A unique propulsion system is being developed for the Space Shuttle Orbiter utilizing airbreathing engines to provide a means for horizontal flight testing and ferrying the Orbiter within the contiguous United States. Primarily, the NASA was concerned with ferrying the Orbiter from manufacturing site to launch site, but it was also recognized that on some occasions weather conditions or other emergency situations might dictate landing at alternate sites when returning from space missions. These situations would also require subsequent takeoff and ferry to a launch site. To fulfill these objectives, certain ground rules and criteria were selected, consisting primarily of takeoff capability on a hot day from a runway 10,000 feet in length, a 423 nautical mile minimum cruise range, engine out cruise ceiling of 10,000 feet, the use of existing engines, and an installation that was easily attached and removed from the Orbiter vehicle.
The current ferry configuration, which meets these requirements and the limitations imposed by the Orbiter itself,consists of six TF33-P-7 non-afterburning engines mounted two in a pod under each wing with a third twin engine pod under the fuselage between the main landing gears. The airbreathing engine arrangement which has resulted, while employing conventional propulsion subsystems, still possesses installation problems because of the low ground clearance. However, it represents the best compromise with the many limitations which exist, and it is a feasible configuration for the limited number of ferry flights anticipated over the life of the Orbiter.