The aft fuselage consists of an
outer shell, thrust structure and internal
secondary structure. It is approximately 18 feet long, 22 feet wide
and 20 feet high.
The aft fuselage supports and
interfaces with the left-hand and
right-hand aft orbital maneuvering system/reaction control system
pods, the wing aft spar, midfuselage, orbiter/external tank rear
attachments, space shuttle main engines, aft heat shield, body flap,
vertical tail and two T-0 launch umbilical panels.
The aft fuselage provides the load
path to the midfuselage main
longerons, main wing spar continuity across the forward bulkhead
of the aft fuselage, structural support for the body flap, and structural
housing around all internal systems for protection from operational
environments (pressure, thermal and acoustic) and controlled internal
pressures during flight.
The forward bulkhead closes off
the aft fuselage from the midfuselage
and is composed of machined and beaded sheet metal aluminum segments.
The upper portion of the bulkhead attaches to the front spar of
the vertical tail.
The internal thrust structure
supports the three SSMEs. The upper
section of the thrust structure supports the upper SSME, and the
lower section of the thrust structure supports the two lower SSMEs.
The internal thrust structure includes the SSMEs, load reaction
truss structures, engine interface fittings and the actuator support
structure. It supports the SSMEs, the SSME low-pressure turbopumps
and propellant lines. The two orbiter/external tank aft attach points
interface at the longeron fittings.
The internal thrust structure is
composed mainly of 28 machined,
diffusion-bonded truss members. In diffusion bonding, titanium strips
are bonded together under heat, pressure and time. This fuses the
titanium strips into a single hollow, homogeneous mass that is lighter
and stronger than a forged part. In looking at the cross section
of a diffusion bond, one sees no weld line. It is a homogeneous
parent metal, yet composed of pieces joined by diffusion bonding.
(In OV-105, the internal thrust structure is a forging.) In selected
areas, the titanium construction is reinforced with boron/epoxy
tubular struts to minimize weight and add stiffness. This reduced
the weight by 21 percent, approximately 900 pounds.
The upper thrust structure of the aft
fuselage is of integral-machined
aluminum construction with aluminum frames except for the vertical
fin support frame, which is titanium. The skin panels are integrally
machined aluminum and attach to each side of the vertical fin to
react drag and torsion loading.
The outer shell of the aft fuselage
is constructed of integral-machined
aluminum. Various penetrations are provided in the shell for access
to installed systems. The exposed outer areas of the aft fuselage
are covered with reusable thermal protection system.
The secondary structure of the aft
fuselage is of conventional
aluminum construction except that titanium and fiberglass are used
for thermal isolation of equipment. The aft fuselage secondary structures
consist of brackets, buildup webs, truss members, and machined fittings,
as required by system loading and support constraints. Certain system
components, such as the avionics shelves, are shock-mounted to the
secondary structure. The secondary structure includes support provisions
for the auxiliary power units, hydraulics, ammonia boiler, flash
evaporator and electrical wire runs.
The two external tank umbilical
areas interface with the orbiter's
two aft external tank attach points and the external tank's liquid
oxygen and hydrogen feed lines and electrical wire runs. The umbilicals
are retracted, and the umbilical areas are closed off after external
tank separation by an electromechanically operated beryllium door
at each umbilical. Thermal barriers are employed at each umbilical
door. The exposed area of each closed door is covered with reusable
The aft fuselage heat shield
and seal provide a closeout of the
orbiter aft base area. The aft heat shield consists of a base heat
shield of machined aluminum. Attached to the base heat shield are
domes of honeycomb construction that support flexible and sliding
seal assemblies. The engine-mounted heat shield is of Inconel honeycomb
construction and is removable for access to the main engine power
heads. The heat shield is covered with a reusable thermal protection
system except for the Inconel segments.