International Space Station

 

International Space Station
ISS after separation from Space Shuttle Endeavour, August 19 2007
Station statistics
Mass:	232,693 kg (513,000 lb) (2007-02-22) 471,736 kg (1,040,000 lb) upon completion [1]
Length:	58.2 m (191 ft) along truss (2007-02-22)
Width:	44.5 m (146 ft) from Destiny to Zvezda 73.15 m (240 ft) span of solar arrays (2007-02-22)
Height:	27.4 m (90 ft) (2007-02-22)
Living volume:	424.75 m³ (15,000 ft³)
Atmospheric pressure:	101.3 kPa (29.91 inHg)
Perigee:	319.6 km (172.6 nmi)
Apogee:	346.9 km (187.3 nmi)
Orbit inclination:	51.63 degrees
Typical orbit altitude:	333.3 km (180.0 nmi)
Average speed:	27,743.8 km/h (17,239.2 mi/h, 7706.6 m/s)
Orbital period:	91.20 minutes
Orbits per day:	15.79
Days in orbit:	3,029
Days occupied:	2,316
Number of orbits:	Made 50,000th orbit on August 14 2007
Distance travelled:	2,000,000,000 km (1,100,000,000 nmi)
Statistics as of June 20 2007 (unless noted otherwise).
References: [2] [3]
Configuration
International Space Station current elements
International Space Station

The International Space Station (ISS) is a research facility currently being assembled in space. The building of ISS started in 1998. The station is in a low Earth orbit and can be seen from Earth with the naked eye: its altitude varies from 319.6 km to 346.9 km above the surface of the Earth (198.6 to 215.6 mi). It travels at an average speed of 27,744 km (17,240 mi) per hour, completing 15.7 orbits per day. The ISS is a joint project between the space agencies of the United States (NASA), Russia (RKA), Japan (JAXA), Canada (CSA) and several European countries (ESA).^[4]

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, especially if it is able to work with the RKA.^[5] The Chinese are not currently involved, however.

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 Kibo, the Japanese Experiment Module. The projected completion date is 2010, with the station remaining in operation until around 2016. As of 2007, the 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 crew of Expedition 15 are currently aboard. 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 and 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. The ISS was also the destination of the first five space tourists.

Origins

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.^[6] 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 Zvezda) and ESA's Columbus that was planned to be a stand-alone spacelab.

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.

Assembly

Main article: Assembly of the International Space Station

See also: ISS assembly sequence

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 2007 assembly is on-going.

Major ISS Systems

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 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 supply.^[7]

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.

The solar array normally tracks the sun to maximize the amount of solar power. 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. (However, until the main truss structure was brought up, 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

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 waste and water produced and used 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. ^[8]

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.^[9] 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 falling due to minute atmospheric drag and gravity gradient effects, it needs to be boosted to a higher altitude multiple times per year.^[10] A graph of altitude over time shows that it drifts down almost 2.5 km per month.^[11] The boosting can be performed by 2 boosters on the Zvezda module, a docked Space Shuttle, or by a Progress resupply vessel and takes approximately 2 orbits (3 hours) in which it is boosted several kilometers higher.^[10] 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

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.^{[12] [13]} The 2005 NASA Authorization Act designated the U.S segment of the International Space Station as a national laboratory with a goal to increase the utilization of the ISS by other Federal entities and the private sector. 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.^[14] 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.^[15] 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.^[16] 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.^[17]

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.^[12]

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).^[12]

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.^[12]

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, more accurate measurements that would be impossible to achieve on Earth, and a more complete understanding of the Universe.^{[12] [13]}

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." He says ISS crews not only will continue to learn how to live and work in space but 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.

Major incidents

2003 Columbia disaster

After the Space Shuttle Columbia disaster on February 1 2003, and the later 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 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.^[18]

On November 2 2006 the payload brought by the Russian Progress M-58 allowed the crew to repair the Elektron using spare parts.^[19]

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.^[20][21] The two computer systems (command and navigation) are each composed of three computers. Each computer is referred to as a Lane. ^[21]

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.^[22] Without the computer that controls the oxygen levels, the station had only 56 days of oxygen available.^[23]

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 would be tested within the next day or two. 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 massive new starboard trusses and solar arrays.^[21] Troubleshooting of the failure by the ISS crew, however, eventually found that the root cause was condensation inside the electrical connectors, leading to a short-circuit which triggered the “power off” command line leading to all three of the redundant processing units.^[24]. This is a concern, because the ESA uses the same computer systems, supplied by EADS Astrium Space Transportation.^[25], for the Columbus Laboratory Module and the Automated Transfer Vehicle. However, with the root cause understood, means are now being implemented to avoid the problem in the future.

Visiting spacecraft

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

Planned

• European (ESA) Automated Transfer Vehicle (ATV) ISS resupply spacecraft (scheduled for January 2008)^[26]
• Japanese (JAXA) H-II Transfer Vehicle (HTV) resupply vehicle for Kibo module (scheduled for 2009)^[27]
• American (NASA) Orion for 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 (Roskosmos) Space Shuttle Kliper for possible crew rotation and as resupply transporter (scheduled for 2012)
• European-Russian Crew Space Transportation System (Soyuz-derived) crew rotation and resupply spacecraft (scheduled for 2014)

Expeditions

See also: List of International Space Station Expeditions

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).

Expeditions to the International Space Station
Completed: Expedition 1 • Expedition 2 • Expedition 3 • Expedition 4 • Expedition 5 • Expedition 6 • Expedition 7 • Expedition 8 • Expedition 9 • Expedition 10 • Expedition 11 • Expedition 12 • Expedition 13 • Expedition 14 • Expedition 15 Current: Expedition 16 Planned: Expedition 17 • Expedition 18 • Expedition 19

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.^[28]

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.^[29]

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.^[28] 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).^[30]

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

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 lists costs for the ISS (without Shuttle costs) as $25.6 billion for the years 1994 to 2005.^[31] 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

The $1.8 billion expensed in 2005 consisted of:^[32]

• 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

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 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 30 year lifetime of the project will be €8 billion.^[33] 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)^[34] In the year 2005, JAXA allocated about 40 billion yen (about 350 million USD) to the ISS program.^[35] 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 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 main contribution to the ISS is the Canadarm2, estimates that through the last 20 years it has contributed about C$1.4 billion to the ISS.^[36]

Criticism

"NASA must complete the ISS so it can be dropped into the ocean on schedule in finished form."

—Robert L. Park, [1]

The ISS and NASA have been the targets of varied criticism over the years. Critics contend 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. ^[37][38] Some critics, like Bob Park, argue that very little scientific research was convincingly planned for the ISS in the first place.^[39] They also argue that the primary feature of a space-based laboratory is its microgravity environment, which can usually be studied more cheaply with a vomit comet -- that is, an aircraft which flies in parabolic arcs.^[40]

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 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,^[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 practical 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;^[41]
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.^[42] 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.^[43] 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.^[44]

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.^[45] NASA maintains a list of spin-offs from the construction of the ISS, as well as from work performed on the ISS.^[46] 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.^[47] Others claim that the ISS is an asset that, if properly leveraged, could allow more economical manned Lunar and Mars missions.^[48] 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.^[49][50]

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 of zero gravity. 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).^[51]

Time zone

The ISS uses Greenwich mean time (GMT) to regulate its onboard day. This is roughly equidistant between its two control centres in Houston and Moscow. ^[52] The windows are covered at "night" to give the impression of darkness since it experiences 16 sunrises/sunsets a day.

See also

• List of International Space Station visitors
• List of ISS spacewalks performed from the ISS or visiting spacecraft
• List of manned spaceflights to the ISS for a comprehensive chronological list of all manned spacecraft that have visited the ISS, including the spacecraft's respective crews
• List of unmanned spaceflights to the ISS — Progress supply flights and unmanned automatic docking space station modules

Other

• Space station for statistics of occupied space stations
• Soyuz spacecraft
• Progress spacecraft
• Mir
• Salyut
• Skylab