"6_2_3_9.TXT" (1415 bytes) was created on 12-12-88

ORBITER PASSIVE THERMAL CONTROL

A passive thermal control system helps maintain the temperature of the
orbiter spacecraft, systems and components within their temperature
limits.  This system uses available orbiter heat sources and heat
sinks supplemented by insulation blankets, thermal coatings and
thermal isolation methods.  Heaters are provided on components and
systems in areas where passive thermal control techniques are not
adequate.  (The heaters are described under the various systems.)

The insulation blankets are of two basic types: fibrous bulk and
multilayer.  The bulk blankets are fibrous materials with a density of
2 pounds per cubic foot and a sewn cover of reinforced acrylic film
Kapton.  The cover material has 13,500 holes per square foot for
venting.  Acrylic film tape is used for cutouts, patching and
reinforcements.  Tufts throughout the blankets minimize billowing
during venting.

The multilayer blankets are constructed of alternate layers of
perforated acrylic film Kapton reflectors and Dacron net separators.
There are 16 reflector layers in all, the two cover halves counting as
two layers.  Covers, tufting and acrylic film tape are similar to that
used for the bulk blankets.

The contractors are Hi-Temp Insulation Inc., Camarillo, Calif.
(fibrous insulation); Scheldahl, Northfield, Minn. (cover materials
and inner layers); Apex Mills, Los Angeles, Calif. (separators).


"6_2_3_10.TXT" (5736 bytes) was created on 12-20-88

ORBITER PURGE, VENT AND DRAIN SYSTEM

The purge, vent and drain system on the orbiter is designed to perform the
following functions: provide unpressurized compartments with gas purge for
thermal conditioning and prevent accumulation of hazardous gases, vent the
unpressurized compartments during ascent and entry, drain trapped fluids (water
and hydraulic fluid) and condition window cavities to maintain visibility.

Three purge circuits are connected by the T-0 umbilical to ground equipment
before launch during the preflight countdown and postlanding phases.  Purge gas
(cool, dry air and gaseous nitrogen) is provided to three sets of distribution
plumbing: the forward fuselage, orbital maneuvering system/reaction control
system pods, wings and vertical stabilizer; the midfuselage; and the aft
fuselage.  The purge gas makes all the unpressurized volumes inert, maintains
constant humidity and temperature, forces out any hazardous gases and ensures
that external contaminants cannot enter.

The active vent system provides the flow area to control pressure
during purge, depressurization during ascent, molecular venting in orbit and
repressurization during entry.

The vent and purge system is controlled exclusively through guidance,
navigation and control software.  The active ports are positioned by the
software on the basis of mission time or mission events during ascent, entry
and aborts and by crew inputs on the CRT and keyboard in the crew compartment
flight deck.

There are 18 active vents in the orbiter fuselage, nine on each side.  Each
vent has a door that can be positioned for a specific purpose at various phases
of flight.  For identification, each door is numbered, starting at the nose of
the orbiter.  Each compartment has