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Countdown! NASA Launch Vehicles and Facilities
PMS 018-B 
October 1991
Section 3



Mobile Launcher Platform  

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Mobile Launcher Platform Crawler -TransporterA Crawler-Transporter moves a fully assembled Space Shuttle that is mounted on a Mobile Launcher Platform
The Mobile Launcher Platform is a two-story steel structure which provides a transportable launch base for the Space Shuttle. First used in the Apollo/Saturn program, the Platforms underwent modifications for the Shuttle.

The main body of each Platform is 25 feet (7.6 meters) high, 160 feet (49 meters) long, and 135 feet (41 meters) wide. At their parking sites north of the Vehicle Assembly Building, in the Vehicle Assembly Building high bays and at the launch pads, the Mobile Launcher Platforms rest on six pedestals 22 feet (6.7 meters) high.

Unloaded, a Platform weighs about 8.23 million pounds (3.73 million kilograms). With an unfueled Shuttle aboard, it weighs about 11 million pounds (5 million kilograms).

The main body of the Platform provides three openings - two for the exhaust of the solid rocket boosters and one for the main engines exhaust.

There are two large devices called Tail Service Masts, one on each side of the main engines exhaust hole. The masts provide several umbilical connections to the orbiter, including a liquid-oxygen line through one and a liquid-hydrogen line through another. These cryogenic propellants feed into the external tank from the pad tanks via these connections. At launch, the umbilicals pull away from the orbiter and retract into the Masts, where protective hoods rotate closed to shield them from the exhaust flames. Each Tail Service Mast assembly is 15 feet (4.6 meters) long, 9 feet (2.7 meters) wide, and rises 31 feet (9.4 meters) above the Platform deck.

Other umbilicals carry helium and nitrogen, as well as ground electrical power and communications links.

Eight attach posts, four on the aft skirt of each SRB, support and hold the Space Shuttle on the Mobile Launcher Platform. These posts fit on counterpart posts located in the Platform's two solid rocket booster support wells. The space vehicle disconnects from the Platform by explosive nuts which release the giant studs linking the solid rocket attach posts with the Platform support posts.

Each Mobile Launcher Platform has two inner levels containing electrical, test and propellant-loading equipment.

A Crawler-Transporter moves a fully assembled Space Shuttle, mounted on a Mobile Launcher Platform, from the Vehicle Assembly Building to the launch pad. The huge tracked vehicles, originally used during the Apollo era, underwent modifications for the Shuttle.

The two Crawlers are about 20 feet (6.1 meters) high, 131 feet (40 meters) long, and 114 feet (34.7 meters) wide - about the size of a baseball diamond. Each one weighs about 6 million pounds (2.7 million kilograms) unloaded. A Crawler has eight tracks, each of which has 57 shoes or cleats. Each shoe weighs approximately one ton (907 kilograms).

With the Space Shuttle aboard, the Crawler can creep at a maximum speed of about 1 mile (1.6 kilometers) per hour; unloaded, it can manage about 2 miles (3.2 kilometers) per hour. The Crawler has a leveling system designed to keep the top of the Space Shuttle vertical while negotiating the 5 percent grade leading to the top of the launch pad. Also, a laser docking system provides almost pinpoint accuracy when the Crawler and Mobile Launcher Platform are positioned at the launch pad or in the Vehicle Assembly Building.

Two 2,750-horsepower diesel engines power each Crawler. The engines drive four 1,000-kilowatt generators which provide electrical power to 16 traction motors. Operators in cabs on either end steer the giant vehicle.

Crawlerway CrawlerwayThe Crawlerway consists of two 40-foot (12-meter) wide lanes, separated by a 50-foot (15-meter) wide median strip. The Crawlerway is a 130-foot-wide (39.6-meter) roadway -- almost as broad as an eight-lane freeway. The Crawler-Transporters use this for their more than 3-mile (4.8-kilometer) trek to one of the launch pads from the Vehicle Assembly Building.

The Crawlerway consists of two 40-foot (12-meter) wide lanes, separated by a 50-foot (15-meter) wide median strip. The Crawlerway has four layers to support the huge weight. The Crawler, Mobile Launcher Platform and Space Shuttle with empty external tank weigh about 17 million pounds (7.7 million kilograms). The top layer of the Crawlerway is river gravel about 8 inches (20.3 centimeters) thick on curves and 4 inches (10.2 centimeters) thick on straightaway sections. The other layers in descending order are: 4 feet (1.2 meters) of graded, crushed stone; 2.5 feet (0.76 meter) of select fill; and 1 foot (0.30 meter) of compact fill. It takes several hours for the journey from the Vehicle Assembly Building to one of the launch pads. The distance to Pad 39A is about 3.4 miles (5.5 kilometers); to Pad 39B, it is approximately 4.2 miles (6.8 kilometers).

The Payload Canister holds payloads in transit from various processing or assembly facilities to the launch pad (for vertically installed payloads) or to the Orbiter Processing Facility (for horizontally installed payloads).

Each environmentally controlled Canister can carry payloads up to 15 feet (4.6 meters) in diameter and 60 feet (18.3 meters) long, matching the capacity of the orbiter payload bay. Maximum payload weight is approximately 50,000 pounds (22,680 kilograms).

The Payload Canister Transporter is a 48-wheel, self-propelled truck which can transport the Canister and its hardware either in a vertical or a horizontal position. It is 65 feet (19.8 meters) long and 23 feet (7 meters) wide, with a flatbed that can be lowered and raised from about 5 feet (1.5 meters) to 7 feet (2.1 meters), if required.

Independently steerable wheels permit the Transporter to move forward, backward, sideways, and diagonally, or turn on its own axis like a carousel. Diagonally opposed operator cabs are located on each end of the truck.

A diesel engine powers the Transporter. Inside a spacecraft facility, it runs on an electric motor. Fully loaded, its top speed is about 5 miles (8 kilometers) per hour. But it can creep as slowly as a 0.25 inch (0.635 centimeter) per second, or approximately 0.014 miles (0.022 kilometers) per hour, for payloads which require precise handling.


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