Engineers successfully re-positioned a wayward nut in the shuttle Discovery's aft engine compartment and finished bolting the orbiter to its external fuel tank early Saturday, keeping the ship on track for roll out to pad 39A Sept. 20 and launch on the ship's 39th and final mission Nov. 1.

Discovery is lowered into position for mating to the fuel tank and boosters. Credit: Stephen Clark/Spaceflight Now

Discovery was hauled from its processing hangar to the Vehicle Assembly Building Thursday. A large sling was attached to the orbiter late in the day and the shuttle was rotated vertical and lifted into the high bay where its external tank and boosters were waiting.

Engineers successfully attached a large separation system bolt on the lower right side of the shuttle's belly, but an internal nut on the left side near a 17-inch liquid hydrogen feed line slipped out of position and fell away inside the aft compartment. The explosive bolts are part of a system that ensures the tank separates from the shuttle after the ship reaches orbit.

Troubleshooters initially worried Discovery would have to be removed from the tank and placed back in a horizontal orientation to make repairs. But they later concluded they could safely open the aft compartment, set up access platforms and reposition the nut with Discovery in a vertical and partially mated configuration.

That work was completed early Saturday and the ship was "hard mated" to the tank at 9:27 a.m. EDT.

Additional coverage for subscribers:
VIDEO: SHUTTLE HOISTED FOR ATTACHMENT TO TANK PLAY | HI-DEF
VIDEO: CRANE ROTATES THE ORBITER VERTICALLY PLAY | HI-DEF
VIDEO: DISCOVERY DEPARTS ITS HANGAR PLAY | HI-DEF

VIDEO: TIME-LAPSE SHOWS DISCOVERY ASCENDING IN VAB PLAY
VIDEO: TIME-LAPSE SHOWS THE MOVE TO ASSEMBLY BUILDING PLAY

VIDEO: DISCOVERY'S MAIDEN FLIGHT: FIRST TRIP TO VAB PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: ROLLOUT TO PAD 39A PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: TEST-FIRING ENGINES PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: ASSORTED VIEWS OF FRF PLAY

VIDEO: THE HISTORY OF SHUTTLE DISCOVERY PLAY
VIDEO: THE HISTORY OF SHUTTLE ENDEAVOUR PLAY
VIDEO: THE HISTORY OF SHUTTLE ATLANTIS PLAY

VIDEO: ROBONAUT ARRIVES AT KENNEDY SPACE CENTER PLAY | HI-DEF
VIDEO: SPACE STATION'S SPARE THERMAL RADIATOR PLAY | HI-DEF
VIDEO: BLANKETING LEONARDO WITH INSULATION PLAY | HI-DEF
VIDEO: RACK INSERTED INTO LEONARDO FOR LAUNCH PLAY | HI-DEF
VIDEO: LEONARDO RETURNS FROM ITS PREVIOUS FLIGHT PLAY | HI-DEF
VIDEO: STATION'S SPARE PARTS DEPOT ARRIVES PLAY | HI-DEF

VIDEO: ORBITER'S PAYLOAD BAY CLOSED FOR ROLLOUT PLAY | HI-DEF
VIDEO: ASTRONAUTS VISIT THEIR SPACECRAFT PLAY | HI-DEF
VIDEO: CREW INSPECTS LEONARDO MODULE PLAY | HI-DEF
VIDEO: DISCOVERY RECEIVES ITS MAIN ENGINES PLAY | HI-DEF
VIDEO: FUEL TANK MATED TO SOLID ROCKET BOOSTERS PLAY | HI-DEF

VIDEO: POST-FLIGHT DESERVICING: OMS POD PLAY | HI-DEF
VIDEO: POST-FLIGHT DESERVICING: OBSS BOOM PLAY | HI-DEF
VIDEO: POST-FLIGHT DESERVICING: ENGINES PLAY | HI-DEF
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