Expanding the new frontier just as they did the old,
railroads will take flight next month as the first space
railroad is launched aboard Space Shuttle Atlantis.

Circling Earth aboard the International Space Station, the
car on this railway will have a top speed of only 300 feet
per hour, but the entire line — tracks and all — will
travel almost nine times faster than a speeding bullet, over
17,000 miles per hour, in orbit. The rail line eventually
will stretch almost 100 yards along the structural backbone
of the station, serving as a mobile base from which the
station’s Canadian-built robotic arm can assemble and
maintain the complex.

“To build the rails that linked the east and west coasts of
the United States, thousands of workers endured desert heat,
frigid mountains and countless obstacles. These rails in
space will run in temperatures far hotter than any desert and
far colder than any mountain,” said NASA Mobile Transporter
Subsystem Manager Tom Farrell at the Johnson Space Center in
Houston. “And just like the transcontinental rails pulled
together our country, these rails pull together 16 nations
around the world, cooperating in orbit.”

Atlantis will launch the railcar, called the Mobile
Transporter, and an initial 43-foot section of track as it
delivers the first segment of the International Space
Station’s exterior truss. Designated “S0 (S-zero),” the first
section of truss will be carried aloft by Atlantis on shuttle
mission STS-110 in April. More sections of track will be
added during the next two years as eight segments of the
girder-like truss are launched aboard the shuttle. By the end
of this year, the tracks already will stretch more than 130
feet. When completed, the truss will stretch over 360 feet,
the longest structure ever built in space.

An additional base system will be attached atop the flatcar-
like Mobile Transporter during a shuttle flight in May, but
the space train will leave the depot for its inaugural run
during Atlantis’ April mission. After spacewalkers loosen
launch restraints and attach electrical and computer cable
reels, Mission Control will command the Mobile Transporter
railcar to inch its way up and down the 43-foot section of

“It’s built for precise positioning and smooth velocity
control; it’s not built for speed,” said Randy Straub,
subcontract technical manager for the system with The Boeing
Company in Huntington Beach, Calif.

The operation of the railway is critical for continued
assembly of the station. It will allow the station’s
Canadarm2 robotic arm to carry future truss segments and
solar arrays down the tracks to install them. Part flatcar
and part locomotive, the Mobile Transporter weighs 1,950
pounds and is a horse made of aluminum, not iron. The Mobile
Transporter was built by TRW Astro in Carpinteria, Calif.,
for Boeing, the prime contractor for station construction. It
measures three feet high, nine feet long and eight feet wide
and moves along two parallel rails attached to the station
truss at speeds varying from one-tenth of an inch to one inch
per second. Although driven by dual electric motors that
generate only about a hundredth of one horsepower, the
transporter can move 23 tons of cargo down the rails.

What is the hardest part about building a zero-gravity

“We’ve done a lot of work to make certain it can’t jump the
tracks,” said Farrell. “We have to be sure it will be safe
during all the station’s activities, like reboosting its
orbit or having visiting vehicles dock.”

The transporter stays on track with three sets of wheels, one
set that propels it and two sets in roller suspension units,
spring-loaded units that have rollers on both sides of the
track to ensure the transporter can’t float loose. The
railcar will have 10 stops, specific locations called
worksites where it can be locked down with a 7,000-pound
grip, allowing the robotic arm to safely maneuver cargo.
Although it can be driven from the station or from the
ground, the engineers for NASA’s space railroad will normally
reside in Mission Control, Houston, driving the train from
thousands of miles away and hundreds of miles below.

Although the Mobile Transporter will be a freight train and
not a passenger train, space- walking astronauts will have
their own form of personal rail transportation aboard the
station. Astronauts will operate a small handcar to maneuver
up and down the rail line, a car that they will pull along
the zero-gravity railway by hand to move themselves and their
gear from place to place. Called the Crew and Equipment
Translation Aid, two such carts will be delivered to the
station before the end of the year.