NASA has closed down personal tours and restricitng peronell up close to the pad of the 22 year old orbiter Atlantis due to the age of the nitrogen and helium tanks on board the orbiter. They have been used for every mission, and the chances of one exploding unexpeditedly are remote but better safe than sorry. having been re-certified in 1988 for another 10 year span but not again in 1998, A Mr Hale said ""That Would be a bad thing" ....the tanks rupture or explode. Space.com reports this. And I wonder how many other systems are aging or nominal at best and being pressed into service?