NASA's associate administrator for space operations William Gerstenmaier has outlined plans for supplying the International Space Station (ISS) after the Space Shuttle is retired in 2010.

With the loss of the Shuttle's 25,000kg (55,000lb) payload capability for delivering and returning cargo, NASA and its ISS partners have been discussing how to continue supplying the station.

Gerstenmaier says his team has been working on the plan for a year, detailing the use of Russian Soyuz and Progress spacecraft, the European Space Agency's Automated Transfer Vehicle (ATV), Japan Aerospace Exploration Agency's HII-B Transfer Vehicle (HTV) and NASA's Commercial Orbital Transportation Services (COTS) programme. Only the Soyuz and Progress have flown so far. ESA's ATV should fly in 2008, Japan's HTV in 2009 and the commercially developed COTS vehicles have a deadline of 2010 for cargo delivery demonstrations.

"Conceptually [the plan is] one ATV per year, one or two HTVs per year, then three Progresses per year for US use and resupply and, depending on the vehicle, two to three COTS vehicles in addition to that," says Gerstenmaier, suggesting at least nine spacecraft will be launched every year in a bid to keep the space station operational.

Under the ISS framework agreement, the station partners have supply and crew transport responsibilities. Gerstenmaier says ATV is part of ESA's ISS contribution, and the HTV is Japan's, while some of the Russian Soyuz and Progress launches would be a cash purchase while others would be agreed under the ISS framework's bartering system. "There are some things [the Russians] would like [NASA] to do for them," he says.

The station crew will also need to return some cargo, including broken ISS components, to Earth. After the Shuttle is retired only manned Soyuz capsules will be able to do that with their small, 75kg downmass capability. The COTS programme may deliver a downmass capability by 2010, but it is not guaranteed.

To cope with this, NASA has been planning for a more disposable approach to ISS systems. The agency is also looking to redesign the station's control movement gyroscopes. These provide ISS attitude control and are currently large wheels - too large for Soyuz to return to Earth. Gerstenmaier expects them to be redeveloped into three smaller wheels that can be transported on Progress, Orion or COTS vehicles.

Source: Flight International