US space agency looks at alternative configurations and assembly options
NASA has launched new studies into the number of Shuttle missions required to complete assembly of the International Space Station (ISS) and confirmed that the planned Space Shuttle return to flight (RTF) is now delayed from March to May next year.
Delays in processing the external tank at NASA's Michoud, Louisiana facility, after shutdowns caused by hurricanes in August and September, have pushed the launch window for first RTF mission, STS 114/Discovery, back to between 12 May and 3 June 2005. "After four hurricanes in a row, we could not make the March launch," says Bill Readdy, associate administrator for space operations. The tank was to be shipped later this month, but is now expected to be ready at the end of December.
The delay has increased pressure on NASA's plan to retire the Shuttle in 2010 after completion of the ISS. The current 28-flight manifest calls for three missions next year and five a year thereafter until the recently endorsed ISS configuration is achieved in 2010. But Readdy reveals NASA is a month into a study looking at other possible ISS configurations, and use of expendable launch vehicles (ELV) for assembly missions, both of which could reduce the number of Shuttle flights required.
"It is a very complex equation," says Readdy, adding that NASA still believes 28 Shuttle flights are needed to achieve the endorsed configuration. Alternative ISS configurations have to be assessed for their stability, supportability and ability to meet the utilisation needs of the USA and its partners, taking account of financial pressures and international agreements, he says.
Readdy does not confirm reports suggesting NASA could cut Shuttle missions to as few as 11 by transferring payloads to ELVs. Russia has said it could launch all but two of the assembly missions - only the Shuttle can carry the European Columbus and Japanese Kibo laboratory modules - on expendable Protons. The USA has the Boeing Delta IV and Lockheed Martin Atlas V available, while Europe has the Ariane 5.
To cover for the delay to Shuttle RTF, Russia has agreed to extend ISS crew transport flights into 2006. Russia will provide additional Soyuz TMA flights in return for writing off its man-hour debt under the 1996 balance of contributions agreement with NASA. Crew rotation flights are now scheduled for April and October 2005 and April 2006. "We are still negotiating what to do after that," says NASA. Talks are planned this month on switching to a mixed system of barter and commercial operations for co-operation from 2006 to 2010, says Russia's Federal Space Agency.
Readdy says ISS crew strength could return to three astronauts with the third Shuttle mission, still planned for late 2005, but its timing is dependent on successful testing of ascent debris imaging on the first two daytime RTF missions, which would allow night flights to resume.
TIM FURNISS / LONDON
ADDITIONAL REPORTING BY ROB COPPINGER IN LONDON AND GRAHAM WARWICK IN WASHINGTON DC
Source: Flight International
