The European Space Agency (ESA) is hoping to minimize the impact NASA's decision to delay its next shuttle flight will have on the organization's plans for the International Space Station (ISS).

ESA is banking on NASA's launch of its STS-121 shuttle mission--delayed from September to no earlier than March 2006--to deliver Thomas Reiter on a six-month-long mission to the ISS, the longest stay of its kind for an ESA astronaut.

Before STS-121's delay, Reiter was slated to spend much of his ISS increment with the crew of Expedition 12, commanded by NASA astronaut Bill McArthur with cosmonaut Valery Tokarev serving as flight engineer. They are set to launch on Sept. 30. Reiter's arrival on-station will bring the ISS back to its three-person complement for the first time since the 2003 Columbia disaster.

"Our plans at the present for Thomas Reiter are still to launch him on [STS-121] and to return him on [STS-116]," said Alan Thirkettle, ESA's Head of Development for the Directorate of Human Spaceflight, in an e-mail interview. "The resolution of the [external tank] problems has to first be achieved and a firm launch date established before any plans can be cast in concrete."

NASA engineers are still working to solve an external tank foam shedding problem detected during Discovery's STS-114 flight. That work will likely prompt repairs or modifications to shuttle external tanks, NASA associate administrator for space operations Bill Gerstenmaier said last week.

Meanwhile, ISS officials are developing plans to complete construction on the space station - which relies on NASA shuttles to deliver large components - before the U.S. space agency retires its three remaining orbiters in 2010.

"Our planning is to use the shuttle fleet...to essentially complete the assembly of the space station in the years that we have remaining," NASA chief Michael Griffin told reporters last week.

ISS astronaut shuffle

While Expedition 12's McArthur and Tokarev hoped Reiter would greet them at the ISS - a September launch would have placed him onboard before the station astronauts arrived - the ESA astronaut will likely spend most of his time with their Expedition 13 successors.

"If we're targeting March [for the shuttle launch], he would arrive onboard just before Expedition 13," said Kylie Clem, a NASA spokesperson at the agency's Johnson Space Center (JSC), adding that Reiter would spend a few weeks with the Expedition 12 astronauts before the end of their increment.

Expedition 13 is slated to launch in the mid-March 2006, NASA officials said.

With shuttle flights grounded between the Columbia accident and Discovery's STS-114 flight, the space station relied on Russia's Soyuz and unmanned Progress spacecraft to deliver new crews and cargo.

ESA is also planning to launch its first unmanned cargo ship to the space station, the Autonomous Transfer Vehicle (ATV) Jules Verne, in 2006.

"The future of ATV as an ISS logistics carrier becomes ever more important with the possible reduction of [shuttle] flights," Thirkettle said.

Future station construction

ESA officials said they are working to at least minimize the effects of NASA's shuttle delays on their hardware contributions to the ISS.

"In principle, the launch dates for the European ISS elements will be delayed as a consequence of the delay to the next shuttle flight," Thirkettle said. "But we are in discussion with NASA to see if there are ways of mitigating these delays."

How that may be done, however, remains unclear.

ESA's major piece of ISS hardware, the billion-dollar Columbus module, cannot fly until NASA delivers Node 2 - the module's station attachment port - to the orbital laboratory during the planned STS-120, ESA officials said.

The STS-120 flight, however, must wait until after a series of missions to add new solar arrays, batters and trusses to the ISS that begin with the launch of STS-115 aboard Atlantis, according to NASA's current shuttle flight plans. Node 2's arrival would mark the completion point for U.S. components, with Columbus slated to launch three flights later.

"Our priority is for the launch of Columbus, and therefore of Node 2 to which Columbus is attached," Thirkettle said. "Then for the establishment of a 6-person permanent ISS crew, to ensure the full utilization of Columbus and thus the full scientific return on the investment we have made in the ISS program."