An extension of Space Shuttle missions beyond 2010 could see orbiters visiting the International Space Station without the assigned rescue flights that have been in place since the loss of the Shuttle Columbia in 2003.
An internal NASA study on extending Shuttle flights says that without the production of "new assets" (external tanks, solid rocket booster parts and other equipment), the last two of three possible additional Shuttle flights beyond the fleet's planned retirement would not have a launch-on-need rescue mission assigned.
A Space Shuttle programme source says "there has been talk for a year" about abolishing launch-on-need rescue missions for the ISS. The source says that in "almost all scenarios" there is enough contingency Shuttle crew support time - NASA's plan to send an orbiter to the ISS to rescue a stranded crew - to ready a mission "after-the-fact". On those last Shuttle flights "that might be a bit problematic if we are out of external tanks and solid rocket boosters", the source says.
NASA decided to conduct a study into operating the Space Shuttle beyond its planned retirement due to US Congressional pressure to keep the fleet going. This pressure stemmed from fears of being reliant on Russian transport when that country was taking a more belligerent stance towards NATO countries.