ME Global helps launch shuttles to space: the track shoes on NASA's crawler transporters, which carry the space shuttles to the launch pad, required refurbishing. But ME Global had a better solution--cast entirely new sets of shoes.

As the National Aeronautics and Space Administration (NASA) returns its space shuttles to flight this May after a two-year hiatus, it required some assistance for ground transportation. ME Global Inc. had the solution. The steel sand casting company in Duluth, Minn., partnered with NASA and the United Space Alliance (USA) to develop new track shoes for the shuttle crawler transporters.

ME Global (a wholly owned business of Elecmetal, Santiago, Chile) came onto the space scene in the winter of 2002 when the company's director of international sales and projects, Jeff Washburn, learned that the original track shoes on the transporters (dating back to the 1960s) and the inventory of spare shoes were soon to be refurbished. The steel caster proposed to NASA that it could cast entirely new sets of shoes at a similar price as refurbishing. But NASA declined because it had prior success with refurbishing the shoes (adding stock to existing roller paths and pin holes and then remachining them to fit the original design specifications).

However, several months later, NASA and USA took a second look into the idea of newly cast shoes. ME Global was asked to make a presentation in mid 2002 at Kennedy Space Center (KSC), Cape Canaveral, Fla., to show NASA exactly how this would be possible.

Further, ME Global offered a complete metallurgical evaluation [microstructure, ultimate tensile strength (UTS) results, RT analysis, Brinell hardness tests, etc.] of a current track shoe. "What (NASA) had been focusing on was refurbishing just the external parts of the shoes," said Washburn. "My concern was the inside of the track shoes. They could have a lot of wear. It's like when you bend a wire back and forth so many times, it will eventually break."

After the tests were completed, ME Global presented the results to NASA and USA in July 2003. It was discovered that the original shoe's UTS did not meet the minimum NASA requirement of 136 KSI. This led NASA to begin its own investigation, and additional deficiencies were found.

Late in 2003, ME Global's research helped prompt NASA to overturn the refurbishment program and charter USA (NASA's largest contractor, which is responsible for the shuttle ground transport systems including the two transporters) to immediately start procurement processes to outfit both transporters with new shoes. NASA was obligated to leave the bidding open to other metalcasting companies, but in May 2004, ME Global was awarded the contract. Now it had to deliver more than 1,000 shoes in six months.

Ground Control

A crawler transporter does exactly what its name implies; it transports a space shuttle from the Vehicle Assembly Building to the launch pad at a crawling pace (1 mph). NASA has two of these vehicles, which carry the space shuttle assembly (the shuttle, two solid rocket boosters and the external fuel tank) and the mobile launch platform to one of two launch pads at KSC. With the aid of hydraulic cylinders, the transporters place the platform and shuttle on the launch pad and then lower and back out from underneath, leaving the shuttle in position for liftoff.

Both transporters weigh 6 million lbs. each, but that triples to 18 million lbs. when carrying the mobile launch platform and the pre-launch shuttle. According to Washburn, a professional baseball diamond could comfortably be placed on top of the transporter.

There are four double-tracked, 10 x 41-ft. crawler units (similar to a tank) on each vehicle, and each track has 57 shoes for a total of 456 shoes per transporter. Each vehicle has two 16 cylinder, 2,750-hp engines with a 5,000-gallon fuel capacity but only gets 42 ft. per gallon.

To completely re-inventory USA with its track shoes, ME Global supplied a set for each transporter, plus a set of spares for a total of 1,024 track shoes. Each shoe measures 90 in. long, 25 in. wide, 16.5 in. tall and weighs 2,200 lbs.

Due to the return-to-flight timeline, the onus was on ME Global to cast all the track shoes by January, only six months after it received the contract. But the chance to help put the space shuttle back in the sky for the first time since January t2003 was an opportunity that the metalcasting facility could not skip, and USA knew ME Global could accomplish the feat.

"Several companies submitted bids, but only one of those companies could meet the schedule of producing more than 1,000 shoes in a six-month period of time, and that was ME Global," said Tracy Yates, USA spokesperson. "The schedule was such a challenge because we wanted to get the shoes done to fit our return-to-flight schedule, which required at least one of the crawlers to be available in January (to begin preparation for a May launch date)."

ME Global in fact met the demand for both crawlers by January (one set completed in November), but as part of a space project, the facility had to tackle the stringent requirements inherent with the shoes.

Countdown

Producing track shoes was nothing new for ME Global (the company produces track shoes for industrial use). For a typical mining shovel order, the company would manufacture and ship 70-90 track shoes in a four-month span. But this NASA project required more than 10-times that production in the same amount of time. However, through some forward thinking, ME Global knew it had to keep ahead of schedule to meet the demanding timeline. During the request-for-quote process, ME Global took a gamble and built a preliminary pattern for the shoes to experiment with manufacturing and heat treatment methods.

"If we didn't build a pattern, there would be no way we could support the return-to-flight timeline," said Washburn. "If we waited until May (after the bid was awarded), it would be the end of June when we had a pattern completed. And then we would make a prototype, which would take two months, and we would be at the end of August before beginning production. How can you make 500 of these in two months?"

ME Global was somewhat wary of how NASA would perceive the proactive thinking, but NASA strongly supported the decision to work on the project before even receiving the bid.

The shoe development was divided into three phases. Phase 1 was to produce a prototype that met all the requirements of USA and NASA and also confirm that the casting process is capable of producing more than 1,000 track shoes. Phase 2 was to outfit one transporter. Phase 3 was to outfit the other transporter. Based on the successful completion of Phase 1, ME Global was awarded Phases 2 and 3.

A large difficulty the company encountered in Phase 1 was trying to obtain the desired mechanical properties with the given NASA shoe design and alloy. USA specified steel alloy 8640 for the project, but it was found to be impossible to manufacture on a large-scale basis as the prototype castings cracked during heat treatment. However, NASA would not alter the shoe design, which forced ME Global to investigate different alloys. The company turned to the CKQ alloys that the original shoes were made and also alloy 8630, but neither met NASA's specifications.

ME Global then looked to alloy M4320 (which it recently used successfully in another project), and it met the requirements needed for the shoes. A low-carbon alloy, M4320 was determined to be the proper casting material in August, but this left ME Global with only four months to complete the project on-time.

With the assistance of 20 extra employees the company hired to work on the track shoe project, ME Global began casting the shoes through V-process molding, which uses unbonded silica sand under one atmosphere of pressure to form and maintain the shape of the mold. Washburn said there were two more challenges in this procedure. One was pouring a 90-in. casting in a 54 x 96-in. flask. The other was with the coremaking process.

Each mold included 19 cores (including two 7-ft. body cores) totaling 700 lbs. of zircon core sand. Not only did these cores improve the smoothness of passageways in the castings, but (unlike with the alloys) they helped convince NASA to augment the original shoe design.

Using its 3D cast modeling software for the shoe design, ME Global determined that porosity would be an intrinsic characteristic of the new castings. Further, NASA had confirmed with ME Global that the inventory of original shoes had porosity defects under the roller path, which was a result of poor design.

Thus, the metalcasting company and NASA agreed to alter the design to prevent any porosity errors in the new track shoes, and this allowed more flexibility for use of the new cores. Washburn also said another challenge with the cores was to prevent them from collapsing under their own weight. But ME Global created a "sling system" that supported the body cores in four different areas to transport them from the coremaking area to the flasks, and this helped prevent core breaking.

ME Global actually cast 1,042 track shoes including 18 (two for prototypes and one for each of the 16 tread belts on the transporters) that were destructively tested to confirm more than 200 dimensions, UTS, through hardness on multiple cross sections, microstructure at depth, Brinell hardness and soundness verification using X-ray.

As the castings were completed, they were sent to Remmele Engineering, Big Lake Minn., for machining. Remmele prior experience on aerospace projects, such as the manufacture of bulkheads for the International Space Station, and understood the tight timeline for the track shoe contract. USA sent several quality assurance inspectors to Remmele, and ME Global had one of its principal metallurgists work full time on-site at to keep the project at pace. Once the track shoes were approved, they were sent from Remmele to KSC and installed on the crawler transporters.

We Have Liftoff

With the newly cast track shoes, NASA plans to initiate a trial run of the crawler transporters carrying a mobile launch platform to one of the launch pads in January. Then, in March, ME Global's castings will be used to bring the entire space shuttle Discovery assembly to launch pad 39B, where it will rest until its May ascension into space.

USA expressed much gratitude in what it received from ME Global as well as the effort the metalcasting company put into the project.

"Our crawler team feels that the ME Global employees bent over backwards to meet all the challenges and rigorous requirements that are a fact of life in the space industry," said Yates. "They are very confident that they have a great set of shoes for that job, and they believe these new shoes will last 100 years, which takes us through the shuttle program and beyond for the next vehicle and the next and the next."

Washburn said that completing the project was a point of pride for ME Global in terms of meeting the time constraints, NASA's standards and embracing the project from top to bottom. "It was a very daunting task," he commented. "There probably isn't another order out there for track shoes on a wire-rope shovel or hydraulic excavator that would even come close to the stringent requirements that we had to do for this NASA order.

"After accomplishing this, there probably isn't much in the way of track shoes that we couldn't do."