April 3, 2013
Roller Bearing Assemblies Replaced On NASA’s Crawler-Transporter
For more than a year, NASA's crawler-transporter (CT) 2 has been undergoing a major tuneup in the Kennedy Space Center's Vehicle Assembly Building (VAB). Recent work has included preparations to install upgraded components that will enable the crawler to carry the greater loads anticipated with the agency's new rocket designed to take astronauts beyond low-Earth orbit for the first time since the early 1970s.The crawler-transporter modifications are part of NASA's Ground Systems Development and Operations Program (GSDO) efforts to upgrade Kennedy's infrastructure to support the 21st-century spaceport. Earlier CT modifications were checked out during an extensive test drive to Launch Pad 39A last November. In February the crawler returned to the VAB's high bay 2 for further work.
"The next step is to remove and replace the roller bearing assemblies," said Mary Hanna, CT project manager in the Vehicle Integration and Launch Branch of GSDO. "We've already begun the process of removing the treads and jacking two of the crawler corners four feet off the ground to remove the old assemblies."
Hanna noted that CT-2 will play a crucial role in future launch operations at Kennedy.
"These upgrades are designed to make sure the crawler will support us for another 50 years," she said. "Many of the older parts were wearing out from years of use."
The crawler-transporters were an integral part of the Apollo and Space Shuttle Programs. For more than 45 years the crawlers were used to transport the mobile launcher platforms and the Apollo-Saturn V rockets and, later, space shuttles to Launch Pads 39A and B. At the end of 2011, engineers began modifying CT-2 to ensure its ability to transport launch vehicles currently in development, such as NASA's Space Launch System (SLS) which will send the Orion spacecraft carrying humans to new destinations in the solar system. The new rocket will have the heaviest lift capability and be the most powerful to date.
The current work is being supported by NASA's Test and Operations Support Contract by Jacobs Technology Inc., NASA's Engineering Support Contract by QinetiQ Inc., both at Kennedy, as well as Mammoet Inc. of Houston, and L&H Industrial Inc. of Gillette, Wyo.
"L&H is producing the rollers, shaft assemblies, sleeves and other hardware needed," Hanna said. "Altogether, that will amount to about a half-million pounds of steel being delivered here at Kennedy."
Technicians from Jacobs are performing the work of removing the crawler treads prior to Mammoet jacking and cribbing the corners. L&H then will remove the old roller bearing assemblies and inspect the structure and integrity of openings to see if any repairs are needed. If there are, they will take place prior to installing the new assemblies.
"We expect the installation to begin in August," Hanna said. "Testing should take place near the end of this year."
The crucial nature of the roller bearings surfaced on one of the first crawler-transporter test drives back in 1965. The crawler moved a launch umbilical tower about one mile on two short stretches of the crawlerway. During the operation, metal fragments were discovered on the crawlerway.
"The original rollers were simply ball bearings," Hanna said. "The roller bearing and associated assembly, including roller shafts and new sleeve bearings were redesigned and installed. That hardware was used successfully throughout the Apollo and shuttle programs."
Present modifications represent a redesign and upgrade to the roller bearings and assemblies to be installed on CT-2.
"There weren't many changes needed, but the new assemblies will help the crawler carry the heavier load," she said. "The newer system will also be better lubricated and that should provide a longer operational life."
The 6.5-million-pound CT will carry a 10.3-million-pound mobile launcher with the 4.4-million-pound SLS rocket (without liquid propellants), resulting in a whopping 21.2-million-pound vehicle lumbering along to the launch pad.
To further aid in transporting the future vehicles, the type of grease and lubricants available today are better and more efficient than those used during the Apollo and shuttle eras.
"When you have that much metal-on-metal carrying such huge loads, there is a tremendous amount of heat and friction," Hanna said. "That creates much of the wear and tear that we see on the crawlers. The improvements will keep the crawler running for a long time."
Future modifications to extend the lifetime of CT-2 systems include upgrades to the jacking, equalization and leveling cylinders. This will increase their load-carrying capacity and reliability. Other work completed includes replacement of electronics, cables, tubing, hydraulic components, as well as cleaning of fuel tanks and hydraulic systems.
"The current schedule calls for all modifications to CT-2 to be complete in early 2016," Hanna said. "Testing will include picking up the new mobile launcher and moving it into the VAB later that year. We'll then move it all to Launch Pad 39B in late 2017."
The SLS rocket is scheduled to launch from Pad 39B in 2017 on a mission around the moon.
On The Net: