April 9, 2002. Copyright 2002. Graphic News. All rights reserved.

Road in space to open new frontier

LONDON, April 9, Graphic News: The space shuttle Atlantis has blasted off on an 11-day mission to deliver the first section of a space railroad to the International Space Station. Just as it did in the 19th century, the railroad will play a vital role in expanding the new frontier in the 21st. 

Circling Earth aboard space station Alpha, the car on this railway will have a top speed of only 300 feet (91.5 metres) 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 (27,400km/h), in orbit. 

The rail line will eventually stretch almost 360 feet (110 metres) along the structural backbone of the station, serving as a mobile base from which the stationŐs Canadian-built robotic arm can assemble and maintain the complex.

The new US$600 million space station segment being hauled aloft is a 44-foot (13-metre) girder and cable assembly called the S-Zero Truss.

The shuttle also carries a $190 million rail flatcar that will run along a track to be built on the truss. The trolley will carry the stationŐs large robotic arm to various work sites. Eventually a hand car for astronauts will be added.

The S-Zero Truss is deceptively simple, jokingly known within NASA as Ňpig iron,Ó a term used by American railroad builders in the 1830s. It is in fact one of the most complicated pieces to go on the station with a total of some 400,000 parts. The truss will support labs, living quarters, payloads and systems equipment, as well as the massive solar arrays, which will supply power to the station.

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 initial section of track.

ŇItŐs built for precise positioning and smooth velocity control; itŐs not built for speed,Ó said Randy Straub, technical manager for the system with The Boeing Company in Huntington Beach, California.

The operation of the railway is critical for continued assembly of the station. It will allow the stationŐs Canadarm2 robotic arm, a 55-foot-long (17-metre-long) robot arm built by the Canadian Space Agency, to carry and install equipment, a job currently done by astronauts. The robot arm is capable of lifting payloads of up to 220,000lb (99,800kg) -- equal to the mass of a space shuttle.

Part flatcar and part locomotive, the Mobile Transporter -- which weighs 1,950lb (885kg) -- is not an iron horse, but one of aluminium. The Mobile Transporter moves along the two parallel rails attached to the station truss at speeds varying from one-tenth of an inch to one inch per second (2.5mm to 25mm). Its dual electric motors can move 23 tonnes of cargo down the rails.

ŇWe've done a lot of work to make certain it can't jump the tracks,Ó 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 for propulsion and two sets of spring-loaded wheels with rollers on both sides of the track to ensure the transporter canŐt float loose. The railcar will have 10 stops -- specific locations called worksites where it can be locked down with a 7,000lb (317kg) grip -- allowing the robotic arm to safely manoeuvre cargo. Although it can be driven from the station, the engineers for NASAŐs space railroad will normally reside in Mission Control, Houston, driving the train from thousands of miles away and hundreds of miles below.

Eight shuttle missions, spread over about four years, will be required to deliver and assemble the 10 planned truss segments.
/ENDS

Sources: NASA, MacDonald Dettwiler Space and Advanced Robotics