Discarded Space Shuttle external tank. Computer artwork of an external tank (upper centre) falling back to a cloud-covered Earth after it has been discarded by a Space Shuttle. The Space Shuttles are reusable spacecraft flown by NASA since 1981. When the fuel in the external tank is finished, the main engines shut down, the tank is discarded, and the Shuttle's orbital engines finalise its orbit. The Shuttle detaches from the external tank 9 minutes after launch. The tank mostly burns up in the atmosphere, and the remnants fall into the ocean 40 minutes later. Over 100 external tanks have been discarded over the course of the Space Shuttle program. Continuing design faults with the external tank led to an indefinite grounding of the Space Shuttles in 2005.