Shuttles coming and going

With the shuttle Endeavour winding up an arduous but successful mission to install a huge two-armed robot named Dextre on the International Space Station (ISS), things look on track for the May 25 launch of the shuttle Discovery with a Japanese laboratory module. The August 28 launch of Atlantis to service the Hubble telescope is not as certain. Since differing orbits make a "safe haven" at the ISS impossible for Atlantis in the event of a mishap, NASA wants Discovery available for a short-notice flight if a rescue mission is needed. Safety-related modifications to the external tank (ET) and other issues at the Michoud assembly facility, however, mean there might not be a flight-ready tank available for the standby shuttle until October. If the Shuttle is to complete its planned slate of missions by the planned retirement date of 2010, it needs to make four more flights in 2008 (May, August, October and December), followed by four in 2009 and up to three in 2010.
COMMENT: The 2010 date is increasingly looking difficult to hit, and there is hardly any margin for unexpected events. The result could well be "schedule pressure," a term which sends a shiver down the spine of NASA managers who remember the Columbia accident. The date should be slipped a year (which, yes, means using money from Constellation and probably slipping that program a year) to allow for safer completion of the scheduled missions and possibly one or two more additional flights to add experiments now in limbo to the ISS.