Pervasive bearing failures have been found in both of NASA's massive Crawler Transporters at Kennedy Space Center, Florida, putting them out of service and endangering the space shuttle's already-tight schedule. These crawlers, the world's largest tracked vehicles, ferry the space shuttle and its launch platform along the KSC Crawlerway from the Vehicle Assembly Building and up a ramp to the launch pad.

The first crawler-transporter, built by the Marion Power Shovel Company and based on coal strip mine load carriers, was put into service in January 1966. Designed to move the Apollo program's Saturn V rockets and portable launch platforms, the transporters were rebuilt in 1976 for use in the shuttle program. In all, the crawlers have covered over 2,500 miles back and forth from the VAB to the launch pad (equivalent to a trip from Kennedy Space Center to Los Angeles). Each trip takes about five hours.

The crawlers are 131 feet long, 114 feet wide and weigh six million pounds. They move on four tank-like tracks at each corner, each driven by four 375 horsepower electric traction motors. The 16 traction motors get their power from four 1,000 kilowatt diesel generators. Top speed is 2 mph unloaded and 1 mph with a full, 13 million pound payload. Not particularly economical to run, the crawler transporters achieve only .007 miles per gallon of diesel fuel.

The shuttle must be kept vertical within ten minutes of arc at all times, under varying load, speed and wind conditions. Adding further challenge, the launch pad is at the end of a 5% incline. So the transporters carry these 13 million pound payloads (4.5 million pounds for the shuttle and 8.8 million pounds for the launch base) on a self-leveling platform.

This leveling platform is controlled by 16 hydraulic cylinders, called Jacking, Equalizing and Leveling (JEL) cylinders. There are four cylinders at each corner of the platform. The 16 cylinders are 20 inches across and can extend up to six feet. At both ends of each cylinder are large pillow block style bearings, for a total of 32 bearings.

Preparing one of the transporters for a planned September 28, 2002 launch of the shuttle Atlantis, technicians discovered bearing failures in two of the JEL cylinders. So far, after ultrasound and x-ray inspections, 19 of 32 JEL bearings in Crawler Transporter #1 were found to be bad, and 15 in the second transporter. In all, 34 of the 64 bearings must be replaced.

NASA spokesman George Diller said, "It varied, anywhere from small cracks to major cracks to some disintegration of the bearings to the point where they are not operating as bearings anymore."

The bearings are original to the 37-year-old launch transport vehicles. Preventive maintenance involved lubrication but not detailed inspection.

NASA does not know how long the bearings may have been damaged, but indicated that at least some of the damage appears to be several years old. Mr. Diller said, "We can't say this is an age-related thing."

Needing at least 34 bearings but having only 9 spares in stock, NASA may opt to scavenge the good bearings from one transporter for the other.

Time is critical, as the shuttle program has already been delayed by cracked fuel lines; the shuttle Atlantis is repaired and being readied for a planned launch on September 28, 2002. "It's too soon to tell what impact, if any, there would be on the schedule," said Mr. Diller.

NASA cannot risk loading the shuttle and launch platform on a questionable transporter. If a bearing failure would occur and hamper a fully loaded transporter, the repair would be, "extremely difficult, to understate it," said one NASA engineer. Similarly, the shuttle cannot be stalled on its trip to the launch pad, potentially exposing it to high winds and lightning.