The shuttle Endeavour's three main engines were installed this week as workers prepare the ship's two solid rocket boosters and external tank for the program's final scheduled launch.

File photo of a space shuttle main engine transferred to the orbiter hangar. Credit: NASA-KSC/Jack Pfaller

A NASA spokesperson confirmed all three engines were bolted to the shuttle by the end of day Thursday.

The reusable hydrogen-fueled engines were moved one-at-a-time from a workshop to the nearby Orbiter Processing Facility bay 2 at the Kennedy Space Center between Tuesday and Thursday.

A modified forklift positioned each engine behind Endeavour as shuttle technicians methodically hooked up electrical cables and propellant lines.

Engine 1, designated serial no. 2059, entered service in 2007 on the STS-117 space station assembly flight that delivered a set of solar arrays to the complex. The unit, which is flying for the fifth time, will occupy the center position on Endeavour.

The lower-left engine, serial no. 2061, will be making its second launch in the Engine 2 slot aboard Endeavour. It first flew in February on Endeavour's most recent mission.

The Engine 3 position on Endeavour's last flight is filled by serial no. 2057, a powerplant that will be launching for the sixth time. Its first flight was on the STS-114 mission in 2005, the first shuttle launch after the Columbia disaster.

All three engines last flew together on Endeavour's STS-130 mission in February.

Each space shuttle main engine produces 400,000 pounds of sea level thrust. The three engines collectively produce more than 37 million horsepower, equivalent to the output of 13 Hoover Dams.

Endeavour's external fuel tank arrived July 13 and was moved the next day into a checkout cell inside the Vehicle Assembly Building. Credit: NASA-KSC/Dimitri Gerondidakis

While workers attached Endeavour's main engines, other crews were busy checking out the shuttle's external fuel tank in a test cell inside the Vehicle Assembly Building. The fuel tank arrived at the spaceport July 13 from a factory in New Orleans.

And Endeavour's two solid rocket boosters are being assembled atop a launch platform in a VAB high bay. So far, teams have stacked the bottom segments of both motors and added the aft-center piece of the left-hand booster.

Each booster consists of four segments loaded with propellant and a frustrum, or nose cone. Stacking of the solid-fueled motors should be finished in the middle of August.

A heavy-duty crane will move the shuttle fuel tank between the boosters this fall. Endeavour is scheduled move from its hangar to join the stack in January.

Liftoff of Endeavour on the STS-134 mission is scheduled for Feb. 26, 2011. The shuttle will carry an outdoor spare parts depot and an international particle physics experiment to the International Space Station.

The STS-134 mission is currently the final planned flight of the shuttle program, but Congress and the White House could add one more launch to the manifest next summer. A decision on an extra shuttle flight is expected soon.