Nasa has declared space shuttle Atlantis ready to launch on 27 August to restart construction of the half-built International Space Station.
The bolt issue was found after Atlantis was moved to the launch pad
Launch has been set for 1630 EDT (2030 GMT), but technical issues must be resolved before the shuttle is formally cleared for flight.
The mission will be the first to resume assembly of the $100bn space station since the Columbia disaster in 2003.
Nasa has since flown two missions designed to test safety upgrades.
Engineers are concerned that two bolts securing the shuttle's primary communications antenna to the cargo bay wall are too short.
They want to make sure that the antenna does not fly off in the payload bay during a launch, something that could cause catastrophic damage.
The antenna transmits images and other essential data from the space shuttle to Mission Control.
"We're not going to fly if we think there's a possibility the antenna will come off," said Nasa's administrator Michael Griffin.
Atlantis has flown with those bolts without trouble since they were first installed two decades ago. The problem was discovered last week, after Atlantis was rolled to the launch pad.
Nasa officials had ordered a review of paperwork on bolts in all three space shuttles because a related problem was found in shuttle Discovery.
Nasa officials are not expected to decide until this weekend whether to leave the bolts in place or change them in a tricky procedure at the launch pad.
Technicians would have to build scaffolding on top of a platform six storeys high in order to change the bolts with the shuttle in a vertical position. This would probably take the two spare days Nasa has in its launch schedule.
"Imagine operating on a surfboard that is tied down at one end, sticking out over a six-storey balcony," said shuttle program manager Wayne Hale.
"You have all kinds of implications that you would really rather not do because of the location and access."
The decision to launch was made after a two-day meeting of Nasa's top managers at the Kennedy Space Center with a poll on whether to go ahead with the launch.
The Atlantis launch would be the second this year. Space shuttle Discovery launched on 4 July on a 13-day mission to test safety upgrades.