The Mobile Transporter is a rail line about 100 meters long located outside the International Space Station (ISS. The train on it carries equipment at a top speed of 300 meters per hour, surely making it the slowest in our universe. The catch is that, being attached to the ISS, it also traveled at a higher speed of 28,000 kilometers per hour, which certainly qualifies it as a top speed performer. RedNova tells us the story of this train, which weighs more than 13 tons, and can be operated by the astronauts aboard the ISS or from Mission Control on the ground.
The Mobile Transporter (MT) is a rail line that runs along the 111 meter long (366-foot) truss outside of the International Space Station (ISS). It's being assembled a section at a time, and will eventually stretch almost 100 meters (328 ft) along the central exterior of the Space Station.
As it moves down the track, the train's top speed is about 300 meters (980 ft) per hour, or 2.5 centimeters (1 inch) per second. The MT isn't a passenger train; it hauls equipment, not people.
The MT's job is to move the ISS's robotic arm so it can help build large structures. Up until now, the robotic arm has stayed in one place, and could extend about 50 feet to work on projects, but as the ISS has grown, it has exceeded the reach of the robotic arm.
Here is a picture of the Mobile Transporter (Credit: NASA). A larger version of this photograph can be found on this page from the John F. Kennedy Space Center, which contains many more pictures and animations.
The transporter is large and bulky; it weighs 13,608 kilograms (30,000 pounds) and is built from 12.7-centimeter (5-inch) thick aluminum and titanium. In space, though, a vehicle that large still risks floating off the tracks because of microgravity.
Even if it is big, the MT can move objects precisely, accurately, and reliably.
Magnetic sensors and strips attached to the track help the vehicle stop exactly where it's supposed to-within 1/4 centimeter (1/10-inch)-so that all power sources and openings can meet in exactly the right location.
Even the most accurate vehicle can't do its job if something goes wrong, however, and the MT is built with double redundancy in almost every component. Double redundancy means that a second part or backup system is in place to take over if the first method fails.
For more information about the MT, this well-illustrated page about ISS contains a diagram of it.
Source: RedNova, March 26, 2004; and various websites