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Countdown! NASA Launch Vehicles and Facilities
PMS 018-B
October 1991
Section 4
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The Rotating Service Structure provides protection
for the orbiter and access to the cargo bay for installation and servicing of
payloads at the pad. It pivots through one-third of a circle, to 120 degrees,
from a retracted position well away from the Shuttle to where its payload
changeout room doors meet and match the orbiter cargo bay doors. This structure
rotates around a vertical hinge attached to one corner of the Fixed Service
Structure. The body of the Rotating Service Structure begins at the 59-foot
(18-meter) level and extends to 189 feet (57.6 meters) above the pad floor,
providing orbiter access platforms at five levels. The hinge and a structural
framework on the opposite end support the structure. This framework rests on two
eight-wheel, motor-driven trucks, which ride on rails installed within the pad
surface. The rotating body is 102 feet (31 meters) long, 50 feet (15 meters)
wide, and 130 feet (40 meters) high. The primary purpose of the Rotating Service
Structure is to receive Space Shuttle payloads while in the retracted position,
rotate, and install them in the orbiter cargo bay. With the exception of
Spacelab and other large payloads, spacecraft are loaded into the Shuttle at the
pad. The largest payloads are installed while the orbiter is in the Orbiter
Processing Facility. The Payload Changeout Room in the center of the structure
provides an environmentally clean or "white room" condition in which
to receive a payload transferred from a protective Payload Canister. Pad
personnel maintain this cleanliness level by never exposing the spacecraft to
the open air during the transfer operations. A clean-air purge maintains
environmental control during cargo operations.
Personnel operate controls to hoist the Payload
Canister to the proper elevation in the retracted Rotating Service Structure and
lock it into position. The environmental seals in the structure inflate against
the sides of the Canister. Clean, temperature- and humidity-controlled air
purges the space between the closed doors of the Rotating Service Structure and
the Canister. After the purge, the doors may be opened. The payload then
transfers from the Canister into the Payload Changeout Room. The Canister and
the Rotating Service Structure doors then close, the environmental seal
deflates, and the Canister lowers to the Transporter to be taken off the pad.
The Rotating Service Structure rolls into position to enclose the orbiter's
payload bay, re-establishing the environmental seals and clean air purge. The
Payload Changeout Room and payload bay doors open so that the payload may be
installed.
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Orbiter Midbody Umbilical Unit provides access to
and permits servicing of the midfuselage area of the orbiter. It extends from
the Rotating Service Structure at levels ranging from 158 to 176 feet (48 to
53.6 meters) above the pad surface, and is 22 feet (6.7 meters) long, 13 feet (4
meters) wide, and 20 feet (6 meters) high. A sliding extension platform and a
horizontally moving, line-handling mechanism offer access to the midbody
umbilical door on the left side of the orbiter. Liquid oxygen and liquid
hydrogen for the fuel cells, and gases such as nitrogen and helium, feed through
this unit.
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Hypergolic Umbilical System carries hypergolic fuel
and oxidizer, as well as helium and nitrogen service lines, from the Fixed
Service Structure to the Space Shuttle. The system also allows rapid connection
of the lines to and disconnection of them from the vehicle. Six umbilical
handling units, manually operated and controlled at the pad, attach to the
Rotating Service Structure. These units are located to the right and left sides
of the aft end of the orbiter. They serve the Orbital Maneuvering System and
Reaction Control System, as well as the payload bay and the nose area of the
orbiter.
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