structure interfaces with the forward fuselage, aft fuselage and
wings. It supports the payload bay doors, hinges, tie-down fittings,
forward wing glove, and various orbiter system components and forms
the payload bay area.
and aft ends of the midfuselage are open, with reinforced skin and
longerons interfacing with the bulkheads of the forward and aft
fuselages. The midfuselage is primarily an aluminum structure 60
feet long, 17 feet wide and 13 feet high. It weighs approximately
skins are integrally machined by numerical control. The panels above
the wing glove and the wings for the forward eight bays have longitudinal
T-stringers. The five aft bays have aluminum honeycomb panels. The
side skins in the shadow of the wing are also numerically control
machined but have vertical stiffeners.
assemblies stabilize the midfuselage structure. The assemblies consist
of vertical side elements and horizontal elements. The side elements
are machined; whereas the horizontal elements are boron/aluminum
tubes with bonded titanium end fittings, which reduced the weight
by 49 percent (approximately 305 pounds).
In the upper
portion of the midfuselage are the sill and door longerons. The
machined sill longerons not only make up the primary body-bending
elements, but also take the longitudinal loads from payloads in
the payload bay. The payload bay door longerons and associated structure
are attached to the 13 payload bay door hinges. These hinges provide
the vertical reaction from the payload bay doors. Five of the hinges
react the payload bay door shears. The sill longeron also provides
the base support for the payload bay manipulator arm (if installed)
and its stowage provisions, the Ku-band rendezvous antenna, the
antenna base support and its stowage provisions, and the payload
bay door actuation system.
The side wall
forward of the wing carry-through structure provides the inboard
support for the main landing gear. The total lateral landing gear
loads are reacted by the midfuselage structure.
also supports the two electrical wire trays that contain the wiring
between the crew compartment and aft fuselage.
wiring in the lower portion of the midfuselage are supported by
fiberglass milk stools.
of the exposed areas of the midfuselage is covered with the reusable
surface insulation thermal protection system.
additional detailed analysis of actual flight data concerning descent
stress thermal gradient loads, torsional straps were added to the
lower midfuselage stringers in bays 1 through 11. The torsional
straps tie all stringers together similarly to a box section, which
eliminates rotational (torsional) capabilities to provide positive
margins of safety.
of additional detailed analysis of actual flight data during descent,
room-temperature vulcanizing silicone rubber material was bonded
to the lower midfuselage from bay 4 through 12 to act as a heat
sink and distribute temperatures evenly across the bottom of the
midfuselage, which will reduce thermal gradients and ensure positive
margins of safety.
for the midfuselage is General Dynamics Corp., Convair Aerospace
Division, San Diego, Calif.