The successful attachment of the European-built Harmony Node 2 module to the port side of the International Space Station's Node 1, called Unity, brings the goal of expanding the orbiting outpost's crew capacity to six from three a step closer. The operation also moved NASA's Space Shuttle fleet one job closer to retirement in 2010.

The stories of the ISS and Space Shuttle are inextricably linked. The Shuttle was always conceived as an assembly and resupply vehicle for a space station. Just three years after its 1981 maiden flight Ronald Reagan, then the US president, announced the Freedom space station initiative. In 1993, under President Bill Clinton, that became the ISS and Russia joined the project.

Harmony space stn

But following the 2003 Columbia disaster and the decision by President George Bush to retire the Shuttle fleet in 2010, it became clear that the station would outlast the world's only reusable spaceplane for at least another six years to 2016.

The STS-120 mission attaching Harmony to ISS is the 23rd orbiter station visit, the 120th Shuttle flight and Discovery's 34th. It is also the first time both the visiting Shuttle and ISS have been commanded by women - Pam Melroy for Discovery and Peggy Whitson for the space station's Expedition 16.

When Discovery returns to Earth this week the Shuttle programme will have 13 missions left, including two contingency resupply missions. The ISS has 16 more crews lined up to operate the station, following the current Expedition 16 team.

In preparation for Shuttle retirement NASA is transferring the spaceplane's facilities to its return-to-the Moon Constellation programme. Three of the orbiter vehicles - Discovery (OV-103), Atlantis (OV-104) and Endeavour (OV-105) - will eventually go to museums. Of the five space-capable orbiters that have been built, the first to be retired, Atlantis, will be stood down after the only non-ISS flight between now and 2010 STS-125 is the Hubble Space Telescope servicing mission planned for September 2008.

Discovery, the oldest operating orbiter, and Endeavour, which is the youngest of the three (built to replace OV-99 Challenger after its destruction 73s into its launch on 28 January 1986) will fly the remaining nine flights. Columbia was OV-102. Of those nine flights, which include the contingency missions, OV-103 will make the last currently confirmed orbital trip, STS-132, in either March or September 2010 to deliver the final module, Node 3, which is identical to Harmony and also built by European companies.

The station will go on and be used by six crew for scientific research, starting in 2009, and from the fourth quarter of 2010 be serviced by Russian Energia-built Soyuz capsules and Progress resupply vehicles. Post-Shuttle, NASA will have to pay Russia for Soyuz and Progress to replace the lost crew and cargo transport and emergency return capability the USA had promised as part of the original inter-governmental framework agreement that underpins the ISS.

Harmony, whose prime contractor was Thales Alenia Spazio Italy, is the seventh ISS module. Besides its two axial hatches, which are needed for the permanent connection to the ISS and for Shuttle docking, Harmony has four radial axes, on the cylindrical side of its structure and it hosts equipment for electrical power distribution, heating, cooling and data exchange support for laboratory payloads.

Now ISS consists of the Zarya, Unity, Zvezda and Harmony modules, the Pirs docking compartment, the Quest joint airlock, NASA's Quest laboratory, and the station's integrated truss structure that has the station's robotic arm, Canadarm2, its mobile servicing system, and also supports the radiators and solar arrays.

However this was not the configuration agreed in 1998. Even during the last nine years of assembly flights the final configuration of the station has changed, especially following the Columbia disaster as elements were dropped to accelerate completion in time for the 2010 permanent grounding of the Shuttles.

The next Shuttle mission will carry the European Space Agency's Columbus laboratory and the two flight's following that will put in place the Japanese Aerospace Exploration Agency's laboratory modules. Officially, the policy of the ISS partners is that the station will be used until 2016. However, NASA officials have been asked to budget for space station use beyond then. If it is not used after 2016, NASA has been discussing de-orbiting ISS into the Pacific Ocean using an automated transfer vehicle.

Source: Flight International