Assembly of the International Space Station.html |
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- See also: ISS assembly sequence
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The assembly of the International Space Station is a major aerospace engineering endeavor currently being conducted in low-Earth orbit by a consortium of governmental and inter-governmental space agencies.
Zarya, the first ISS module, was launched by a Proton rocket on 20 November 1998. The STS-88 shuttle mission followed two weeks after Zarya was launched, 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 minimum crew of two astronauts or cosmonauts to be on the ISS permanently.
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. Building the complete station will require more than 40 assembly flights. Of these flights, currently 35 are planned to be Space Shuttle flights, with 26 ISS-shuttle flights currently flown and 9 more planned between 2008 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.
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Logistics
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 kilometers due to atmospheric drag and reboosts). It orbits Earth in a period of about 90 minutes; by August 2007 it had completed more than 50,000 orbits since launch of Zarya on November 20, 1998.
A total of 14 main pressurized modules are currently scheduled to be part of the ISS by its completion date in 2010.1 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 Multi-Purpose Logistics Module, the Automated Transfer Vehicle and the H-II Transfer Vehicle).
The ISS, when completed, will consist of a set of communicating pressurized modules connected to a truss, on which four large pairs of photovoltaic modules (solar panels) are attached. 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.2
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 and the Japanese HTV.
Columbia disaster and changes in construction plans
Disaster and consequences
At one point, there was some uncertainty over the future of the ISS. The Space Shuttle Columbia disaster on February 1, 2003, the subsequent two and a half year suspension of the U.S. Space Shuttle program, followed by problems with resuming flight operations in 2005, were major obstacles.
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 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.
Changes in construction plans
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 stand-down, 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 were made to the originally planned ISS, even before the Columbia disaster. Modules and other structures were cancelled or replaced and the number of Shuttle flights to the ISS was 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 intended 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 2010.3 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.
Current assembled components
The ISS currently consists of ten main pressurized modules: four US modules (Destiny, Unity, Quest and Harmony), three Russian modules (Zarya, Zvezda, and Pirs ), two Japanese modules (Kibo's Experiment Logistics Module and Kibo's Pressurized Module) and one European module (Columbus). Spacecraft docked to the ISS also extend the pressurized volume. At least one Soyuz spacecraft is always docked 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, a Multi-Purpose Logistics Module (MPLM) forms part of the ISS during Shuttle missions that include an MPLM. The MPLM is attached to Unity and later to Harmony and is used for resupply and logistics flights.
As of June 2008 the station consists of several modules and elements:
*P6 Truss was relocated to its final position, the P5 truss mounting position, on STS-120.
Components to be launched
Nearly all already built pressurized modules are planned to be launched by the Space Shuttle. By the time the ISS is completed in 2010, it will have, in addition to the modules already in orbit:
- The Node 3 module.
- The Multipurpose Laboratory Module.
- A Cupola.
- A Mini-Research Module 1 to assist in the docking of Soyuz and Progress spacecraft to the station.
In addition, there is also a large unpressurized truss system partially in place that supports the prominent solar arrays, as well as external experiments like the Alpha Magnetic Spectrometer and the Plasma Contactor Unit.4 An addition to unpressurized experiment accommodations on ISS is being developed by the Goddard Space Flight Center, called EXPRESS Logistics Carrier, or ELC (formerly EXPRESS Pallet). "EXPRESS" stands for "EXpedite the PRocessing of Experiments to the Space Station". Several ELC units will be installed on the exterior of ISS to provide a home for space science experiments. ELC units provide not just a berth for experiments, but also provide power, heat, and command & telemetry links to experiments.
Canceled modules
- Centrifuge Accommodations Module - would have been attached to Node 2, now named Harmony
- Universal Docking Module - replaced by Multipurpose Laboratory Module
- Docking and Stowage Module - replaced by Multipurpose Laboratory Module
- Habitation Module5
- Crew Return Vehicle (CRV)
- Interim Control Module - no need to replace Zvezda (in storage ready to launch at short notice if required)
- ISS Propulsion Module - no need to replace Zvezda
- Science Power Platform - power will be provided to the Russian segments partly by the US solar cell platforms
- Russian Research Module - Replaced by Docking Cargo Module (DCM)
References
- ^ "NASA - Consolidated Launch Manifest" (in English). NASA. Retrieved on 2006-07-15.
- ^ "What are the ISS attitudes?" (Flash) (in English). NASA. Retrieved on 2006-09-11.
- ^ "flightglobal.com NASA commits to Shuttle missions to International Space Station". International Space Station. FlightGlobal (3 March 2006). Retrieved on 16 September, 2006.
- ^ http://space-power.grc.nasa.gov/ppo/projects/iss/plasmacontactor.html
- ^ With the cancellation of the Habitations Module, sleeping places are now spread throughout the station. There will be three in the Russian segment once the ISS is completed and three in the US segment. It is however not necessary to have a separate 'bunk' in space at all, many visitors just strap their sleeping bag to the wall of a module, get into it and sleep.
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