The shoes are critical for safely transporting the Space Shuttle to the launch pad. Cracks on old shoes can prevent the cleats from moving along the crawlerway and can compromise the structural integrity of the shoes.

Each of the vehicles has eight belts, and each belt has 57 shoes. Most shoes on the crawlers date back to 1965, when the vehicles were built and first put into service for Apollo launches.

Inspections in late 2003 revealed fatigue cracks in many of the shoes, leading to complete replacement of shoes on both crawlers. Crawler transporter No. 2, designated for Discovery's Return to Flight mission to the International Space Station, will receive its new shoes first.

“The crawler transporters are going to be in great shape for Return to Flight and the crawler team is delivering,” said Mark Hamilton, NASA crawler transporter systems engineer. "This is by far the most active maintenance period in the history of the crawlers, requiring continuous heavy equipment crane support and the use of custom rigging and tooling."

NASA and United Space Alliance (USA) crawler transporter systems engineers and USA technicians are repairing the sprockets and rollers on each belt before the new shoes are installed. Welding repair and inspection of some of the sprockets and manufacture of some of the rollers also is being performed at KSC.

The new shoes, each 7.5 feet long and 1.5 feet wide, are being made by ME Global Manufacturing of Duluth, Minn. They arrive at KSC in truckloads of 20 to comply with shipping load limits.

Other upgrades or modifications recently completed on crawler No. 2 include complete electrical rewiring of the motor control center and installation of new driver cabs, mufflers, radiators and ventilation systems. The same work is now under way on crawler No. 1.

Hamilton noted the majority of mechanical crawler parts are unique to the vehicle and are specially manufactured. “We are fortunate that the massive precision components, such as the large drive gear sets and gear shaft bearings, still look new.”