidistant between its two control centres in Houston and Moscow. The windows are covered at "night" to give the impression of darkness since it experiences 16 sunrises/sunsets a day. The crew typically wakes up at around 7:00 UTC; they work for about ten hours each weekday and five hours each Saturday, with Sundays reserved for relaxation and games, including a modified version of baseball^[75] During visiting shuttle missions, the ISS crew will mostly follow the shuttle's Mission Elapsed Time (MET), which is a flexible timezone based solely on the launchtime of the shuttle mission.^[76]^[77] Because the sleeping periods between the UTC timezone and the MET usually differ, the ISS crew often has to adjust their sleeping pattern before the shuttle arrives and after it leaves to shift from one timezone to the other, therefore this is called sleepshifting.

Atmosphere

The atmosphere on board the ISS is maintained to have a composition similar to that of the Earth's atmosphere.^[78] Normal air pressure on the Space Station is 101.3 kPa (14.7 psi),^[79] the same as at sea level on Earth. This does not match the atmosphere on the shuttle, so adjustments are performed during visits.