The thermal protection system
consists of various materials applied externally to the outer
structural skin of the orbiter to maintain the skin within acceptable
temperatures, primarily during the entry phase of the mission.
The orbiter's outer structural skin is constructed primarily of
aluminum and graphite epoxy.
During entry, the TPS materials protect the orbiter outer skin
from temperatures above 350 F. In addition, they are reusable
for 100 missions with refurbishment and maintenance. These materials
perform in temperature ranges from minus 250 F in the cold soak
of space to entry temperatures that reach nearly 3,000 F. The
TPS also sustains the forces induced by deflections of the orbiter
airframe as it responds to the various external environments.
Because the thermal protection system is installed on the outside
of the orbiter skin, it establishes the aerodynamics over the
vehicle in addition to acting as the heat sink.
Orbiter interior temperatures also are controlled by internal
insulation, heaters and purging techniques in the various phases
of the mission.
The TPS is a passive system consisting of materials selected
for stability at high temperatures and weight efficiency. These
materials are as follows:
1. Reinforced carbon-carbon is used
on the wing leading edges; the nose cap, including an area immediately
aft of the nose cap on the lower surface (chine panel); and the
immediate area around the forward orbiter/external tank structural
attachment. RCC protects areas where temperatures exceed 2,300
F during entry.
2. Black high-temperature reusable surface
insulation tiles are used in areas on the upper forward fuselage,
including around the forward fuselage windows; the entire underside
of the vehicle where RCC is not used; portions of the orbital
maneuvering system and reaction control system pods; the leading
and trailing edges of the vertical stabilizer; wing glove areas;
elevon trailing edges; adjacent to the RCC on the upper wing surface;
the base heat shield; the interface with wing leading edge RCC;
and the upper body flap surface. The HRSI tiles protect areas
where temperatures are below 2,300 F. These tiles have a black
surface coating necessary for entry emittance.
3. Black tiles called fibrous refractory
composite insulation were developed later in the thermal protection
system program. FRCI tiles replace some of the HRSI tiles in selected
areas of the orbiter.
reusable surface insulation white tiles are used in selected areas
of the forward, mid-, and aft fuselages; vertical tail; upper wing;
and OMS/RCS pods. These tiles protect areas where temperatures are
below 1,200 F. These tiles have a white surface coating to provide
better thermal characteristics on orbit.
5. After the initial delivery of Columbia from Rockwell International's
Palmdale assembly facility, an advanced
flexible reusable surface insulation was developed. This material
consists of sewn composite quilted fabric insulation batting between
two layers of white fabric that are sewn together to form a quilted
blanket. AFRSI was used on Discovery and Atlantis to replace the
vast majority of the LRSI tiles. Following its seventh flight,
Columbia also was modified to replace most of the LRSI tiles with
AFRSI. The AFRSI blankets provide improved producibility and durability,
reduced fabrication and installation time and costs, and a weight
reduction over that of the LRSI tiles. The AFRSI blankets protect
areas where temperatures are below 1,200 F.
6. White blankets made of coated Nomex felt
reusable surface insulation are used on the upper payload
bay doors, portions of the midfuselage and aft fuselage sides,
portions of the upper wing surface and a portion of the OMS/RCS
pods. The FRSI blankets protect areas where temperatures are below
7. Additional materials are used in other special areas. These
materials are thermal panes for the windows; metal for the forward
reaction control system fairings and elevon seal panels on the
upper wing to elevon interface; a combination of white- and black-pigmented
silica cloth for thermal barriers and gap fillers around operable
penetrations, such as main and nose landing gear doors, egress
and ingress flight crew side hatch, umbilical doors, elevon cove,
forward RCS, RCS thrusters, midfuselage vent doors, payload bay
doors, rudder/speed brake, OMS/RCS pods and gaps between TPS tiles
in high differential pressure areas; and room-temperature vulcanizing
material for the thick aluminum T-0 umbilicals on the sides of
the orbiter aft fuselage.